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Helical CT in Emergency Radiology¹

¹ From the Department of Radiology, Massachusetts General Hospital, Blossom St, PO Box 9657, FND 210, Boston, MA 02114. Received July 20, 1998; revision requested August 28; revision received January 26, 1999; accepted June 18. Address reprint requests to R.A.N.

Abstract

Today, a wide range of traumatic and nontraumatic emergency conditions are quickly and accurately diagnosed with helical computed tomography (CT). Many traditional emergency imaging procedures have been replaced with newer helical CT techniques that can be performed in less time and with greater accuracy, less patient discomfort, and decreased cost. The speed of helical technology permits CT examination of seriously ill patients in the emergency department, as well as patients who might not have been taken to CT previously because of the length of the examinations of the past. Also, helical technology permits multiple, sequential CT scans to be quickly obtained in the same patient, a great advance for the multiple-trauma patient. Higher quality CT examinations result from decreased respiratory misregistration, enhanced intravenous contrast material opacification of vascular structures and parenchymal organs, greater flexibility in image reconstruction, and improved multiplanar and three-dimensional reformations. This report summarizes the role and recommended protocols for the helical CT diagnosis of thoracic aortic trauma; aortic dissection; pulmonary embolism; acute conditions of the neck soft tissues; abdominal trauma; urinary tract stones; appendicitis; diverticulitis; abdominal aortic aneurysm; fractures of the face, spine, and extremities; and acute stroke.

Index terms: Computed tomography (CT), helical • Emergency medical service system • State-of-art reviews • Trauma

Since its clinical introduction in the 1970s, computed tomography (CT) has revolutionized the imaging work-up of patients in the emergency department. CT now is considered to be one of the most valued tools in the diagnostic work-up of trauma patients and patients with nontraumatic emergency conditions. Today, most emergency centers are equipped with CT scanners that are available for the evaluation of emergency patients, 24 hours a day, 7 days a week. During the past 20 years, improvements in scanner hardware and software have provided increased scanning speed and faster data acquisition, as well as improved spatial resolution and increased low-contrast detectability. As a consequence, emergency patients now benefit from faster and more accurate CT examinations.

Helical (or spiral) CT, the most important CT development of the current decade, permits simultaneous patient translation and data acquisition through the use of a continuously rotating x-ray source and detector array combined with the use of a high-heat-capacity x-ray tube. Helical CT offers a number of imaging advantages for the emergency patient. Respiratory misregistration due to variations in the depth of inspiration on successive breath holds is essentially eliminated, decreasing the likelihood of overlooking small traumatic injuries of the thorax and abdomen. Shorter scanning time permits better intravenous (IV) contrast material opacification of blood vessels and improved IV contrast material enhancement of parenchymal organs. Fast scanning permits the performance of multiple consecutive CT examinations on the same trauma patient in a very short period of time. CT investigations of trauma patients are therefore possible today that could not have been performed in the past. Current helical technology permits a head CT scan, chest-abdomen-pelvis CT scan, and a CT scan of the entire cervical spine to be obtained within 20–30 minutes of total scanner room time. Newer multidetector scanners may decrease this time to 10–15 minutes. With 1970s technology, it might have taken 30 minutes to obtain only the head CT scan.

The acquisition of data from a single scan permits greater flexibility in image reconstruction. For example, scans obtained with a collimation of 5 or 3 mm can be reconstructed into overlapping sections at 1-mm image spacing to better show small abnormalities and to provide improved coronal, sagittal, and three-dimensional (3D) reformations. When CT is performed in a single breath hold, these multiplanar and 3D reformations will be free of respiratory artifact. The ability of helical CT to quickly image blood vessels when optimally opacified and to decrease respiratory and even pulsatile motion has made CT angiography a feasible alternative to catheter angiography in patients with aortic and other vascular emergencies.

A separate computer workstation is a desirable addition to an emergency helical CT scanner installation, as it will permit the review of just completed, but not yet printed, scans without interrupting the performance of the scan in progress. In the multiple-trauma patient, for example, the head CT scan can be reviewed with the neurosurgical consultant on the separate workstation, while the CT technologist continues to perform chest-abdomen-pelvis scanning in the same patient. One would not want to delay the performance of emergency CT by using the scanner itself for review purposes. In addition, the workstation can be used to construct multiplanar and 3D reformations, again without interrupting the performance of an ongoing scan. If the CT scanner is connected to a PACS (picture archiving and communications system), a PACS terminal could also be used for review purposes.

PROTOCOLS AND STAFFING FOR EMERGENCY HELICAL CT

Complete and accurate CT assessment of emergency patients requires the routine use of optimal CT protocols. For each anatomic area of trauma, and for each suspected nontraumatic emergency condition, a detailed and custom-tailored protocol that best depicts that anatomy or that condition will produce the most informative CT examination. The collimation, table speed (pitch), and image reconstruction intervals should be clearly defined. The use of any IV, oral, rectal, or other contrast materials should be specified, as well as the details relevant to their administration. Also noted should be the recommended window settings for converting to hard-copy film and any suggested multiplanar and 3D reformations. In our emergency radiology division, the emergency CT protocols have been assembled in a special notebook available in our CT scanner control room. This book is opened to the appropriate protocol for each emergency CT scan to eliminate any confusion among our large staff of CT technologists and radiology staff, fellows, and residents. These CT protocols are continuously revised and updated as experience identifies improvements (examples are provided in later sections herein).

To take best advantage of the speed of helical CT in the emergency setting requires sufficient staffing of the CT scanning suite. Two CT technologists are routinely scheduled together, so that one can prepare the patient and set up the injector, while the other schedules the patient and programs the scanner. A radiology resident or staff radiologist is present for each scan to confirm the choice of protocol and to provide immediate scan interpretation. In many emergency cases, the CT scanning protocol may need to be altered while scanning is in progress and the patient rescanned with a different protocol because of findings on the initial scan. For example, when a nonenhanced helical abdominal CT scan obtained for new flank pain fails to show any signs of ureteral stone or urinary tract obstruction but an abnormality of colon is revealed, a repeat CT scan with colon contrast material may be indicated to confirm a diagnosis of diverticulitis. If a radiologist is not available for monitoring the scan and instituting indicated alternative protocols, then the work-up of many emergency patients will be unnecessarily delayed. In our years of performing emergency CT, we have become aware that much less is known about the emergency department patient prior to CT than the more thoroughly evaluated inpatient. As a consequence, there are more surprises in CT and more post-CT alterations in diagnosis among our emergency department patients.

Another important staffing consideration is the team to manage the patient; very ill and potentially unstable emergency patients require the presence of emergency department nurses and/or physicians to monitor vital signs and provide any emergency therapies required while the patient is in the scanner suite. The CT technologists performing scanning and the radiologists monitoring and interpreting the scan are generally too occupied with scanning to optimally manage a seriously ill patient.

THE MULTIPLE-TRAUMA PATIENT

Of all emergency conditions, the multiple-trauma patient has perhaps benefited most from the introduction of helical CT. The speed of helical technology permits the CT evaluation of seriously injured patients who might not have been previously taken to CT for the lengthy examinations of the past and the performance of rapid successive CT scanning on the same patient. A remarkable advance has been the combined chest-abdomen-pelvis CT scan obtained with one bolus of IV contrast material. For the usual abdominopelvic CT scan for trauma, one would wait 70 seconds after starting the IV contrast material injection before beginning abdominal scanning. It is possible with helical CT technology to scan the entire chest with excellent aortic opacification during this 70-second delay, beginning the chest CT scanning at 25 seconds and the abdominal CT scanning at 70 seconds after the start of the injection. On this single CT scan, one can search for injuries of the chest, abdomen, and pelvis. The availability of helical scanning and the introduction of this combined scanning protocol has substantially decreased the need for more lengthy and costly angiographic procedures in those patients suspected of having aortic injury.

CHEST AND NECK EMERGENCIES

Helical CT examinations of the chest are performed in our emergency imaging area with 5-mm collimation, a pitch of 1.5, and 5-mm image spacing. Images are obtained from the pulmonary apices through the lung bases and are reviewed at lung and soft-tissue window settings. If trauma is a consideration, then all sections are also reviewed at bone window settings to better identify bone injuries. When IV contrast material is indicated, we power inject 135 mL of 60% contrast material at 2 mL/sec and begin scanning after a 25-second delay. Injection of the right antecubital fossa is preferred to the left so that the origins of the brachiocephalic arteries (brachiocephalic trunk, left common carotid artery, and left subclavian artery) are not obscured by opacification of the left brachiocephalic vein as it crosses the mediastinum anteriorly. Scanning during a single breath hold permits imaging at maximum contrast material enhancement. The images, or data, are reconstructed at 3-mm or 1-mm spacing when coronal, sagittal, oblique, or 3D reformations are indicated.

For soft-tissue examinations of the neck, we scan from the skull base to the thoracic inlet with 5-mm collimation, a pitch of 1.5, and 5-mm image spacing, whereas for examinations to evaluate the cervical spine we use 3-mm collimation, a pitch of 1.5, and 3-mm image spacing. Nearly all our soft-tissue neck examinations are performed with an IV injection of 100 mL of 60% contrast material injected at 2 mL/sec, beginning 25 seconds prior to scanning

Thoracic and Aortic Trauma
Helical CT of the chest can show a variety of conditions in trauma patients that may be overlooked on conventional radiographs; these include small pneumothoraces, thoracic aortic trauma, lung injuries, tracheobronchial trauma, thoracic spine fractures, and sternal fractures. CT may also show abnormal positions of endotracheal tubes, chest tubes, and nasogastric tubes not appreciated on the conventional chest radiograph. The lower thorax is routinely included on abdominal trauma CT scans, and it has been recognized that a substantial proportion of even abdominal CT scans show trauma pathologic conditions in the chest not recognized on the chest radiograph (1,2).

A major advance of helical CT has been the rapid diagnosis of thoracic aortic injury (3–6). This is an emergency condition that must be detected and treated rapidly in order to save the lives of those patients who survive transport to the trauma center. An aortic injury may be clinically suspected on the basis of trauma history, physical examination findings, and suggestive abnormalities on the chest radiograph. Traditionally, patients suspected of this injury have been examined with emergency aortography, which may require mobilization of the on-call angiography team, transportation of the patient to the angiographic suite, and performance of transcatheter aortography. This process may take up to 1–2 hours. With helical CT technology, thoracic aortic injury can be accurately and rapidly diagnosed or excluded in the CT scanner suite, precluding the need for an invasive arteriographic examination.

Patients with suspected aortic injury are examined with our routine chest CT protocol with use of IV contrast material. Multiplanar and 3D reformations are performed in positive cases to show the relationship of the brachiocephalic arteries (brachiocephalic trunk, left common carotid artery, and left subclavian artery) to the injury. The examination is considered to be positive when an actual aortic injury is seen, such as an intimal flap, intimal interruption, or false aneurysm (Fig 1). Even in the presence of mediastinal hematoma, if there are no direct signs of an aortic injury on the CT scan, then the study is considered to be negative for aortic injury.

View larger version (119K): [in this window] [in a new window]   Figure 1a. Helical CT of thoracic aortic injury. (a) Transverse section at the aortic arch shows an intimal disruption with a false aneurysm (arrow), as well as blood (H) in the mediastinum. Bilateral hemothoraces are present. (b) Slightly lower transverse section also shows the false aneurysm (large arrow). A ring of hematoma (small arrow) surrounds the descending aorta. (c) Oblique reformation shows the relationship of the injury and false aneurysm (A) with the left common carotid artery (C) and left subclavian artery (S). Arrow indicates torn intimal flap. (d) Three-dimensional reformation (CT angiogram) shows the relationship of the injury and false aneurysm (A) to the brachiocephalic trunk (B), left common carotid artery (C), and left subclavian artery (S).

View larger version (126K): [in this window] [in a new window]   Figure 1b. Helical CT of thoracic aortic injury. (a) Transverse section at the aortic arch shows an intimal disruption with a false aneurysm (arrow), as well as blood (H) in the mediastinum. Bilateral hemothoraces are present. (b) Slightly lower transverse section also shows the false aneurysm (large arrow). A ring of hematoma (small arrow) surrounds the descending aorta. (c) Oblique reformation shows the relationship of the injury and false aneurysm (A) with the left common carotid artery (C) and left subclavian artery (S). Arrow indicates torn intimal flap. (d) Three-dimensional reformation (CT angiogram) shows the relationship of the injury and false aneurysm (A) to the brachiocephalic trunk (B), left common carotid artery (C), and left subclavian artery (S).

View larger version (121K): [in this window] [in a new window]   Figure 1c. Helical CT of thoracic aortic injury. (a) Transverse section at the aortic arch shows an intimal disruption with a false aneurysm (arrow), as well as blood (H) in the mediastinum. Bilateral hemothoraces are present. (b) Slightly lower transverse section also shows the false aneurysm (large arrow). A ring of hematoma (small arrow) surrounds the descending aorta. (c) Oblique reformation shows the relationship of the injury and false aneurysm (A) with the left common carotid artery (C) and left subclavian artery (S). Arrow indicates torn intimal flap. (d) Three-dimensional reformation (CT angiogram) shows the relationship of the injury and false aneurysm (A) to the brachiocephalic trunk (B), left common carotid artery (C), and left subclavian artery (S).

View larger version (114K): [in this window] [in a new window]   Figure 1d. Helical CT of thoracic aortic injury. (a) Transverse section at the aortic arch shows an intimal disruption with a false aneurysm (arrow), as well as blood (H) in the mediastinum. Bilateral hemothoraces are present. (b) Slightly lower transverse section also shows the false aneurysm (large arrow). A ring of hematoma (small arrow) surrounds the descending aorta. (c) Oblique reformation shows the relationship of the injury and false aneurysm (A) with the left common carotid artery (C) and left subclavian artery (S). Arrow indicates torn intimal flap. (d) Three-dimensional reformation (CT angiogram) shows the relationship of the injury and false aneurysm (A) to the brachiocephalic trunk (B), left common carotid artery (C), and left subclavian artery (S).

We recently reviewed our experience with helical CT for chest trauma and noted similar results. In a series of 210 patients examined with helical CT for suspected aortic injury, there were 204 true-negative cases, no false-negatives case, five true-positive cases, and one false-positive case. The overall accuracy was 99%. None of 29 patients with "definite" mediastinal hematoma and none of 12 additional patients with "possible" mediastinal hematoma (vs thymus, vs other mediastinal abnormality or artifact) and no CT evidence of aortic injury later proved to have an aortic injury (7). The absence of false-negative cases in both series confirms the value of helical CT as a screening test for suspected thoracic aortic injury. Even in the presence of mediastinal hematoma, if no aortic injury was seen at CT then none was seen at aortography or detected clinically. Formerly, the identification of periaortic hematoma was considered such an important CT secondary sign of aortic injury that aortography was recommended whenever this sign was present. Recent experience suggests that this may be unnecessary, that a good quality helical CT scan showing a normal aorta can help exclude injury even in the presence of periaortic and mediastinal hematoma.

Aortic Dissection
The initial reports on the role of conventional CT in the diagnosis of aortic dissection were met with less than enthusiastic optimism. Nienabar et al (8) found a sensitivity of only 82% in the detection of type A dissection. However, more recent investigations (9–11) using helical CT have reported higher accuracy not only in the detection of aortic dissection, but also in the assessment of its extent. Zeman et al (10) reported on a series of 23 patients examined with helical CT for suspected aortic dissection in which there were 15 true-negative cases, seven true-positive cases, and one false-positive case, resulting in a diagnostic accuracy rate of 96%. In another investigation, Quint et al (11) examined 49 patients preoperatively with helical CT and multiplanar reconstructions for suspected thoracic aortic pathologic conditions, including 36 aneurysms, six penetrating ulcers, five dissections, and two pseudoaneurysms. The findings at helical CT were compared with findings at surgery, and the diagnostic accuracy rate was 92% for helical CT. In both reports, the investigators noted that the correct diagnoses could be made from the transverse sections, although the multiplanar reformations can better show the extent of abnormality in positive cases.

In patients suspected of having aortic dissection, we perform helical scanning with 5-mm collimation, a pitch of 1.5, and 7.5-mm image spacing, from the thoracic inlet to the top of the L5 vertebra. Scanning between these landmarks will enable assessment of the entire aorta, with extension slightly beyond the aortic bifurcation. All examinations are performed with 135 mL of nonionic intravenous contrast material, power injected at 2 mL/sec; scanning starts after a 40-second delay. This is generally a sufficient examination for negative cases. When a dissection is identified on the helical scan, then repeat scanning immediately follows, which provides delayed imaging of the false lumen and aortic branches. If heat loading is a problem, then the repeat CT scan can be obtained nonhelically. In all positive cases, the helical sections are reconstructed at 3-mm spacing for coronal, right posterior oblique, and 3D reformations. These overlapping sections considerably improve the quality of the multiplanar reformations.

The findings of aortic dissection include demonstration of an intimal flap and second aortic lumen or false lumen, which may or may not opacify with IV contrast material (Fig 2). When no false-lumen opacification is identified, even on the delayed scans, it usually signifies that the false lumen is thrombosed. The transverse sections are generally sufficient to identify a dissection in nearly all cases. However, the multiplanar reformations can provide more accurate assessment of the extent of the dissection and effect on the aortic branches. One should beware that aortic pulsation may result in false-positive examinations by producing a "double aortic image" that may be confused with an intimal flap or thrombosed false lumen. When such a phenomenon is suspected, a review of the thinner-spaced, overlapping sections may be helpful.

View larger version (86K): [in this window] [in a new window]   Figure 2a. Helical CT of aortic dissection. (a) Transverse section at the pulmonary artery level shows a normal ascending aorta (AA) but type III dissection in the descending aorta. The true lumen (T) is well opacified at the time this section was acquired, but there is delayed opacification of the patent false lumen (F). (b) Oblique reformation across the diaphragm shows the patent true lumen (T) and patent, larger caliber false lumen (F). (c) Coronal reformation through the renal arteries shows the thin intimal flap (arrows) between the true and false lumens. (d) Three-dimensional reformation of the abdominal aorta shows patency of the true and false lumens, as well as patency of the celiac artery (C), superior mesenteric artery (S), and renal arteries (arrows). The upper poles of the kidneys were imaged at CT prior to full parenchymal opacification; by comparison the lower pole parenchyma is well opacified.

View larger version (152K): [in this window] [in a new window]   Figure 2b. Helical CT of aortic dissection. (a) Transverse section at the pulmonary artery level shows a normal ascending aorta (AA) but type III dissection in the descending aorta. The true lumen (T) is well opacified at the time this section was acquired, but there is delayed opacification of the patent false lumen (F). (b) Oblique reformation across the diaphragm shows the patent true lumen (T) and patent, larger caliber false lumen (F). (c) Coronal reformation through the renal arteries shows the thin intimal flap (arrows) between the true and false lumens. (d) Three-dimensional reformation of the abdominal aorta shows patency of the true and false lumens, as well as patency of the celiac artery (C), superior mesenteric artery (S), and renal arteries (arrows). The upper poles of the kidneys were imaged at CT prior to full parenchymal opacification; by comparison the lower pole parenchyma is well opacified.

View larger version (169K): [in this window] [in a new window]   Figure 2c. Helical CT of aortic dissection. (a) Transverse section at the pulmonary artery level shows a normal ascending aorta (AA) but type III dissection in the descending aorta. The true lumen (T) is well opacified at the time this section was acquired, but there is delayed opacification of the patent false lumen (F). (b) Oblique reformation across the diaphragm shows the patent true lumen (T) and patent, larger caliber false lumen (F). (c) Coronal reformation through the renal arteries shows the thin intimal flap (arrows) between the true and false lumens. (d) Three-dimensional reformation of the abdominal aorta shows patency of the true and false lumens, as well as patency of the celiac artery (C), superior mesenteric artery (S), and renal arteries (arrows). The upper poles of the kidneys were imaged at CT prior to full parenchymal opacification; by comparison the lower pole parenchyma is well opacified.

View larger version (152K): [in this window] [in a new window]   Figure 2d. Helical CT of aortic dissection. (a) Transverse section at the pulmonary artery level shows a normal ascending aorta (AA) but type III dissection in the descending aorta. The true lumen (T) is well opacified at the time this section was acquired, but there is delayed opacification of the patent false lumen (F). (b) Oblique reformation across the diaphragm shows the patent true lumen (T) and patent, larger caliber false lumen (F). (c) Coronal reformation through the renal arteries shows the thin intimal flap (arrows) between the true and false lumens. (d) Three-dimensional reformation of the abdominal aorta shows patency of the true and false lumens, as well as patency of the celiac artery (C), superior mesenteric artery (S), and renal arteries (arrows). The upper poles of the kidneys were imaged at CT prior to full parenchymal opacification; by comparison the lower pole parenchyma is well opacified.

Pulmonary emboli appear as filling defects within the pulmonary arteries (Fig 3) that may completely occlude their lumen. A "railroad track" sign may be seen when intraluminal thrombi are shown surrounded by contrast material. Central and large branch pulmonary emboli are well depicted with CT, but small peripheral emboli may be overlooked. Although CT does not reliably image thrombi in subsegmental arteries, it is somewhat reassuring that in the PIOPED (prospective investigation of pulmonary embolism diagnosis) study (18), just 6% of patients had emboli in subsegmental vessels only. The clinical importance of subsegmental emboli has not yet been completely determined. An advantage of CT over nuclear medicine scanning is that the number of indeterminate cases is lower especially in patients with abnormalities on their chest radiograph.

View larger version (91K): [in this window] [in a new window]   Figure 3a. Helical CT of pulmonary embolus. (a) Transverse section obtained just below the aortic arch shows an embolus (arrow) in the left pulmonary artery. (b) Transverse section at a lower level shows an embolus (arrow) in the left lower lobe pulmonary artery.

View larger version (106K): [in this window] [in a new window]   Figure 3b. Helical CT of pulmonary embolus. (a) Transverse section obtained just below the aortic arch shows an embolus (arrow) in the left pulmonary artery. (b) Transverse section at a lower level shows an embolus (arrow) in the left lower lobe pulmonary artery.

When no embolism is found, CT may show other thoracic causes for the patient's symptoms, such as pneumothorax, pneumonia, or neoplastic disease. CT costs less and is safer, faster, and easier for the patient than pulmonary arteriography. CT is most helpful when there is suspicion of a large central pulmonary embolus either on the basis of clinical presentation or when confirmation is required of a high-probability ventilation-perfusion lung scan.

Soft-Tissue Neck Emergencies
Most commonly, we perform emergency helical CT examinations of the neck for the evaluation of patients suspected of having cervical spine trauma; this topic will be discussed later in the section Skeletal Emergencies. However, we also perform many emergency neck CT examinations for the evaluation of suspected neck abscesses (Fig 4), neck masses, parotitis or other sialadenitis, and upper airway trauma. Helical CT offers several advantages over conventional CT. The short acquisition time minimizes motion artifact due to breathing and swallowing, and the volumetric nature of the data acquisition eliminates misregistration.

View larger version (131K): [in this window] [in a new window]   Figure 4a. Helical CT of neck abscess. (a) Transverse scan shows a low-attenuating abscess (straight arrows) in the lateral retropharyngeal soft tissues, anterior to the right carotid artery and jugular vein (small curved arrows), which are compressed; compare with the normal left common carotid artery (C) and left jugular vein (J). The abscess displaces the airway (A) to the left. Extensive edema is seen in the soft tissues of the right side of the neck, lateral to the abscess; compare with the left soft tissues. (b) Coronal reformation shows the abscess (long arrows) medial to the lateral pharyngeal fat plane (short arrows). Compare with normal left lateral pharyngeal fat plane (L). Extensive edema is again seen in the soft tissues of the right side of the neck.

View larger version (64K): [in this window] [in a new window]   Figure 4b. Helical CT of neck abscess. (a) Transverse scan shows a low-attenuating abscess (straight arrows) in the lateral retropharyngeal soft tissues, anterior to the right carotid artery and jugular vein (small curved arrows), which are compressed; compare with the normal left common carotid artery (C) and left jugular vein (J). The abscess displaces the airway (A) to the left. Extensive edema is seen in the soft tissues of the right side of the neck, lateral to the abscess; compare with the left soft tissues. (b) Coronal reformation shows the abscess (long arrows) medial to the lateral pharyngeal fat plane (short arrows). Compare with normal left lateral pharyngeal fat plane (L). Extensive edema is again seen in the soft tissues of the right side of the neck.

ABDOMINAL EMERGENCIES

A variety of helical CT protocols are routinely used in the evaluation of emergency abdominal and pelvic conditions. Most are custom-tailored and focused for the condition that is clinically suspected; several are detailed in this section. In general, our emergency helical abdominal and pelvic CT scans are obtained with 5-mm collimation, a pitch of 1.5, and 5-mm image spacing. Sections are obtained from above the highest hemidiaphragm to below the ischial tuberosities. All sections are imaged with soft-tissue window settings, and those that include the lungs are also imaged with lung window settings. For trauma patients, imaging of all sections with bone window settings is also performed for identification of suspected and unsuspected bone injuries. Lung window settings of the abdomen may be particularly helpful in showing small amounts of traumatic intraperitoneal or retroperitoneal air, and these can be viewed on the CT console or workstation. Similarly, narrow soft-tissue window settings can be imaged for the identification of subtle organ injuries.

When IV contrast material is indicated, we inject 135 mL of 60% contrast material with a power injector at 2 mL/sec and begin scanning after a 70-second delay. We have obtained excellent opacification with this technique, although other trauma centers use larger volumes of 130–180 mL of 60% contrast material injected at 2–4 mL/sec. For oral contrast material, we administer three cups of 1/4 oz of meglumine diatrizoate (Gastrografin; Bristol-Meyers Squibb, Wallingford, Conn) in 10 oz of water at 20-minute intervals, scanning 60–90 minutes later. With trauma patients, however, we do not delay for the passage of oral contrast material but administer the contrast material and scan them as soon a possible. As many emergency patients may have traumatic or nontraumatic bowel rupture, we prefer water-soluble bowel contrast agents to dilute barium sulfate agents. When rectal contrast material is indicated, we inject 30 mL of meglumine diatrizoate into a 1-L bag of normal saline, and administer this mixture through an IV line connected to a small pediatric rectal catheter. After placement of the rectal catheter, about 500 mL of this mixture are instilled to fill the left colon for evaluation of suspected sigmoid diverticulitis or a left flank penetrating injury, whereas about 1,000 mL are instilled to fill the ascending colon and cecum for appendiceal and other right-sided colon examinations. Colonic filling by this technique can be accomplished within 5–7 minutes.

For examinations requiring bladder contrast material, we use a similar mixture of 40 mL of 60% iothalamate meglumine (Conray; Mallinckrodt Medical, St Louis, Mo) or other water-soluble contrast material in 1,000 mL of normal saline. The IV tubing is attached to the patient's Foley catheter by means of a Christmas tree adapter, and the bladder is filled with 300–400 mL of the mixture by means of gravity drip.

Abdominal Trauma
Trauma is the leading cause of death in the United States for men and woman under the age of 40 years, and approximately 10% of trauma deaths are due to abdominal injuries. Since the first reports of the early 1980s (20), CT has proved to be an excellent technique for diagnosing abdominal injuries. The rapid diagnostic capability afforded by CT has contributed toward a decrease in morbidity and mortality from abdominal injuries.

Hemoperitoneum is easily identified with CT, as are injuries of the spleen, liver, gallbladder, kidneys, pancreas, bowel, mesentery, and diaphragm (21–27) (Figs 5, 6). CT can differentiate intraperitoneal hemorrhage from retroperitoneal hemorrhage and can differentiate hemoperitoneum from water-attenuation, posttraumatic peritoneal fluid collections, such as urine with intraperitoneal bladder rupture or bile with gallbladder rupture. CT can demonstrate active arterial bleeding as sites of intravenous contrast material extravasation and bowel rupture as sites of oral contrast material extravasation. The aorta, inferior vena cava, and other vascular structures can be assessed from their opacification with IV contrast material. And even bone injuries of the lumbar spine and pelvis may be identified on sections reviewed with bone window settings. Even in the previous decade, the accuracy of CT in the diagnosis of blunt abdominal trauma was reported to be as high as 97.6% (28).

View larger version (134K): [in this window] [in a new window]   Figure 5a. Helical CT of liver and right kidney injury. (a) Transverse scan shows a low-attenuating laceration (black arrow) of the right lobe of the liver in a patient who suffered right-sided blunt abdominal trauma. A small amount of hemoperitoneum (white arrows) can be seen around the right lobe of liver and behind the spleen. (b) Slightly lower transverse scan in the same patient shows an additional laceration of the right kidney (black arrow) with hemorrhage (H) in the right perirenal space. Hemoperitoneum (white arrow) can be seen adjacent to the liver.

View larger version (131K): [in this window] [in a new window]   Figure 5b. Helical CT of liver and right kidney injury. (a) Transverse scan shows a low-attenuating laceration (black arrow) of the right lobe of the liver in a patient who suffered right-sided blunt abdominal trauma. A small amount of hemoperitoneum (white arrows) can be seen around the right lobe of liver and behind the spleen. (b) Slightly lower transverse scan in the same patient shows an additional laceration of the right kidney (black arrow) with hemorrhage (H) in the right perirenal space. Hemoperitoneum (white arrow) can be seen adjacent to the liver.

View larger version (155K): [in this window] [in a new window]   Figure 6a. Helical CT of splenic fracture and left renal trauma. (a) Transverse section obtained in a patient who experienced blunt left abdominal trauma with a fracture (straight arrow) of the spleen and lack of perfusion of the posterior splenic fragment. Hemorrhage is seen in the perisplenic space (curved arrow) and in the left perirenal space (H); there is no perfusion of the upper pole of the left kidney. (b) Slightly lower transverse scan shows hemorrhage (H) in the left perirenal space and further signs of the left renal artery injury; only a small segment (arrow) of the posterior left kidney is perfused.

View larger version (152K): [in this window] [in a new window]   Figure 6b. Helical CT of splenic fracture and left renal trauma. (a) Transverse section obtained in a patient who experienced blunt left abdominal trauma with a fracture (straight arrow) of the spleen and lack of perfusion of the posterior splenic fragment. Hemorrhage is seen in the perisplenic space (curved arrow) and in the left perirenal space (H); there is no perfusion of the upper pole of the left kidney. (b) Slightly lower transverse scan shows hemorrhage (H) in the left perirenal space and further signs of the left renal artery injury; only a small segment (arrow) of the posterior left kidney is perfused.

View larger version (174K): [in this window] [in a new window]   Figure 7a. Helical CT of traumatic avulsion of the gallbladder. (a) Transverse scan shows hemorrhage in the gallbladder bed with a point of active bleeding; arrow indicates extravasation of IV contrast material. Hemoperitoneum (and probably also bile) can be identified lateral to the right lobe of liver and in the Morison pouch (H). (b) Slightly lower transverse scan shows the gallbladder (arrow) located inferior to its fossa, surrounded by hemoperitoneum. The enhancement of the gallbladder wall indicates that the cystic artery remains intact. (c) Coronal reformation confirms traumatic avulsion of the gallbladder (white arrows) from the gallbladder fossa (black arrows).

View larger version (169K): [in this window] [in a new window]   Figure 7b. Helical CT of traumatic avulsion of the gallbladder. (a) Transverse scan shows hemorrhage in the gallbladder bed with a point of active bleeding; arrow indicates extravasation of IV contrast material. Hemoperitoneum (and probably also bile) can be identified lateral to the right lobe of liver and in the Morison pouch (H). (b) Slightly lower transverse scan shows the gallbladder (arrow) located inferior to its fossa, surrounded by hemoperitoneum. The enhancement of the gallbladder wall indicates that the cystic artery remains intact. (c) Coronal reformation confirms traumatic avulsion of the gallbladder (white arrows) from the gallbladder fossa (black arrows).

View larger version (139K): [in this window] [in a new window]   Figure 7c. Helical CT of traumatic avulsion of the gallbladder. (a) Transverse scan shows hemorrhage in the gallbladder bed with a point of active bleeding; arrow indicates extravasation of IV contrast material. Hemoperitoneum (and probably also bile) can be identified lateral to the right lobe of liver and in the Morison pouch (H). (b) Slightly lower transverse scan shows the gallbladder (arrow) located inferior to its fossa, surrounded by hemoperitoneum. The enhancement of the gallbladder wall indicates that the cystic artery remains intact. (c) Coronal reformation confirms traumatic avulsion of the gallbladder (white arrows) from the gallbladder fossa (black arrows).

View larger version (126K): [in this window] [in a new window]   Figure 8a. Helical CT of mesenteric injury and Chance fracture. (a) Transverse scan obtained in an automobile accident victim who was wearing a lap-type seat belt. Hemoperitoneum (H) was identified adjacent to the liver and spleen. No parenchymal organ injury was seen, and there were no signs of bowel rupture. (b) Slightly lower scan showed a fracture (black arrow) of a lumbar vertebra. Fluid is shown around the aorta and inferior vena cava (white arrows). Laparotomy identified a mesenteric injury with venous bleeding. (c) Targeted lumbar spine CT scan shows fractures of the posterior vertebral body (straight black arrows) and left lamina (curved arrow). (d) Sagittal reformation confirms a Chance fracture (arrow) extending horizontally through the pars interarticularis and pedicles and then extending anteroinferiorly through the posterior vertebral body.

View larger version (127K): [in this window] [in a new window]   Figure 8b. Helical CT of mesenteric injury and Chance fracture. (a) Transverse scan obtained in an automobile accident victim who was wearing a lap-type seat belt. Hemoperitoneum (H) was identified adjacent to the liver and spleen. No parenchymal organ injury was seen, and there were no signs of bowel rupture. (b) Slightly lower scan showed a fracture (black arrow) of a lumbar vertebra. Fluid is shown around the aorta and inferior vena cava (white arrows). Laparotomy identified a mesenteric injury with venous bleeding. (c) Targeted lumbar spine CT scan shows fractures of the posterior vertebral body (straight black arrows) and left lamina (curved arrow). (d) Sagittal reformation confirms a Chance fracture (arrow) extending horizontally through the pars interarticularis and pedicles and then extending anteroinferiorly through the posterior vertebral body.

View larger version (182K): [in this window] [in a new window]   Figure 8c. Helical CT of mesenteric injury and Chance fracture. (a) Transverse scan obtained in an automobile accident victim who was wearing a lap-type seat belt. Hemoperitoneum (H) was identified adjacent to the liver and spleen. No parenchymal organ injury was seen, and there were no signs of bowel rupture. (b) Slightly lower scan showed a fracture (black arrow) of a lumbar vertebra. Fluid is shown around the aorta and inferior vena cava (white arrows). Laparotomy identified a mesenteric injury with venous bleeding. (c) Targeted lumbar spine CT scan shows fractures of the posterior vertebral body (straight black arrows) and left lamina (curved arrow). (d) Sagittal reformation confirms a Chance fracture (arrow) extending horizontally through the pars interarticularis and pedicles and then extending anteroinferiorly through the posterior vertebral body.

View larger version (196K): [in this window] [in a new window]   Figure 8d. Helical CT of mesenteric injury and Chance fracture. (a) Transverse scan obtained in an automobile accident victim who was wearing a lap-type seat belt. Hemoperitoneum (H) was identified adjacent to the liver and spleen. No parenchymal organ injury was seen, and there were no signs of bowel rupture. (b) Slightly lower scan showed a fracture (black arrow) of a lumbar vertebra. Fluid is shown around the aorta and inferior vena cava (white arrows). Laparotomy identified a mesenteric injury with venous bleeding. (c) Targeted lumbar spine CT scan shows fractures of the posterior vertebral body (straight black arrows) and left lamina (curved arrow). (d) Sagittal reformation confirms a Chance fracture (arrow) extending horizontally through the pars interarticularis and pedicles and then extending anteroinferiorly through the posterior vertebral body.

All our patients are given oral contrast material to opacify the bowel lumen, to optimize the diagnosis of bowel injury. In the acute-trauma patient, we do not wait for the passage of oral contrast material; rather, we take the patient directly to CT. One 10-oz cup of oral contrast material is injected down the patient's nasogastric tube in the trauma room of the emergency department, another cup is injected in transit to the scanner, and a third cup is injected while positioning the patient on the CT table. In the time window routinely available for the passage of oral contrast material, usually only the stomach, duodenum, and proximal small bowel are opacified. Fortunately, most abdominal injuries with blunt trauma involve the proximal gastrointestinal tract. If a colon injury is suspected, then additional rectal contrast material is also administered (ie, the triple-contrast scan, consisting of oral, IV, and rectal contrast media). One should be concerned about possible colonic injuries in patients with flank or back penetrating injuries and in those with pelvic fractures and hematochezia.

The patient's Foley catheter is clamped prior to scanning to optimize bladder filling. It has been well recognized that when abdominal CT is performed without maximal bladder filling, both intraperitoneal and extraperitoneal bladder rupture can be overlooked. If the bladder is not distended on the initial CT scan, especially in patients with an increased likelihood of bladder injury because of pelvic fractures or gross hematuria, repeat CT of the pelvis is performed after the retrograde administration of bladder contrast material (CT cystogram). To perform this examination, the Foley catheter is unclamped, the bladder is allowed to drain, 300–400 mL of bladder contrast material is administered through the Foley catheter, and then the pelvis is rescanned. It should be noted that the appearance of a "full" or "distended" bladder on the initial CT scan may be unreliable and that performance of CT cystography is recommended when any doubt exists regarding bladder integrity. Also, if blood was seen at the urethral meatus at initial evaluation of the patient in the trauma room, then a retrograde urethrogram should have been obtained prior to Foley placement to rule out urethral injury.

Ureteral Stone Disease
Nonenhanced helical CT is rapidly replacing IV urography in the diagnosis of patients with acute flank pain and a suspected ureteral stone. CT has a high sensitivity and a high specificity for detection of ureteral stones, and it can show signs of urinary tract obstruction (31-34). In fact, more ureteral stones can be shown with CT than with urography (31). No IV contrast material is required in nearly all cases. Helical CT is preferred over urography because it is faster, safer, and more accurate than urography, and when no stone is present CT may help identify the alternative diagnosis.

In the emergency center, helical CT can expedite the evaluation of patients with acute flank pain who can be examined with a 90-second helical CT scan, often spending no more than 10–15 minutes on the CT scanner table. IV urography may tie up a conventional radiography room for 30–60 minutes, and some patients may require delayed radiographs after 1 hour. Helical CT has been enthusiastically received by patients and referring physicians. Patients with recurrent stone disease who have been examined with IV urography in the past have been delighted not only with the speed of CT, but also with the avoidance of an IV line and IV injection of contrast material.

Smith et al (32) reported on a series of 220 patients with acute flank pain evaluated with CT. Nonenhanced helical CT was false-negative for stone disease in three patients and false-positive for stone disease in four, yielding a sensitivity of 97%, specificity of 96%, and accuracy of 97%. A recent retrospective review of 339 cases in our own emergency radiology division (34) showed similar results with a sensitivity of 96%, specificity of 99%, and accuracy of 96%. When no urinary tract stone was seen, alternative diagnoses were made in 46 cases (34%).

The hallmark CT finding of ureteral stone disease is direct visualization of a stone within a dilated ureter (Fig 9). The dilated ureter is visually followed distally from the kidney on the symptomatic side on sequential CT sections to the level of the stone. More commonly, a stone within a dilated ureter is not so clearly shown, but the CT scan is interpreted as positive when the secondary signs of ureteral obstruction are present in combination with a stone shown overlying the course of the ureter, often at the ureterovesicle junction. The usual secondary signs are perinephric and periureteral stranding, dilatation of the intrarenal collecting system and ureter, and renal enlargement. Smith et al (33) reported that ureteral dilatation and perinephric stranding were both present or both absent in 181 of the 220 patients with a confirmed diagnosis. In addition to diagnosing ureteral stones, the size of the stone can also be accurately measured at CT to help predict outcome. Stones measuring less than 5 mm usually pass spontaneously, whereas stones larger than 5 mm may require intervention for stone removal. Stones located in the distal ureter and at the ureterovesicle junction are more likely to pass than are stones located in the proximal ureter (3333a).

View larger version (141K): [in this window] [in a new window]   Figure 9a. Helical CT of ureteral stone. (a) Transverse section from a nonenhanced helical CT scan shows slight enlargement of the right kidney and dilatation of the right intrarenal collecting system (arrow). (b) Slightly lower transverse section shows perinephric and periureteral fat stranding (black arrow) on the right; the normal left ureter is indicated by the white arrow. (c) Transverse section, just below the kidneys, shows a stone (arrow) in the proximal right ureter with edema of the ureteral wall and periureteral stranding. (d) Coronal reformation shows the stone (arrow) within an obstructed proximal right ureter.

View larger version (137K): [in this window] [in a new window]   Figure 9b. Helical CT of ureteral stone. (a) Transverse section from a nonenhanced helical CT scan shows slight enlargement of the right kidney and dilatation of the right intrarenal collecting system (arrow). (b) Slightly lower transverse section shows perinephric and periureteral fat stranding (black arrow) on the right; the normal left ureter is indicated by the white arrow. (c) Transverse section, just below the kidneys, shows a stone (arrow) in the proximal right ureter with edema of the ureteral wall and periureteral stranding. (d) Coronal reformation shows the stone (arrow) within an obstructed proximal right ureter.

View larger version (148K): [in this window] [in a new window]   Figure 9c. Helical CT of ureteral stone. (a) Transverse section from a nonenhanced helical CT scan shows slight enlargement of the right kidney and dilatation of the right intrarenal collecting system (arrow). (b) Slightly lower transverse section shows perinephric and periureteral fat stranding (black arrow) on the right; the normal left ureter is indicated by the white arrow. (c) Transverse section, just below the kidneys, shows a stone (arrow) in the proximal right ureter with edema of the ureteral wall and periureteral stranding. (d) Coronal reformation shows the stone (arrow) within an obstructed proximal right ureter.

View larger version (167K): [in this window] [in a new window]   Figure 9d. Helical CT of ureteral stone. (a) Transverse section from a nonenhanced helical CT scan shows slight enlargement of the right kidney and dilatation of the right intrarenal collecting system (arrow). (b) Slightly lower transverse section shows perinephric and periureteral fat stranding (black arrow) on the right; the normal left ureter is indicated by the white arrow. (c) Transverse section, just below the kidneys, shows a stone (arrow) in the proximal right ureter with edema of the ureteral wall and periureteral stranding. (d) Coronal reformation shows the stone (arrow) within an obstructed proximal right ureter.

The radiologist should carefully monitor the helical CT examination while in progress because when no stone is detected, a search for an alternative diagnosis should be instituted at CT. This may require extending the scan or repeating the examination with IV, oral, or rectally administered contrast material. One of the most life-threatening alternative diagnoses is a leaking abdominal aortic aneurysm, which can present clinically as unilateral acute flank pain, particularly when the retroperitoneal bleeding is unilateral. Consequently, scanning of older patients with acute flank pain should not be unduly delayed, especially if there is knowledge of an aneurysm by history or suspicion of an aneurysm at physical examination. Other alternative conditions that have been commonly diagnosed in patients with suspected ureteral stone include diverticulitis, appendicitis, cholecystitis, pyelonephritis, renal infarction, and acute gynecologic conditions.

Appendicitis and Diverticulitis
Helical CT combined with newer scanning protocols has substantially improved the diagnostic imaging of appendicitis and diverticulitis (37–39). Not only can CT help confirm or exclude a diagnosis of appendicitis and diverticulitis with high accuracy, but CT can often facilitate diagnosis of the alternative conditions that mimick their clinical presentation when no appendicitis or diverticulitis is present.

Patients with appendicitis typically present with a history of abdominal pain that is initially generalized, but later localizes to the right lower quadrant of the abdomen. The onset of pain is often accompanied by nausea, vomiting, anorexia, and fever. Tenderness to palpation in the right lower abdominal quadrant may be elicited at physical examination, as may rebound tenderness and guarding. The patient's white blood cell count is usually elevated. The clinical diagnosis of appendicitis is often difficult, and large prospective trials have cited 22%–30% normal appendix removal rates on the basis of clinical evaluation alone (40–42). Consequently, the advent of an accurate imaging examination for appendicitis could make a substantial impact on the diagnosis of this common condition. With helical CT, high diagnostic accuracy is possible and accuracy rates as high as 98% have been reported in prospective trials (37,38).

Our technique for appendiceal CT uses rectally instilled contrast material for maximum opacification of the right side of the colon, the cecum, and the appendix; no IV contrast material; and scanning limited to the abdominopelvic junction. With rectal administration of colon contrast material, time is saved for the emergency patient as there is no delay in waiting for the passage of oral contrast material to reach the colon. For many patients with abdominal pain and nausea, rectal contrast material is preferred to drinking three 10-oz cups of oral contrast material and waiting 60–90 minutes. With our technique, the risks and increased costs associated with IV contrast material are avoided. Finally, limited scanning minimizes patient radiation exposure.

On the CT scanner table, up to 1,000 mL of a 3% meglumine diatrizoate (Gastrografin; Bristol-Meyers Squibb) solution are infused into the colon by means of gravity drip through IV tubing and a small soft rubber catheter. A digital radiograph confirms cecal opacification. A helical CT series covering approximately 15 cm of the abdominopelvic junction is performed, centered about 3 cm above the cecal tip. If appendicitis is present, scanning is complete. If a normal appendix is seen and an alternative condition is identified, then scanning is also complete; but if no alternative condition is demonstrated, then the scan is extended on an individual patient basis. If a normal or abnormal appendix is not seen, then the patient is placed in a left-side-down decubitus position to promote filling of a normal appendix and highlight the cecal apical changes of appendicitis.

A normal appendix may be shown filled with contrast material (Fig 10) or air. A normal appendix may also have a collapsed lumen, and it should not measure more than 6 mm in diameter. The CT signs of appendicitis include an abnormal appendix, periappendiceal inflammation, and cecal apical changes (Fig 11). An abnormal appendix at CT measures greater than 6 mm in diameter, fails to fill with contrast material, and may contain one or more appendoliths. Periappendiceal inflammation may manifest as fat stranding, fluid collections, phlegmon, extraluminal air bubbles, abscess, and adenopathy. The cecal apical changes indicative of appendicitis include focal cecal apical thickening, the arrowhead sign, and the cecal bar (43). The more common alternative diagnoses made with CT when appendicitis is not present include mesenteric adenitis or ileitis complex, cecal or sigmoid diverticulitis, ovarian cystic disease, and urinary tract stones.

View larger version (147K): [in this window] [in a new window]   Figure 10. Helical CT of a normal appendix. Helical CT scan obtained with rectally administered contrast material shows a normal appendix (arrow) filling with contrast material and adjacent to a well-opacified cecum (C).

View larger version (147K): [in this window] [in a new window]   Figure 11a. Helical CT scans obtained in two patients with appendicitis. (a) The abnormal appendix (arrows) does not fill with rectally administered contrast material. It is dilated, measures 10 mm in diameter, and is surrounded by periappendiceal fat stranding and inflammation. (b) Abnormal appendix in another patient. The appendix is kinked and imaged in cross section at two different sites (arrows). There is no contrast material opacification of the appendix. Rather, the appendix is pus-filled and dilated, with adjacent fat stranding.

View larger version (145K): [in this window] [in a new window]   Figure 11b. Helical CT scans obtained in two patients with appendicitis. (a) The abnormal appendix (arrows) does not fill with rectally administered contrast material. It is dilated, measures 10 mm in diameter, and is surrounded by periappendiceal fat stranding and inflammation. (b) Abnormal appendix in another patient. The appendix is kinked and imaged in cross section at two different sites (arrows). There is no contrast material opacification of the appendix. Rather, the appendix is pus-filled and dilated, with adjacent fat stranding.

The traditional diagnostic imaging examination for suspected diverticulitis has been the barium enema examination, which can show the secondary effects on the barium column produced by this condition. Today, most centers now perform CT, which provides direct visualization of the intramural and peritoneal manifestations of diverticulitis. CT can better show the complications of diverticulitis such as perforation and abscess formation, as well as the alternative conditions when no diverticulitis is present.

In a prospective investigation comparing barium enema examination and CT in the diagnosis of 56 patients suspected of having sigmoid diverticulitis, Cho et al (45) found that CT was positive in 93% of the positive cases (25 of 27) compared to barium enema examination, which was positive in 80% (20 of 25). Of the 29 patients who did not have diverticulitis, however, an alternative diagnosis was made with CT in 20, but in only three cases with barium enema examination. Helical technology permits these examinations to be performed faster than conventional CT with less respiratory and other motion artifacts.

We perform our diverticular helical CT examinations with contrast material administered rectally, a technique with a reported accuracy of 99% (39). Rectally administered colon contrast material again saves time and provides excellent opacification of the colon. After the patient is placed on the CT scanner table, between 400 and 600 mL of a 3% meglumine diatrizoate (Gastrografin; Bristol-Meyers Squibb) solution is infused through the colon by means of gravity drip, and helical scanning is performed of the entire abdomen. Examinations are nearly always complete after the initial scan series, although a repeat scan with IV contrast material may be indicated in some instances to elucidate alternative conditions when no diverticulitis is seen.

The CT findings of colonic diverticulitis include inflammatory thickening of the colon wall and paracolic inflammatory changes such as fat stranding, phlegmon, air bubbles, abscess formation, or free fluid (Fig 12). Intramural and extracolonic contrast material may be seen with an intramural and extraluminal sinus tract, fistula, or perforation. The alternative conditions that are commonly diagnosed with CT when no diverticulitis is present include bowel obstruction, primary epiploic appendagitis, appendicitis, acute cholecystitis, ileitis, and ovarian cystic disease.

View larger version (181K): [in this window] [in a new window]   Figure 12a. Helical CT of sigmoid diverticulitis. (a) Helical scan obtained with rectally administered contrast material shows thickening of the sigmoid colon wall (straight arrow) with inflammatory stranding (curved arrow) in the adjacent mesenteric fat. (b) Helical CT scan obtained in another patient with sigmoid diverticulitis. Also seen is marked thickening of the sigmoid colon wall (arrow) with extensive surrounding inflammation in the mesenteric fat. Free fluid (F) is seen adjacent to the diseased segment of colon.

View larger version (195K): [in this window] [in a new window]   Figure 12b. Helical CT of sigmoid diverticulitis. (a) Helical scan obtained with rectally administered contrast material shows thickening of the sigmoid colon wall (straight arrow) with inflammatory stranding (curved arrow) in the adjacent mesenteric fat. (b) Helical CT scan obtained in another patient with sigmoid diverticulitis. Also seen is marked thickening of the sigmoid colon wall (arrow) with extensive surrounding inflammation in the mesenteric fat. Free fluid (F) is seen adjacent to the diseased segment of colon.