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What the Clinician Wants to Know |
1 From the Departments of Radiology (M.N.B.Z.), Orthopedic Surgery (S.C.D., M.P.W.), and Neurosurgery (G.F.G.), Hoag Memorial Hospital Presbyterian, One Hoag Dr, Newport Beach, CA 92658. Received July 8, 1999; revision requested September 9; revision received November 5; accepted November 19. Address correspondence to M.N.B.Z. (e-mail: ezbz@primenet.com).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONNONSPECIFIC LOW BACK PAINLOW BACK PAIN AND...LOW BACK PAIN AND...POSTOPERATIVE EXAMINATION OF...REFERENCES |
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Index terms: Spine, abnormalities, 33.77, 33.78, 33.82, 33.86 • Spine, CT, 33.1211 • Spine, intervertebral disks, 33.7833 • Spine, MR, 33.121411, 33.12143 • Spine, radiography, 33.11 • Spine, surgery, 33.45
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONNONSPECIFIC LOW BACK PAINLOW BACK PAIN AND...LOW BACK PAIN AND...POSTOPERATIVE EXAMINATION OF...REFERENCES |
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Because of these statistics, treating patients with low back pain can be particularly frustrating for clinicians, and imaging is a common diagnostic tool used to gather information and direct therapy. The same frustrations of natural history, diagnostic dilemmas, and posttherapeutic outcomes prey on the radiologist. There is a considerable lack of standardization in terms of diagnosis, both clinically and in the imaging arena. For example, a group of experienced spine surgeons, when given a set of eight specific surgical observations, provided more than 50 diagnostic terms to label the conditions presented (18). Similarly, the terminology for disk abnormalities at imaging includes a variety of labels, including bulge, herniation, rupture, protrusion, extrusion, and sequestration, that can vary in meaning and importance from patient to patient and from location to location (9–20). Controversies in clinical management are paralleled by the choices of modalities within the diagnostic armamentarium. The choices of imaging modalities include radiography, computed tomography (CT), magnetic resonance (MR) imaging, myelography with postmyelographic CT scanning as an adjunct, and diskography. Each modality has certain strengths and limitations (21–23).
Considering the above issues, it was difficult to produce an article that answers the question posed by the editor for this particular assignment—namely, what does the clinician want to know? The answer actually depends on the specific clinician and on the milieu in which the clinicians and radiologists toil. What follows is a question and answer discourse between one radiologist and three clinicians–two orthopedists and a neurosurgeon. It is hoped that the questions and answers are representative of the nuances that this vast problem presents and can be generalized to many practices. Obviously, given the broad spectrum of opinions and discourse and only nascent formal practice guidelines, any specific situation may not find resonance with what is presented. The questions were posed and answered in some cases by all three clinicians and in other cases by one or two of them (as specified by their initials). The editorial comments provided by the questioner (M.N.B.-Z.) are not meant to be dogma, but rather they are personal observations.
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NONSPECIFIC LOW BACK PAIN |
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TOPABSTRACTINTRODUCTIONNONSPECIFIC LOW BACK PAINLOW BACK PAIN AND...LOW BACK PAIN AND...POSTOPERATIVE EXAMINATION OF...REFERENCES |
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M.P.W.: Nonspecific back pain is not an indication for imaging unless it has been present for a long time—6–8 weeks at the very least and longer if the pain is subacute (24). The specific information that I use to refer a patient for prompt imaging is pain that does not get better with rest; pain that is associated with fever, chills, or night sweats; or weight loss. Such symptoms are causes for concern for possible malignancy, compression fracture, or infection.
S.C.D.: I also factor in the age of the patient, the length of time he or she has had the symptoms, and the specific pattern of the pain with regard to its frequency, severity, duration, and time of occurrence—that is, night versus day and whether the pain awakens the patient—as well as the modalities or treatments that have been employed already. For example, because back pain is an uncommon complaint in children and adolescents (25), it prompts early imaging in these patients, particularly if constitutional symptoms are present (Fig 1).
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S.C.D.: The radiograph is quite useful in evaluating patients for potential congenital abnormalities or developmental defects, such as spondylolysis and spondylolisthesis. The presence of scoliosis or bone abnormalities, either of the benign or malignant variety, can be detected on radiographs, and any relevant findings of this nature should appear in the radiologist’s report. These include the presence of facet sclerosis and anomalous lumbosacral transitional vertebral bodies, which may influence musculoligamentous loads. I still feel that conventional radiographs are important for evaluating degenerative or chronic situations and offer an easy screening opportunity. I always perform MR imaging at follow-up, unless there is a contraindication such as a pacemaker. If the patient has had prior surgical intervention with a metal implant, MR imaging is less valuable, but it still allows one to visualize other areas around the metallic fixation.
M.N.B.-Z.: Are there specific aspects of disk bulges and/or mild broad-based protrusions that affect your treatment plan in the patient with nonspecific back pain?
M.P.W.: The majority of times, bulges or mild broad-based disk protrusions do not affect my treatment plan, unless they are superimposed on congenital spinal stenosis (26). The additive effects of minor disk bulges superimposed on congenital stenosis can precipitate the syndrome of spinal stenosis, in which the classic presentation of patients includes low back pain with or without radiculopathy. Most borderline congenital types of stenoses do not manifest clinically until an acquired process is superimposed.
M.N.B.-Z.: Are there specific aspects of facet arthropathy, as interpreted by the radiologist, that are important in your formulation of pain management when you are examining patients with nonspecific low back pain?
S.C.D.: I look for a description of any foraminal encroachment of the superior facets. Certainly, when substantial spondylolisthesis or lateral listhesis is present in association with facet arthropathy, I view this as potentially important contributory information on the back pain syndrome (27). Such listhesis in patients with severe back pain syndromes may be an indication for spine stabilization surgery, particularly if no other causes of chronic low back pain are evident at the work-up. Facet arthropathy is less important in and of itself (28) because of its rather frequent prevalence in the general population, particularly in patients in the later decades of life.
M.P.W.: I believe that facet arthropathy is a minor component of back pain and that the disk component is much more important. However, when the radiologist describes fluid in the facet joints in association with degenerative spondylolisthesis, I strongly consider it as a possible source of the low back pain, particularly when the facet joint is expanded by the fluid. Similar to any other synovial joint in the body, the facet joint contains nociceptive fibers and may be a source of pain when it is inflamed.
M.N.B.-Z.: There is some evidence that severe facet arthropathy, particularly that with spondylolisthesis, can lead to compromise of the nerve roots with physiologic loading (ie, dynamic spinal stenosis) (29). Flexion and extension lateral spine radiographs can prove to be helpful in evaluating stability. Occasionally, such views are helpful with myelography if dynamic spinal stenosis is suspected, particularly in patients in the upright position. Thus, obvious facet arthropathy should always be mentioned in the radiologist’s report. A number of treatment approaches in these patients have been popular at various times. Despite the lack of statistically validated clinical data, the popularity of facet and epidural injections seems to be growing (30–32). Is any patient with nonspecific low back pain a candidate for facet injection, epidural injection, or nerve root block? Does imaging help in the selection of such candidates?
S.C.D.: I believe that imaging is of paramount importance in selecting these candidates. I believe also that in isolated facet disease of severe nature, facet joint blocks are often helpful in individual cases, if only to temporize or break the pain cycle. Actually, CT scanning—particularly with use of bone windows—may better depict the status of the facet joints when the initial radiographs suggest facet arthropathy as a substantial abnormality. MR imaging is extremely useful for nerve root blocks, but only when nerve root compromise at a specific foraminal window is apparent. In addition, MR imaging helps to evaluate the spinal canal prior to any consideration of epidural injection.
M.P.W.: A number of years ago I believed that facet injections were helpful in patients with nonspecific low back pain; however, with time, I have found that long-term relief is rarely achieved by using such an approach, and my enthusiasm for facet injections has waned (30). In addition, epidural steroid injections and nerve root blocks are not approaches that I consider for patients who have only nonspecific back pain, particularly because localizing such injections in patients with diffuse back pain is impossible. One does not know the appropriate level to treat in such cases.
M.N.B.-Z.: In reviewing the whole history and topic of diskography, my cynical nature is unearthed. I sometimes believe that diskography is a punitive rather than provocative examination that is ordered for patients who are particularly frustrating for the clinician. Obviously, such thoughts come in my darker moments, and I do recognize that diskographic provocation does have some diagnostic value. Yet the controversies around this topic are rampant (33–35). At what point do you resort to diskography, and what type of results from this procedure would you use to suggest fusion as a potential management? Does anything on the image itself help to indicate the need for fusion?
M.P.W.: I usually do not recommend diskography unless a patient has been complaining of pain for at least 6 and probably 9 months and has not responded to physical therapy, anti-inflammatory agents, or other conservative measures. Before obtaining the diskogram, I order an MR imaging examination, which should indicate disk desiccation. On the diskogram itself, I need to see an abnormal disk with annular fissures, and provocatively, I need to see the patient’s pain reproduced (Fig 2). More important, I also expect to have at least one and preferably two other disks that do not reproduce this pain injected. In other words, I typically request a three-level diskogram to ensure that there are two normal levels prior to considering fusion of the abnormal level in appropriate patients (36).
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LOW BACK PAIN AND SCIATICA OR OTHER DISCRETE RADICULOPATHIES |
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TOPABSTRACTINTRODUCTIONNONSPECIFIC LOW BACK PAINLOW BACK PAIN AND...LOW BACK PAIN AND...POSTOPERATIVE EXAMINATION OF...REFERENCES |
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S.C.D.: The terminology does not matter, although I do believe that consistency in reporting is important. Since all posterior disk extensions are considered herniations, specifying whether the extension is extruded or simply protruding is helpful. We have learned that protrusions are quite common at MR imaging in the general population and need not be symptomatic. On the other hand, extrusions imply more fragmentary or larger volumes of disk material and often a breach of the annuloligamentous complex—conditions that are much more likely to be associated with symptomatic complaints. When the fragment is truly sequestered, that is, separated from the parent disk, its location and direction of migration are important to report, as is the level to which it may migrate. This information helps direct the surgical approach.
M.P.W.: Terminology is particularly important to me when I am explaining the situation to the patient. However, no matter what term is used, I like to view the image myself and determine the amount of disk abnormality—particularly, how much pressure is actually placed on the nerve root. The identification of nerve root impingement or compression in a patient with appropriate symptoms means that a successful surgical outcome is much more likely to be achieved than that in patients who have nonspecific appearances of disk degeneration. Pathophysiologic consequences of nerve root impingement have been well studied (39).
M.N.B.-Z.: Unfortunately, the lack of standardized terminology for morphologic disk abnormalities makes life difficult for all of us. Radiologists in particular like to use the short term "HNP" (herniated nucleus pulposus), even for degenerated disks that have not had a histologically distinct nucleus for years. The term "compression" is overused, because nerves float in the thecal sac and are more often deviated or stretched rather than compressed. I agree that the most important observation is whether there is any extension of disk material posteriorly from the intervertebral space, and the relative degree of encroachment on the neural channels, particularly the lateral recesses and neural foramina, as well as the impact on the nerve roots, also is of paramount importance (Fig 3).
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S.C.D.: My threshold is very low. If focal neurologic findings, such as reflex changes, weakness, and discrete numbness, are present in addition to low back pain and do not resolve within a short period, imaging follows.
M.P.W.: I agree that the threshold for these patients is much lower. I will order an MR imaging examination if 1 week to 10 days of conservative treatment does not produce any improvement. If there is no weakness, I may go up to 3–4 weeks before ordering MR imaging, unless the pain is incapacitating. The presence of weakness is semialarming to the clinician, because it may be seen with more ominous diseases than simply disk herniation. Weakness with sciatica from disk herniation is also a strong indication for prompt surgery if imaging results verify the findings. On the other hand, spontaneous recovery from sciatica due to disk extrusion can certainly occur as the disk scars down (40,41).
M.N.B.-Z.: Is MR imaging the study that you prefer for the first examination of these patients, and what, if any, is the role of myelography following a screening examination?
M.P.W., S.C.D.: MR imaging is the preferable examination (Fig 4). CT myelography can be performed additionally when looking for foraminal disk herniations that perhaps were missed at MR imaging.
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M.N.B.-Z.: What do you look for in the radiologist report that helps you most in treating such patients? Is the size of a protruding or extruded disk of importance in terms of absolute measurement, and if so, which dimension?
G.F.G.: I want the radiologist to identify and describe the abnormalities and suggest their importance. This is particularly useful in MR imaging reports, given the multiple parameters and variables with even routine sequences. As for the size of a protruding disk, that is less important than how the abnormality correlates with the patient’s symptoms and examination results. Large disk extrusions in very capacious canals, contained in the epidural fat and not encroaching on the thecal sac or the nerve roots, may have relatively little symptomatology compared with smaller fragments that efface or displace nerve roots in the lateral recess or in the neural foramen.
S.C.D., M.P.W.: We agree. The size of the disk and the resultant amount of stenosis or encroachment is key. Such findings, when they correlate with the patient’s specific radiculopathy localized to the same level, help to predict an immediately favorable response to surgical intervention. Noting substantial deviation of the nerve root also is important. Deviation of the nerve root indicates that there is a sufficient volume of disk extrusion to produce mechanical compromise—at the very least, some stretching—of the nerve root. Again, this is an indication for more immediate surgical intervention if the patient has corresponding signs and symptoms.
M.N.B.-Z.: I am sometimes surprised when reading the operative notes at the description of what was found at surgery. How often do you see discrepancies between the surgical findings and the original imaging reports after operating on patients with extruded disks?
G.F.G.: Given a technically adequate study that has been carefully reviewed before surgery, in my experience, it is rare to find a substantial discrepancy between what was expected on the basis of the imaging findings and what was actually found at surgery.
S.D.: I agree. It is unusual to find major discrepancies, although, depending on the timing, there may be changes when a relatively long time has passed between the imaging study and the surgery. Occasionally, at surgery, one may see more foraminal narrowing or some inflammatory changes that may not have been visualized at imaging. I assume that inflammatory changes may not produce morphologic alteration, but they simply are represented as hypervascularity, which may not be detectable on MR images. In general, however, there is usually quite good correlation between imaging and surgical findings.
M.P.W.: I think that there is some discrepancy when a large epidural vein is overlying the disk and thus makes it appear larger on the image. For whatever reason, with foraminal disks, images may not show the degree of encroachment that is seen at surgery, particularly when there are multiple extruded fragments that are depicted at MR imaging as one fragment. Thus, separate fragments across the back of an intervertebral space can have a unified appearance on an MR image, presumably owing to partial volume effects.
M.N.B.-Z.: The timing issue is important. As you know, in a number of imaging studies it has been reported that there is considerable shrinkage of large extruded disks over time if no surgery is performed (42,43). Presumably, natural reparative forces, including ingrowth of granulation tissue and resorption, occur (44). Speaking of direct surgical observations, some authors (45) have suggested that epidural hematomas can simulate large disk extrusions and that these masses occur more often than imaging findings suggest. How often have you seen direct evidence of an epidural hematoma when operating on an extruded disk, and is this finding easy to ascertain at surgery?
G.F.G.: I cannot recall finding an epidural hematoma while operating on an extruded disk; however, if one were present, it should be readily apparent.
M.P.W., S.C.D.: We agree that these are very rare. Occasionally, we see some large engorged vessels that were not visualized and may have been mistaken as components of disk extrusion at MR imaging, and that can complicate the actual technical aspects of surgery, but such hematomas are extremely rare.
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LOW BACK PAIN AND SPINAL STENOSIS |
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TOPABSTRACTINTRODUCTIONNONSPECIFIC LOW BACK PAINLOW BACK PAIN AND...LOW BACK PAIN AND...POSTOPERATIVE EXAMINATION OF...REFERENCES |
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M.P.W.: Absolutely. Classic neurogenic claudication manifests as progressive cramping, fatigue, and dysfunction in the lower extremities, particularly the posterior thighs and calves with ambulation, and it is not resolved by standing but rather by sitting and/or bending forward (46–50).
S.C.D.: The syndrome of neurogenic claudication is more common in older age groups and may start out simply as generalized low back pain and buttock pain, but it typically progresses to the syndrome described. Usually, patients will tell you that they have to lean forward as they walk and that they can walk further if they push a grocery cart (51,52).
G.F.G.: One may also see other syndromes, such as radiculopathy or a progressive cauda equina syndrome. Back pain, although it may be present, is not in my opinion usually a direct result of the stenosis, but rather it is a concurrent symptom of the associated osteoarthritic degeneration that produced the stenosis.
M.N.B.-Z.: I sometimes hear from clinicians that MR imaging is not as useful in delineating stenosis. What imaging modality is most helpful to you in evaluating for the presence of stenosis? Do you think imaging patients in the supine position leads to an underestimation of the degree of stenosis?
M.P.W.: In my opinion, MR imaging is the most useful in general, particularly in depicting the cross-section of the spinal canal on T2-weighted images and differentiating the soft-tissue component from the facet arthropathy. I do not think that imaging in the supine position leads to an underestimation of stenosis.
S.C.D.: MR imaging is the most helpful to me also, although I sometimes request a CT myelogram to determine the amount of stenosis present and the number of levels that might be needed to address at surgery. I do not believe that imaging in the supine position leads to an underestimation of stenosis, unless it is performed in a setting of spinal instability, such as degenerative spondylolisthesis (29).
M.N.B.-Z.: Do absolute measurements of the spinal canal help in evaluating these patients?
M.P.W.: In my opinion, they help predominantly only in the cervical spine, the area for which there is greater documentation of the numeric relationships in the literature. There are fewer absolute data on the lumbar spine (53,54).
G.F.G.: I do not find absolute measurements of the canal that useful. The morphologic appearance of the lumbar spine, the trefoil shape of the short pedicle stenosis, the complete loss of epidural fat, and the relative overgrowth of the facets and/or the ligamentum flavum are much more useful in assessing stenosis.
M.N.B.-Z.: Is there a difference in the symptomatology or management plan when the stenosis involves predominantly the lateral recesses or the central canal, and is this distinction important for radiologists to note in their reports?
S.C.D.: It is important to note this distinction in the radiology report. If surgery is to be contemplated, a facetectomy may be necessary in addition to laminectomy and fusion in cases in which the lateral recess compromise is particularly severe. Certainly, it is a little more unusual to encounter isolated lateral recess changes without some component of a central problem. It is particularly relevant to know that there is something that we should be looking for from the standpoint of the superior facet encroaching on the inferior aspect of the foramen.
M.P.W.: In younger individuals it is particularly important if the stenosis is predominantly at one level and associated with unilateral radiculopathy. This distinction is not as important in an older person with bilateral pain, in which the stenosis results in central compression, because the wide decompression procedure will address both the lateral recess and the central canal stenosis.
M.N.B.-Z.: To what degree does patient age influence your management decision?
S.C.D.: Age is certainly a great influence in the patient with spinal stenosis. It is my opinion that the success rate of spinal stenosis decompression dramatically decreases in patients after age 70, and after age 80, it is almost uniformly unsuccessful.
G.F.G.: Age and its accompanying intercurrent diseases increase the surgical risk as well, and they prolong recovery. The older age group, however, may be more able and willing to alter their activities and lifestyle to lessen their symptoms and thus avoid surgery.
M.N.B.-Z.: What about the specific case of spondylolisthesis (Fig 5)? It seems to me that the relative frequency of this condition, 7% in the general population, makes it particularly hard to select patients for a surgical approach when their symptoms are relatively nonspecific. Does imaging help you decide which patients are operative candidates, particularly when the same degree of spondylolisthesis may be present in completely asymptomatic as well as severely symptomatic individuals?
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POSTOPERATIVE EXAMINATION OF PATIENTS |
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M.P.W.: In a typical situation, I would not recommend repeated imaging for at least 4 weeks. Pain during the postsurgical period, when nonspecific, is very difficult to interpret clinically. We know that imaging—even with MR—does not help and may be confusing, in that separation of postoperative phlegmon, early granulation tissue versus recurrent disk is quite difficult.
S.C.D.: I might wait even longer. I might not repeat imaging for at least 3 months, depending on the length of time the patient had symptoms prior to surgery. The longer a nerve root was compromised or irritated, the longer it make take for the symptoms to resolve. If there was an asymptomatic period following surgery and exacerbation occurred because of activity, then initially, I would treat the patient on the basis of his or her symptoms. If the patient remained dysfunctional or the symptoms once again became radicular in nature, a repeated imaging study at 2 months would be a consideration.
M.N.B.-Z.: That is good news for radiologists, because postoperative changes on images obtained shortly after surgery can simulate recurrent or residual disk extrusion and there is little that can be done to differentiate the possibilities (56). Enhancement of a previously involved nerve root on an MR image is quite difficult to interpret. Which imaging modality do you prefer for examining patients postoperatively?
S.C.D., M.P.W.: MR imaging with and without contrast material is preferable, unless osseous abnormalities, such as facet fracture, which may be missed at MR imaging, are suspected. Contrast material helps to visualize the neovascularity within granulation tissue by virtue of the rapid enhancement of the neovascularity compared with that of residual or recurrent disk protrusion. In addition, prominent enhancement of multiple nerve roots can suggest arachnoiditis. A postoperative fluid collection may be more ominous if it is surrounded by an enhancing capsule, which is suggestive of focal abscess.
M.N.B.-Z.: It is not unusual to see epidural granulation tissue at MR imaging following surgery in patients who are recurrently symptomatic. Does the presence of an epidural scar affect your management decisions?
G.F.G.: I believe that epidural scarring increases the difficulty and risk of reoperation and that it reduces the chances of a successful result. I know of no definitive studies on this subject, but it makes intuitive sense, because scar tissue forms after every surgery, that it will reform with the same or perhaps an accelerated rate when repeated surgery is performed. Early clinical trials of substances that inhibit scar formation have just begun.
M.N.B.-Z.: If there were epidural scar tissue surrounding a small residual disk fragment, would you reoperate?
G.F.G.: In most circumstances, I would not; I would continue conservative care and perhaps consider an epidural injection of a steroid agent.
S.C.D.: It depends on the size of the fragment, its location, and the patient’s specific symptoms. Thus, if a small disk fragment were surrounded by a considerable amount of epidural granulation tissue, this would probably be a reparative response that would eventually diminish. On the other hand, if a relatively symptom-free period after surgery were supplanted by recurrent radiculopathy and a moderately large disk fragment were shown to be compromising the nerve once again, then repeated surgery would certainly be a consideration.
M.N.B.-Z.: I hate to harp on this issue, but it is a particular problem for radiologists postoperatively in terms of interpretation. If we see an epidural scar surrounding a transiting nerve root in the lateral recess and there is radiculopathy in that nerve distribution, does surgery have a role?
G.F.G., M.P.W.: I think that in the majority of circumstances and for the reasons stated above, surgery does not have a role unless there is a pathologic entity other than just the epidural scar.
S.C.D.: Surgery has a role only when there is associated osseous and/or ligamentous hypertrophy or narrowing around the scar.
M.N.B.-Z.: Let us get beyond epidural scarring. What about retrospinal fluid collections depicted at imaging following surgery? What additional information other than the finding of the fluid would you like from the radiologist?
S.C.D.: I would like to know the location of the suspected leakage and the extent of the fluid accumulation in specific spaces. For instance, is all the fluid subjacent to the muscle fascia or is it above the fascia and/or up and down the canal (Fig 6)? Subfascial fluid is more likely to produce mass effect on the decompressed spinal canal. The full extent of the fluid collection needs to be understood in order for proper drainage to be undertaken.
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G.F.G.: Whether the fluid can be characterized as an infection versus a hematoma, seroma, or pure spinal fluid also is important.
M.N.B.-Z.: That may be asking too much from imaging, at least in terms of characterization. Enhancement surrounding a fluid collection can be a sign of inflammation, but it is entirely nonspecific; needle aspiration may be the most definitive way to answer that particular question. Speaking of enhancement, as I suggested earlier, radiologists often see some degree of nerve root enhancement at MR imaging with intravenous contrast material following surgery (59,60). Do you think this is physiologic, or can it correlate with radiculopathy?
M.P.W.: I think it is hard to correlate enhancement of the nerve root with radiculopathy in patients postoperatively. The enhancement most often reflects simply the physiologic features of the hyperemia related to the preexisting disk herniation and the local epidural granulation tissue (61).
M.N.B.-Z.: That raises the next question. Is arachnoid inflammation a common clinical problem following routine laminectomy and diskectomy (Fig 7)?
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G.F.G.: If by arachnoid inflammation you mean the inflammatory response to the manipulation of the nerve roots during surgery, then this is probably common. However, if one equates this inflammation to postoperative radicular pain, then I doubt that this occurs commonly.
M.N.B.-Z.: How often is the dura breached during routine lumbar disk surgery?
M.P.W.: It is my opinion that dural punctures probably occur approximately 5%–6% of the time, but dural tears larger than 2 mm occur less than 2%–3% of the time.
G.F.G.: I believe that a dural tear during a routine lumbar disk operation is a rare occurrence. Repeated surgery with substantial epidural scarring may lead to a higher risk of dural laceration, but dural tear still should not be a common occurrence.
M.N.B.-Z.: Are there any specific imaging findings that you look for in patients with posterior pedicle screw fusion, and which modalities do you prefer for this evaluation?
S.C.D.: I prefer CT for evaluating screw planes in this setting; it is also a better choice when looking for maturation of the fusion. CT depicts osseous fusion more accurately than does MR imaging. For the same reasons, the relationship between the screw and the surrounding pedicle and its cortical bone is shown to a better advantage with CT. However, MR imaging is more useful for evaluating the levels above and below the fusion for the same reasons that it is superior in nonsurgical cases (62).
M.P.W.: I also prefer CT, particularly for imaging in patients with stainless steel implants. However, in patients with titanium implants, MR imaging can provide considerable information and I choose it first (Fig 8). I like to evaluate the placement of the screw, particularly in any assessment of the pedicle wall.
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