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Obstetric MR Imaging¹

¹ Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215 (D.L., R.R.E.), and the Department of Radiology, Children's Hospital, Boston (P.D.B.). Received September 8, 1998; revision requested October 22; revision received November 23; accepted January 6, 1999. Studies of the fetal central nervous system were supported by National Institutes of Health grant NS 37945. Address reprint requests to D.L.

View larger version (146K): [in a new window]   Figure 1a. Ovarian edema in a 28-year-old woman with twins (initially quadruplets) at 14 weeks gestation who had undergone ovulation induction and had an enlarging solid left ovarian mass at US. (a) Sagittal turbo spin-echo MR image (5,139/90, two acquisitions, 140 x 256 matrix, echo train length of seven, 5-mm section thickness, 26 x 35-cm field of view, acquisition time of 3 minutes 3 seconds) of the gravid uterus (U) and enlarged (14 x 9 x 8 cm) left ovary with small peripheral follicles (arrows). The follicles have low signal intensity, which is likely due to hemorrhage. The enlargement of the left ovary was histopathologically shown to be caused by massive ovarian edema. Because of the long imaging time, fetal structures could not be identified. (b) Half-Fourier RARE MR image (single shot/60; field of view, 26 x 35 cm; matrix, 192 x 256; echo train length, 72; one signal acquired; section thickness, 5 mm) in the coronal plane demonstrates the gravid uterus (U) with the body of one fetus (arrowhead), hyperstimulated right ovary (open arrow), and edematous left ovary (O). (c) Coronal RARE MR image obtained slightly more anteriorly shows fetuses (one of which is not alive) in three gestational sacs.

View larger version (159K): [in a new window]   Figure 1b. Ovarian edema in a 28-year-old woman with twins (initially quadruplets) at 14 weeks gestation who had undergone ovulation induction and had an enlarging solid left ovarian mass at US. (a) Sagittal turbo spin-echo MR image (5,139/90, two acquisitions, 140 x 256 matrix, echo train length of seven, 5-mm section thickness, 26 x 35-cm field of view, acquisition time of 3 minutes 3 seconds) of the gravid uterus (U) and enlarged (14 x 9 x 8 cm) left ovary with small peripheral follicles (arrows). The follicles have low signal intensity, which is likely due to hemorrhage. The enlargement of the left ovary was histopathologically shown to be caused by massive ovarian edema. Because of the long imaging time, fetal structures could not be identified. (b) Half-Fourier RARE MR image (single shot/60; field of view, 26 x 35 cm; matrix, 192 x 256; echo train length, 72; one signal acquired; section thickness, 5 mm) in the coronal plane demonstrates the gravid uterus (U) with the body of one fetus (arrowhead), hyperstimulated right ovary (open arrow), and edematous left ovary (O). (c) Coronal RARE MR image obtained slightly more anteriorly shows fetuses (one of which is not alive) in three gestational sacs.

View larger version (171K): [in a new window]   Figure 1c. Ovarian edema in a 28-year-old woman with twins (initially quadruplets) at 14 weeks gestation who had undergone ovulation induction and had an enlarging solid left ovarian mass at US. (a) Sagittal turbo spin-echo MR image (5,139/90, two acquisitions, 140 x 256 matrix, echo train length of seven, 5-mm section thickness, 26 x 35-cm field of view, acquisition time of 3 minutes 3 seconds) of the gravid uterus (U) and enlarged (14 x 9 x 8 cm) left ovary with small peripheral follicles (arrows). The follicles have low signal intensity, which is likely due to hemorrhage. The enlargement of the left ovary was histopathologically shown to be caused by massive ovarian edema. Because of the long imaging time, fetal structures could not be identified. (b) Half-Fourier RARE MR image (single shot/60; field of view, 26 x 35 cm; matrix, 192 x 256; echo train length, 72; one signal acquired; section thickness, 5 mm) in the coronal plane demonstrates the gravid uterus (U) with the body of one fetus (arrowhead), hyperstimulated right ovary (open arrow), and edematous left ovary (O). (c) Coronal RARE MR image obtained slightly more anteriorly shows fetuses (one of which is not alive) in three gestational sacs.

View larger version (164K): [in a new window]   Figure 2. Partial placenta previa in a woman in 29th week of pregnancy. Sagittal RARE MR image (single shot/60) of the cervix shows placental tip (arrow) partially covering the internal os of the cervix.

View larger version (169K): [in a new window]   Figure 3. Placenta accreta diagnosed with MR imaging in a patient who previously underwent posterior myomectomy. Coronal RARE MR image (single shot/60) shows an absent myometrial-placental interface in a posterolateral location (arrowhead) surrounded by a normal myometrial-placental interface (arrows). This region was not well identified with US. A fibroid (F) is present in the right lateral aspect of the uterus. (Reprinted, with permission, from reference 36.)

View larger version (153K): [in a new window]   Figure 4a. Distal small-bowel obstruction in a pregnant woman who previously underwent abdominal surgery and had adhesions. (a) Coronal and (b) axial RARE MR images (single shot/60) show a dilated small bowel (sb), nondilated small-bowel loop (curved arrow) in the right lower region, and nondilated colon (straight arrows).

View larger version (110K): [in a new window]   Figure 4b. Distal small-bowel obstruction in a pregnant woman who previously underwent abdominal surgery and had adhesions. (a) Coronal and (b) axial RARE MR images (single shot/60) show a dilated small bowel (sb), nondilated small-bowel loop (curved arrow) in the right lower region, and nondilated colon (straight arrows).

View larger version (156K): [in a new window]   Figure 5a. Posterior encephalocele in a fetus at 20 weeks gestation. (a) Axial US scan shows a posterior encephalocele. A small amount of tissue (arrow) is seen within the sac. (b) On the axial RARE MR image (single shot/60), the structures of the posterior fossa appear to be normal. A portion of the encephalocele (arrowheads) is seen posteriorly. The information that the majority of the brain appeared to be normal was helpful to the patient in deciding to continue the pregnancy. Postnatally, a meningocele sac was excised, and the neural content returned to the posterior fossa. At the time this article was written, the baby was doing well at 1 year of age.

View larger version (160K): [in a new window]   Figure 5b. Posterior encephalocele in a fetus at 20 weeks gestation. (a) Axial US scan shows a posterior encephalocele. A small amount of tissue (arrow) is seen within the sac. (b) On the axial RARE MR image (single shot/60), the structures of the posterior fossa appear to be normal. A portion of the encephalocele (arrowheads) is seen posteriorly. The information that the majority of the brain appeared to be normal was helpful to the patient in deciding to continue the pregnancy. Postnatally, a meningocele sac was excised, and the neural content returned to the posterior fossa. At the time this article was written, the baby was doing well at 1 year of age.

View larger version (163K): [in a new window]   Figure 6a. Dandy-Walker malformation in a fetus at 34 weeks gestation. (a) Axial and (b) sagittal RARE MR images (single shot/60) show a Dandy-Walker malformation (M), with a large posterior fossa and key-hole deformity (arrows in a). The additional information provided by MR imaging, beyond that available with US, was that the corpus callosum (arrows in b) appeared to be normal and the aqueduct (not shown) was not grossly enlarged. It is hoped that, in the future, performing MR examinations in the late third trimester will obviate MR imaging immediately after birth, which requires sedation of the neonate.

View larger version (147K): [in a new window]   Figure 6b. Dandy-Walker malformation in a fetus at 34 weeks gestation. (a) Axial and (b) sagittal RARE MR images (single shot/60) show a Dandy-Walker malformation (M), with a large posterior fossa and key-hole deformity (arrows in a). The additional information provided by MR imaging, beyond that available with US, was that the corpus callosum (arrows in b) appeared to be normal and the aqueduct (not shown) was not grossly enlarged. It is hoped that, in the future, performing MR examinations in the late third trimester will obviate MR imaging immediately after birth, which requires sedation of the neonate.

View larger version (136K): [in a new window]   Figure 7a. Severe ventriculomegaly in a fetus at 30 weeks gestation. (a) Oblique axial US scan shows a 34-week head size and massively enlarged lateral ventricles. It is difficult to assess the cortical mantle. The posterior fossa appears to be small, and there is a dilated fourth ventricle (arrow), but the cerebellum is difficult to visualize ultrasonographically. (b) Sagittal and (c) coronal RARE MR images (single shot/60) demonstrate a definite rim of smooth cortical tissue (arrowheads in b), malformed brain stem (arrow in b), and Dandy-Walker malformation (M). These findings make hydranencephaly unlikely and suggest a cerebrocerebellar malformation, such as Walker-Warburg syndrome, with aqueductal stenosis. This type of information is important in counseling patients prior to delivery.

View larger version (136K): [in a new window]   Figure 7c. Severe ventriculomegaly in a fetus at 30 weeks gestation. (a) Oblique axial US scan shows a 34-week head size and massively enlarged lateral ventricles. It is difficult to assess the cortical mantle. The posterior fossa appears to be small, and there is a dilated fourth ventricle (arrow), but the cerebellum is difficult to visualize ultrasonographically. (b) Sagittal and (c) coronal RARE MR images (single shot/60) demonstrate a definite rim of smooth cortical tissue (arrowheads in b), malformed brain stem (arrow in b), and Dandy-Walker malformation (M). These findings make hydranencephaly unlikely and suggest a cerebrocerebellar malformation, such as Walker-Warburg syndrome, with aqueductal stenosis. This type of information is important in counseling patients prior to delivery.

View larger version (140K): [in a new window]   Figure 7b. Severe ventriculomegaly in a fetus at 30 weeks gestation. (a) Oblique axial US scan shows a 34-week head size and massively enlarged lateral ventricles. It is difficult to assess the cortical mantle. The posterior fossa appears to be small, and there is a dilated fourth ventricle (arrow), but the cerebellum is difficult to visualize ultrasonographically. (b) Sagittal and (c) coronal RARE MR images (single shot/60) demonstrate a definite rim of smooth cortical tissue (arrowheads in b), malformed brain stem (arrow in b), and Dandy-Walker malformation (M). These findings make hydranencephaly unlikely and suggest a cerebrocerebellar malformation, such as Walker-Warburg syndrome, with aqueductal stenosis. This type of information is important in counseling patients prior to delivery.

View larger version (179K): [in a new window]   Figure 8. Agenesis of the corpus callosum in a fetus at 34 weeks gestation. Coronal RARE MR image (single shot/60) shows the characteristic vertical orientation of the frontal horns (arrows) in agenesis of the corpus callosum. Arrowheads point to the region where the corpus callosum should be depicted. The US scan demonstrated only asymmetric mild ventriculomegaly. (Reprinted, with permission, from reference 55.)

View larger version (148K): [in a new window]   Figure 9a. Arachnoid cyst in a fetus at 27 weeks gestation. (a–c) C = extraaxial collection. (a) Axial US scan demonstrates an extraaxial collection, but it is difficult to assess the involvement of the ventricular system. (b) Coronal and (c) sagittal RARE MR images (single shot/60) clearly demonstrate the extraaxial nature of this extensive arachnoid cyst with mass effect on the surrounding structures.

View larger version (164K): [in a new window]   Figure 9b. Arachnoid cyst in a fetus at 27 weeks gestation. (a–c) C = extraaxial collection. (a) Axial US scan demonstrates an extraaxial collection, but it is difficult to assess the involvement of the ventricular system. (b) Coronal and (c) sagittal RARE MR images (single shot/60) clearly demonstrate the extraaxial nature of this extensive arachnoid cyst with mass effect on the surrounding structures.

View larger version (163K): [in a new window]   Figure 9c. Arachnoid cyst in a fetus at 27 weeks gestation. (a–c) C = extraaxial collection. (a) Axial US scan demonstrates an extraaxial collection, but it is difficult to assess the involvement of the ventricular system. (b) Coronal and (c) sagittal RARE MR images (single shot/60) clearly demonstrate the extraaxial nature of this extensive arachnoid cyst with mass effect on the surrounding structures.

View larger version (162K): [in a new window]   Figure 10a. Gastric duplication cyst in a fetus at 28 weeks gestation. (a) Oblique coronal US scan shows an echogenic abdominal mass (calipers), which is suggestive of a meconium pseudocyst. (b–d) m = mass, s = stomach. (b) Sagittal T2-weighted RARE MR image (single shot/60) shows the mass impressing on the stomach. The mass is of slightly lower signal intensity than the stomach on this image. (c) Axial RARE MR image (single shot/60) shows findings similar to those in b. (d) Axial T1-weighted image (126/4, 80° flip angle, 24 x 32-cm field of view, 96 x 256 matrix, 5-mm section thickness, one signal acquired) shows that the mass has slightly lower signal intensity than that of the adjacent stomach. The appearance of the mass suggests a duplication cyst, which was confirmed postnatally.

View larger version (148K): [in a new window]   Figure 10b. Gastric duplication cyst in a fetus at 28 weeks gestation. (a) Oblique coronal US scan shows an echogenic abdominal mass (calipers), which is suggestive of a meconium pseudocyst. (b–d) m = mass, s = stomach. (b) Sagittal T2-weighted RARE MR image (single shot/60) shows the mass impressing on the stomach. The mass is of slightly lower signal intensity than the stomach on this image. (c) Axial RARE MR image (single shot/60) shows findings similar to those in b. (d) Axial T1-weighted image (126/4, 80° flip angle, 24 x 32-cm field of view, 96 x 256 matrix, 5-mm section thickness, one signal acquired) shows that the mass has slightly lower signal intensity than that of the adjacent stomach. The appearance of the mass suggests a duplication cyst, which was confirmed postnatally.

View larger version (104K): [in a new window]   Figure 10c. Gastric duplication cyst in a fetus at 28 weeks gestation. (a) Oblique coronal US scan shows an echogenic abdominal mass (calipers), which is suggestive of a meconium pseudocyst. (b–d) m = mass, s = stomach. (b) Sagittal T2-weighted RARE MR image (single shot/60) shows the mass impressing on the stomach. The mass is of slightly lower signal intensity than the stomach on this image. (c) Axial RARE MR image (single shot/60) shows findings similar to those in b. (d) Axial T1-weighted image (126/4, 80° flip angle, 24 x 32-cm field of view, 96 x 256 matrix, 5-mm section thickness, one signal acquired) shows that the mass has slightly lower signal intensity than that of the adjacent stomach. The appearance of the mass suggests a duplication cyst, which was confirmed postnatally.

View larger version (126K): [in a new window]   Figure 10d. Gastric duplication cyst in a fetus at 28 weeks gestation. (a) Oblique coronal US scan shows an echogenic abdominal mass (calipers), which is suggestive of a meconium pseudocyst. (b–d) m = mass, s = stomach. (b) Sagittal T2-weighted RARE MR image (single shot/60) shows the mass impressing on the stomach. The mass is of slightly lower signal intensity than the stomach on this image. (c) Axial RARE MR image (single shot/60) shows findings similar to those in b. (d) Axial T1-weighted image (126/4, 80° flip angle, 24 x 32-cm field of view, 96 x 256 matrix, 5-mm section thickness, one signal acquired) shows that the mass has slightly lower signal intensity than that of the adjacent stomach. The appearance of the mass suggests a duplication cyst, which was confirmed postnatally.

View larger version (135K): [in a new window]   Figure 11a. Fetal cloacal exstrophy. (a,b) Fetus at 20 weeks gestation. (a) Sagittal US scan shows a low anterior abdominal wall defect (solid arrows). A fluid collection (open arrow) is seen in the pelvis, which is suggestive of a deformed bladder; however, the bladder should not be seen in a case of exstrophy. The kidneys are not visible. (b) Axial RARE MR image (single shot/60) shows a pelvic kidney (arrowheads in b and c) in the region of the fluid collection seen in a. The spinal cord (arrow in b and c) is seen at this level, which is consistent with a tethered cord. (c) Axial RARE MR image (single shot/60) of the fetus at 38 weeks gestation again shows the pelvic kidney and tethered cord. These diagnoses were made prospectively after discussions with specialists in pediatric surgery and pediatric radiology. One of the benefits of fetal MR imaging is that specialists who are not accustomed to obstetric US can view MR images, with which they may be more familiar.

View larger version (169K): [in a new window]   Figure 11b. Fetal cloacal exstrophy. (a,b) Fetus at 20 weeks gestation. (a) Sagittal US scan shows a low anterior abdominal wall defect (solid arrows). A fluid collection (open arrow) is seen in the pelvis, which is suggestive of a deformed bladder; however, the bladder should not be seen in a case of exstrophy. The kidneys are not visible. (b) Axial RARE MR image (single shot/60) shows a pelvic kidney (arrowheads in b and c) in the region of the fluid collection seen in a. The spinal cord (arrow in b and c) is seen at this level, which is consistent with a tethered cord. (c) Axial RARE MR image (single shot/60) of the fetus at 38 weeks gestation again shows the pelvic kidney and tethered cord. These diagnoses were made prospectively after discussions with specialists in pediatric surgery and pediatric radiology. One of the benefits of fetal MR imaging is that specialists who are not accustomed to obstetric US can view MR images, with which they may be more familiar.

View larger version (154K): [in a new window]   Figure 11c. Fetal cloacal exstrophy. (a,b) Fetus at 20 weeks gestation. (a) Sagittal US scan shows a low anterior abdominal wall defect (solid arrows). A fluid collection (open arrow) is seen in the pelvis, which is suggestive of a deformed bladder; however, the bladder should not be seen in a case of exstrophy. The kidneys are not visible. (b) Axial RARE MR image (single shot/60) shows a pelvic kidney (arrowheads in b and c) in the region of the fluid collection seen in a. The spinal cord (arrow in b and c) is seen at this level, which is consistent with a tethered cord. (c) Axial RARE MR image (single shot/60) of the fetus at 38 weeks gestation again shows the pelvic kidney and tethered cord. These diagnoses were made prospectively after discussions with specialists in pediatric surgery and pediatric radiology. One of the benefits of fetal MR imaging is that specialists who are not accustomed to obstetric US can view MR images, with which they may be more familiar.