(Radiographics. 2000;20:1227-1243.)
© RSNA, 2000
MR Imaging of Non-CNS Fetal Abnormalities: A Pictorial Essay1
Hiroshi Shinmoto, MD,
Kyoko Kashima, MD,
Yuji Yuasa, MD,
Akihiro Tanimoto, MD,
Yasuhide Morikawa, MD,
Hitoshi Ishimoto, MD,
Yasunori Yoshimura, MD and
Kyoichi Hiramatsu, MD
1 From the Departments of Diagnostic Radiology (H.S., K.K., Y. Yuasa, A.T., K.H.), Pediatric Surgery (Y.M.), and Obstetrics and Gynecology (H.I., Y. Yoshimura), Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan. Presented as a scientific exhibit at the 1999 RSNA scientific assembly. Received February 1, 2000; revision requested March 17 and received April 24; accepted April 25. Address correspondence to H.S. (e-mail: shinmoto@med.keio.ac.jp).
 |
Abstract
|
|---|
The recent popularity of prenatal magnetic resonance (MR) imaging has been associated with the development of ultrafast MR imaging techniques such as the single-shot fast spin-echo sequence. However, the majority of previous reports have concerned the fetal central nervous system (CNS) and chest disorders. MR imaging can demonstrate non-CNS fetal anatomy and pathologic conditions clearly. With its excellent tissue contrast, MR imaging provides information that supplements that provided by ultrasonography (US), especially in cases of neck, chest, and gastrointestinal lesions. Because of its large field of view, MR imaging allows evaluation of the relationship between a large lesion and adjacent structures. MR imaging should be considered if the diagnosis of a suspected non-CNS lesion is unclear at fetal US. MR imaging plays an important complementary role to US in cases of non-CNS fetal lesions and will be further accepted for fetal imaging in the future.
Index Terms: Fetus, abnormalities, 856.87 • Fetus, MR, 856.121416 • Fetus, US, 856.1298 • Magnetic resonance (MR), comparative studies, 856.121416, 856.1298 • Magnetic resonance (MR), rapid imaging, 856.121416 • Pregnancy, MR, 856.121416
|
Introduction
|
|---|
Although magnetic resonance (MR) imaging was sometimes used for fetal imaging in the past, its usefulness was limited by fetal motion owing to the long acquisition times of the conventional spin-echo technique (1). Maternal or fetal sedation was frequently needed to achieve motion-free fetal imaging; however, such complicated manipulations prevented prenatal MR imaging from being widely used. Even with the fast spin-echo technique, the image quality is not sufficient to obtain a reliable diagnosis for clinicians. The recent popularity of prenatal MR imaging has been associated with the development of ultrafast MR imaging techniques such as the single-shot fast spin-echo sequence (2–4). This sequence significantly reduces motion artifact. With this technique, T2-weighted images of the fetus are obtained in less than 1 second per section without image degradation.
Ultrasonography (US) is the method of choice for evaluating the fetus because of its real-time display and noninvasive nature. In general, MR imaging is relatively operator independent and offers better tissue contrast than does US. In addition, the larger field of view of MR imaging allows easy understanding of the relationship between adjacent structures. However, the majority of previous reports on fetal MR imaging have concerned the central nervous system (CNS) and thoracic disorders (5–9). A few reports have described fetal MR imaging of the neck and gastrointestinal and genitourinary diseases (10–12), but the accepted role of MR imaging in these areas has yet to be determined.
In this article, the technique of fetal MR imaging is described, non-CNS normal anatomy and pathologic conditions are presented, and advantages and disadvantages of fetal MR imaging are discussed.
|
Technique
|
|---|
Studies were performed with a 1.5-T unit (Signa; GE Medical Systems, Milwaukee, Wis) and a torso-array coil. Fifty-one fetuses with suspected non-CNS abnormalities at US (two face and neck lesions, nine chest lesions, two heart lesions, nine abdominal wall lesions, six gastrointestinal lesions, eight genitourinary lesions, five neoplasms, and 10 other lesions) underwent MR imaging between November 1997 and October 1999 at our institution. Informed consent was obtained in all cases. The fetuses were imaged at 20 weeks gestation or later to allow completion of organogenesis.
After a scout acquisition was performed with a fast spoiled gradient-echo sequence, a series of fetal images in the axial, sagittal, and coronal planes were obtained with the single-shot fast spin-echo technique. Each new acquisition was prescribed by using images from the immediately prior acquisition to avoid the misregistration caused by fetal movement. The single-shot fast spin-echo sequence began with a 90° pulse followed by a train of refocusing 180° pulses, creating a series of images sequentially. Because this sequence is a single-shot technique, a series of images is not severely degraded by fetal movement. The imaging parameters were 
/98 (repetition time msec/effective echo time msec), 0.5 signal acquired, 31.2-kHz bandwidth, and imaging time of approximately 18–25 seconds for 15 contiguous sections, which allowed maternal breath-hold studies. T1-weighted fast spin-echo imaging (460/8.3, one signal acquired, 31.2-kHz bandwidth, 25-second imaging time for 18 sections) in the most suitable plane for revealing a fetal pathologic condition was also performed with a maternal breath hold.
|
Normal Anatomy
|
|---|
Single-shot fast spin-echo images show the major thoracic and abdominal structures clearly (Fig 1), whereas T1-weighted fast spin-echo images are useful for detecting bowel loops (Fig 2). The lungs are moderately hyperintense on single-shot fast spin-echo images and hypointense on T1-weighted fast spin-echo images because they contain amniotic fluid. The nasopharynx, oropharynx, and trachea, which are filled with amniotic fluid, are also bright on single-shot fast spin-echo images and dark on T1-weighted fast spin-echo images. The aorta, pulmonary vessels, and heart are dark on single-shot fast spin-echo images due to flow void. The four chambers of the heart cannot be distinguished with MR imaging. The thymus has intermediate signal intensity on single-shot fast spin-echo images. The thyroid gland is indistinct and isointense to surrounding structures on single-shot fast spin-echo images; however, on T1-weighted fast spin-echo images, the thyroid appears as a characteristic hyperintense structure compared with surrounding tissues (Fig 3).
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1a. Normal anatomy in a 35-week-old fetus as shown on single-shot fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). (a) Image shows the scrotum (arrow). (b) Image shows the thymus (open arrow) and urinary bladder (solid arrow). (c) Image shows the heart (arrow), liver (*), and stomach (arrowhead). (d) Image shows the trachea (solid white arrow), gallbladder (open white arrow), and jejunum (black arrow). (e) Image shows the right kidney (arrow). (f) Image shows the spleen (arrow) and left kidney (arrowhead).
|
|
View larger version (118K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1b. Normal anatomy in a 35-week-old fetus as shown on single-shot fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). (a) Image shows the scrotum (arrow). (b) Image shows the thymus (open arrow) and urinary bladder (solid arrow). (c) Image shows the heart (arrow), liver (*), and stomach (arrowhead). (d) Image shows the trachea (solid white arrow), gallbladder (open white arrow), and jejunum (black arrow). (e) Image shows the right kidney (arrow). (f) Image shows the spleen (arrow) and left kidney (arrowhead).
|
|
View larger version (118K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1c. Normal anatomy in a 35-week-old fetus as shown on single-shot fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). (a) Image shows the scrotum (arrow). (b) Image shows the thymus (open arrow) and urinary bladder (solid arrow). (c) Image shows the heart (arrow), liver (*), and stomach (arrowhead). (d) Image shows the trachea (solid white arrow), gallbladder (open white arrow), and jejunum (black arrow). (e) Image shows the right kidney (arrow). (f) Image shows the spleen (arrow) and left kidney (arrowhead).
|
|
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1d. Normal anatomy in a 35-week-old fetus as shown on single-shot fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). (a) Image shows the scrotum (arrow). (b) Image shows the thymus (open arrow) and urinary bladder (solid arrow). (c) Image shows the heart (arrow), liver (*), and stomach (arrowhead). (d) Image shows the trachea (solid white arrow), gallbladder (open white arrow), and jejunum (black arrow). (e) Image shows the right kidney (arrow). (f) Image shows the spleen (arrow) and left kidney (arrowhead).
|
|
View larger version (118K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1e. Normal anatomy in a 35-week-old fetus as shown on single-shot fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). (a) Image shows the scrotum (arrow). (b) Image shows the thymus (open arrow) and urinary bladder (solid arrow). (c) Image shows the heart (arrow), liver (*), and stomach (arrowhead). (d) Image shows the trachea (solid white arrow), gallbladder (open white arrow), and jejunum (black arrow). (e) Image shows the right kidney (arrow). (f) Image shows the spleen (arrow) and left kidney (arrowhead).
|
|
View larger version (117K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1f. Normal anatomy in a 35-week-old fetus as shown on single-shot fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). (a) Image shows the scrotum (arrow). (b) Image shows the thymus (open arrow) and urinary bladder (solid arrow). (c) Image shows the heart (arrow), liver (*), and stomach (arrowhead). (d) Image shows the trachea (solid white arrow), gallbladder (open white arrow), and jejunum (black arrow). (e) Image shows the right kidney (arrow). (f) Image shows the spleen (arrow) and left kidney (arrowhead).
|
|
View larger version (122K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2a. Normal anatomy in a 35-week-old fetus (same subject as in Fig 1) as shown on T1-weighted fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). The distal ileum (arrowhead) and entire colon (black arrow) show high signal intensity. White arrow = rectum.
|
|
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2b. Normal anatomy in a 35-week-old fetus (same subject as in Fig 1) as shown on T1-weighted fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). The distal ileum (arrowhead) and entire colon (black arrow) show high signal intensity. White arrow = rectum.
|
|
View larger version (117K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2c. Normal anatomy in a 35-week-old fetus (same subject as in Fig 1) as shown on T1-weighted fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). The distal ileum (arrowhead) and entire colon (black arrow) show high signal intensity. White arrow = rectum.
|
|
View larger version (120K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2d. Normal anatomy in a 35-week-old fetus (same subject as in Fig 1) as shown on T1-weighted fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). The distal ileum (arrowhead) and entire colon (black arrow) show high signal intensity. White arrow = rectum.
|
|
View larger version (115K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2e. Normal anatomy in a 35-week-old fetus (same subject as in Fig 1) as shown on T1-weighted fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). The distal ileum (arrowhead) and entire colon (black arrow) show high signal intensity. White arrow = rectum.
|
|
View larger version (109K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2f. Normal anatomy in a 35-week-old fetus (same subject as in Fig 1) as shown on T1-weighted fast spin-echo MR images. Coronal images are presented from anterior (a) to posterior (f). The distal ileum (arrowhead) and entire colon (black arrow) show high signal intensity. White arrow = rectum.
|
|
View larger version (180K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3a. Normal thyroid in a 34-week-old fetus. (a) Coronal T1-weighted fast spin-echo MR image shows the thyroid as a symmetric, hyperintense structure (arrows). (b) Coronal single-shot fast spin-echo MR image shows the thyroid as isointense compared with surrounding structures.
|
|
View larger version (182K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3b. Normal thyroid in a 34-week-old fetus. (a) Coronal T1-weighted fast spin-echo MR image shows the thyroid as a symmetric, hyperintense structure (arrows). (b) Coronal single-shot fast spin-echo MR image shows the thyroid as isointense compared with surrounding structures.
|
|
In the abdomen, the stomach shows typical fluid signal intensity. Because the stomach is easily recognized as a saccular structure, one should confirm that the stomach is in its expected anatomic location. The signal intensity of the proximal small intestine is different from that of the distal small intestine and colon. The former appears hyperintense on single-shot fast spin-echo images and hypointense on T1-weighted images, whereas the latter appears hypointense on single-shot fast spin-echo images and hyperintense on T1-weighted images. The amniotic fluid in the proximal small intestine and the meconium in the distal small intestine and colon cause these signal intensity differences (9,11). The liver is clearly visualized as a moderately dark structure on single-shot fast spin-echo images. The signal intensity of the spleen is similar to that of the liver. The gallbladder is detected as a cystic structure under the lower aspect of the liver. The kidneys and renal pelves are clearly seen on single-shot fast spin-echo images. The urinary bladder is easily recognized as a fluid-filled structure in the pelvis. The scrotum and penis are often recognized in the male fetus, but the female genital organs are hardly ever detected.
|
Pathologic Conditions
|
|---|
Neck
The most common type of cervical mass detected prenatally is a cystic hygroma, which is usually located posterolaterally in the neck (13). Most anterior neck masses are either goiter or teratoma (13). Fetal goiter is usually associated with maternal thyroid disease. Goiter is indistinguishable from surrounding tissues on single-shot fast spin-echo images; however, it is easy to recognize on T1-weighted fast spin-echo images because of its homogeneous high signal intensity (Fig 4). MR imaging is useful in differentiating goiter from other masses that occur in the anterior neck (eg, teratoma and hemangioma) because of the characteristic signal intensity of goiter.
View larger version (151K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4a. Goiter in a 30-week-old fetus. (a) Sagittal T1-weighted fast spin-echo MR image shows a huge anterior neck mass with homogeneous high signal intensity, which suggests the diagnosis of fetal goiter. (b) Sagittal single-shot fast spin-echo MR image shows the mass, which is isointense and compresses the bright trachea posteriorly (arrowhead). (c) Axial T1-weighted fast spin-echo MR image obtained at 35 weeks gestation after intrauterine hormonal therapy shows the goiter, which is now smaller and has the normal symmetric thyroid shape.
|
|
View larger version (155K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4b. Goiter in a 30-week-old fetus. (a) Sagittal T1-weighted fast spin-echo MR image shows a huge anterior neck mass with homogeneous high signal intensity, which suggests the diagnosis of fetal goiter. (b) Sagittal single-shot fast spin-echo MR image shows the mass, which is isointense and compresses the bright trachea posteriorly (arrowhead). (c) Axial T1-weighted fast spin-echo MR image obtained at 35 weeks gestation after intrauterine hormonal therapy shows the goiter, which is now smaller and has the normal symmetric thyroid shape.
|
|
View larger version (175K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4c. Goiter in a 30-week-old fetus. (a) Sagittal T1-weighted fast spin-echo MR image shows a huge anterior neck mass with homogeneous high signal intensity, which suggests the diagnosis of fetal goiter. (b) Sagittal single-shot fast spin-echo MR image shows the mass, which is isointense and compresses the bright trachea posteriorly (arrowhead). (c) Axial T1-weighted fast spin-echo MR image obtained at 35 weeks gestation after intrauterine hormonal therapy shows the goiter, which is now smaller and has the normal symmetric thyroid shape.
|
|
Chest
The major causes of an intrathoracic mass are congenital diaphragmatic hernia, cystic adenomatoid malformation, and bronchopulmonary sequestration (14). Congenital diaphragmatic hernia usually occurs posterolaterally on the left side (Bochdalek hernia) (15,16). The diaphragm is clearly seen separating the chest from the abdomen on coronal and sagittal single-shot fast spin-echo images. At MR imaging, the displaced organs extending into the chest beyond the diaphragm are clearly seen (Fig 5). The stomach, small intestine, and colon frequently herniate into the chest, whereas the liver, gallbladder, and spleen herniate less commonly. Because the presence of liver herniation and the size of the hernia are associated with the degree of pulmonary hypoplasia, these factors are important for fetal prognosis. At MR imaging, the liver, small intestine, and colon are differentiated from the lung by means of their characteristic signal intensities; however, at US, differentiation of the liver and bowel loops from the lung and lung masses is sometimes difficult. The stomach and proximal small intestine appear bright on single-shot fast spin-echo images, and the distal small intestine and colon appear bright on T1-weighted images. In addition, the position of the liver is easily recognized on both single-shot fast spin-echo and T1-weighted images.
View larger version (154K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5. Congenital diaphragmatic hernia in a 36-week-old fetus. Coronal single-shot fast spin-echo MR image shows the stomach (straight solid arrow), small intestine (open arrow), and colon (arrowhead) to the left of the mediastinum. The mediastinal structures are shifted to the right, and the lungs show marked hypoplasia. The normal right hemidiaphragm is clearly seen (curved arrow).
|
|
Cystic adenomatoid malformation is classified into three types: large macrocyst (type I), small macrocyst (type II), and solid (type III) (17). The MR imaging appearance of cystic adenomatoid malformation depends on the size of the cysts. The cysts have fluid signal intensity, forming a contrast to normal lung (Fig 6). Polyhydramnios and hydrops are associated with cystic adenomatoid malformation and indicate a poor prognosis. The prognosis for type III cystic adenomatoid malformation is also poor. The cysts occasionally decrease in size and improve spontaneously.
View larger version (159K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 6a. Type II cystic adenomatoid malformation in a 29-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows multiple small cysts in the lower lobe of the right lung. (b) Coronal gadolinium-enhanced MR angiogram obtained 4 days after birth clearly shows an aberrant artery from the abdominal aorta.
|
|
View larger version (144K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 6b. Type II cystic adenomatoid malformation in a 29-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows multiple small cysts in the lower lobe of the right lung. (b) Coronal gadolinium-enhanced MR angiogram obtained 4 days after birth clearly shows an aberrant artery from the abdominal aorta.
|
|
Bronchopulmonary sequestration is classified into two types: extralobar and intralobar (14). The extralobar type has its own pleura, which separates it from normal lung tissue (Fig 7). Most cases of extralobar sequestration occur on the left side, whereas intralobar sequestration occurs with equal frequency on either side. Sequestered lung tissue is markedly hyperintense on single-shot fast spin-echo images and hypointense on T1-weighted fast spin-echo images relative to normal lung tissue.
View larger version (135K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7a. Bronchopulmonary sequestration in a 23-week-old fetus. (a) Oblique sagittal US scan shows cystic structures in a hyperechoic left lung (the cranial direction of the fetus is on the right). This appearance was diagnosed as cystic adenomatoid malformation. (b, c) Oblique coronal single-shot fast spin-echo MR images show the left side of the thorax mostly occupied by an abnormal mass with small cysts (arrowhead), which compresses the hypoplastic left lung superiorly (arrow in b). The mass is markedly hyperintense relative to the normal right lung. An aberrant artery from the descending aorta is seen as a flow void (arrow in c). (d) Autopsy photograph shows an extralobar sequestration covered by normal pleura with an aberrant vessel. The hypoplastic left lung can be separately identified (arrow).
|
|
View larger version (171K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7b. Bronchopulmonary sequestration in a 23-week-old fetus. (a) Oblique sagittal US scan shows cystic structures in a hyperechoic left lung (the cranial direction of the fetus is on the right). This appearance was diagnosed as cystic adenomatoid malformation. (b, c) Oblique coronal single-shot fast spin-echo MR images show the left side of the thorax mostly occupied by an abnormal mass with small cysts (arrowhead), which compresses the hypoplastic left lung superiorly (arrow in b). The mass is markedly hyperintense relative to the normal right lung. An aberrant artery from the descending aorta is seen as a flow void (arrow in c). (d) Autopsy photograph shows an extralobar sequestration covered by normal pleura with an aberrant vessel. The hypoplastic left lung can be separately identified (arrow).
|
|
View larger version (151K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7c. Bronchopulmonary sequestration in a 23-week-old fetus. (a) Oblique sagittal US scan shows cystic structures in a hyperechoic left lung (the cranial direction of the fetus is on the right). This appearance was diagnosed as cystic adenomatoid malformation. (b, c) Oblique coronal single-shot fast spin-echo MR images show the left side of the thorax mostly occupied by an abnormal mass with small cysts (arrowhead), which compresses the hypoplastic left lung superiorly (arrow in b). The mass is markedly hyperintense relative to the normal right lung. An aberrant artery from the descending aorta is seen as a flow void (arrow in c). (d) Autopsy photograph shows an extralobar sequestration covered by normal pleura with an aberrant vessel. The hypoplastic left lung can be separately identified (arrow).
|
|
View larger version (153K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7d. Bronchopulmonary sequestration in a 23-week-old fetus. (a) Oblique sagittal US scan shows cystic structures in a hyperechoic left lung (the cranial direction of the fetus is on the right). This appearance was diagnosed as cystic adenomatoid malformation. (b, c) Oblique coronal single-shot fast spin-echo MR images show the left side of the thorax mostly occupied by an abnormal mass with small cysts (arrowhead), which compresses the hypoplastic left lung superiorly (arrow in b). The mass is markedly hyperintense relative to the normal right lung. An aberrant artery from the descending aorta is seen as a flow void (arrow in c). (d) Autopsy photograph shows an extralobar sequestration covered by normal pleura with an aberrant vessel. The hypoplastic left lung can be separately identified (arrow).
|
|
Abdomen
Abdominal Wall Abnormalities.—Gastroschisis is a paraumbilical defect of the abdominal wall, typically on the right side (18). The intestine prolapses through the defect and floats in the amniotic fluid without a covering membrane. The small intestine is usually prolapsed, and the colon, stomach, and liver are occasionally involved. A cystic dilated intestine, suggesting bowel obstruction, is easily recognized at MR imaging (Fig 8), whereas it is sometimes difficult to distinguish a cystic dilated bowel loop from a cystic neoplasm at US. Omphalocele is a midline defect of the abdominal wall at the attachment of the umbilical cord (18). The prolapsed organs are covered by an omphalocele sac, which is clearly demonstrated at MR imaging (Fig 9). The intestine, stomach, and liver may prolapse into the omphalocele sac. The presence or absence of the liver in the sac is easily recognized at MR imaging.
View larger version (162K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 8a. Gastroschisis in a 28-week-old fetus. (a) Sagittal single-shot fast spin-echo MR image shows a midline abdominal wall defect and prolapse of a bowel loop (arrow) into the amniotic fluid. (b) Follow-up sagittal MR image obtained 3 weeks later shows progressive change in the bowel prolapse; the markedly dilated small bowel loops are clearly identified (arrow). Polyhydramnios has increased in volume.
|
|
View larger version (166K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 8b. Gastroschisis in a 28-week-old fetus. (a) Sagittal single-shot fast spin-echo MR image shows a midline abdominal wall defect and prolapse of a bowel loop (arrow) into the amniotic fluid. (b) Follow-up sagittal MR image obtained 3 weeks later shows progressive change in the bowel prolapse; the markedly dilated small bowel loops are clearly identified (arrow). Polyhydramnios has increased in volume.
|
|
View larger version (149K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9a. Omphalocele in a 35-week-old fetus. (a) Sagittal single-shot fast spin-echo MR image shows prolapse of the liver (white arrowhead) and small bowel loops (black arrowhead) into an omphalocele sac as a lump. (b) Axial single-shot fast spin-echo MR image also shows prolapse of the stomach (solid arrow) and colon (open arrow).
|
|
View larger version (153K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9b. Omphalocele in a 35-week-old fetus. (a) Sagittal single-shot fast spin-echo MR image shows prolapse of the liver (white arrowhead) and small bowel loops (black arrowhead) into an omphalocele sac as a lump. (b) Axial single-shot fast spin-echo MR image also shows prolapse of the stomach (solid arrow) and colon (open arrow).
|
|
Gastrointestinal Abnormalities.—Hiatal hernia is categorized as a congenital diaphragmatic defect. At MR imaging, protrusion of the stomach through the esophageal hiatus is clearly demonstrated (Fig 10). Duodenal atresia is diagnosed by means of the double bubble sign (Fig 11). The differential diagnosis for the double bubble sign includes duodenal stenosis, annular pancreas, Ladd bands, and volvulus. Small bowel atresia is seen as dilated bowel loops proximal to the obstructed segment, and the colon is not usually visualized (Figs 12–14). The signal intensities of the bowel contents on single-shot fast spin-echo and T1-weighted fast spin-echo images may be useful in identifying the obstructed segment: Hyperintense bowel dilatation on single-shot fast spin-echo images indicates proximal small bowel obstruction, whereas hypointense bowel dilatation on single-shot fast spin-echo images and hyperintense bowel dilatation on T1-weighted fast spin-echo images indicate distal small bowel or colonic obstruction (9,11). These characteristic differences in signal intensity give MR imaging an advantage over US in identification of the obstructed segment. Care should be taken to distinguish marked bowel dilatation from cystic masses such as choledochal cyst and ovarian cyst.
View larger version (169K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 10a. Hiatal hernia in a 31-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows the stomach (arrow) protruding through the esophageal hiatus. (b) Barium esophagogram shows a sliding hiatal hernia.
|
|
View larger version (99K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 10b. Hiatal hernia in a 31-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows the stomach (arrow) protruding through the esophageal hiatus. (b) Barium esophagogram shows a sliding hiatal hernia.
|
|
View larger version (150K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11a. Duodenal atresia in a 35-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows dilatation of the stomach (top arrow) and the proximal portion of the duodenum (bottom arrow), producing a "double bubble" appearance. (b) Coronal T1-weighted fast spin-echo MR image shows an empty small intestine and a meconium-filled colon (arrow). The distention of the stomach and the duodenum suggests duodenal atresia. (c) Radiograph obtained after birth shows distention of the stomach and proximal duodenum.
|
|
View larger version (157K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11b. Duodenal atresia in a 35-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows dilatation of the stomach (top arrow) and the proximal portion of the duodenum (bottom arrow), producing a "double bubble" appearance. (b) Coronal T1-weighted fast spin-echo MR image shows an empty small intestine and a meconium-filled colon (arrow). The distention of the stomach and the duodenum suggests duodenal atresia. (c) Radiograph obtained after birth shows distention of the stomach and proximal duodenum.
|
|
View larger version (123K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11c. Duodenal atresia in a 35-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows dilatation of the stomach (top arrow) and the proximal portion of the duodenum (bottom arrow), producing a "double bubble" appearance. (b) Coronal T1-weighted fast spin-echo MR image shows an empty small intestine and a meconium-filled colon (arrow). The distention of the stomach and the duodenum suggests duodenal atresia. (c) Radiograph obtained after birth shows distention of the stomach and proximal duodenum.
|
|
View larger version (151K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 12. Small bowel atresia in a 31-week-old fetus. Coronal single-shot fast spin-echo MR image shows equally distended small bowel loops with homogeneous high signal intensity, an appearance suggestive of proximal small bowel obstruction.
|
|
View larger version (192K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13. Double small bowel atresia in a 34-week-old fetus. Coronal single-shot fast spin-echo MR images (presented from anterior [top left] to posterior [bottom right]) show small bowel distention with two different patterns of signal intensity, an appearance suggestive of multiple obstructions. At surgery, the presence of two obstructions was confirmed and two separate distended small intestines were seen.
|
|
View larger version (164K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14a. Small bowel atresia with meconium peritonitis in a 33-week-old fetus. Coronal single-shot fast spin-echo MR images (presented from anterior [a] to posterior [c]) show a huge cystic structure (arrow in a) and a small amount of ascites in the abdomen. The stomach (arrowhead in b) and small bowel loops (arrow in b) appear normal. The diagnosis of ileal perforation and meconium pseudocyst with underlying ileal atresia was confirmed at surgery.
|
|
View larger version (158K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14b. Small bowel atresia with meconium peritonitis in a 33-week-old fetus. Coronal single-shot fast spin-echo MR images (presented from anterior [a] to posterior [c]) show a huge cystic structure (arrow in a) and a small amount of ascites in the abdomen. The stomach (arrowhead in b) and small bowel loops (arrow in b) appear normal. The diagnosis of ileal perforation and meconium pseudocyst with underlying ileal atresia was confirmed at surgery.
|
|
View larger version (166K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14c. Small bowel atresia with meconium peritonitis in a 33-week-old fetus. Coronal single-shot fast spin-echo MR images (presented from anterior [a] to posterior [c]) show a huge cystic structure (arrow in a) and a small amount of ascites in the abdomen. The stomach (arrowhead in b) and small bowel loops (arrow in b) appear normal. The diagnosis of ileal perforation and meconium pseudocyst with underlying ileal atresia was confirmed at surgery.
|
|
Genitourinary Tract
Ureteropelvic junction obstruction is the most common cause of hydronephrosis detected prenatally (19). The dilated renal pelvis may hang down and is sometimes confused with a hydroureter (Fig 15). A duplicated renal collecting system is the most common urinary tract anomaly (20). The dilated upper collecting system may be associated with ectopic ureterocele (Fig 16). It is easier to detect this condition with MR imaging than with US. In multicystic dysplastic kidney, numerous cysts are scattered around the kidney (Fig 17). No normal renal parenchyma and ureter are seen at MR imaging. Potter syndrome is a group of diseases that includes bilateral renal abnormalities, hypoplastic lungs, and oligohydramnios (21) (Fig 18). MR imaging demonstrates such multiple changes easily. Most genitourinary tract disorders are associated with oligohydramnios, evaluation of which is sometimes difficult with US; MR imaging can be helpful under these circumstances.
View larger version (141K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 15. Ureteropelvic junction obstruction in a 31-week-old fetus. Coronal single-shot fast spin-echo MR image shows a dilated right renal pelvis without dilatation of the ureter, an appearance indicative of ureteropelvic junction obstruction.
|
|
View larger version (133K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 16a. Duplicated renal collecting system and ureterocele in a 34-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows a duplicated right renal collecting system. (b) Coronal single-shot fast spin-echo MR image shows an ectopic ureterocele (arrow) associated with dilatation of the upper calices. (c, d) Intravenous pyelogram (c) and MR urogram (d) obtained 12 days after birth show bilateral duplicated collecting systems with right upper caliectasis (arrows) and a huge filling defect in the urinary bladder.
|
|
View larger version (131K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 16b. Duplicated renal collecting system and ureterocele in a 34-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows a duplicated right renal collecting system. (b) Coronal single-shot fast spin-echo MR image shows an ectopic ureterocele (arrow) associated with dilatation of the upper calices. (c, d) Intravenous pyelogram (c) and MR urogram (d) obtained 12 days after birth show bilateral duplicated collecting systems with right upper caliectasis (arrows) and a huge filling defect in the urinary bladder.
|
|
View larger version (167K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 16c. Duplicated renal collecting system and ureterocele in a 34-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows a duplicated right renal collecting system. (b) Coronal single-shot fast spin-echo MR image shows an ectopic ureterocele (arrow) associated with dilatation of the upper calices. (c, d) Intravenous pyelogram (c) and MR urogram (d) obtained 12 days after birth show bilateral duplicated collecting systems with right upper caliectasis (arrows) and a huge filling defect in the urinary bladder.
|
|
View larger version (139K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 16d. Duplicated renal collecting system and ureterocele in a 34-week-old fetus. (a) Coronal single-shot fast spin-echo MR image shows a duplicated right renal collecting system. (b) Coronal single-shot fast spin-echo MR image shows an ectopic ureterocele (arrow) associated with dilatation of the upper calices. (c, d) Intravenous pyelogram (c) and MR urogram (d) obtained 12 days after birth show bilateral duplicated collecting systems with right upper caliectasis (arrows) and a huge filling defect in the urinary bladder.
|
|
View larger version (153K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 17a. Multicystic dysplastic kidney in a 34-week-old fetus. (a) Oblique sagittal US scan obtained at 33 weeks gestation shows multiple cysts in the left side of the abdomen (the cranial direction of the fetus is on the right). The cysts mimic small bowel dilatation. (b) Coronal single-shot fast spin-echo MR image shows multiple large cysts in the left kidney without normal renal parenchyma. The right kidney is normal.
|
|
View larger version (162K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 17b. Multicystic dysplastic kidney in a 34-week-old fetus. (a) Oblique sagittal US scan obtained at 33 weeks gestation shows multiple cysts in the left side of the abdomen (the cranial direction of the fetus is on the right). The cysts mimic small bowel dilatation. (b) Coronal single-shot fast spin-echo MR image shows multiple large cysts in the left kidney without normal renal parenchyma. The right kidney is normal.
|
|
View larger version (157K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 18a. Potter syndrome in a 34-week-old fetus. Coronal single-shot fast spin-echo MR images show bilateral renal dysplasia (arrows in a), hypoplastic lungs (arrows in b), and oligohydramnios, findings compatible with Potter syndrome.
|
|
View larger version (143K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 18b. Potter syndrome in a 34-week-old fetus. Coronal single-shot fast spin-echo MR images show bilateral renal dysplasia (arrows in a), hypoplastic lungs (arrows in b), and oligohydramnios, findings compatible with Potter syndrome.
|
|
Neoplasms
Congenital hepatic masses include hepatic cyst, hemangioma, mesenchymal hamartoma, hepatoblastoma, and infantile hemangioendothelioma (22,23). Our experience is limited to infantile hemangioendothelioma; it seems to be difficult to differentiate this tumor from other solid tumors such as hemangioblastoma at plain MR imaging (Fig 19). Sacrococcygeal teratoma is the most common fetal tumor. Sacrococcygeal teratomas can be exophytic, internal, or a combination of the two. The tumor can be solid, solid and cystic, or completely cystic. If the mass is completely cystic, myelomeningocele or meningocele must be ruled out (Figs 20, 21). The absence of spinal dysraphism, which is a clue to the diagnosis of sacrococcygeal teratoma, is easily demonstrated with MR imaging.
View larger version (173K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 19a. Liver tumor (infantile hemangioendothelioma) in a 40-week-old fetus. (a, b) Coronal (a) and axial (b) single-shot fast spin-echo MR images show an inhomogeneous tumor (arrows) hanging from the lower aspect of the left hepatic lobe. (c) Contrast material-enhanced computed tomographic scan obtained 3 days after birth shows the characteristic findings of a hemangioma. (d) Surgical photograph shows the tumor, which was proved to be an infantile hemangioendothelioma.
|
|
View larger version (157K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 19b. Liver tumor (infantile hemangioendothelioma) in a 40-week-old fetus. (a, b) Coronal (a) and axial (b) single-shot fast spin-echo MR images show an inhomogeneous tumor (arrows) hanging from the lower aspect of the left hepatic lobe. (c) Contrast material-enhanced computed tomographic scan obtained 3 days after birth shows the characteristic findings of a hemangioma. (d) Surgical photograph shows the tumor, which was proved to be an infantile hemangioendothelioma.
|
|
View larger version (113K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 19c. Liver tumor (infantile hemangioendothelioma) in a 40-week-old fetus. (a, b) Coronal (a) and axial (b) single-shot fast spin-echo MR images show an inhomogeneous tumor (arrows) hanging from the lower aspect of the left hepatic lobe. (c) Contrast material-enhanced computed tomographic scan obtained 3 days after birth shows the characteristic findings of a hemangioma. (d) Surgical photograph shows the tumor, which was proved to be an infantile hemangioendothelioma.
|
|
View larger version (115K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 19d. Liver tumor (infantile hemangioendothelioma) in a 40-week-old fetus. (a, b) Coronal (a) and axial (b) single-shot fast spin-echo MR images show an inhomogeneous tumor (arrows) hanging from the lower aspect of the left hepatic lobe. (c) Contrast material-enhanced computed tomographic scan obtained 3 days after birth shows the characteristic findings of a hemangioma. (d) Surgical photograph shows the tumor, which was proved to be an infantile hemangioendothelioma.
|
|
View larger version (162K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 20. Sacrococcygeal teratoma in a 31-week-old fetus. Sagittal single-shot fast spin-echo MR image shows a large multilocular cystic mass in the sacrococcygeal region. An isointense nodular component is seen (arrow), and no communication with the dural sac could be appreciated. The diagnosis of sacrococcygeal teratoma was confirmed at neonatal surgery.
|
|
View larger version (164K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 21. Meningocele in a 37-week-old fetus. Sagittal single-shot fast spin-echo MR image shows a large multilocular cystic mass in the sacrococcygeal region, an appearance similar to that in Figure 20. There is a communication between the cyst and the thecal sac (arrow), a finding suggestive of meningocele.
|
|
|
Advantages and Disadvantages
|
|---|
One advantage of MR imaging over US is better tissue contrast. For instance, because the thyroid is clearly seen as a characteristic bright structure on T1-weighted images, differentiation of goiter from other neck masses is easier with MR imaging than with US. Hubbard et al (9) reported that MR imaging helped further characterize fetal chest lesions on the basis of their characteristic signal intensities. In congenital diaphragmatic hernia, MR imaging allows identification of the herniated organs by means of their signal intensities. The signal intensity of sequestered lung tissue is higher than that of normal lung tissue on single-shot fast spin-echo images and lower on T1-weighted images. In our patient with bronchopulmo
Top
Abstract
Introduction
