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1
Department of Pediatric Imaging, University Children Hospital Queen Fabiola,
15 Ave. J J Crocq, 1020 Brussels, Belgium.
2
Department of Pediatric Imaging, Debrousse Hospital, 29 Rue Soeurs Bouvier,
69004 Lyon, France.
3
Department of Pediatric Imaging, Jeanne de Flandre Hospital, Ave.
Eugène Aimée,
59037 Lille-Cedex, France.
4
Department of Pathology, University Children Hospital Queen Fabiola, 1020
Brussels, Belgium.
5
Department of Pediatric Surgery, University Children Hospital Queen Fabiola,
1020 Brussels, Belgium.
6
Department of Medical Imaging, Erasme Hospital, 808 Rte. de Lennik, 1070
Brussels, Belgium.
Received May 18, 2001;
accepted after revision July 23, 2001.
Address correspondence to F. E. Avni.
Abstract
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SUBJECTS AND METHODS. Twelve pregnant women were referred for fetal MR imaging of sacrococcygeal teratoma seen at obstetric sonography. The presence, size, content extension, and compressive effects of each mass were determined and correlated with the sonographic findings and with postnatal studies, including surgery and pathology. The extent of each sacrococcygeal teratoma was classified according to the American Association of the Pediatrics Surgery Section (types I-IV).
RESULTS. There is a complete agreement of sonographic and MR imaging measurements. The sacrococcygeal teratomas appeared cystic with few septa in three fetuses, markedly septated or even microcystic in eight, and completely solid in one. The sonographic description of the content corresponded well to MR imaging findings in 10 of 12 fetuses. An agreement on the extent of each mass was observed in nine patients, whereas there is a disagreement in three, including in one fetus with an extension of the tumor within the spinal canal recognized only at MR imaging. The MR imaging findings were confirmed by postnatal studies in 10 patients.
CONCLUSION. Sacrococcygeal teratomas had characteristic MR imaging appearances that allowed a complete assessment in most fetuses. Because of MR imaging, the prenatal evaluation was changed in some patients and affected counseling of the parents and treatment. MR imaging is a valuable adjunct to obstetric sonography for the prenatal evaluation of sacrococcygeal teratoma.
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Marked improvement in obstetric sonography has increased our ability to detect and characterize numerous fetal malformations. Yet, in sacrococcygeal teratoma, several factors (e.g., size of the mass, hemorrhagic changes, and intrapelvic or intraspinal extent of the mass or pelvic bones shadowing the area) may render the evaluation incomplete [3,4,5].
MR imaging has been used to evaluate uterine and fetal anatomy. As a result of the development of faster MR imaging sequences, the applications of fetal MR imaging are rapidly increasing.
The purpose of our study was to compare the diagnostic usefulness of fetal MR imaging with obstetric sonography for the evaluation of sacrococcygeal teratoma and to determine if MR imaging could provide additional and clinically important information.
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Clear information about the examination was given to the parents, and the examinations were performed in accordance with the recommendations of our institutional ethics committee.
The gestational age range of the fetuses at the time of MR imaging was 21-36 weeks (mean, 30.5 weeks). MR imaging was performed in three institutions with a 0.5-T magnet (Gyroscan NT-5 [n = 5]; Philips, Eindhoven, The Netherlands), with a 1.5-T magnet (Gyroscan ACSII [n = 3]; Philips or Vision [n = 2], Siemens, Erlangen, Germany) or with a 1.0-T magnet (Expert [n = 2], Siemens); all machines were equipped with a phased array body coil. The nonsedated mothers were positioned either supine or in a partial left lateral position. The coil was selected according to magnet and patient size.
Multishot (multislice acquisitions; TR, 6) or single-shot (consecutive single-slice acquisitions) techniques were used to obtain T2-weighted turbo spin-echo images. The acquisitions consisted of 12-20 slices of 3- to 6-mm thickness with an inplane spatial resolution of 1.2 x 1.5 mm (multishot) or 1.6 x 1.7 mm (single shot). Images were acquired in 18-44 sec without respiratory triggering with TR range/TE range, 5900-9900 (multishot)/87-140 (single shot); echo-train length, 24 (multishot) or 132 (single shot); half Fourier acquisition, 55-70%; flow compensation, 1 transverse presaturation band above the imaging sections. The specific absorption rate remained less than 3.0 W/kg body weight.
T1-weighted images were acquired using turbo field echo T1-weighted or fast low-angle shot T1-weighted sequences. Twelve transverse sections were acquired sequentially with the following parameters: thickness, 5.0-8.0 mm; intersection gap, 0. Fast low-angle shot images had a spatial resolution of 1.6 x 3.2 mm; 108-149/4.1-6.0; excitations, 1 acquired in 18-20 sec. Images had a spatial resolution of 0.9 x 1.6 mm; TR/TE, 20/4; flip angle, 20°; inversion time enhancement (radiofrequency spoiling) with an inversion prepulse, 650 msec; presaturation bands parallel to the imaging sections, 2; excitations, 12 acquired in 4 min 24 sec. The field of view, number and orientation of scans, and number and thickness of slices were individualized in each patient.
All images were reviewed on hard-copy films by one radiologist who also knew the results of the sonographic examinations. MR imaging results were compared with the sonographic reports (not all sonographic images were available for comparison). The presence, size, content, extent, and compressive effects of the sacrococcygeal teratomas were determined and correlated with the findings from postnatal studies, including those of imaging, pathology, and surgery. The extent of the tumor was classified according to the American Academy of Pediatrics Surgery Section Survey staging classification: type I, the sacrococcygeal teratoma developing only outside the fetus; type II, extrafetal and intrapelvic presacral extent; type III, extrafetal and abdominopelvic extent; type IV, the tumor developing completely in the fetal pelvis [6].
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On the basis of MR imaging, the sacrococcygeal teratomas were classified as type I in three patients, type II in six, type III in three, and type IV in none. There is agreement with the conclusions at sonography in all type I and III patients and in three type II patients. There is a disagreement of prenatal MR imaging and prenatal sonography in three fetuses with a type II tumor; in two fetuses at gestational age of 32 weeks (the tumor extent was diagnosed as type I at sonography and type II at MR imaging); and in a third fetus at gestational age of 36 weeks (MR imaging showed an extension of the sacrococcygeal teratoma into the spinal canal [Fig. 4A,4B,4C] that was not shown at sonography). A dilatation of the fetal urinary tract was revealed at MR imaging in two fetuses as it was at sonography (Figs. 1B and 2B); the dilatation had increased at MR imaging in one of the two fetuses. Bladder displacement was observed at MR imaging, but not at sonography, in a fetus at gestational age of 30 weeks.
At follow-up, the MR imaging findings were confirmed in nine patients (Fig. 2C); there was a disagreement of fetal MR imaging and postnatal findings in three patients. In a fetus who had been imaged at gestational age of 32 weeks, a type III instead of type II tumor was found at surgery performed 6 weeks after MR imaging. In another fetus imaged at gestational age of 29 weeks, a spinal canal extension was found at surgery but was recognized only retrospectively at prenatal MR imaging (Fig. 3). In a third fetus at gestational age of 31 weeks, hemorrhage was found at pathology but not a MR imaging (the fetus had died in utero 2 weeks after MR imaging).
All MR images were evaluated. All were of diagnostic quality even in case of polyhydramnios or in second-trimester pregnancies. The image sharpness was better at 1.5 T than at 0.5 T because of the gradient strength and the duration of acquisition time. Yet, we did not find any difference in analysis of the tumoral content or extent at 0.5 or at 1.5 T. Intraspinal extension was shown accurately at 0.5 T. The mother's position (decubitus or lateral position) did not influence our findings.
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Our study shows that MR imaging may provide additional information about tumor extent and content, both factors that affect the prognosis. Solid-type masses and masses with large intraabdominal or pelvic components carry an increased risk of hemorrhage and fetal hydrops [3,4,5]. Because of fetal pelvic bone shadowing (Fig. 1A), the sonographer may be unable to assess precisely the extent of the mass; consequently, the type of the sacrococcygeal teratoma may be underestimated as it was in two fetuses, both at gestational age of 32 weeks, whose tumors were considered type I at sonography instead of type II as was shown on fetal MR imaging (Fig. 2A,2B,2C). Furthermore, in two fetuses at gestational ages of 30 and 32 weeks, bladder displacement was not evaluated adequately by obstetric sonography (Fig. 1A) as it was by MR imaging (Fig. 1C) and postnatal findings. Sonography correctly classified the tumor in a fetus of 30 weeks' gestation as type III, yet the intrapelvic part of the tumor could not be visualized at sonography as it was on MR imaging because of the iliac wing shadowing (Figs. 1A and 1B). In another fetus of 32 weeks' gestation, MR imaging also underestimated the intrapelvic and intraabdominal extension, diagnosing a type II instead of a type III tumor that was found at surgery. This error must be related to the delay between the time of prenatal MR imaging and surgery (6 weeks), during which the tumor continued to grow. This potential continuous growth of sacrococcygeal teratoma renders postnatal MR imaging mandatory to reassess the tumor, especially if time has elapsed between fetal MR imaging and delivery. An extent of the sacrococcygeal teratoma into the spinal canal that existed in two fetuses in our series is difficult to depict at sonography. Because it may affect the surgical approach, an antenatal diagnosis is important. This extent was recognized on MR imaging prospectively in one fetus at the gestational age of 36 weeks and retrospectively in another fetus of 29 weeks gestation (Figs. 3 and 4A,4B,4C); no extent was diagnosed at sonography. The extent was equally well imaged at 0.5 and 1.5 T and raised the possibility of an associated meningocele, which was excluded at surgery [4].
Another important contribution of MR imaging in the assessment of sacrococcygeal teratoma is the evaluation of the tumoral content and its potential complications. Sonography seems sufficient for evaluating completely or almost completely cystic masses, as it was in three fetuses at gestational ages of 29, 32, and 36 weeks. When the tumoral content appears echogenic, it is more difficult for sonography to characterize precisely the tissular content. The echogenicity can result from a solid content (Fig. 5), a hemorrhagic complication (both circumstances carrying a poorer prognosis), or from a diffusely microcystic tumor (in which the echogenicity results from the multiple interfaces) that carries a better prognosis [3,4,5] (Fig. 2A). The content of the mass may also modify the method of delivery. Some obstetricians advocate vaginal delivery in case of cystic masses and cesarean section in case of solid or complicated masses [2, 5].
Prenatal MR imaging is helpful in the assessment of sacrococcygeal teratoma, providing information that may help counsel parents and plan postnatal treatment. In one fetus at gestational age of 30 weeks, the delivery date changed to an earlier date after the visualization of the extensive intraabdominal extent of the sacrococygeal teratoma. In another fetus at a gestational age of 32 weeks, the visualization on MR imaging of a micro- and macrocystic pattern rather than of a solid-type pattern (as suggested at sonography) encouraged the obstetrician to favor a vaginal delivery. In a third fetus at a gestational age of 36 weeks, the visualization of the intraspinal extent rendered the surgeon more cautious in planning the neonatal surgery.
Furthermore in several centers, fetal surgery has been developed as an alternative treatment in selected cases of life-threatening fetal conditions, including rapidly growing sacrococcygeal teratoma. In such fetuses, MR imaging may provide important information for planning fetal surgery [12, 13]. Finally, knowing the exact extent and content of the sacrococcygeal teratoma should prompt closer clinical and sonographic follow-up in fetuses with urinary tract dilatation or with tumors with mainly solid content.
In conclusion, MR imaging provides additional and helpful information for the assessment of fetal sacrococcygeal teratoma.
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