MR imaging was performed of the fetus on a 1.5-T superconductive system (Vision; Siemens, Erlangen, Germany) with a four-element phased array surface coil. The whole-body specific absorption rate was less than 3.0 W/kg. Half-Fourier acquisition single-shot turbo spin-echo (HASTE) images were acquired in the axial, coronal, and sagittal planes (echo spacing, 4.2 msec; effective TE, 60 msec; echo train length, 72; number of acquisitions, one; section thickness, 4 mm; field of view, 26 x 35 cm; acquisition matrix, 192 x 256). A 130° refocusing pulse was used to minimize the amount of radiofrequency power deposition. The scan time was 420 msec per image with a 1-sec delay between acquisitions applied to decrease the specific absorption rate. An image from each scan served as the scout for the subsequent sequence. The total scan time for a single data acquisition of 13 sections was 17 sec. The MR examination revealed a focal 2-mm low-signal-intensity nodule in the periventricular region on the right (Fig. 1B). This nodule was seen in two separate image acquisitions in orthogonal planes. The lesion caused a contour deformity of the ventricular wall. The patient was counseled that this lesion likely was a subependymal tuber, but because prenatal diagnosis had not been made previously at this early gestational age, it was not certain whether this finding could be an artifact. View larger version (119K):[in this window][in a new window][as a PowerPoint slide] Fig. 1B. —31-year-old woman who presented for genetic counseling because her husband and one child have tuberous sclerosis. Fetus was screened for tuberous sclerosis. Coronal half-Fourier acquisition single-shot turbo spin-echo (HASTE) MR image obtained at 21 weeks' gestational age shows 2-mm low-signal-intensity nodule (arrow) in subependymal region.
The patient elected to continue the pregnancy and returned for imaging at 32 weeks' gestation. At that time, three cardiac rhabdomyomas were visualized on sonography. The remainder of the sonographic fetal survey, including images of the brain, was normal. Fetal MR imaging showed at least seven subependymal low-signal-intensity nodules, one of which was in the region seen on the MR images at 21 weeks' gestational age (Figs. 1C and 1D), and one subcortical low-signal-intensity nodule. View larger version (135K):[in this window][in a new window][as a PowerPoint slide] Fig. 1C. —31-year-old woman who presented for genetic counseling because her husband and one child have tuberous sclerosis. Fetus was screened for tuberous sclerosis. Coronal (C) and sagittal (D) HASTE MR images at 32 weeks' gestational age show low-signal-intensity nodule (arrow) in location similar to that seen in B. Other low-signal-intensity nodules were seen in subependymal and subcortical regions (not shown).
View larger version (163K):[in this window][in a new window][as a PowerPoint slide] Fig. 1D. —31-year-old woman who presented for genetic counseling because her husband and one child have tuberous sclerosis. Fetus was screened for tuberous sclerosis. Coronal (C) and sagittal (D) HASTE MR images at 32 weeks' gestational age show low-signal-intensity nodule (arrow) in location similar to that seen in B. Other low-signal-intensity nodules were seen in subependymal and subcortical regions (not shown).
MR imaging after birth was performed using a standard neonatal brain protocol. The image in this case report has the following scan parameters: a TR/TE of 500/14, two acquisitions, 4-mm section thickness, a field of view of 17.5 x 20 cm, and an acquisition matrix of 112 x 256. This study confirmed the presence of multiple subependymal and cortical tubers (Fig. 1E). View larger version (134K):[in this window][in a new window][as a PowerPoint slide] Fig. 1E. —31-year-old women who presented for genetic counseling because her husband and one child have tuberous sclerosis. Fetus was screened for tuberous sclerosis. Sagittal T1-weighted MR image obtained on day of birth shows high-signal-intensity nodule (arrow) in location similar to that in D. Other subependymal and cortical tubers also were present (not shown).
A second case of second-trimester diagnosis of (presumed) tuberous sclerosis is shown in Figure 2. Review of 180 fetal MR examinations revealed no similar subependymal lesions in patients examined for other indications. View larger version (153K):[in this window][in a new window][as a PowerPoint slide] Fig. 2. —37-year-old woman was referred at 24 weeks' gestation for tuberous sclerosis screening because three cardiac rhabdomyomas were seen on routine prenatal sonogram. No family history of tuberous sclerosis was present. Axial half-Fourier acquisition single-shot turbo spin-echo MR image shows multiple small low-signal-intensity nodules (arrows) in periventricular regions that were seen on orthogonal image planes (not shown) and caused contour abnormality of ventricular margin. Patient was counseled that these findings likely were subependymal tubers but that specificity of these findings was unknown. Patient elected to terminate pregnancy. No autopsy was performed.
Discussion TopIntroductionCase ReportDiscussionReferences The underlying brain lesions of tuberous sclerosis are subependymal nodules and cortical tubers. Subependymal nodules are situated at the edges of the lateral ventricles. The subependymal nodules of tuberous sclerosis have been detected in a preterm fetus as early as at 28 weeks' gestational age . The prenatal visualization of tubers has been reported by Sonigo et al.  in the third trimester in fetuses with sonographically detected cardiac rhabdomyomas. In their study, the researchers sedated the pregnant women to decrease fetal motion, and they used T1-weighted imaging. In our patients, we did not use sedation, and we used T2-weighted imaging. The tubers appear dark on this sequence either because of magnetic susceptibility artifacts (from calcification) and/or low concentration of mobile water. The tubers stand out on the T2-weighted images because they are adjacent to the bright signal of water in the cerebrospinal fluid spaces. To avoid confusing these lesions with artifacts, we set our criteria for subependymal lesions to be seen on at least two scanning sequences in orthogonal planes and to cause a contour deformity of the ventricular wall. Multiplicity of lesions increases the likelihood that tuberous sclerosis is the cause of the lesions. Although in the two patients reported here, the prenatal diagnosis of tuberous sclerosis was suggested on the basis of the cardiac findings of rhabdomyomas, the finding of cortical tubers at such an early gestational age has not previously been possible. Use of the ultrafast MR technique of HASTE allowed prenatal visualization of cortical tubers without maternal or fetal sedation. Because cortical tubers are more common than cardiac rhabdomyomas and because cardiac rhabdomyomas are not frequently visualized on sonography until the third trimester, it is possible that MR imaging combined with sonography would allow improved prenatal diagnosis of tuberous sclerosis complex. Further studies will be needed to determine the sensitivity and specificity of prenatal MR imaging for screening for tuberous sclerosis complex. References TopIntroductionCase ReportDiscussionReferences
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