Fetal brain volume measurements by magnetic resonance imaging

We describe three fetuses with malformations of the brain detected by ultrasound imaging. Magnetic resonance imaging (MRI) was then used to measure the fetal brain volumes, in order to gain more information to aid in the counseling of parents and further perinatal management. This was performed with a phased-array body coil on a 1.5-T Magnetom Symphony (Siemens, Erlangen, Germany) machine using fast T1- and T2-weighted sequences. T2-weighted half-Fourier acquisition turbo spin-echo (HASTE) sequences of the whole fetus were acquired in three orthogonal planes (slice thickness, 3 mm; interslice gap, 1 mm). Examinations were done during maternal breath-holding, with acquisition times of < 30 s. Data in DICOM format generated by the MR tomograph were transferred to a PC (Windows XP, Microsoft Corp., Redmond, WA, USA; graphic input screen Wacom Cintiq 18SX, Vancouver, WA, USA), executing the multi-purpose three-dimensional (3D) visualization and modeling software, Amira® (vers. 3.0; TGS, San Diego, CA, USA). Using an input pen, structures of interest in the fetal cephalic region (including skull, ventricles, hemispheres, cerebellum and eyes) were identified on stacked slices and marked manually (by T.A.) with different colors; this is referred to as ‘segmentation’. Amira then allowed volume measurement and surface rendering of selected structures in any desired combination. Measured brain volumes included the tissue volume of both hemispheres and the cerebellum. Our first patient was referred at 25 weeks' gestation with a diagnosis of left-sided ventriculomegaly. The brain volume of 116 mL at referral had increased to 203 mL by 31 weeks, with hemispheric parenchymal volumes of equal size (right, 106 mL; left, 97 mL). Volumes of side ventricles were approximately 16 mL on the right and 100 mL on the left side (Figure 1). The fetus was delivered by elective Cesarean section at 38 weeks. Therapeutic endoscopic fenestration of the septum pellucidum was complicated by post-surgical infection. By the age of 2 years, the child had developed right-sided hemiparesis and focal epilepsy. The second patient was referred at 32 weeks' gestation with a diagnosis of microcephaly and oligohydramnios. Lissencephaly was diagnosed based on MRI, and the brain volume was determined as 63 mL at 32 + 2 weeks. After intensive counseling, the parents requested termination of pregnancy. The third patient was referred at 35 weeks' gestation with a diagnosis of a large left-sided intracranial cyst. The brain volume was 210 mL and the volume of the cyst was 337 mL. MRI did not allow separation of the hemispheres for volume measurements due to compression of the brain tissue by the cyst. ‘Open-lip schizencephaly’ was diagnosed by MRI 10 days after delivery by elective Cesarean section. The newborn developed spastic seizures, and its electroencephalogram was abnormal. Figure 2 puts the brain weights of our three cases in the context of ‘normal’ human fetal brain weights during pregnancy, based on Gruenwald and Minh1, Singer et al.2 and Guihard-Costa and Larroche3 (see also Duncan et al.4). Magnetic resonance image (coronal view) showing left-sided ventriculomegaly (Case 1, 31 weeks). The brain mass is translucent yellow to allow visualization of the side ventricles (translucent blue). Eyes are colored brownish. Growth of the fetal brain from 17 weeks' gestation1-3. Median (solid line) and 5th and 95th percentiles (dashed lines) are indicated3. Open circles with solid whiskers ( ± 2 SD) are fortnightly means1, while triangles with dashed whiskers ( ± 2 SD) are weekly means2. The data from Singer et al.2 are shifted slightly to the right with respect to their true position to allow them to be distinguished. Filled circles represent brain volumes of unaffected fetuses based on our own magnetic resonance imaging measurements (unpubl. observ.). Filled squares represent the three cases described here. In conclusion, differentiated brain volume measurements using MRI may help in making an appropriate decision for further perinatal management.

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