Assessment of fetal midbrain and hindbrain in mid-sagittal cranial plane by three-dimensional multiplanar sonography. Part 2: application of nomograms to fetuses with posterior fossa malformations.

OBJECTIVES: To apply fetal midbrain (MB) and hindbrain (HB) nomograms, developed using three-dimensional multiplanar sonographic reconstruction (3D-MPR) in the mid-sagittal cranial plane, to fetuses with known posterior fossa malformations. METHODS: In this retrospective study we examined sonographic volumes obtained by sagittal acquisition in 43 fetuses diagnosed with posterior fossa abnormalities and evaluated in the mid-sagittal cranial plane, using 3D-MPR, the following: MB parameters tectal length (TL) and anteroposterior midbrain diameter (APMD), and HB parameters anteroposterior pons diameter (APPD), superoinferior vermian diameter (SIVD) and anteroposterior vermian diameter (APVD). Fetuses were grouped, according to malformation, into eight categories: cobblestone malformation complex (CMC, n = 3), Chiari-II malformation (C-II, n = 7), pontocerebellar hypoplasia (PCH, n = 2), rhombencephalosynapsis (RES, n = 4), Dandy-Walker malformation (n = 8), vermian dysgenesis (VD, n = 7), persistent Blake's pouch cyst (n = 6) and megacisterna magna (n = 6). In each case and for each subgroup, the MB-HB biometric parameters and their z-scores were evaluated with reference to our new nomograms. RESULTS: The new MB-HB nomograms were able to identify the brainstem and vermian anomalies and differentiate fetuses with MB-HB malformations from those with isolated enlarged posterior fossa cerebrospinal fluid spaces. Use of the nomograms enabled detection of an elongated tectum in fetuses with CMC, C-II and RES, and a flattened pontine belly in cases of CMC, PCH and VD. In the fetuses with VD, the nomograms enabled division into three distinctive groups: (1) those with small SIVD and APVD, (2) those with normal SIVD but small APVD, and (3) those with small SIVD but normal APVD. CONCLUSIONS: Application of our new reference data, that for the first time include the MB, enables accurate diagnosis of brain malformations affecting the MB and HB and makes possible novel characterization of previously described features of posterior fossa anomalies.

Assessment of fetal midbrain and hindbrain in mid-sagittal cranial plane by three-dimensional multiplanar sonography. Part 1: comparison of new and established nomograms.

OBJECTIVE: To construct nomograms for fetal midbrain (MB) and hindbrain (HB) dimensions, assessed in the mid-sagittal cranial plane by three-dimensional multiplanar sonographic reconstruction (3D-MPR). METHODS: This was a prospective cross-sectional study of 334 healthy fetuses in low-risk singleton pregnancies between 16 and 35 gestational weeks. All sonographic volumes were obtained by sagittal acquisition. The following MB and HB parameters were evaluated in the mid-sagittal cranial plane using 3D-MPR: MB parameters tectal length (TL) and anteroposterior midbrain diameter (APMD), and HB parameters anteroposterior pons diameter (APPD), superoinferior vermian diameter (SIVD), anteroposterior vermian diameter (APVD) and anteroposterior diameter of the fourth ventricle (APDFV). The measurements were presented as growth charts according to gestational age. RESULTS: MB and HB biometry were best assessed between 19 and 29 weeks. During this period, adequate visualization was achieved for successful measurement of TL in 90.9% of cases, APMD in 86.6%, APPD in 73.7%, SIVD in 74.2%, APVD in 71% and APDFV in 71%. There was a linear growth pattern, with Pearson correlation coefficients of 0.79 for TL, 0.88 for APMD, 0.91 for APPD, 0.95 for SIVD, 0.88 for APVD and 0.88 for APDFV (P < 0.0001 for each). The mean intra- and interobserver variations for the MB measurements and vermian diameters ranged between 4.3% and 9%. APPD and APDFV showed highest mean variations: 9.0% and 19.4% (intraobserver) and 11.6% and 17.7% (interobserver), respectively. CONCLUSION: We present new nomograms for assessment of the fetal MB and HB using 3D-MPR in the mid-sagittal cranial plane. To our knowledge, these are the first proposed nomograms for fetal MB dimensions.