Establishment of normative values for the fetal posterior fossa by magnetic resonance imaging

Abstract

Objective Suspected Dandy‐Walker continuum anomalies constitute a significant percentage of prenatal cases evaluated by magnetic resonance imaging (MRI). To unify the description of posterior fossa malformations, we sought to establish objective measurements for the posterior fossa in normal fetuses between 18 and 37 weeks gestation. Methods T2‐weighted images of normal fetal brains in sagittal projection were obtained from fetal magnetic resonance (MR) studies of normal brains performed from 2009 to 2017.121 fetal brains were included in the analysis. Three radiologists reviewed images and recorded the following for each case: superior posterior fossa angle (SPFA), posterior fossa perimeter, and tegmento‐vermian angle (TVA). Results For each feature, the mean of the measurements, the percentage of absolute difference of the reader measurement compared with mean measurement, and the interclass correlation (ICC) were calculated. Values are reported as mean ± standard deviation. Perimeter increases linearly with age, whereas the SPFA and the TVA are independent of gestational age. For all included cases, the SPFA averaged 100.9° ± 8° and the TVA averaged 2.5° ± 2.3°. Conclusion The superior posterior fossa angle, a novel measurement, and the posterior fossa perimeter can be used for establishing the expected size of the posterior fossa in second‐ and third‐trimester fetuses by MRI.

Biometric assessments of the posterior fossa by fetal MRI: A systematic review

“…A total of 804 studies were initially screened and 59 publications were included in the final systematic review 4,5,7,15‐69 (Figure 1) (Table S1). Separate publications with duplicated data from those included were assessed 51,70‐80 …”

Evaluation of Posterior Fossa Biometric Measurements on Fetal MRI in the Evaluation of Dandy-Walker Continuum

“…We chose to use an 18°TVA cutoff for BP based on fetal sonography literature by Volpe et al, 18 though more recent literature in healthy fetuses on MR imaging described the average TVA as 2.5°(SD, 2.3°). 11 This was the case for our review based on the interpretations of fetal MRIs during the study period, though it is possible that patients with smaller BPs may have been inadvertently excluded, particularly given the variation in the existing sonography literature. [28][29][30] Also, because patients included in our VH group had coexisting BP, which explains vermis rotation in VH, there may be some unintended overlap in patients with mild VH and BP, which can be explained, at least in part, by the inherent limitations in the reproducibility in PACS measuring tools.…”

“…Measurements were acquired using PACS measuring tools and recorded in millimeters, rounding to the nearest millimeter. Methods used to acquire these measurements have been described by Tilea et al 9,10 The TVA and superior posterior fossa angle were measured with values rounded to the nearest degree; the methods are described by Chapman et al 11 The cisterna magna was described as normal or enlarged; this was a subjective assessment by the radiologist because reproducible measurements were not possible, given vermian rotation and distortion. Vermian foliation was described as normal or abnormal.…”

The brainstem-tentorium angle revisited. Difficulties encountered and possible solutions

“…Fetal PFFC associated with upward displacement of the tentorium and rotation of the cerebellar vermis can range from normal variants to severe anomalies with highly variable neurological prognosis [4][5][6] (Blake's pouch cyst, megacisterna magna, vermian hypoplasia and Dandy-Walker malformation). Although prenatal ultrasound is currently the standard technique for the diagnosis of fetal anomalies, fetal MRI is increasingly applied as a complementary technique, mainly in central nervous system defects, diaphragmatic hernias or placental anomalies [7,8].…”