Diagnostic Evaluation of the Posterior Fossa with Antenatal and Post-Mortem MRI: An Unfolded View

The role of post-mortem fetal conventional autopsy (CA) is undisputed but poses challenges with small, macerated bodies, and increasing parental refusal. Fetal post-mortem magnetic resonance imaging (PMMRI) is a less invasive alternative that can be used for assessment of the brain, including the posterior fossa (PF) structures. The purpose of this study was to evaluate the imaging characteristics of the PF in PMMRI compared to antenatal MRI (ANMRI), using CA as the gold standard. A retrospective, single-center study of ten fetuses who underwent ANMRI, PMMRI, and CA from August 2010 to May 2018. The PF structures were evaluated qualitatively for imaging findings, and quantitatively by obtaining the transcerebellar diameter, vermian length, brainstem thickness, width of the fourth ventricle and cisterna magna, skull base angles, and PF volume. Twenty MRI exams were included. The median gestational age of ANMRI was 21.7 weeks. The median age at termination of pregnancy (TOP) and PMMRI was 23.7 weeks. There was good congruence between PMMRI, ANMRI, and CA, with 60% complete congruence and 40% partial congruence between ANMRI and PMMRI. PMMRI and CA showed 70% complete congruence, and 20% partial congruence. No incongruence was noted. PF evaluation on CA was not possible in 1 case due to maceration. Quantitative evaluation in PMMRI showed significant enlargement of most PF structures compared to ANMRI and smaller CSF-filled spaces (p value < 0.05). PMMRI is an acceptable imaging modality for the macroscopic evaluation of PF structures. Smaller CSF-filled spaces and enlargement of the brain are expected findings when evaluating PMMRI.