Congenital Posterior Fossa Malformations: Imaging Patterns and Diagnostic Approach.

Congenital posterior fossa malformations comprise a diverse group of cerebellar and brainstem anomalies, typically detected prenatally or in early childhood. Radiologists play a vital role in recognizing characteristic imaging patterns, suggesting diagnoses, and guiding optimal management strategies. The authors review the embryology of these malformations, briefly discuss the signaling factors guiding patterning and segmentation, and summarize imaging phenotypes using a pattern-based approach to diagnosing congenital posterior fossa malformations. Based on the imaging phenotype, the malformations are categorized as posterior fossa cystic and cystlike malformations, predominantly cerebellar anomalies, cerebellar and brainstem anomalies, and predominantly brainstem anomalies. Although posterior fossa malformations manifest with overlapping imaging findings, use of a pattern-based approach to imaging evaluation helps to differentiate types of posterior fossa malformations, identify associated abnormalities, and ultimately, facilitate informed patient counseling and planning of perinatal management and follow-up. ©RSNA, 2026 Supplemental material is available for this article.