Chiari III malformation with defect in Liliequist membrane on MR imaging

The Liliequist membrane is a radiologically neglected structure, with routine evaluation only carried out in pre-operative and post-operative cases of third ventriculostomy. We report two cases of Chiari III malformation in two unrelated females with similar findings on magnetic resonance imaging study including occipital and low cervical encephalocele, hydrocephalus, and segmentation anomalies in cervical spine. Along with these findings, we report a flow void on T2-weighted images observed in both cases across the site of Liliequist membrane between interpeduncular and chiasmatic cistern. Our findings of CSF flow across the Liliequist membrane may represent spontaneous third ventriculostomy or another congenital defect in the myriad of anomalies seen in cases of Chiari III malformation.