The Liliequist membrane is a membrane of the Arachnoid mater and represents an important intraoperative anatomical landmark in certain neurosurgical procedures.
Anatomy
Anatomically, the Liliequist membrane consists of two leaves, which together originate from the Dorsum sellae and then divide into a diencephalic and a mesencephalic component. In 75 % of cases, the diencephalic layer inserts at the anterior margin of the Mammillary bodies[^1]. The mesencephalic component of the Liliequist membrane inserts directly anterior to the apex of the Basilar artery[^1] [^2].
Figure
Schematic illustration of the Liliequist membrane showing its various components. Adapted from Fushimi et al.
\n\nImaging
The Liliequist membrane can often be visualized on MRI imaging.
MRI CISS sequences of the Liliequist membrane. Figure adapted from Fushimi et al.
\n\nClinical relevance
During endoscopic Third ventriculostomy, if a Liliequist membrane is present, it should also be opened to achieve an optimal stoma[^3].