Liliequist membrane

Liliequist membrane is an arachnoid membrane separating the chiasmatic cistern, interpeduncular cistern and prepontine cistern. It arises anteriorly from the diaphragma sellae and extends posteriorly separating into two sheets, although some authors delineate three discrete components ⁹.

One extends posterosuperiorly to the posterior edge of the mammillary body (known as the diencephalic membrane); it separates the suprasellar cistern from the interpeduncular cistern ⁸.

The second sheet extends posteroinferiorly to the pontomesencephalic junction (known as the mesencephalic membrane); it separates the interpeduncular and prepontine cisterns ⁸.

Laterally it is described as being attached to the oculomotor nerve (CN III), although there is some disagreement concerning the sites of the superior attachment and its lateral border ⁶. 

The Liliequist membrane has neurosurgical importance, especially in endoscopic and microsurgery, and historically needed to be negotiated when performing pneumoencephalography ⁷. 

Radiographic features

Direct visualization of this membrane has until recently not been possible as it is very thin. Today, however, it can be visualized, in the vast majority of patients, on high-resolution heavily T2 weighted 3D sequences, usually constructive interference in steady state (CISS) sequences (e.g. FIESTA/FISP/FFE) ⁹. 

History and etymology

It was originally described by Key and Retzius in 1875, and more precisely described by Liliequist in 1956 in his pneumoencephalographic work on cadavers ^7,9.