Liliequist’s membrane anatomical variations impact the probability of successful endoscopic third ventriculostomy: discussion of surgical techniques with novel illustrations and 3D animation

• Liliequist’s Membrane variations influence the probability of ETV success. • Novel illustrations provide useful conceptual models for improving ETV success • A successful ETV connects the third ventricle to the prepontine cistern. • Liliequist’s Membrane was first identified in 1875 by Key and Retzius. A naked basilar artery has been demonstrated to improve ETV success rates; however, existing literature does not adequately convey variation in Liliequist’s Membrane (LM) anatomy in relationship to performing a successful ETV. This publication summarizes published literature examining LM anatomy and adds novel illustrations and discussion on surgical technique to improve the probability of ETV success. A qualitative literature review was undertaken to elucidate anatomical descriptions of LM. Information from this review, along with insights from a pediatric neurosurgeon and cadaveric dissections, guided development of novel illustrations of LM and other relevant ETV anatomy. LM has been reported to have either 2 or 3 leaflets that separate the suprasellar, interpeduncular/intercrural, and prepontine cisterns. There is some variability in the attachment sites of LM; however, classical definitions report the dorsum sella as the anterior attachment, the mamillary bodies and ventral midbrain-pontine junction as posterior attachments, and the oculomotor nerves as the lateral attachments. Variation in positioning of LM leaflets in relationship to the floor of the third ventricle and basilar artery influences the probability of successful ETV. A naked basilar artery is defined by a clear pathway for CSF flow from the third ventricle into prepontine cistern, with no unpunctured arachnoid membranes or leaflets of LM remaining as a barrier to flow. There is variable favorability in LM and other arachnoid membrane anatomy for achieving a naked basilar artery. Novel illustrations in this manuscript highlight this variation and discuss techniques for improving the probability of ETV success.