Liliequist membrane may be understood as a projection formed by an arachnoid membrane extending from the dorsum sellae to the mammillary bodies coined after Liliequist (1956). It has surgical importance in Endoscopic third ventriculostomy and cisternostomy.

1. cka
SURESH BISHOKARMA, MS
MCH RESIDENT, NEUROSURGERY
NINAS
Lillequist membrane
Beyond the Third Ventricle:
Inside the Interpeduncular and Prepontine Cisterns

2. Initially described by Key and Retzius in 1875, it was further investigated
by Liliequist in 1956 in his studies with pneumoencephalography in
cadavers.
It may be considered a remnant of the primary tentorium
History

3. Liliequist membrane may be understood as a projection formed by an
arachnoid membrane extending from the dorsum sellae to the mammillary
bodies.
The LM can be identified as a thin structure (≤ 1 mm) with a thickness that
is ever inferior to that of the tuber cinereum, located under the floor of the
third ventricle, anteriorly extending from the dorsum sellae to the
mammillary bodies.
The membrane presents lateral insertions into the oculomotor nerves or
adjacent to them, generally into the circumjacent arachnoid sheaths
Lillequist membrane

4. Schematic illustration of the LM anatomy, demonstrating the three segments of the Liliequist
membrane in the sagittal plane
THREE SEGMENTS OF THE
LILIEQUIST MEMBRANE
It is formed by either a single or double arachnoid layer and divided into three
segments. Sellar, Diencephalic and Mesencephalic segments

5. The subarachnoid space below the third ventricle is reached after opening
the ependymal layer just ahead of the mammillary bodies (tuber cinereum)
when an endoscopic third ventriculostomy (ETV) is performed.
The structure in this region that divides the space into individual cisterns is
the membrane of Liliequist.
the LM isolates the interpedun- cular cistern from the chiasmatic cistern,
with complete blockage in about 10-30% of cases.

6. Visualisation of basilar artery after opening the membrane of liliequist.

7. This membrane presents a sellar portion, which is inserted in the dorsum
sellae, and this sellar portion is subdivided into a posterior projection, a
diencephalic portion, and a mesencephalic portion.
The diencephalic portion is in close contact with the ependymal layer and
extends to the mammillary bodies, and the mesencephalic portion has a
posterior inferior projection, surrounding the mesencephalon

8. Liliequist just below the third ventricle
Pars profunda of the interpeduncular cistern (1), pars superficialis of the
interpeduncular cistern (2), prepontine cistern (3), and pia mater (4)

9. The membrane of Liliequist limits the interpeduncular cistern.
This cistern has a pars profunda, adjacent to the ependymal layer, and a pars
superficialis, just below the pars profunda. The diencephalic portion of the
membrane of Liliequist divides the two segments

10. The pars profunda contains the anterior group of thalamoperforating arteries.
Located in the pars superficialis is the bifurcation of the basilar artery with
its two main branches, the posterior cerebral arteries (P1) and the superior
cerebellar arteries (located immediately before the bifurcation of the basilar
artery), and the oculomotor nerves (CN III).
The lower limit of the pars superficialis is the mesencephalic portion of the
membrane of Liliequist.
The recess below the latter is the prepontine cistern

11. the key to the success of an ETV is the opening of the membrane of
Liliequist, at least of its diencephalic portion.
In certain cases progression of the endoscope inside the prepontine cistern is
possible, enabling visualization of the trajectory of the basilar artery, and the
nerves that emerge from the anterior side of the brainstem, such as the
abducens nerve (CN VI), in the transition between the pons and the medulla
oblongata, and the hypoglossal nerve (CN XII), at the medulla oblongata

12. The endoscopic viewing angle for the interpeduncular and prepontine
cisterns
The endoscopic viewing angle for the interpeduncular and prepontine cisterns

13. Trajectory of the neuroendoscope through the
pars profunda of the interpeduncular cistern.
This step is mandatory for ETV success.
TRAJECTORY OF THE NEUROENDOSCOPE
Insertion of the mesencephalic portion of the
membrane of Liliequist at the
pontomesencephalic rim (a), insertion of the
diencephalic portion of the membrane of
Liliequist at mammillary body (b), bulging of
this segment against the chiasmatic cistern (c),
insertion of the membrane of Liliequist at the
dorsum sellae (d), gap of the mesencephalic
segment (e). Bifurcation of the basilar artery
(1), posterior bundle of the thalamoperforating
arteries, penetrating the posterior perforated
substance (2), anterior bundle of the
thalamoperforating arteries, crossing pars
superficialis of the interpeduncular cistern (3),
prepontine cistern (4), pars superficialis of the
interpeduncular cistern (5), pars profunda of
the interpeduncular cistern (6), chiasmatic
cistern (7)

14. In such a procedure, the neurosurgeon performs the puncture of the floor of
the third ventricle, by direct visualization, communicating the third ventricle
with the basal cisterns. Intraoperatively, the CSF flow can already be seen
through the orifice. Also, in order to guarantee the success of the treatment, it
is necessary to create a patent pathway from the interpeduncular and pre-
pontine cisterns to the chiasmatic/suprasellar cistern.

15. Occlusion caused by the LM or even by other pre-pon- tine arachnoid
trabeculae is already a well established cause of failure of endoscopic third-
ventriculostomy, a surgical approach classically utilized for obstructive
hydrocephalus resulting from aqueductal stenosis.
Surgical implication

16. 1. Dias DA, castro FLO, yared JH, júnior AL, filho LAF, nelson fortes
ferreira PD. Liliequist membrane: radiological evaluation, clinical and
therapeutic implications. Radiol bras. 2014;47(3):182–5.
2. Fushimi y. Et al. Liliequist membrane: three-dimensional constructive
interference in steady state MR imaging. Neuroradiology;22:360-5.
REFERENCES

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