Keywords
colloid cyst - cavum septum pellucidum - interfornicial approach
Introduction
Colloid cysts (CCs) occur predominantly in the midline with majority involving roof
of the third ventricle. Approaches for CC are directed toward the Foramen of Monroe
(FoM), and the first step after reaching the lateral ventricle after either transcallosal-interhemispheric
or transcortical approach is to follow the choroid plexus to the foramen. In normal
anatomic conditions, the trans-FoM approach is a safe method for reaching the roof
and anterior part of the third ventricle to remove the lesion. In cases of cavum septum
pellucidum (CSP), the surgeon can lose orientation when normal intraventricular structures
are not encountered.[1] Though forniceal injury may cause significant memory disturbances, when adequate
space is available in the interfonicial space, this route may be used for excision
of lesion.
A 39-year-old woman presented with history of severe headaches for 2 months. Evaluation
with plain computed tomography (CT) of the brain showed a hyperdense lesion in the
region of the FoM suggestive of CC with enlarged lateral ventricles. The presence
of CSP was also noted ([Fig. 1A], [B]). The patient underwent right frontal parasagittal craniotomy, interhemispheric,
transcallosal approach to reach the lesion. After callosotomy, no ventricular landmarks
were identified, and position within the CSP was understood by the flapping of its
walls. Both fornices were slightly elevated and splayed, by the CC that was bulging
upward from the third ventricular roof ([Fig. 2]). After opening the right-side flap of the CSP, the FoM was difficult to identify
from the ventricular side as it was pushed laterally by the CC. Therefore, the CC
was removed from the interfornicial approach with careful preservation of both fornices.
The internal cerebral veins were identified posterior to the lesion after careful
separation from the cyst wall. Postoperative period was uneventful, and postoperative
CT scan showed complete excision of the lesion with reduction in ventricle size ([Fig. 1C]).
Fig. 1 (A) Computer tomography (CT) showing a hyperintense spherical lesion suggestive of colloid
cyst in the region of the anterior third ventricle. (B) A coexisting cavum septum pellucidum (CSP) was noticed in the same scan. (C) Postoperative CT following excision of colloid cyst showing no residual lesion,
with reduction in ventricle size and air in bilateral frontal horns.
Fig. 2 Intraoperative view through the cavum septum pellucidum showing the colloid cyst
(CC) bulging upward from the roof of the third ventricle splaying and displacing the
right fornix (RF) and left fornix (LF) laterally.
Cavum septum pellucidum is a rare association with CC. Identifying CSP in preoperative
images and understanding its relationship with the CC are essential to modify the
operative approach, as in such cases the cyst may not be seen in its usual location
of the FoM and entering the cavum may be confusing because no intraventricular landmarks
will be seen.[1]
[2] Excision of the cyst through the CSP usually requires interfornicial approach, and
this structure must be separated gently to avoid injury.[3] However, other routes must be carefully considered if the space between the fornices
is less as interforniceal approach may not always be feasible or safe.[3]
