Skull Base Surgery of the Posterior Fossa

167

capsule is ideal to reduce the risk of recurrence,
but it is almost impossible to predict preopera-
tively how adherent the cyst capsule is to the brain-
stem and the traversing CPA neurovascular
structures. Hence, the goal of surgical resection for
these lesions should be maximum safe resection.
Some studies have demonstrated that recurrence
risk for CPA epidermoid cysts is the same with
complete removal and incomplete removal [ 17 ,
30 ]. However, these studies are limited by short
follow-up periods. Epidermoid cysts are com-
posed of soft white material and are often amena-
ble to suctioning. In some cases, however, the
lesion grows around the cranial nerves and blood
vessels in the CPA, making it difficult to distin-
guish between the cyst contents and the cranial
nerves, especially the sixth and fourth cranial
nerves, which are small and fragile and can be eas-
ily injured during surgery. Identifying the cranial
nerves where they enter the skull base foramina

during surgery may be a helpful trick during sur-

gery for safe resection.

Surgery is the mainstay of treatment for epi-

dermoid cysts. Epidermoid cysts of the fourth

ventricle are removed using a standard midline

suboccipital craniotomy. Most of the epidermoid

cysts confined to the CPA are removed using a

standard retrosigmoid approach [ 17 , 30 , 33 ], but

epidermoids that extend into the middle fossa can

be removed using a combined retrosigmoid and

subtemporal transtentorial approach simultane-

ously or in separate stages [ 28 , 30 ] or an extended

retrosigmoid transtentorial approach. More

recently, the endoscopic-assisted retrosigmoid

approach [ 28 ] or pure endoscopic retrosigmoid

approach has been described [ 24 ]. In the follow-

ing section, we describe the keyhole retrosigmoid

transtentorial approach for epidermoid cyst of the

CPA extending into the supratentorial (middle

fossa) compartment.

Fig. 12.2 Brain MRI demonstrating a right CPA
epidermoid cyst with characteristic T1-weighted hypoin-
tense signal (a), T2-weighted hyperintense signal (b), het-
erogeneous signal intensity in FLAIR (c), and restricted

diffusion signal in DWI (d) and ADC (e) sequences. Note

the supratentorial extension and the mass effect on the

brainstem and mesiotemporal structures

12 Epidermoid Cyst