173better understanding of these lesions has led to
0% perioperative mortality rate in the contempo-
rary series (Table 12.1). On the other hand, post-
operative morbidity—both worsening of
pre-existing deficit or development of new neuro-
logical deficit—is common. The reported inci-
dence approaches 60% in some studies, and the
injuries are mainly related to sixth, seventh, and
eighth nerve complex and lower cranial nerve
deficits [ 7 , 30 , 37 ]. However, most of these defi-
cits resolve completely or improve on long-term
follow-up [ 7 ].
Management of Recurrence
and Malignant Transformation
Recurrence rates for these cysts vary depending
on the follow-up periods; they have been reported
to be 8–29.4% in the series published between
2002 and 2016 over a follow-up period ranging
from 2.25 to 11.5 years [ 7 , 14 , 17 , 28 , 30 , 37 ].
One recently published study including 50
patients with CPA epidermoid cysts reported a
44.5% recurrence rate over 9.3 years of follow-
up, a high rate attributed to the long follow-up
period [ 11 ]. Some authors have found that the
recurrence rate is not influenced by the extent of
resection [ 30 , 37 ]; however, the follow-up peri-
ods for these studies were less than 5 years, and it
is important to remember that these cysts are
benign and slowly growing. Thus, a follow-up
period longer than 5 years is necessary to reflect
the true recurrence rate.
Recurrent cysts are managed based on the
clinical status of the patients. Recurrent epider-
moid on imaging with no evidence of a new neu-
rological deficit or worsening of a baseline
neurological deficit can be monitored with serial
imaging. A second surgery for symptomatic
recurrent epidermoid cysts in the CPA is unlikely
to result in complete removal, but the postopera-
tive result is generally comparable to that of the
first surgery, with no increased mortality or mor-
bidity [ 11 ].
Malignant transformation in epidermoid cysts
is rare phenomena. Degeneration of the epider-
moid cyst into squamous cell carcinoma, primary
malignant epidermoid carcinoma, and leptomen-
ingeal carcinomatosis with malignant epidermoid
carcinoma has been reported [ 25 ]. Containment
of the tumor within the intracranial and intradural
compartment, evidence of benign squamous cell
epithelium, and exclusion of metastasis or exten-
sion from a nasopharyngeal carcinoma are the
criteria to diagnose malignant epidermoid [ 10 ,
13 ]. Metastasis occurs more commonly in male
patients than in females, with a reported 4:3
male-to-female ratio [ 21 ]. Management options
for this rare type of epidermoid cyst may include
palliative treatment, surgery, stereotactic radio-
surgery (SRS), chemotherapy, or a combination
of these. In a systematic review of 58 patients
with malignant epidermoids, the average survival
was 5.3 months with palliative treatment,
29.5 months with SRS, and 25.7 months with
chemotherapy (alone, combined with surgery,
radiation, or SRS) [ 21 ]. When surgical resection
is combined with radiation, SRS, or chemother-
apy, the average survival was 36.3 months [ 21 ].
For leptomeningeal carcinomatosis associated
with malignant epidermoids, the average survival
was 9.1 months without treatment and
14.5 months with multimodality treatment [ 21 ].Conclusion
Posterior fossa epidermoid cysts including those
in the CPA and the fourth ventricle are typically
benign and slow-growing lesions. When discov-
ered incidentally and causing no significant mass
effect or hydrocephalus, they can be managed
conservatively. However, when symptomatic,
surgery is the mainstay of treatment. Most of
these cysts are amenable to surgical resection
through a standard retrosigmoid or midline sub-
occipital craniotomy/craniotomy approach.
These cysts are soft and often a small craniotomy
will suffice to obtain access. The goal of treat-
ment is safe gross total resection; however, epi-
dermoid cysts wall can be very adherent to the
surrounding neurovascular structure, and
attempts to remove these parts of the wall should
be resisted. Long-term follow-up with serial
imaging postoperatively for completely removed12 Epidermoid Cyst