© Springer International Publishing AG 2018 165
W.T. Couldwell (ed.), Skull Base Surgery of the Posterior Fossa,
https://doi.org/10.1007/978-3-319-67038-6_12
Epidermoid Cyst
Gmaan Alzhrani and William T. Couldwell
G. Alzhrani, MD • W.T. Couldwell, MD, PhD (*)
Department of Neurosurgery, Clinical Neurosciences
Center, University of Utah, 175 N. Medical Drive
East, Salt Lake City, UT 84132, USA
e-mail: [email protected]
12
Introduction
Epithelial inclusion cysts generally form con-
genitally between the third and fifth weeks of
gestation secondary to an early dysjunction and
entrapment of the ectoderm before neural tube
closure [ 11 , 27 , 29 ]. Iatrogenic implantation of
the skin after lumbar puncture and traumatic
implantation after gunshot wound have been
proposed as rare mechanisms underlying the
development of these lesions [ 12 , 32 ].
Epidermoid cyst walls are lined with stratified
squamous epithelium overlying a connective
tissue lamina that closely adheres to the pia
mater and is grossly anatomically indistinguish-
able from the latter. Tumor growth results from
continuous desquamation and degradation of
epithelial cells inside the cyst, forming pearly
and shiny debris composed of cholesterol crys-
tals and keratin [ 7 , 9 , 23 ]. These cysts constitute
0.2–1.8% of all intracranial tumors [ 11 , 17 , 18 ,
25 ]. The most common location for epidermoid
tumors is the cerebellopontine angle (CPA). In
the posterior fossa, these represent 5–7% of all
CPA lesions [ 11 , 31 ], and 40–50% of all intra-
cranial epidermoid cysts are located in the CPA
[ 11 , 31 ]. The paramedian location of this lesion
is thought to be related to the otic vesicles dis-
placing the e pithelia rest more peripherally
toward the CPA [ 3 , 4 , 19 ]. The second most
common location in the posterior fossa is the
fourth ventricle, accounting for 5–18.5% of all
intracranial epidermoid tumors [ 9 , 20 , 35 ].Clinical Presentation
Epidermoid cysts can remain asymptomatic clin-
ically for a long time because they have a slow
and linear growth pattern similar to the normal
epidermis but are insinuated into the surrounding
subarachnoid spaces [ 2 , 11 , 14 ]. Patients usually
become symptomatic between the third and fifth
decades of life, and a latency period of clinical
presentation of CPA epidermoids of 2–4.6 years
has been reported [ 1 ]. This latency period may be
shorter for fourth ventricular epidermoids, which
have a reported average of 1.6 years from the
onset of symptoms to diagnosis [ 11 , 34 ]. The
pathophysiological mechanism for symptoms
and signs of onset of posterior fossa epidermoid
cysts may be related to compression of neurovas-
cular structures, encasement and strangulation of
the cranial nerves and blood vessels, or irritation
of the neurovascular structures secondary to the
cyst rupture and spillage of its content into the
subarachnoid space (Mollaret’s meningitis) [ 14 ].