Dermoids and epidermoids are the result from
an abnormality of surface ectoderm, and invariably associated with one or
more mesodermal malformations, such as, those involving the vertebrae.
Similarly, neuroenteric cysts are due to an
Other developmental cysts,
including the Arachnoid cysts are discussed elsewhere.
constitute approximately 0.2 to 1.8% of all intracranial tumors and less
than 1% of all intraspinal tumors. Cranial sites outweigh spinal sites by
14:1. Although these lesions are congenital, patients are usually not
symptomatic until they are aged 20-40 years.
congenital lesions of ectodermal origin. Epidermoid cysts represent nests
of cutaneous tissues misplaced during embryogenesis and found along lines
of ontogenic neurocutaneous differentiation. These ectodermal inclusions
occur between 3rd & 5th Weeks of embryonic life.
This inclusion can result in heterotopia of these elements. The median
location of these tumors can be explained by the separation of
neuroectoderm & its cutaneous counterpart which occurs dorsally along the
midline. Laterally situated lesions may result from inclusion of ectoderm
at a later stage of embryogenesis, especially during the formation of
secondary otic and optic cerebral vesicles.
spine these lesions are usually associated with spinal dysraphism .
Acquired epidermoid cysts in the lumbar area are due to repeated lumbar
punctures or incidental formation of a skin pocket by suturing.
Grossly, they are
well circumscribed, smooth or lobulated, encapsulated friable lesions
with a characteristic glistening pearl like sheen. Typically, the
epidermoid contains white, flaky, kertinous debris.
they appear as an internal layer of keratinized, stratified squamous
epithelium with a whitish fibrous capsule; these features account for
the term pearly tumor. They tend to slowly enlarge as epithelial cells
desquamate, with the formation of keratin and cholesterol crystals in
the center of the lesion.
Approximately, 25% are situated intradiploically in the skull or
The vast majority of epidermoids are intradural The most common
locations are within the cerebellopontine (CP) angle, parasellar
region,pineal region and middle cranial fossa.
Epidermoid cyst (H&E):
The cyst is lined by
epidermal layer(arrow) (keratinized, stratified
The CP angle is the most
common site for epidermoids. Of all CP angle masses, epidermoids are the
third most common after vestibular schwannomas and meningiomas.
Occurrences within the ventricular system, brain parenchyma, and even the
spinal cord, have been reported.
At diagnosis, epidermoids
usually insinuate within the sulci and cisterns, and they may engulf
cranial nerves and blood vessels.
Clinical features depend
on the site of location, and indistinguishable from any other mass lesion.
The average age of presentation is 35 years with a female predominance.
They grow linearly, similar to normal skin, and thus have an insidious
onset. Rarely, there may be features of aseptic meningitis, caused by
leakage of the debris into the subarachnoid spaces.
Spinal epidermoids are
usually associated with vertebral anomalies.
may reveal a lytic lesions with well-defined sclerotic borders.
epidermoids show calcifications.
CT and MRI are
both helpful in diagnosing epidermoids. Although CT findings may be
nonspecific, MRI findings are reliable in diagnosis.
usually have the same attenuation as that of cerebrospinal fluid (CSF);
this characteristic makes their differentiation from arachnoid cysts
however, the margins of
these lesions are typically lobulated and may contain fine linear strands.
They may also envelope rather than displace surrounding structures such as
Enhancement is rare, but can sometimes be seen around the
margin of the tumor.
Differentiation from CSF filled lesions can be made on
diffusion weighted MRI because these lesions have diffusion
characteristics of solid tissue whereas the diffusion characteristics of
an arachnoid cyst are similar to CSF. These lesions also show significant
magnetization transfer on magnetization transfer sequences whereas
arachnoid cysts show no magnetization transfer.
The contents of the cyst may also rarely demonstrate high
signal on T1-weighted sequences similar to a lipoma or dermoid. Because
the latter two lesions contain fat chemical shift artefact will be present
whereas an epidermoid contains no fat. This distinction can also be made
by applying a fat saturation sequence which will leave an epidermoid
unchanged whereas the high signal from fat will disappear if the lesion is
a dermoid or lipoma.
and then fluid-attenuated inversion recovery (FLAIR) images
were first used to differentiate epidermoids from arachnoid cysts. These
sequences demonstrate epidermoids as being hyperintense relative to CSF.
imaging can be used to differentiate these entities, because epidermoids
have markedly restricted diffusion and, therefore, high signal
intensity on the diffusion-weighted trace images. The free water in arachnoid cysts has low signal intensity.
are helpful in assessing residual epidermoid tumors after surgical
Contrast enhancement suggest a malignant epithelial component.
is surgical removal. Asymptomatic, incidentally discovered cysts need not
be removed, but followed up regularly. Gross total resection is the goal,
but because the cysts can be very adherent to adjacent blood vessels,
total excision is not always possible. The capsule is the living portion
of the tumor, and viable portions that remain will likely regrow, but at
such a slow rate that the tumor may not become symptomatic during the
patient's life time. Spillage of the contents must be prevented, as they
may cause severe chemical meningitis.
There is no role for
radiotherapy or chemotherapy.
The tumor marker CA 19-9
is positive in many cases and may provide a means of follow up for the
residual and recurrence.
They are also been
described as hamartomas, hamartomatous tumor, dermoid cystic tumor, cystic
teratoma, congenital cyst of the spine, spinal dermoid cysts, subcutaneous
Dermoid cysts can be
intracranial, intraspinal, or perispinal.
Dermoid cysts are
true hamartomas. Dermoid cysts are a result of
the sequestration of
the skin along the lines of embryonic closure.
They are benign and
demonstrate both dermal and epidermal elements.
The tumor is covered
by a thick dermis like wall that contains
glands and almost all skin adnexa.
contents include cheesy, granular material.
Hairs and large amounts of
fatty masses cover
poorly to fully differentiated structures derived
from the ectoderm.
The dermoid cyst also contains pilosebaceous
units with hair shafts and sebaceous glands. Dermal elements may
be found in only a small part of the capsule, and the rest of the cyst
wall may closely resemble an epidermoid cyst.
A dermal sinus tract may connect the cyst to the skin surface,
especially when the cyst is located in the posterior fossa,
or spinal canal.
(H&E): The cyst shows both epidermal and dermal (adnexal
Symptoms depend on the
location and are, usually, that of any other mass lesion.
They are more commonly
seen in the spine than the brain.
When found in the brain,
they tend to be in the midline.
Dermoid cysts are usually
seen in children, unlike the epidermoids which are seen in adults and can
be associated with episodes of aseptic meningitis, due to leakage of its
In some patients,
spinal dermoid cysts, especially those connected to dermal sinus
tract, lead to severe neurologic complications such as secondary
spinal subdural abscesses caused by the spread of the infection in the
CT and MRI are
helpful in making the correct differential diagnosis of dermoid cysts.
20% of the dermoids calcify.
MRI is particularly
helpful in diagnosing intracranial or intramedullary dermoid cysts and
in assessing the dissemination of fatty masses or droplets and also
the associated sinus tracts. MRI is helpful in planning surgical
procedures and in assessing therapeutic success. They are usually
hyper dense on both T1 and T2, and more solid than epidermoids, they
are less likely to insinuate between neurovascular structures and tend
to demonstrate more of a local mass effect with no edema.
Surgical excision is the
treatment of choice in any localization, and the excision is easier than
in an epidermoid. Several possible complications of spontaneous or
posttraumatic rupture and surgical procedures have been described. In
patients with a ruptured spinal dermoid cyst, fatty droplets can
disseminate in the cerebrospinal fluid or in a dilated central canal of
the spinal cord. In other patients, subarachnoid and ventricular fat
dissemination can occur after the cerebellopontine angle dermoid cyst is
resected. Spinal subdural abscesses are a possible complication because
of the bacterial infection of spinal dermoid cysts in a dermal sinus
As in epidermoids, the
tumor marker CA 19-9 is positive in many cases and may provide a means of
follow up for the residual and recurrence.
as enterogenous cysts, endodermal cysts, archenteric cysts, gastrocystomas,
intestinomas, cystic teratomas, foregut cysts)
approximately 0.7% of tumors and 16% of cysts in the CNS. 5% of patients
with Klippel-Feil syndrome and vertebral fusion abnormalities may have
development, the neuroenteric canal closes and the notochord separates
from the primitive gut in the third week of embryonic life. It is proposed
that during the same period, a transient adhesion occurs between the
neural ectoderm and endoderm, or a communication develops along the
neuroenteric canal. When such a developmental abnormality persists because
of the incomplete separation at this adherence or remnant canal, the cyst
forms. They are often associated with developmental defects of the
overlying skin and/or vertebral bodies.
Enterogenous cysts of
the central nervous system occur most frequently in the spinal canal,
especially in the lower cervical and upper thoracic(42%) regions with
intradural, extramedullary location. Intracranial neurenteric cysts are
typically intradural, extra-axial posterior fossa masses.
They are benign
epithelial lined cysts, with the lining resembling that of the
delineated, thin walled, fluid containing masses.
These cysts are similar to Rathke cleft cysts and
colloid cysts at histologic and immunochemical analysis.
The location of these lesions on images is
an important distinguishing feature. A Rathke cleft
cyst is usually sellar or suprasellar, whereas a colloid
cyst is related to the anterior wall of the third ventricle adjacent
to foramen of Monro. Neurenteric cysts
have been reported in the cervical, thoracic, and lumbar
portions of the spinal canal, the posterior
cranial fossa, the suprasellar cistern and
the anterior cranial fossa.
The cyst wall is
composed of fibrous connective tissue with an underlying epithelium
that resembles gastrointestinal or respiratory tract mucosa (unlike
the arachnoid cyst which is lined with meningothelial cells).
Cyst contents vary
from colorless, transparent fluid resembling CSF to milky or mucinous
like secretions. Occasionally they can have fistulous connection with
similar mediastinal, thoracic or abdominal cysts, thus supporting an
endodermal origin of these cysts.
Enteric cyst (H&E): Cyst lined
by simple columnar and cuboidal epithelium.
occurrence and the lumbar spine are rare sites.
Between 85% and 90%
are midline; most are located ventral to the spinal cord or brain
stem. Spinal variety is more common in men, whereas the intracranial
ones are commoner in women. They may be asymptomatic lesions that are
discovered incidentally; the larger ones present with gross ataxia,
nystagmus, visual symptoms and cranial nerve palsies. Pain and
myelopathic symptoms are common in spinal lesions; septic or chemical
meningitis may occur. They may present prenatally up through
adulthood. In adults the presentation is slow and insidious.;
progession is rapid in children.
CT scan reveals a
well delineated, non enhancing, noncalcified lobulated mass that is
typically hypodense compared to adjacent brain parenchyma. It may be
difficult to defferentiate from arachnoid cyst on CT.
MRI signal varies
with cyst content; most lesions are iso to mildly hyperintense
to CSF on
T1-weighted images and moderately hyperintense on proton density and
T2-weighted sequences. Spinal ones are, invariably associated with
diagnosis includes arachnoid and neuroepithelial cysts, epidermoid
cyst, cystic schwannoma and inflammatory cysts such as cysticercosis.
Cervical neuroenteric cyst-MRI
Treatment is surgical excision.
The goal is complete excision, which is not always possible.
Simple aspiration, cyst wall
marsupialization, or cysto-subarchnoid shunt may be employed when total
removal is not possible. There is no role for radiotherapy or