Keywords
cerebellar convexity - dermoid cyst - epidermoid - extradural - interdural - maximum
safe decompression - microneurosurgery - posterior fossa - sigmoid sinus - total resection
Introduction
Intracranial dermoid cysts (DCs) are rare dysembryonic tumors of benign nature, accounting
for 0.04 to 0.7% of all intracranial space-occupying lesions.[1] Because of their congenital origin, they are mostly seen in infants and young adults,
and comparatively rarely in older age groups.[2] They have a predilection for midline or lines of embryonic fusion. The common locations
are cisternal spaces, mainly in the cerebellopontine angle and the parasellar cisterns.
DCs of the suboccipital and occipital regions are uncommon. If present, they are remarkably
in midline within the vermis or in the fourth ventricle. Laterally located intracerebellar
dermoids are also reported.[3] DCs of interdural space or extradural space are infrequent and only few cases have
been reported.[1]
[2]
[4] Herein, the authors present an interesting case of a large cerebellar convexity
DC with both interdural and extradural components, compromising venous drainage of
the ipsilateral transverse and sigmoid sinus. The patient was managed successfully
by microneurosurgical decompression.
Discussion
The history of intracranial dermoid and epidermoid cysts dates back to 1829 when Cruveilhier
coined the term “tumeur perlees” for them.[5] These tumors possess both ectodermal and mesodermal components. They are supposed
to originate from inclusion of the ectodermal elements within the neural tube during
its closure between the third and fifth week of embryonic development.[3] This explains their preponderance in midline, in the diploe of the fontanel extradurally,
and in the parasellar region intradurally.[6] Traumatic implantation has also been an alternate hypothesis in the genesis of dermoids.[5] Lateral extradural dermoids have been postulated to develop from dural multipotent
embryonic cells or from translocation of the epithelial cells of developing neovasculature.[7]
These rare tumors account for 0.04 to 0.7% of all intracranial lesions. These are
mostly intradural lesions located at the frontobasal, suprasellar, parasellar, etc.,
regions. Extradural DCs are much rarer and have been reported in the midline of the
posterior fossa, anterior fontanel, and orbital region in children.[1]
[2] Interdural DC in the lateral wall of cavernous sinus has also been cited.[1]
[4] But DC in the region of cerebellar convexity at an unusual lateral location with
both interdural and extradural components holds its paucity. Esaki et al have described
an atomically similar case.[8]
These are commonly diagnosed in infants to young adults owing to their congenital
origin and association with sinuses and sinus tract infections. Thus, they are relatively
rare in the middle-aged or elderly population.[2]
There is a wide array of presenting symptoms of these slow-growing tumors, depending
upon the size and location, namely headache, dizziness, seizure, blurring of vision,
progressive hearing loss, facial deviation, lower cranial nerve palsy, etc. Rupture
may lead to severe aseptic meningitis, ventriculitis, and death.[5]
MRI of the cranium is the investigation of choice. Dermoids show variable relaxation
time depending upon fat content. Typically, these are hyperintense on T1- and T2-weighted
images due to partially liquified fat content. However, low-/mixed-intensity T1-weighted
images can also be found, as in the indexed case, because of solid crystalline cholesterol
and keratin. Usually, these tumors do not enhance on contrast administration, but
there was peripheral enhancement in our case. It can be attributed to peripheral granulation
with or without previous infection.[9] These show diffusion restriction in ADW images.
These are benign slow-growing radio-resistant tumors with rare chance of malignant
transformation in long-standing cases. Tsugu et al reported a case of squamous cell
carcinoma arising in an intracranial DC.[10] Complete surgical excision renders effective treatment for prevention of recurrence
and complications. But in cases of extensive adhesion between the cyst wall and the
surrounding vital neurovascular structures, subtotal resection can be contemplated.[1]
[2]
[4]
Conclusion
The authors have reported an extremely rare case of laterally located cerebellar convexity
DC in a middle-aged lady with both interdural and extradural components with unusual
MRI findings in T1-weighted and postcontrast sequence images. Maximum safe resection
should be the goal of surgery considering the low risk of recurrence.
