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| Discussion |
A 30-year-old female patient, presented with the chief complaints of
headache, fever with chills, vomiting and nuchal pain for the past 15 days.
There was no history of seizures, limb weakness or facial asymmetry. The
patient was afebrile, conscious and oriented. Vitals were stable. Higher
functions were normal. Examination of cranial nerves was normal. Motor and
sensory system examination was normal. With a clinical diagnosis of meningitis,
a CSF examination was performed - this was reported as being normal. Hence
a CT Scan was performed to rule out an intracranial SOL.
RADIOLOGICAL Examination:
Plain and contrast enhanced CT scan of the brain showed expansion of the
right frontal sinus noted due to a soft tissue lesion with inward deviation
of the inner table of frontal bone. There is expansion of anterior ethmoid
air cells with pressure erosion of the right cribriform plate with remodeling
of bone. There is mass effect on right frontal lobe due to an extra axial
lesion (Figs. 1-4).
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Fig.
1
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Fig.
2
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Fig.
3
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Fig.
4
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MR shows a large well
defined lobulated soft tissue density lesion within the frontal sinus causing
expansion of frontal sinus and protruding in intracranial extra axial space
causing mass effect on the frontal horn of lateral ventricle. The lesion
shows mild to moderate, heterogeneous enhancement on post contrast scans
(Figs 5-11)
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Fig.
5
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Fig.
6
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Fig.
7
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Fig.
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Fig.
9
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Fig.
10
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Fig.
11
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DISCUSSION:
In the above described
case imaging features were thought to represent frontal mucocele. The frontal
schwannoma was considered as a unusual differential diagnosis as schwannoma
in frontal sinus is very uncommon. However imaging features are consistent
with diagnosis of schwannoma.
A schwannoma is defined as a tumor composed entirely of nerve supporting
cells without any neural element. It is predominantly an adult tumor occurring
from 30 to 60 yrs of age. It is 2-5 times. Schwannomas compromise 6-7 %
of all intracranial tumors. Approximately 40 % of schwannomas occur in head
and neck region; the sino-nasal region being an uncommon location- being
found in 4 % of the cases. Vestibular schwannomas are the most common of
the cranial nerve schwannomas; followed by trigeminal and facial schwannomas
and then glossopharyngeal, vagus, and spinal accessory nerve schwannomas.
Schwannomas involving
the oculomotor, trochlear, abducens, and hypoglossal nerves are rare. Schwannomas
of terminal branches of trigeminal nerve are also uncommon.
IMAGING FINDINGS : On
non enhanced CT scans, most schwannomas are iso-attenuating relative to
brain parenchyma. Calcification or areas of hemorrhage are rare. On contrast-enhanced
CT scans, the enhancement pattern is typically homogeneous. Bone-window
images can demonstrate remodeling of the adjacent skull base, such as expansion
of the internal auditory canal by vestibular schwannomas and expansion of
the facial canal by facial schwannomas. Expansion of the jugular foramen
by CN IX, CN X, or CN XI schwannomas can also be seen. On MRI, they are
iso to hypo intense to brain parenchyma on T1-weighted images. Most schwannomas
have mild to markedly increased signal intensity on proton density and T2-weighted
images. Gadolinium enhancement is typically homogeneous, although larger
schwannomas can show areas of cystic degeneration and heterogeneous signal
intensity; these findings are based on increased numbers of areas with Antoni
type B histology
HISTOPATHOLOGY: Histologically, schwannomas have two distinct components.
The Antoni A regions are highly ordered and cellular with spindle shaped
Schwann cells that have poorly defined eosinophilic cytoplasm and basophilic
nuclei. Verocan T bodies are configurations of palisading cells that alternate
with acellular eosinophilic areas. The Antoni B regions are much less cellular
and are characterized by large thin walled vessels surrounded by edematous
stroma. Schwannomas stain positive for S100 and vimentin.