Optic neuritis is a condition often quoted as a
problem in which clinician sees nothing and patient see nothing. Diagnosis is
clinical and treatment empirical. Clinically another entity that closely
mimics optic neuritis is optic nerve sheath meningioma(ONSM). Unless one specifically look for it, it is easy to miss
this tumour.
Prof.Alan
Jackson article in AJNR discussed about
6 cases of intracanlicular meningioma in whom diagnosed is missed for more than
a year. Inappropriate imaging protocols will delay the
diagnosis. Radiologists should have high index of suspicion and should adhere
to standard imaging protocols. Prof.Alan Jackson in a seminal study way
back in 1998 stressed the importance both water and fat suppression for
evaluation of the optic nerve pathology (Radiology Jan 1998 20657-63).Recently
in May 2013 Acta Radiological issue Alexander M.McKinney discussed role of
contrast enhanced T1W imaging, fat suppressed FLAIR & DWI sequence in
evaluation of acute optic neuritis.
Meningioma is a common brain tumor but
ONSM is a rarity and is said to constitute 1 to 2% of meningiomas. When a tumor arise near planum
sphenoidale and extends to involve optic nerve it is called as secondary tumor
but when it arises from arachnoid cap cell with in the dural sheath of optic
nerve it is called as primary optic nerve sheath meningioma. Canalicular
variety is often (40%) bilateral.
Management :
You can’t excise tumor while keeping
nerve intact. Surgery is attempted with the concern of developing
intracranial extension but often leaves patient blind. Medical management is
unsuccessful. Meningiomas are considered as radiotherapy
resistant tumors. But ONSM is a type of meningioma where radiotherapy is
considered as primary treatment option.
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