Primary Schwannoma of the Olfactory Groove: A Rare Extra-Axial Tumour Mimicking Meningioma.

Schwannomas originate from Schwann cells, have a benign character and are classified as nerve sheath tumours. These tumours can occur anywhere within the nervous system that contains Schwann cells. Intracranially, they are most commonly found in the posterior fossa. The occurrence of schwannoma in the region of the olfactory groove is very rare and often exhibits variable enhancement, cystic degeneration, and involvement of adjacent cranial nerves.
A 33-year-old lady presented with complaints of bifrontal headache. Her neurological examination revealed impaired olfactory function (anosmia) in the left nostril and decreased visual acuity on the Snellen chart to 6/18 without any pinhole correction. Radiological imaging showed a large, well-defined, lobulated extra-axial tumour likely originating from the cribriform plate. She underwent a gross total resection of the tumour via a left coronal incision and left frontal craniotomy. The postoperative period was uneventful. After a period of one month, the patient returned with frank CSF rhinorrhea. CT cisternography detected a 2.0×1.5 cm defect in the left anterior skull base. She underwent a modified Liu trans-basal approach and repair of the defect on the left side of the cribriform plate using a split calvarial bone graft. Her postoperative period was uneventful, and she made an uneventful recovery. Meningioma is considered the most common diagnosis of an extra-axial contrast-enhancing lesion at the frontal base. The peripheral nerves that contain Schwann cells are prone to developing schwannomas. The presence of Schwann cells around the peripheral nerves creates a conducive environment for saltatory conduction in the nerve. Schwannoma of the olfactory nerve is rare. Olfactory groove schwannoma is a rare and challenging condition with an inherent character of erosion of the cribriform plate. The novel technique of split calvarial graft repair is suitable for large defects with a rewarding outcome.

Olfactory groove meningioma olfactory groove schwannoma anterior skull base defect CSF rhinorrhea.