Trigeminal schwannomas are extradural tumors originating from the Schwann cells of the myelin sheath of the trigeminal nerve. Tumors arising from the trigeminal ganglion are usually located extradural in the middle cranial fossa, whereas those originating from the trigeminal nerve root are found in the posterior cranial fossa. Approximately 50% of trigeminal schwannomas are located in the middle cranial fossa. These tumors account for about 0.2%–1% of all intracranial tumors and often exhibit cystic degeneration, hemorrhage, and necrosis. They are encapsulated and most commonly present in middle-aged individuals, with a slightly higher prevalence in females than in males.
The most common symptom is sensory impairment on the ipsilateral side of the face, typically experienced as numbness. Some patients may also present with trigeminal neuralgia. Tumor expansion and compression of surrounding structures can lead to unilateral facial muscle spasms, symptoms of Eustachian tube obstruction, increased intracranial pressure, as well as cranial nerve palsy involving the third, fourth, and sixth cranial nerves, along with cerebellar symptoms.
MRI typically shows low or isointense signals on T1-weighted imaging and hyperintense signals on T2-weighted imaging, often accompanied by cystic changes. Contrast enhancement reveals uniform, ring-like, or irregular patterns of enhancement. Characteristic features include disappearance of ipsilateral petrous apex fat signals, or an enlarged and deformed ipsilateral Meckel's cave. Smaller tumors may cause localized widening of cisterns, with tumor shadows visible within the cisterns.
CT imaging often shows the tumor arising from the trigeminal ganglion in Meckel's cave, presenting as a round, oval, or doughnut-like mass. Bone windows may reveal destruction of the petrous apex, and the tumor may extend extracranially or intraorbitally through the foramen ovale, foramen rotundum, or superior orbital fissure, leading to enlargement and destruction of these foramina or fissures. Contrast-enhanced CT scans typically reveal homogeneous or annular enhancement, with sharply demarcated margins.
Endoscopic tumor removal via the nasal and/or oral route is the primary treatment method for this condition.