Huge Greater Superficial Petrosal Nerve Schwannoma with Intradural Peritumoral Cyst.

Background: Schwannoma originating from the greater superficial petrosal nerve is an extremely rare type of facial nerve schwannoma located in the middle cranial fossa around the midportion of the petrous bone. Here, we provide the first report of greater superficial petrosal nerve schwannoma presenting with contralateral facial palsy and hemiparesis due to compression of the pyramidal tract by associated intradural peritumoral cyst.

Case Description: A 69-year-old woman presented with a 6-month history of gradually worsening gait unsteadiness. Magnetic resonance imaging demonstrated a well-defined tumor occupying the right middle cranial fossa and extending into the tympanic cavity. Notably, the tumor accompanied a large cyst in the intradural space, resulting in a leftward midline shift. Extradural exploration through thinned periosteal dura mater revealed the tumor within the interdural space. After debulking of most of the tumor in a pull-out, piecemeal fashion, intradural exploration revealed the peritumoral cyst located between the meningeal dura mater and brain parenchyma. Following the disappearance of the mass effect from the tumor, fenestration of the peritumoral cyst, which had been deeper-seated than the tumor, was easily achieved while avoiding excessive retraction of the temporal lobe. Postoperatively, mild left hemiparesis involving the face resolved completely and no new symptoms such as right facial palsy, hearing disturbance, or xerophthalmia developed as postoperative complications.

Conclusion: The combination of extradural and intradural approaches in the appropriate order is essential for fenestration of an intradural peritumoral cyst along with removal of an interdural tumor.