Ascending Perineural Spread of a Parotid Gland Adenoid Cystic Carcinoma Masquerading as a Local Recurrence of Skull Base Meningioma: Illustrative Case.

The skull base is an intricate interface between the cranium and the face. Both intracranial and extracranial pathologies can occur at this location. Although the tumor origin is clear in most cases, certain extracranial tumors may mimic primary intracranial pathologies. A 48-year-old woman with a history of resection of a right tentorial meningioma 17 years earlier presented with worsening right facial palsy. No obvious enlargement of the parotid gland was noted. Imaging revealed a residual tentorial meningioma and a homogenously enhancing mass extending alongside the right facial nerve. The patient underwent several biopsies, and the diagnosis of adenoid cystic carcinoma arising from the parotid gland was made. She subsequently underwent carbon-ion radiation therapy and remained stable for 28 months after surgery. The representative case reiterates the importance of evaluating both intracranial and extracranial pathologies when a clinician encounters skull base tumors, especially those with perineural spreading. The tendency of meningiomas to involve the trigeminal nerve while sparing the facial nerve may provide a clue for the differential diagnosis.