Arachnoid cyst with extraordinary extracranial extension in the skull base as a result of an iatrogenic defect of the middle cranial fossa floor: case report and literature review.

Arachnoid cysts are benign intracranial lesions that are typically diagnosed incidentally. They are divided into two types: congenital and acquired. Acquired arachnoid cysts are rare and usually arise after trauma, infection, or haemorrhage. In this report, a rare case of an iatrogenic multiloculated arachnoid cyst as an unusual complication of a skull base defect is presented. It extended extracranially into the sphenoid sinus, the ethmoid, the infratemporal fossa, the nasopharynx and the nasal cavity, as well as into the pterygomaxillary and retromaxillary space, appearing with a distinct clinical picture. We discuss the differential diagnosis and the potential causes of the lesion and provide a brief review of the literature.