Long-term follow-up of a multiloculated arachnoid cyst of the middle cranial fossa.

Abstract

Arachnoid cysts are benign intracranial lesions that are typically diagnosed incidentally. We describe the case of a 56-year-old man who presented with a multiloculated arachnoid cyst of the middle cranial fossa that extended into the sphenoid sinus. The lesion was identified on computed tomography of the head, which had been obtained for an unrelated investigation. However, establishing a definitive diagnosis proved to be difficult. Because the cyst had caused extensive skull base erosion, the patient was managed conservatively with close observation. We report the radiographic progression of this lesion during more than a decade of follow-up, and we review the literature pertaining to the presentation, pathophysiology, and treatment of arachnoid cysts.

Introduction

Arachnoid cysts are uncommon benign masses. (1,2) They are more common in men than in women. This entity was first described by Bright in 1831 as a "serous cyst forming in connection with the arachnoid." (3) Since then, a substantial number of reports have described the presentation and management of arachnoid cysts. However, the patterns of their occurrence and their associated pathophysiology have yet to be entirely elucidated.

Approximately 50% of intracranial arachnoid cysts are located in the middle cranial fossa and 30% in the posterior fossa; most (64%) arise on the left side. (2,4) Our review of the English-language literature found only 2 cases in which an arachnoid cyst extended into the sphenoid sinus. (5,6) Moreover, we found only one citation that pertained to a loculated arachnoid cyst; that report concerned 3 patients with cervical spinal cord postsurgical collections that appeared to be arachnoid cysts. (7)

In this article, we report a case of multiloculated arachnoid cyst that originated in the middle cranial fossa and extended into the sphenoid and ethmoid paranasal sinuses, causing substantial skull base erosion. The diagnosis in this case initially remained uncertain, even after we performed computed tomography (CT), magnetic resonance imaging (MRI), and surgical exploration for a presumed erosive sphenoid sinus mucocele.

Case report

A 56-year-old man presented to an outside hospital in 1994 after he had been involved in a motor vehicle accident. At that time, he had a history of chronic rhinosinusitis that had been treated with endoscopic sinus surgery. CT of his head identified a sphenoid sinus mass that had eroded the left skull base (figure 1, A). MRI confirmed the presence of an extra-axial cystic lesion in the sphenoid sinus that extended to the floor of the middle cranial fossa (figure 1, B and C). The presumptive diagnosis was a large mucocele, and the patient underwent an…