Temporosphenoidal Arachnoid Cyst: When Not to Operate. A Series of 8 Cases

Objectives: The intra-diploic arachnoid cyst is a benign and rare disease. The aim of the study is to describe the clinical and radiological features of arachnoid cysts involving the sphenoid and temporal bones and to propose a therapeutic management.

Patients: This retrospective study included all cases of arachnoid cyst diagnosed in our department between 2001 and 2010. Clinical signs, CT scan, and MRI were analyzed.

Results: Eight patients and nine cysts were included (three in the sphenoid and six in the temporal bone; one patient had a cyst on each temporal bone). On CT scan, the cyst eroded or blew the bone with regular limits. On MRI, the signal of the lesion followed the CSF signal and did not enhance with gadolinium. A communication between the cyst and the cistern may be observed at the level of Meckel's cave. On flair and diffusion sequences, the cyst disappears, which is typical and rules out cholesteatoma. In one single patient with a history of meningitis, the arachnoid cyst was closed to the rhinopharynx but not the sinus. Only one patient underwent surgery (preoperative misinterpretation of the imaging data); CSF leak was immediately obturated. All other patients underwent a wait-and-see attitude based on repeated CT.

Conclusion: This disorder is usually diagnosed incidentally. Diagnosis from other skull base lesions relies on flair and diffusion sequences on MRI, which helps to avoid unnecessary surgery with massive CSF leakage. In case of meningitis, the management remains controversial and the ratio of risks to benefits of a surgical exploration should be carefully evaluated.