Petrous and sphenoid arachnoid cysts: diagnosis and management.

BACKGROUND Intraosseous arachnoid cysts are rare and difficult to diagnose. The purpose of this study was to describe the clinical and radiological semiology of petrous and sphenoid arachnoid cysts and to propose a specific management strategy. METHODS This was a retrospective, descriptive study of patients with arachnoid cysts, which utilized CT, MRI, and the patients' medical histories. RESULTS Ten patients were included in this study. On CT, the lesions were lytic with bony delineation. On MRI, the lesions exhibited the same signals as cerebrospinal fluid and were not enhanced after contrast. On fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted sequences, the arachnoid cysts' signal disappeared, which is a key feature for eliminating the diagnosis of cholesteatoma. Two patients underwent surgery because of misdiagnosis, either with a meningocele or a cholesteatoma. CONCLUSION MRI FLAIR and diffusion-weighted sequences, together with osseous CT scans, help to distinguish arachnoid cysts from meningoceles and avoid unnecessary surgeries with potential complications.