CT and MRI features of arachnoid cyst of the petrous apex: report of 3 cases

Purpose. To describe the CT and MRI features of 3 cases of arachnoid cyst of the petrous apex. Patients and methods. Three patients with isolated trigeminal neuralgia, trigeminal hypoesthesia,, and sinusitis. Axial and coronal CT images were obtained. T1 W, FSE T2W, FLAIR, T2*W and diffusion-weighted MR sequences were obtained. Results. In all cases, both CT and MRI showed expansile lesions eroding the petrous apex. Lesions were hypodense on CT and isointense to CSF on MRI, without contrast enhancement. In one case, the lesion was contiguous with Meckel's cave with temporal fossa and sphenoid sinus extension. CT and MR imaging features are useful to distinguish arachnoid cysts of the petrous apex from other benign lesions of the petrous apex. Conclusion. CT and MRI imaging features allow diagnosis of arachnoid cyst of the petrous apex because its imaging features, especially on DWI, are different from other cystic lesions of the petrous apex, namely cholesteatoma. It should be considered in patients with trigeminal involvement, especially trigeminal neuralgia.