Ápice Petroso: mucocele x cisto aracnoide. Um diagnóstico cirúrgico?

Introduction: Petrous apex lesions are usually asymptomatic or related to unspecific symptoms. Its diagnosis depends on the results obtained by computed tomography (CT) or magnetic resonance imaging (MRI) combined. Objective: to report a case of incidental lesions in the petrous apex (AP) and review of the literature about differential diagnosis. Case Report: patient with cervical pain underwent MRI, which presented incidental lesions in the petrous apex. Head CT and MRI investigations were carried out. The lesions presented cystic content, expansive bone remodeling and close relation with left carotid canal. The presumed diagnosis was mucocele and surgery was planned. However, the intraoperative diagnosis was arachnoid cyst. Discussion: petrous apex lesions might be characterized in accordance to the origin, alterations in the adjacent bone structure and signal characteristics of the lesions in MRI sequences. Lesions filled with cerebrospinal fluid (CSF) represent a clinical challenge, since they do not have specific characteristics. In MRI, mucocele follows the CSF signal in all sequences, which is undistinguishable from the arachnoid cyst by the imagining techniques. Arachnoid cysts represent about 1% of the intracranial lesions and they may take place in atypical locations, such as the petrous apex. Conclusion: Despite the rarity of the feature, its diagnosis must be considered in CSF filled lesions.