CASE 6520 Published on 15.02.2008

Petrous Apex Cephalocele

Section

Neuroradiology

Case Type

Clinical Cases

Authors

Bastos Lima P., Gouveia P., Lopes da Silva S. Neuroradiology. Coimbra University Hospitals

Patient

60 years, female

Clinical History
Asymptomatic. Patient had clinical history of colon tumour.
Imaging Findings
Asymptomatic, no complaints of trigeminal neuralgia/neuropathy, CSF otorrhea or recurrent meningitis. Patient had clinical history of colon tumour. Brain CT and MR were performed to find out metastasis. Brain CT without contrast showed a hypodense lesion (density similar to CSF) of right petrous apex (PA) that directly communicates with Meckel cave, causing smooth noninvasive bony excavation of PA. Contrast (iodine) was not given due to patient's allergic antecedents. Brain MR confirmed the lesion with low signal on T1WI, bright oval area with CSF intensity within PA with connection to Meckel cave on T2WI and fluid attenuation with CSF on FLAIR. After gadolinium no enhancement was seen.
Discussion
Petrous apex Cephalocele (PAC) is an uncommon lesion that is usually incidental but may be symptomatic. The petrous apex cannot be directly examined, so imaging plays an important role in the evaluation of lesions in this area. They can be divided into surgical lesions (neoplastic lesion, inflammatory complications of air cell disease- cholesterol granuloma, cholesteatoma or mucocele) and incidental nonsurgical findings. Also known as Petrous Apex arachnoid cyst or apical meningocele, PAC is a congenital or acquired herniation of posterolateral wall of Meckel cave into petrous apex. It consists of a CSF density/intensity lesion of petrous apex with direct communication with Meckel cave and causes smooth, noninvasive excavation of petrous apex. In this case, as in the majority of reported cases, it was an incidental MR brain finding. PAC usually does not enhance after contrast, but it can present mild enhancement in the area of trigeminal ganglion. If this diagnosis is not considered, it may suggest mistakenly a tumour. Some lesions need to be considered in differential diagnosis of PAC. Accurate radiological diagnosisof different petrous apex lesions, combining CT and MR, is important in order to plan the appropriate treatment. They can be classified as cystic or solid lesions. Cholesterol granuloma and colesteatoma are the two main destructive lesions of the petrous apex. Cephalocele or Aracnoid cyst is much less common, accounting for less than 1% of petrous apex lesions. These three expansile lesions are often indistinguishable on clinical grounds. In the differentiation of petrous apex cystic lesions (cholesterol granuloma, cholesteatoma and mucocele) it can be difficult to discern between congenital cholesteatomas and arachnoid cysts since both are smoothly marginated expansile lesions without contrast enhancement, homogeneous signal closely resembling CSF sign (hypointense on T1-WI and hyperintense on T2-WI). Congenital cholesteatoma in PA doesn't have connection to MC. Mucocele in PA, a very rare lesion, simulates congenital cholesteatoma. Cholesterol granuloma has trabecular breakdown and cortical expansion-thinning in PA on CT and high signal on T1 and T2WI, without suppression on FLAIR. In cases of Trapped fluid in PA, PA air cell trabeculae are preserved, without expansion, and with all surrounding cortical margins intact. On MRI it's usually hyperintense on T2WI and hypointense on T1WI (but can be intermediate or rarely high signal). Apical petrositis is defined by permeative and destructive changes of PA cortex and trabeculae. It has low signal on T1WI, high signal on T2WI, and variable enhance. Meckel cave trigeminal schwannoma has smooth expansion of PA and MC. On MR it usually presents intermediate signal on T1 and T2-WI and dense enhancement of mass lesion. PACs can usually be differentiated from inflammatory air cell complications (that require surgical treatment) by careful consideration of the lesion centre, osseous margins and relationship to adjacent structures. PACs are more benign and usually do not require surgical treatment (unless complicated ones).
Differential Diagnosis List
Petrous Apex Cephalocele
Final Diagnosis
Petrous Apex Cephalocele
Case information
URL: https://www.eurorad.org/case/6520
DOI: 10.1594/EURORAD/CASE.6520
ISSN: 1563-4086

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