Lesions of the Petrous Apex: Classification and Findings at CT and MR Imaging

Abstract

The petrous apex is a complex region of the central skull base that is surrounded by a number of important vascular and neural structures and can be home to a wide range of disease processes. Lesions arising in or spreading to the petrous apex cause varied and occasionally severe clinical sequelae, which typically result from mass effect or direct invasion of the cranial nerves, brainstem, or internal carotid artery. Because the petrous apex is not amenable to direct examination, cross-sectional imaging with computed tomography and magnetic resonance (MR) imaging plays an important role in diagnosis and characterization of lesions occurring there. Petrous apex lesions can be classified on the basis of their origin into the following categories: developmental lesions, inflammatory lesions, benign tumors, malignant tumors, vascular lesions, and osseous dysplasias. The most common lesions arising in the petrous apex are cholesterol granulomas, which can be reliably diagnosed with MR imaging due to their high signal intensity on both T1-weighted images and T2-weighted images. In addition, one should also be familiar with anatomic variants or pseudolesions in the petrous apex that can be mistaken for pathologic conditions.

Imaging of skull base pathologies: Role of advanced magnetic resonance imaging techniques

“…13 Even though both the tumors show intense contrast enhancement the difference in perfusion characteristics is because of increased vascularity of meningiomas which is low in schwannomas. 14 Identification of microhemorrhages on T2* gradient sequence or SWI can help differentiate a schwannoma from a meningioma.…”

‘Do not touch’ lesions of the skull base

“…Asymptomatic lesions may be followed on serial imaging to ensure that they do not enlarge over time, while the rare lesion that produces symptoms can be surgically obliterated. 3,6 Arrested pneumatisation Arrested pneumatisation of the skull base is a benign anatomical variant that occurs when pneumatisation is regionally interrupted or never commences. 9 The most common location of arrested pneumatisation is the basisphenoid, though other commonly affected regions include the pterygoid process and petrous apex.…”

Computed tomography and magnetic resonance imaging of lesions at masticator space

“…Inflammatory lesions of the masticator space commonly arise from odontogenic infections (80 %), although other sources such as malignant otitis externa, maxillary sinus fracture, and parotid infection are possible etiologies as well [3,15].…”

“…High flow arterial malformations are uncommon in the masticator space. On MR imaging, it appears as multiple signal voids which represent dilated tortuous hypertrophied vascular structures [15,25]. Time resolved imaging of contrast kinetics (TRICKS) MRA better delineates the arterial feeder, venous drainage, and nidus of high flow arterial vascular malformations [34].…”