Atypical radiographic features of skull base cholesterol granuloma

Cholesterol granulomas (CGs) are the most common benign lesions of the petrous apex (PA) and have distinct computed tomography (CT) and magnetic resonance imaging (MRI) characteristics. On CT, CGs of the PA (PACG) present as expansile lesions with erosion of bony trabeculae. MRI shows a hyperintense lesion on T1-and T2-weighted images and do not enhance with gadolinium. The objective is to describe the radiographic features of CGs of the skull base that do not arise from the PA. This study is a retrospective review. Three patients were operated on for suspected recurrent endolymphatic sac tumor, intracranial cholesteatoma, and recurrent sphenoid wing meningioma based on CT and MRI findings. Pathology results were consistent with CG in all three cases. All patients had bone erosion on CT. These skull base CGs did not demonstrate similar MRI features. These lesions were hyperintense, iso-to-hyperintense, and hypointense on T1-weighted MRI, respectively. These CGs were hyperintense in two cases and iso-to-hyperintense in one case on T2-weighted MRI. These lesions either demonstrated central or rim enhancement after gadolinium administration. Skull base CGs that do not arise from the PA demonstrate a broad spectrum of radiographic characteristics on MRI that are not typical of PACG.