PMC7593741_01
CT scan: left petrous apex smooth expansile lesion with internal soft tissue density and bone erosion.
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CT scan of the head was obtained and revealed a 2.6 cm smoothly expansile left PA lesion with large areas of bone dehiscence around the margins (Figure 1).
Axial T1 noncontrast (a-c), and postcontrast with fat-saturation (d-f): increased T1 signal in the left petrous apex lesion (a-b; long white arrows) that does not suppress on fat-saturated images (d-e; long black arrows), consistent with cholesterol granuloma. However, the thick rim of peripheral enhancement and abnormal meningeal enhancement (d-f, short black arrows) is consistent with a superimposed inflammatory process. Note that the right petrous apex also displays increased T1 signal (a-b; short white arrows), but becomes dark ("suppresses") on fat-saturated images (d-e; short white arrows), consistent with normal fatty marrow.
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MRI demonstrated increased signal intensity within the lesion on noncontrast T1 images that did not suppress on fat-saturation images (Figure 2) and hyperintense signal on T2-weighted images (Figure 3), all of which are characteristic of cholesterol granulomas. However, atypical thick contrast enhancement around the periphery of the lesion and heterogeneous diffusion restriction suggested superimposed infection (Figures 2 and 4). Leptomeningeal enhancement was present over the left pons, in the location of the cisternal CN VI, Dorello canal, and into Meckel cave (Figure 2).
Axial T2: increased T2 signal in the left petrous apex lesion, typical for cholesterol granuloma (long arrow). Fluid signal in the left middle ear, mastoid air cells, and sphenoid sinus (short arrows).
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MRI demonstrated increased signal intensity within the lesion on noncontrast T1 images that did not suppress on fat-saturation images (Figure 2) and hyperintense signal on T2-weighted images (Figure 3), all of which are characteristic of cholesterol granulomas.
(a) Axial diffusion-weighted image (DWI). (b) Apparent diffusion coefficient image (ADC): heterogeneously restricted diffusion (increased signal on DWI and decreased signal on ADC) in the petrous apex lesion, likely reflecting viscous fluid. Simple cholesterol granulomas typically show decreased DWI signal.
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However, atypical thick contrast enhancement around the periphery of the lesion and heterogeneous diffusion restriction suggested superimposed infection (Figures 2 and 4).
CT angiogram: the left carotid canal wall is dehiscent, and the ICA is narrowed (arrows), presumably due to vasospasm from adjacent inflammation. CTA is valuable to confirm that an expansile petrous apex lesion is not an ICA aneurysm.
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CTA confirmed smooth erosion of and displacement of the left carotid canal, and petrous ICA was narrowed, presumed secondary to vasospasm (Figure 5).
Axial T1 postcontrast with fat-saturation midway through antibiotic therapy: Leptomeningeal enhancement has resolved, and dural enhancement has decreased (compared to Figures 2(e) and 2(f)).
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Repeat MRI brain midway through his antibiotic course showed stable size of the cholesterol granuloma, a decrease in dural and leptomeningeal enhancement, and resolution of ICA vasospasm and the middle ear and mastoid inflammation (Figure 6).
Cholesterol granuloma (100X, hematoxylin and eosin stained), also known as a xanthoma or xanthogranuloma, referring to the cholesterol clefts (arrowheads), lipid-laden macrophages, and multinucleated foreign-body giant cells. In addition, these lesions can demonstrate varying amounts of histiocytes, hemosiderin-laden macrophages (arrows), fibrosis, and calcification. Cholesterol granulomas can be locally destructive, but are typically painless lesions that remain subclinical until discovered incidentally.
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Tissue collected intraoperatively later demonstrated xanthogranulomatous inflammation consistent with the radiologically suspected cholesterol granuloma (Figure 7).