PMC9218261_01
Axial high-resolution computed tomography (HRCT) of the skull base shows a destructive process in the petrous apex (arrow) with regional sclerosis involving the petroclival fissure (asterisk) and clivus (arrowhead).
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F1
High-resolution computed tomography (HRCT) of the skull base demonstrated an aggressive erosive disease process centered on the left petrous apex involving the petroclival fissure and inferolateral clivus (Figure 1).
(A) Axial T1-weighted MRI shows a hypointense mass centered on the left petrous apex (asterisk) and regional marrow hypointensity due to infiltration and marrow replacement (arrowheads). (B) Axial T1 following contrast administration shows avid homogenous enhancement of the lesion (asterisk) and intracranial disease extension with pachymeningeal enhancement and thickening of the retroclival dura (arrowhead).
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F2
T1/T2 signal (Figure 2A) and mild apparent diffusion coefficient (ADC) reduction. The lesion was enhanced avidly following gadolinium contrast administration (Figure 2B).
Middle cranial fossa craniotomy demonstrating the lesion in the petrous apex (arrowhead).
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F3
The macroscopic appearance of the tissue was pink, firm, and without a clear capsule or vascularity (Figure 3).
IgG4 immunohistochemical stain highlights the IgG4-positive plasma cells. There are more than 50 IgG4-positive cells in this field (magnification x 200).
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F4
IgG4 showed greater than 50 IgG4-positive plasma cells in some high-power fields (Figure 4). IgG4/IgG ratio was greater than 20%.