Granulomatosis With Polyangiitis With Multifocal Pancreatic and Renal Pseudotumors, Mimicking Neoplasm: A Case Report.

Granulomatosis with polyangiitis (GPA) is an ANCA-associated small-vessel vasculitis that can rarely present as a mass-like inflammatory pseudotumor in the abdomen. We report a 52-year-old woman with systemic symptoms and laboratory evidence of GPA with multiple heterogeneous mass lesions involving the pancreas and both kidneys on CT imaging. These lesions mimicked a neoplasm, prompting further characterization with tissue sampling. Histopathology of the pancreatic lesion confirmed granulomatous inflammatory changes. The patient was treated with glucocorticoids and rituximab, resulting in marked progressive resolution of lesions on follow-up imaging. This case highlights the importance of recognizing atypical mass-like abdominal manifestations of GPA, the pivotal role of cross-sectional imaging in diagnosis and follow-up, and the need to consider inflammatory pseudotumor in the differential diagnosis to avoid unnecessary surgery.