IgG4-related paratesticular pseudotumor in a patient with autoimmune pancreatitis and retroperitoneal fibrosis: an extrapancreatic manifestation of IgG4-related disease.

In this report, we describe the first case of a patient with an IgG4-related paratesticular pseudotumor. He had histologically proven autoimmune pancreatitis, then later developed a scrotal mass. The orchiectomy specimen revealed that this was a paratesticular pseudotumor with histopathologic and immunohistochemistry findings characteristic of IgG4-related disease. Paratesticular pseudotumors are uncommon causes of intrascrotal masses and have an unexplained pathogenesis. A variety of genitourinary manifestations of IgG4-related disease including IgG4-related tubulointerstitial nephritis, IgG4-related ureteral pseudotumors, and IgG4-related prostatitis has been previously reported. The current case highlights the need to have a high index of suspicion for IgG4-tissue infiltration in patients with known autoimmune pancreatitis, particularly those with a pseudotumor.