Paratesticular fibrous pseudotumor—an IgG4-related disorder?

Paratesticular fibrous pseudotumor (nodular periorchitis, inflammatory pseudotumor of the spermatic cord) is a rare, benign condition of unknown etiology characterized by solitary or multiple intrascrotal nodules composed of dense fibrous tissue with a variable, sometimes sparse inflammatory infiltrate. Based on certain similarities to other fibroinflammatory disorders characterized by infiltrates of IgG4-expressing plasma cells and recently subsumed under the heading of IgG4-mediated diseases, we investigated the plasma cell distribution and immunoglobulin isotypes in three cases of paratesticular fibrous and inflammatory pseudotumor. All three cases showed a high number of IgG4-positive plasma cells with an IgG4 to IgG ratio of 44–48%. This finding indicates that paratesticular fibrous pseudotumor might belong to the growing list of IgG4-related diseases, which by now includes such diverse entities as retroperitoneal fibrosis, sclerosing pancreatitis and cholangitis, Riedel’s thyroiditis, or sclerosing sialadenitis.