Idiopathic granulomatous orchitis: morphology and evaluation of its relationship to IgG4 related disease

Idiopathic granulomatous orchitis (IGO) is rare, thought to result from an autoimmune reaction to spermatogenic elements. Its relationship to IgG4-related disease (IgG4-RD) has not been evaluated. Sixteen orchiectomy specimens (1984-2012) with a prominent intratubular granulomatous reaction were reviewed: IGO (n = 6); intratubular germ cell neoplasia unclassified (IGCNU) with a granulomatous reaction and associated seminoma (GS, n = 6); and unclassified intratubular granulomatous orchitis not fitting into a specific entity (UGO, n = 4). Men with IGO were 32 to 86 years old, presenting with a mass suspicious for malignancy. Only one patient had a history of an inflammatory disease. Clinical follow-up was available for 2 patients with IGO, and both had no evidence of systemic IgG4-RD. All IGO cases had an epithelioid granulomatous reaction confined to seminiferous tubules, an extensive interstitial lymphoplasmacytic inflammation, 3 of 6 had prominent interstitial fibrosis, and 3 of 6 cases had plasma cells with an IgG4+/IgG+ ratio >40%. In GS, 10% to 100% of tubules with IGCNU had a granulomatous reaction, which in 3 cases replaced IGCNU cells. In contrast to IGO, GS had more intratubular multinucleated giant cells, more peritubular sclerosis, fewer interstitial plasma cells, and no interstitial fibrosis. Of the 4 UGO cases, most had predominantly interstitial with less intratubular granulomatous inflammation. Only 1 non-IGO case had elevated tissue IgG4 (GS case). It is critical and sometimes difficult to distinguish GS from IGO. IGO shares some features with IgG4-RD, yet current evidence does not support its classification as a localized manifestation of IgG4-RD occurring in the testis.