An in-depth look at Leydig cell tumor of the testis.

Leydig cell tumor (LCT) is a rare tumor of the male testicular interstitium. This article provides an overview of the major pathologic manifestations of LCT of the testis; patient characteristics; clinical, radiologic, and laboratory features; prognosis; and management. LCTs of the testis are frequently hormonally active, leading to either feminizing or virilizing syndromes. The tumor is usually benign, but malignant variants can occur. The pathologic diagnosis of LCT is usually made based on morphologic characteristics of the tumor cells. The significance of Reinke crystals in the diagnosis of LCT both cytologically and histologically is underscored. Pathologists have to be familiar with the diagnostic histopathologic features, immunohistochemical panel of this tumor, and its principal differential diagnoses to prevent tumor misdiagnosis.