Leydig cell tumors are among the most common testicular tumors, comprising approximately 2-3% of the total. It can occur in all age groups, but is most common in males age 20-50. In this age group, the most common presenting sign is gynecomastia; the tumor is usually small and nonpalpable. It is bilateral in up to 3% of cases.
When the tumor appears in childhood, it commonly presents with pseudoprecocious puberty due to the production of androgenic hormones by the lesion. Gynecomastia may also supervene on this general state of virilization. The tumors tend to form a well-circumscribed, lobulated, yellow to tan nodule within the interstitial tissue of the testis. Extra- or paratesticular Leydig cell tumors (such as the lesion in this case, which was outside the seminiferous tissue proper and located in the rete testis) are less common but do occur.
Microscopically, the cells of the lesion are commonly arranged in nests and cords surrounded by a fibrous stroma. The cells are generally polygonal with eosinophilic to clear color (depending upon the lipid content). The nuclei are round and pleomorphism and mitoses are infrequent. In up to 40% of the cases, cylindrical crystals of Reinke (testosterone) can be found, which aids in the diagnosis. Immunostaining of this lesion is usually positive for vimentin and androgenic hormones. The differential diagnosis includes diffuse Leydig cell hyperplasia (often seen in Kleinfelter's syndrome), prostatic adenocarcinoma metastatic to testis, and testicular lymphoma. In addition to these entities, one must consider that up to 10% of Leydig cell tumors may behave in a malignant fashion, with extratesticular spread and distant metastases. Bilateral orchiectomy with retroperitoneal lymph node dissection may be curative.
Contributed by Kevin D. Horn, MD