Clinical history: 43 year old male with a small testicular mass discovered incidentally.
What is the diagnosis?
The cytomorphology and immunoprofile are in keeping with a Leydig cell tumour
Leydig cell tumor is the most common sex cord–stromal tumor of the testis, constitutes approximately 2% of all testicular neoplasms. These tumors may occur at any age. Only 3% of these tumors occur bilaterally, and 15% of them extend beyond the testis at presentation. Adults usually complain of testicular swelling, 30% have gynecomastia, and 20% have decreased libido. Children usually do not present with a mass lesion but with isosexual pseudoprecocity.
The tumor is malignant in approximately 15% of cases. Other than the presence of metastasis, no single criterion predicts malignant behavior. Clinicopathologic features associated with an adverse outcome include older age, large size, infiltrative margins, angiolymphatic invasion, foci of necrosis, mitotic count of more than 3 per 10 high-power fields, and significant nuclear atypia. The presence of at least four of these features strongly correlates with malignancy. Malignant Leydig cell tumors most often spread to regional lymph nodes, followed by lungs, liver, and bone.
Testosterone and, uncommonly, androstenedione and dehydroepiandrosterone are secreted by Leydig cell tumors. Malignant tumors are rarely functional.
Grossly, the tumor is usually a sharply circumscribed solid mass, 3 to 5 cm in diameter, with a relatively typical yellow or yellow-brown color. Involvement of the entire testis or spread beyond the testis is rare; foci of hemorrhage or necrosis or both are seen in approximately 25% of tumors.
Microscopically, diffuse and nodular growth patterns are most common. Sheets and cords of cells are separated by fibrous bands of variable thickness that may have focal or conspicuous edematous or myxoid character. The tumor cells are large and polygonal with round nuclei and abundant eosinophilic cytoplasm. The nuclei typically have a single prominent nucleolus. Mitoses are rare but may be abundant when striking nuclear atypia is present. Reinke crystals, which are rod-shaped or oval to elongated pink cytoplasmic structures that are considered pathognomonic, are seen in only one third of tumors. Lipofuscin is present in 10% to 15%. Tumor cells test positive for inhibin, melan A (A103), calretinin, and vimentin; negative for keratins and S-100 protein.
Leydig cell hyperplasia, large cell calcifying Sertoli cell tumor, testicular tumors of adrenogenital syndrome, malakoplakia, hepatoid yolk sac tumor, carcinoid tumor, lymphoma, and metastases to the testis.