Leydig cell tumors (LCT) are most commonly arranged in a diffuse or nodular pattern, although trabecular, tubular and pseudofollicular patterns are occasionally seen. The broad cords and sheets of tumor cells are separated by an inconspicuous fibroma stroma. Numerous delicate thin-walled blood vessels are present.

The tumors cells are large, polygonal with abundant eosinophilic and vacuolated (lipid-filled) cytoplasm. The nuclei are round, centrally placed with prominent nucleoli. Note the smattering of lipochrome pigment in the cytoplasm of several tumor cells in the right lower corner. This imparts a brown color to the tumor. Although not shown here, Reinke's crystals (rhomboid-shaped intracytoplasmic crystals) are pathognomonic and are present in approximately 40% of LCTs.2

A different case of LCT shows similiar features. Although the stroma usually consists of inconspicuous fibrous strands, it can also be hyalinzed, edematous or myxoid. Note again the numerous delicate blood vessels permeating the tumor. Although not seen in this case, Leydig tumor cells can occasionally be spindled or vacuolated to the point of adipose differentiation.

Leydig (interstitial) cell tumor, along with Sertoli cell tumors, are the most important sex cord-stromal tumors of the testis. Leydig cell tumors elaborate androgens or a combination of androgens and estrogens.

Grossly, the tumor is well-circumscribed, solid with a soft yellow-brown homogeneous cut surface. Foci of necrosis and hemorrhage are seen in 25% of cases.

There is no single histologic feature that separate benign from malignant LCT. Malignant LCTs generally demonstrate at least 3 of the following features: large size (greater than 5 cm), necrosis, greater than 3 mitoses per 10 HPF, intratesticular blood vessel invasion and infiltrative margins. Note, however, that metastasis is the definitive criterion for malignancy.1,2

May occur at any age, but peak incidence is between 2nd to 6th decades. The vast majority are unilateral. Presents with testicular swelling and hormonal affects which vary depending on the age of the patient. In prepubertal males, LCT may manifest as precocious puberty (deep voice, maturation of external genitalia, hair loss) before a testicular mass is discovered. In postpubertal males, a painless testicular mass is the usual presentation, however, 30% of adult males experience impotence, decreased libido and gynecomastia which precede the discovery of the mass.2

Radical orchiectomy is sufficent if the tumor is confined to the testicle. For malignant tumors, retroperitoneal lymph node dissection may be considered. Unfortunately, there is currently no effective treatment for LCT that have metastasized to parenchymal organs.

Malignancy (defined solely on the basis of metastasis) occurs in 10-25% of cases and affects older patients. Mean age of malignant LCT is 63, versus mean age of 40 for benign LCT.2

• Testis : Large Cell Calcifying Sertoli Tumor