A 13-year-old male presents with bilateral enlargement of his breasts. Physical exam is otherwise unremarkable, and the breast enlargement is thought to be a normal variation at pubey. Histologic sections of breast tissue would most likely reveal

Gynecomastia (enlargement of the male breast) histologically reveals epithelial hyperplasia within the ducts that is surrounded by hyalinized fibrous tissue. It is caused by an increase in the estrogen-to-androgen ratio. This abnormality may sometimes be found in males at the time of pubey. Other causes of gynecomastia include Klinefelter's syndrome (decreased secretion of testosterone), testicular feminization (androgen insensitivity), testicular tumors, cirrhosis of the liver, alcohol abuse, increased gonadotropin levels (such as choriocarcinoma of the testis), increased prolactin levels, drugs (such as digoxin), or hypehyroidism. Testicular neoplasms that are associated with gynecomastia are tumors that secrete human chorionic gonadotropin (hCG), which increases the synthesis of estradiol. Testicular tumors associated with the production of hCG include germ cell tumors (choriocarcinoma and seminoma), Leydig cell tumors, and Seoli cell tumors Gynecomastia Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition