We report four cases of
Leydig cell tumor of the testis with a microcystic pattern that mimicked
yolk sac tumor. The patients ranged in age from 27 to 35 years and, except for one
tumor that was discovered incidentally, presented with testicular masses. All
tumors were intratesticular, and three were well circumscribed by a rim of fibrous tissue, whereas one showed minor, focal extension into the adjacent testis. The
tumors typically had a vaguely lobular architecture subdivided by fibrous bands. Three of the cases had a complex microcystic appearance caused by individually vacuolated cells and coalescent cystic spaces; this pattern accounted for the majority of two
tumors. Another case had focal collections of Leydig cells with prominent cytoplasmic vacuoles but lacked the coalescent spaces. The microcyst contents ranged from optically clear to eosinophilic or lightly basophilic, with the latter having the staining qualities of
acid mucopolysaccharide. Three
tumors had uniform, bland nuclei and low mitotic rates (<1 mitotic figure per 10 high power fields), but one had marked, random nuclear pleomorphism and an average mitotic rate of five mitotic figures per 10 high power fields. By immunohistochemistry, all were diffusely positive for
vimentin; two of three were positive for
inhibin, and one showed focal positivity for
cytokeratin (CAM 5.2). All were negative for
alpha-fetoprotein and placentalike
alkaline phosphatase and, apart from having microcystic and solid areas, lacked other features typical of
yolk sac tumor. Clinical follow-up ranged from 2 months to 2 years with no patient having recurrence or
metastasis. The distinction of
Leydig cell tumor from
yolk sac tumor has important clinical implications because patients with the former usually receive only clinical follow-up, but the latter often requires
chemotherapy.