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Hypospermia (immaturity of the seminiferous tubules) is a normal condition in very young mice ( < 4 weeks of age), but it may be induced in older mice with toxicants. The testicles appear morphologically normal, but maturing and mature spermatozoa are absent from both the testes and the epididymus.


Testicular atrophy occurs as an aging lesion in mice and may also be due to other factors such as exposure to specific toxic compounds, irradiation and hypoxia. The lesion may be focal (Fig. 166) or diffuse (Fig. 167). The seminiferous tubules and germinal epithelial cells are reduced in number and the testis may also be reduced grossly in size. A relative increase of Sertoli cells, interstitial cells (Fig. 167) or multinuclear cells may be seen. The lipofuscin pigment ceroid may be associated with the atrophy. Ceroid is acid fast and PAS positive.


Focal dystrophic mineralization of the seminiferous tubules may occur occasionally. It may represent previous areas of injury. The mineralization is composed of basophilic concentric masses which may be amorphous or concentrically laminated (Fig. 168).

Interstitial Cell Hyperplasia

An increase in the relative number of interstitial cells may be associated with testicular atrophy. Focal hyperplasia of interstitial cells may also occur and possibly represent a preneoplastic condition (Fig. 169).

Interstitial Cell Tumors

Both benign and malignant spontaneous tumors of the interstitial cells of Leydig are rare in mice, but the neoplasms can be induced with synthetic or natural estrogens in certain strains, particularly BALB/c mice. The cytoplasm of the neoplastic cells is distinctly eosinophilic. Small, well circumscribed tumors can be referred to as adenomas and large tumors which are invasive or metastasize can be referred to as carcinomas (Figs. 170 and 171). The larger carcinomas occasionally metastasize to the lungs (Fig. 172).



Spermatocele of the epididymus is a dilatation of a duct of the epididymus with the lumen filled with spermatozoa (Fig. 173). If the duct ruptures, the release of spermatozoa in surrounding tissue may result in the formation of a spermatic granuloma.

Accessory Sex Glands

Preputial and Clitoral Glad Ectasia

The preputial and clitoral glands are accessory sex glands of the male and female mouse, respectively. The gland is smaller in the female mouse. It is composed of modified sebaceous acini and squamous ducts. The glands may become markedly dilated (ectasia) (Fig. 174) and acute suppurative and chronic inflammation is common.

Preputial Gland Abscess

Abscesses of the preputial gland are frequently seen in male mice as a consequence of fighting. The abscess is characterized by the presence of numerous neutrophils and liquefactive necrosis. Grossly, the exudates are frequently green in color.


Neoplasms of all of the male accessory sex glands (prostate, seminal vesicles, preputial and coagulating glands) are extremely rare. Adenocarcinomas of the prostate may be composed of relatively well differentiated neoplastic cells (Figs. 175 and 176). Squamous metaplasia may occasionally be seen. Adenomas and carcinomas of the seminal vesicle and coagulating gland (Figs. 177, 178, 179 and 180) have been reported very infrequently. Squamous cell carcinomas are very occasionally seen in the preputial gland (Fig. 181).

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