Interstitial Cell Tumor in a dog

History:  The testicles from an 11 year old male German Shepherd were submitted for histopathology after castration. The dog had been showing signs of feminization and endocrine disease such as flank alopecia, pruritis, enlarged mammae, small prepuce, and testicular atrophy.

Histopathology:

Two testicles were submitted for histopathology.

The smaller testicle contains an expansile encapsulated neoplasm composed of interstitial cells arranged in packets in a fine fibrovascular stroma.   Neoplastic cells are elongated with ample eosinophilic cytoplasm and indistinct cell borders. Nuclei are round to oval with coarse chromatin and variably distinct nucleoli. There is moderate anisocytosis and anisokaryosis. There are 5 mitotic figures in 10 400x fields.   Seminiferous tubules are devoid of germinal cells or mature spermatids and multifocally contain syncytial cells. There is one focus of neoplastic germ cells consisting of large tubules filled with large round cells with moderate anisocytosis and anisokaryosis  and occasional mitotic figures.  Multiofocally the walls of arterioles are thickened by amphophilic homogenous material (amyloid) which causes luminal narrowing.

Small Testicle- A well circumscribed mass is present in the lower right corner, and atrophic seminiferous tubules are seen in the upper left corner

Small Testicle: Closer view showing pattern of cells with foamy pink cytoplasm typical of interstitial cells

Small Testicle: even closer view of the neoplasm

The second, larger testicle contains seminiferous tubules largely devoid of seminiferous activity. The tubules of the epididymis are separated by increased amounts of fibrous tissue and collagen and contain few spermatids. The epithelial cells are multifocally necrotic, swollen and hypereosinophilic. The arteriolar walls are also thickened by amyloid.

Contralateral testicle: Atrophy of seminiferous tubules and arterioles with amyloid

Comment:

Interstitial cell tumors are the most common testicular neoplasm of dogs. They variably secrete estrogen which could explain the alopecia and feminization in this dog.

The amyloid was considered an incidental finding.