PATHOPHYSIOLOGY

General Considerations

•testicular tumors are common and account for 4%-7% of all tumors in male dogs

•testicular tumors broadly classified into 2 groups based on histology:

•group I: germ cell tumors such as seminoma, embryonal carcinoma, and teratoma

•group II: Sertoli cell tumor, interstitial cell tumor, and mixed testicular tumors

•mixed testicular tumors may be classified separately

•mixed germ cell-stromal tumors have a dual population of germ and Sertoli cells and account for 7% of canine testicular tumors

•breed predisposition: Siberian Husky, Norwegian Elkhound, Fox Terrier, Afghan Hound, and Shetland Sheepdog

•Dachshund, Rottweiler, Shih Tzu, Yorkshire Terrier, Toy Poodle, Miniature Schnauzer, and mixed breed dogs have a significantly decreased risk of developing testicular tumors

From: Withrow SJ & MacEwen EG (eds): Small Animal Clinical Oncology (3rd ed).

•50% of dogs over 10 years have multiple tumors of different histologic types

•testicular tumors are uncommon in dogs < 6 years

•Sertoli cell tumor and seminoma are more common with cryptorchid testicles

Interstitial Cell Tumor

•interstitial or Leydig cells are found in the fibrovascular stroma of the testicle and produce testosterone

•interstitial cell tumors are the most common testicular tumor in dogs

•interstitial cell tumors are benign but functional tumors and associated with prostatic disease and enlargement, circumanal gland hyperplasia, and perianal tumors ± perineal hernia

•interstitial cell tumors are bilateral in 43% dogs

CLINICAL FEATURES

Clinical Signs

•incidental finding at surgery or necropsy

•scrotal or inguinal mass or enlargement

•hypertrophic osteopathy reported in 1 dog with metastatic Sertoli cell tumor to lungs and kidney

•feminization is rare in dogs with interstitial cell tumors

Diagnosis

•scrotal palpation

•rectal examination, lateral abdominal radiograph, abdominal ultrasonography, or direct examination during exploratory celiotomy to assess ± biopsy the sublumbar lymph nodes

•ultrasound examination is a sensitive and relatively specific technique for the diagnosis of testicular tumors with:

•interstitial cell tumors appearing as a well-circumscribed mass with predominantly hypoechoic and small hyperechoic areas

•Sertoli cell tumors disrupting internal architecture with echogenic pattern varying from anechoic to mixed echogenicity

•aspiration or biopsy are invasive, compromise testicular-blood barrier and may predispose to infertility and spermatic granuloma formation

•± thoracic radiographs

•histopathology following castration

Treatment

•castration with resection of a large amount of the spermatic cord

Prognosis

•castration is curative if no bone marrow hypoplasia, myelosuppression, or metastatic disease