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

Sertoli Cell Tumor

•Sertoli cells produce estrogen, support germ cells, and form seminiferous tubule basement membrane

•Sertoli cell tumors tend to grow in expansile fashion that compress and destroy surrounding parenchyma

•Sertoli cell tumors are bilateral in 11% dogs

•54% of Sertoli cell tumors are found in cryptorchid testicles

•8.8-times risk of developing a Sertoli cell tumor in the cryptorchid testicle compared to descended testicle in dogs with unilateral cryptorchidism

•testicular microenvironment influences the development of testicular tumors as, in humans, early surgical correction of cryptorchidism (i.e., orchipexy) decreases risk of testicular neoplasia

•Sertoli cell tumor in descended testicle found in younger dogs and associated with contralateral cryptorchid testicle

•Sertoli cell tumors are associated with a decreased risk of prostatic disease, circumanal gland hyperplasia, perianal tumors, and perineal hernia

•0.6%-9.0% metastatic rate with metastatic sites including sublumbar lymph node (common), lungs, liver, spleen, adrenal glands, kidney, and pancreas

CLINICAL FEATURES

Clinical Signs

General Considerations

•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 Syndrome

•feminization is rare in dogs with interstitial cell tumors and seminomas, but can occur with Sertoli cell tumors

•feminization dependent on testicular location with feminization occurring in 16% of scrotal testes, 50% of inguinal testes, and 70% of intra-abdominal testes

•hyperestrogenism has been implicated in the pathogenesis of feminization but this has not been proven

•clinical signs of feminization include:

•bone marrow hypoplasia with thrombocytopenia, hemorrhage, anemia and granulocytopenia

•symmetrical and squamous metaplasia of the prostate resulting in cystic benign prostatic hyperplasia

•gynecomastia and galactorrhea

•attractiveness to other males

•atrophy of non-neoplastic testicle due to negative feedback of estrogen on the pituitary-hypothalamus axis

•penile atrophy with pendulous prepuce

•bilaterally symmetrical alopecia in the genital area, inner thighs, abdomen, chest, shoulders, and thighs

•69% mortality rate

Diagnosis

•scrotal palpation

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

•hematology: anemia, leukopenia, and thrombocytopenia in dogs with Sertoli cell tumors and feminization

•increased plasma estrogen levels (with ultrasonographic evidence of a testicular mass) has been used to diagnose Sertoli cell tumor in 3 dogs with acute onset of infertility

•infertility associated with spermatozoal abnormalities such as lesions in mid-piece region, poor spermatozoal motility, and low total spermatozoal output

•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

•fresh whole blood transfusion for dogs with Sertoli cell tumors if myelosuppressed with thrombocytopenia and anemia

Prognosis

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

•mortality > 80% if severe myelosuppression

•hematologic parameters usually improve within 2-4 weeks but can take up to 5 months to return to normal