Dr. Douglas Brum
Testicular tumors are the second most common tumors in intact male dogs, the first being skin tumors. The condition usually appears in older dogs but has been seen in dogs as young as three years old. There are three main types of testicular tumors and about a third of dogs that develop a tumor will actually have more than one type present. Orchitis and epididymitis are inflammations of the testicle and epididymis, which is the tube-like structure along-side the testicle. They are usually caused by a bacterial infection. The condition is generally painful, and dogs tend to feel ill. Affected dogs may also have a fever. If the infection is severe, the swelling in the testicle may begin to spread up the scrotum and into the inguinal area. Epididymitis may sometimes be caused by Brucella infection.
Dogs often have tumors in both testicles, even if only a single mass is palpated, so it is important that both testicles be removed when removing a neoplastic or cancerous testicle. Occasionally, testicular tumors may predispose the testicle to twist and cause an acute (sudden) swelling of the scrotum and significant pain. This is testicular torsion. If the testicle were undescended or cryptorchid, the torsion would cause abdominal pain. At other times the neoplastic testicle may cause an obstruction of the lymph drainage in the scrotum, leading to a swollen, but generally not painful scrotal sack.
The largest risk factor for the development of testicular tumors is having a cryptorchid testicle. A cryptorchid testicle is about 14 times more likely to develop a tumor than a scrotal testicle. Sertoli cell and interstitial cell tumors account for nearly 100 percent of tumors in these cryptorchid testicles. In descended scrotal testes, all three tumor types appear in nearly equal percentages.
Occasionally, testicular cancer can lead to a condition known as male feminizing syndrome. This occurs if the tumor causes hormonal changes that result in an increase or relative increase in blood estrogen levels. The most common tumor to cause this is a Sertoli cell tumor, although the other tumors may occasionally be responsible. About 25 percent of Sertoli cell tumors and 70 percent of all cryptorchid testicular tumors cause this syndrome. This can be a very serious illness, as increased estrogen production not only affects a dog's outward appearance, it can also affect the bone marrow.
The clinical signs associated with the feminizing syndrome include: enlargement of the mammary glands, possibly with the production of milk, symmetrical hair loss, increased skin pigmentation, infertility, decreased libido, a pendulous penile sheath and atrophy of the non-neoplastic testicle. Squamous metaplasia and enlargement of the prostate may also be seen. High levels of estrogen also cause a suppression of the bone marrow (bone marrow hypoplasia), and may lead to significant decreases in the white blood cells, red cells and platelets (blood cells that help in clotting). This may lead to infections, anemia and bleeding problems that may be life-threatening and require emergency treatment.
Other testicular tumors can also produce increased levels of male hormones called androgens. Elevated androgens may predispose animals to the development of prostatic disease and perianal (around the anus) disease. Symptoms of prostatic disease may include hyperplasia (enlargement), cyst formation, or infection. Perianal diseases associated with prostatic neoplasia include perianal adenomas (benign tumors), adenocarcinoma (malignant tumors), and perianal hernias.
The causes of testicular enlargement or swellings include:
Testicular torsion is a twisting of the testicle where blood supply and or lymphatic drainage is compromised. The testicle is usually symmetrically enlarged and painful. The condition is often associated with testicular neoplasia. Testicular torsions occur with greater frequency in abdominal cryptorchid testes.
A spermatocele also called a sperm granuloma may occur due to a cyst-like dilation of the epididymis. Sperm may become trapped inside the dilation, and an inflammatory response may occur. This response may produce a small swelling in the epididymis. It is a benign condition, but may result in infertility.
An inguinoscrotal hernia occurs when abdominal contents pass into the scrotal sack. Most commonly, it is fatty tissue or a loop of bowel that enter through the inguinal canal. It is not a common condition.