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The most important diseases of the epididymis of all species are involve inflammation. Infectious epididymitis is the most important but unlike the ram, is not well studied. One very important and often missed disease is spermatic granuloma of the epididymal head. This is an inflammatory (granulomatous inflammation to spermatozoa) disease with an anomalous and potentially genetic basis.

Epididymitis

Epididymitis is a sporadic disease in stallions.

Bacterial infection of the epididymis usually occurs via two main routes, ascending infection from the urethra via the deferent duct and accessory genital glands, or hematogenous spread. Descending infection from the testis, and direct penetrating injury are both theoretically possible, but much less likely

Bacterial epididymitis

There are many bacteria that could potentially cause epididymitis. reports where specific bacteria are cultured from cases are indicated below. Where the lesions are characteristic of bacterial disease but no organism is recovered, the references are listed here.

Kasaback et al (1999) reported on a case of right unilateral epididymitis, periorchitis and orchitis.

Kasaback CM, Rashmir-Raven AM, Black SS. Theriogenology question of the month. Septic orchitis-periorchitis and epididymitis.J Am Vet Med Assoc 1999; 215: 787-789.

Proteus mirablis

Brinsko et al (1992) reported on a case of bilateral epididymitis from which Proteus mirablis was cultured as the only organism. Lesions were in the tail of the epididymis with some extension into the body of the epididymis. Histologically the lesions were characteristic of epididymitis in other species with interstitial lymphocytes and plasma cells, tubular neutrophilic inflammation and spermatic granulomas. There was tubular degeneration in the testis.

Brinsko SP, Varner DD, Blanchard TL, Relford RL, Johnson L. Bilateral infectious epididymitis in a stallion. Equine Vet J. 1992; 24: 325-328.

Streptococcus equi subsp zooepidemicus

Macroscopic changes

The gross lesions of epididymitis usually involve the tail and sometimes the body of the epididymis. This may be bilateral or unilateral, and the severity can vary tremendously. The severity reflects the degree of damage including necrosis and vascular changes.

orchitis or with necrosis.

With time, fibrosis becomes the major gross lesion, and there will be a marked interstitial fibrosis visible in the affected areas of the epididymis. Adhesion of the parietal to the visceral vaginal tunic is a common occurrence, and the tunics can become markedly thickened with granulation and fibrous tissue.

Figure : Unilateral epididymitis (lower). The epididymides are viewed from the ventral surface such that the tail of the epididymis is visible and the testis is beneath it.

Microscopic changes

There are no sequential studies of the lesions in dogs. The most acute or recent cases had large numbers of neutrophils within the duct of the epididymis. The epithelium often has degenerative changes including single cell death. The interstitial tissues are expanded with edema and neutrophils and macrophages. Severe cases will have fibrin deposition. Some cases will have whole regions of coagulation necrosis. With time, there may be the formation of abscesses with pools of neutrophils and necrotic debris between the duct or involving the ducts. Rupture of the ducts will allow spermatozoa to enter these areas. The tunics will initially be covered with fibrin and enmeshed neutrophils, but soon develop granulation tissue. With time, there will be infiltrates and accumulations of plasma cells and lymphocytes, especially around vessels and also around the duct.

Organisation of edema and fibrin will eventually cause the formation of fibrous tissue within the interstitium and around areas of necrosis. Spermatic granulomas form where sperm are extravasated.

It is unusual to find bacteria or bacterial colonies within the lesions, even with a Gram stain.

Figure : Histology of epididymitis. The epididymal duct is surrounded by lymphocytes and plasma cells, and there is a spermatic granuloma ventrally.

 

Spermatic granuloma of the epididymal head (SGEH)

Spermatic granuloma of the epididymal head is a condition s

 

 

 

 

Noninflammatory disease

Dislocation of epididymis

Pozor et al (2016) described 8 variations of the attachment of the epididymis to the testis including variation in the length of the proper ligament of the testis and variations in the length of the mesorchium. They reported 2 cases of dislocation of the epididymis so that the tail was cranial and wrapped around the deferent duct.

Pozor M, Freeman D, Troedsson M, Brown M, Morton A, Smith A, McNaughten J. Anatomical variations in epididymal-testicular fusion in stallions and their possible clinical significance. Equine Vet J 2016; 48: 490-495.

Segmental aplasia of the mesonephric duct (SAMD)

Segmental aplasia or lack of development of any part of the mesonephric duct, from which is derived the epididymis, deferent duct and vesicular gland, is a heritable condition in stallions, and is assumed to be so in other species. Only animals with unilateral disease are fertile, and most cases reported are unilateral in distribution. Most cases involve the epididymis, but some also have a lack of the deferent duct.

  

Epididymal hypoplasia

Development of the epididymis parallels that of the testis, and in particular, the passage of spermatozoa. A small and hypoplastic epididymis occurs with concurrent testicular hypoplasia, or with obstruction to the flow of fluid (and spermatozoa) from the testis such as with segmental aplasia of the epididymis (upstream of the hypoplastic segment) or with spermatic granuloma of the epididymal head

Epididymal atrophy

Epididymal hyperplasia (intraepithelial cysts or luminae)

Adenomyosis of the epididymis

Adenomyosis is when there is an outpouching of the epitheliium of the epididymis into the smooth muscle layer. This cavity can be a site of spermiostasis and subsequent spermatic granuloma formation. It can be induced by exposure to estrogens.

 

Cysts of epididymis

Neoplasia of the epididymis

Neoplasms of the epididymis is extremely rare!

Epithelial neoplasms

 

Stromal neoplasms

Smooth muscle tumor 

Kaye et al (2020) reported on an older stallion with a smooth muscle tumor of the head of the epididymis.

Kaye SJ, Owen HC, van Eps AW, Hodder ADJ. Theriogenology Question of the Month. Epididymal leiomyoma. J Amer Vet Med Assoc 2020; 256: 1225-1228

Round cell neoplasms

Lymphoma of the epididymis is reported

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Disease of the deferent duct (ductus deferens)

Vasectomy

Segmental aplasia

Aplasia of a segment of the deferent duct is discussed inder segmental aplasia of the mesonephric duct above.

Neoplasia