History

A 16-year-old Quarter Horse stallion was examined to determine the cause for bilateral enlargement of the scrotum. The scrotum had gradually become enlarged during the preceding 12-month period, with enlargement most noticeable during the past 6 to 8 months. The stallion had signs of discomfort during the past 2 to 3 months.

The year prior to the scrotal enlargement, the stallion had been used for breeding. According to the owner, the stallion had normal fertility and impregnated numerous mares. During the 12 months prior to examination, the stallion was also used for breeding but did not successfully impregnate any mares.

Initial examination revealed that the stallion had enlarged, bilateral swelling of the scrotum (Figure 1). All other physical variables were within acceptable limits. Palpation of the external genitalia revealed that the neck of the scrotum was firm and that there was fluctuance in the ventral aspect. Mild signs of discomfort were elicited from the stallion during palpation of the scrotum. There were no accompanying signs of inflammation or edema. Transrectal palpation revealed a large spermatic cord that entered the left inguinal ring. The right inguinal ring was also palpable, but no abnormalities were detected. Results of a CBC and serum biochemical analyses were within the respective reference ranges for all variables.

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Photograph of the scrotum of a 16-year-old Quarter Horse stallion with a history of gradual bilateral enlargement of the scrotum during a 12-month period.

Citation: Journal of the American Veterinary Medical Association 231, 4; 10.2460/javma.231.4.531

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Ultrasonographic evaluation of the scrotal contents revealed abnormal, heterogeneous, multilobulated tissue throughout the right and left testes with no evidence of normal testicular parenchyma (Figure 2). The left spermatic cord was slightly larger than the right. The left testis included a large testicular blood vessel (0.8 cm [0.3 inch] in diameter) and several other large vessels, although it was unclear whether the other vessels were veins or lymphatic vessels.

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Ultrasonographic view of a testis of the stallion in Figure 1. Both testes in this stallion were similar in ultrasonographic appearance. Marks on the ultrasonogram are at intervals of 1 cm.

Citation: Journal of the American Veterinary Medical Association 231, 4; 10.2460/javma.231.4.531

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Question

What is the most likely cause for the scrotal enlargement in this stallion? Please turn the page.

Answer

These findings are most consistent with bilateral testicular neoplasia.

Results

On the basis of the clinical findings, ultrasonographic examination, and transrectal palpation results, a tentative diagnosis of bilateral testicular neoplasia was made. The selected treatment option was abdominal laparoscopy to evaluate for evidence of metastatic disease followed by closed castration.

Perioperative treatment included administration of cefazolin (10 mg/kg [4.5 mg/lb], IV, q 6 h for 48 hours), gentamicin (6.6 mg/kg [3 mg/lb], IV, q 24 h), phenylbutazone (4.4 mg/kg [2 mg/lb], IV, q 24 h), and a single dose of tetanus toxoid (1 mL, IM). The horse was sedated by administration of medetomidine (2.25 mg, IV). Anesthesia was induced by IV administration of diazepam (10 mg) and ketamine hydrochloride (1.0 g) and maintained by administration of isoflurane in oxygen via a semiclosed circle system. A balanced electrolyte solution^a was administered IV at a rate of 5 mL/kg/h (2.3 mL/lb/h) during the anesthetic period. The horse was positioned in dorsal recumbency. The caudoventral abdomen and scrotal region were clipped and aseptically prepared for surgery. Abdominal exploration by laparoscopy was performed through a 2-cm (0.9-inch) skin incision made through the umbilicus. To improve surgical exposure of the caudal abdomen, the surgery table was tilted 30° to place the horse's head on a downward slope (Trendelenburg recumbency).

The left and right internal inguinal rings were examined. The spermatic cords were bilaterally large. The testes were manipulated to allow complete examination of the spermatic cords (Figure 3). A 2-cm skin incision was made approximately 6 cm (2.7 inches) medial to the left inguinal ring, and a 10-mm laparoscopic trocar-cannula unit was introduced into the abdomen under laparoscopic guidance. Laparoscopic grasping forceps were used to gently manipulate intestinal loops away from the left and right internal inguinal rings to allow examination of the left and right spermatic cords within the caudal abdomen. No abnormal masses were identified in the left or right inguinal region or throughout the abdomen. The surgery table was returned to a horizontal position, the laparoscope was removed, and the abdomen was decompressed. Both incisions were closed in a routine manner.

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Laparoscopic view of the left (A) and right (B) spermatic cord (arrow) in a stallion with bilateral seminomas.

Citation: Journal of the American Veterinary Medical Association 231, 4; 10.2460/javma.231.4.531

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A closed-castration was performed via scrotal ablation to remove both testes.¹ The cremaster muscle and spermatic cord were ligated with 2 transfixation and 1 circumferencial ligature placed as proximally as possible in an effort to remove as much abnormal tissue as possible.

The left testis was 14 × 11 × 10 cm (5.5 × 4.3 × 3.9 inches), and the right testis was 17 × 14 × 10 cm (6.7 × 4.3 × 3.9 inches). Examination of cut sections revealed that the testes consisted of bulging, multilobular, firm, pale tan tissue.

The testes were histologically similar. Testicular parenchyma was replaced by a diffuse infiltrate of neoplastic cells, which were bordered externally by the outer tunic of the testis. Neoplastic cells were grouped in packets, cords, and sheets separated by anastomosing trabeculae of fibrous connective tissue. Cells were polyhedral, with moderate amounts of poorly demarcated amphophilic cytoplasm (Figure 4). Nuclei were round to oval, with a vesicular chromatin distribution and 1 or 2 prominent nucleoli. There were 1 or 2 mitotic figures/hpf (400 × magnification). There were scattered focally dense collections of lymphocytes and foci of necrosis throughout the neoplastic tissue. In both testes, neoplastic cells had invaded the subcapsular and interstitial connective tissue, and there were rare collections of tumor cells in venules and lymphatics. These findings were consistent with seminoma. The spermatic cords were not histologically evaluated.

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Photomicrograph of a section of neoplastic tissue from a testis of a stallion with bilateral seminomas. Notice that the cells are polyhedral with moderate amounts of poorly demarcated amphophilic cytoplasm. Nuclei are round to oval, with a vesicular chromatin distribution and 1 or 2 prominent nucleoli. Mitotic figures (arrow) are common. H&E stain; bar = 50 Mm.

Citation: Journal of the American Veterinary Medical Association 231, 4; 10.2460/javma.231.4.531

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Discussion

Testicular neoplasia is considered to be a rare condition in stallions, although it is difficult to calculate the true incidence because of the high number of male horses gelded at an early age.^2,3 Testicular neoplasia can be categorized into germinal (seminomas, teratomas, teratocarcinomas, and embryonal carcinomas) or nongerminal (interstitial [Leydig] cell and sustentacular [Sertoli] cell tumors) origin as well as secondary tumors (lipomas and mast cell tumors).

Seminomas arise from spermatogenic cells and are the most common testicular neoplasms in horses. In dogs and humans, seminomas are more frequent in cryptorchid than in scrotal testes. Many cases of seminoma in horses have involved cryptorchid stallions, but a definitive association has not been determined.² In stallions, seminomas appear more likely to metastasize than seminomas in other domestic species, with multiple reports in a study² of malignant seminomas in horses. Stallions with seminomas range from 8 to 22 years of age, with most stallions being > 10 years old.²

Stallions with seminomas frequently have progressive scrotal enlargement during a course of weeks to months. Most commonly, only 1 testis is affected, although both testes can be affected.² Scrotal palpation does not elicit signs of pain in most stallions with seminomas, although it will in some affected stallions, even to the point of causing colic, and some affected stallions may have varying degrees of discomfort during ejaculation.

Testicular neoplasia must be differentiated from other causes of scrotal enlargement, including orchitis, periorchitis, epididymitis, hematocele, spermatocele, hydrocele, varicocele, hematoma, torsion of the spermatic cord, and inguinal or scrotal hernia. Inflammatory conditions and spermatic cord torsion typically result in tissues that feel warm or hot, and palpation tends to elicit signs of pain. Most of the differential diagnoses can be evaluated adequately with ultrasonography. Pathologic conditions such as hernia, hydrocele, and torsion of the spermatic cord have characteristic ultrasonographic appearances. In horses, ultrasonography of seminomas has revealed diffuse heterogeneous echogenic areas with ill-defined, scattered hyperechogenic regions, which give the appearance of hypoechoic nodules throughout the affected testis.⁴ Seminomas in humans and dogs have been described as homogenously or heterogeneously echogenic, depending on the particular lesion.⁵ Normal testicular parenchyma is obliterated throughout the area of the tumor and is not evident in the testis by the time of examination.

In the horse reported here, enlarged vessels were detected during ultrasonography. To our knowledge, enlargement of vessels has not been detected during ultrasonographic evaluation of other horses with seminomas. Despite the fact that results of ultrasonography may make neoplasia a highly likely differential diagnosis, ultrasonography cannot replace histologic evaluation as a definitive diagnostic test. Examination of biopsy specimens is not commonly used to differentiate between neoplastic and inflammatory conditions because of concerns about the spread of neoplasia and possible damage to normal testicular parenchyma.^2,3 However, in normal testes of horses and dogs, evidence indicates that no substantial histologic damage is sustained in healthy testicular tissue as a result of biopsy.⁶ To our knowledge, no studies have been conducted on the long-term effects of testicular biopsy on fertility or on inflamed or neoplastic tissue. In many animals with testicular neoplasms, it is more practical to perform a hemicastration and submit the entire testis for histologic examination.

Treatment for seminomas is removal of the affected testis. Hemicastration can be performed because in a stallion with a unilateral, benign tumor, the remaining testis may allow the stallion to regain sufficient fertility such that it can be used as a stud horse. The entire testis should be submitted for histologic examination to determine evidence of metastasis. In stallions, seminomas can metastasize aggressively to the contralateral testis, abdomen, and thorax. In a few horses, metastasis to lymphatics surrounding the kidneys has resulted in hydroureter, hydronephrosis, and other secondary renal complications. Transrectal palpation can sometimes reveal enlarged medial iliac or lumbar aortic lymph nodes when there has been metastasis. A guarded prognosis should be given for a stallion in which a seminoma has metastasized, with an expected survival time between 10 and 24 months.

To our knowledge, the horse described here is the first report in which laporoscopy was used to examine the abdominal cavity for evidence of metastasis prior to castration in a stallion with a seminoma. Although the seminoma may have metastasized to areas within the abdominal cavity that could have been evaluated more completely by use of laparoscopy in a standing patient, dorsal recumbency was elected for this horse to address surgical concerns such as hemorrhage, ligation of vessels, the possibility of other surgical approaches to the abdomen (median or paramedian), and emasculation of the spermatic cord. Dorsal recumbency also was the surgeon's preference to gain access to the inguinal rings and spermatic cords without interference from the colon and for providing adequate evaluation of the spleen, liver, stomach, omentum, mesentery, peritoneum, and diaphragm.⁷

Gross examination of affected testes usually reveals a soft, off-white, multilobulated, glistening tumor that typically oozes from cut sections. The tumor often contains hemorrhagic or necrotic foci. Histologic examination reveals a monocellular population of large, round-to-oval neoplastic cells with large, round nuclei containing prominent nucleoli. Mitotic figures are common. Spermatogenesis is usually not evident. The horse reported here had all of these findings.

Outcome

The horse recovered without complications from surgery and was discharged from the hospital 2 days after surgery. The owners reported no postoperative complications. The histologic findings and bilateral nature of the testicular lesions indicated that metastasis was likely in this horse. Despite the poor prognosis that would accompany metastasis, the owners of the stallion reported that the animal was healthy 12 months after surgery (24 months after onset of clinical signs). The stallion was not available at that time for a follow-up examination to evaluate progression of disease, but it had already exceeded the survival time reported for other horses with malignant seminomas.