History

A 2-year-old sexually intact male Vietnamese potbellied pig that weighed 113 kg (249 lb) was admitted and examined to determine the cause of inappetance, irritability, and an enlargement in the inguinal region. The clinical signs had become more evident and the pig's condition had gradually worsened during the preceding week. No treatment had been initiated prior to our examination.

The owners reported that the boar would attempt to mate with a piece of polyvinyl chloride pipe. Physical examination revealed massive distention (40 × 25 cm [15.7 × 9.8 inches]) in the inguinal region and caudoventral portion of the abdomen. Palpation of the enlargement revealed it was firm and excessively warm but could be compressed, which suggested it was filled with fluid. The prepuce was edematous. There was evidence of irritation of the skin over the right inguinal region.

Question

What are the most likely differential diagnoses for the enlargement in the inguinal region of this boar?.

Answer

Trauma-induced hematoma or seroma, peritesticular hematoma or abscess, penile injury, orchitis attributable to Brucella suis, testicular neoplasia, testicular abscess, inguinal hernia, rupture of the bladder or urethra, penile hematoma, or preputial abscess.

Results

Initial evaluation included a CBC, serum biochemical analysis, urinalysis, ultrasonography, and cytologic examination of a fine-needle aspirate. Results for hematologic and serum biochemical analyses were essentially unremarkable, except for a mild increase in creatine kinase activity. Creatinine and BUN concentrations were within the respective reference ranges, and there was no evidence of an inflammatory leukogram. A urine sample was collected via cystocentesis; results of urinalyis were within expected limits.

Ultrasonography revealed a normal-appearing urinary bladder and penis and a small amount of fluid in the abdomen. Ultrasonography of the inguinal and perineal regions revealed numerous large (> 5 cm [> 2 inches] in diameter), septated cystic structures, which were surrounded by a small amount of fluid. Cystic structures in the perineal and inguinal region were assumed to be associated with the testes and epididymides. Normal testicular characteristics were not apparent on ultrasonographic images.

Aspirates from one of the cystic structures were submitted for cytologic examination as well as aerobic and anaerobic bacterial culture. Results of cytologic examination were suggestive of a seroma because of the high protein content, low total number of nucleated cells, macrophages containing hemosiderin, and lack of neoplastic cells. All bacterial cultures yielded negative results.

Analysis of results of the diagnostic tests did not enable us to determine the reason for the enlargement in the inguinal region nor the origin of the cystic structures. Because of a lack of a definitive diagnosis, exploratory surgery was performed.

During surgery, it was found that both testes were abnormally large (Figure 1). The right testis was 30 × 16 cm (11.8 × 6.3 inches). The left testis was slightly smaller (20 × 15 cm [7.9 × 5.9 inches]). Both abnormal testes were removed by use of a closed castration technique. The spermatic cords were ligated by use of circumferential and transfixation ligatures. Dead space was eliminated, and the skin was closed in a routine manner. After completion of the surgery, the pig was administered oxytetracycline hydrochloride (19.8 mg/kg [9 mg/lb], IM) and butorphanol tartrate (0.2 mg/kg [0.09 mg/lb], IM).

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Excision of the right testis of a 2-year-old Vietnamese potbellied pig with an enlargement in the inguinal region. The right testis was 30 × 16 cm (11.8 × 6.3 inches). The left testis was also enlarged but slightly smaller (20 × 15 cm [7.9 × 5.9 inches]).

Citation: Journal of the American Veterinary Medical Association 230, 6; 10.2460/javma.230.6.827

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Both testes were submitted for pathologic examination. Gross examination indicated that both testes were greatly enlarged and turgid. Examination of cut sections revealed that characteristic parenchyma had been replaced by numerous large cystic cavitations. The cysts were filled with clear serous fluid. There was a thin rim of tissue around the periphery of each testis.

Histologic examination revealed that characteristic testicular parenchyma had been replaced by multifocal to coalescing infiltrates of moderately large polygonal cells (interstitial [Leydig] cells). In some areas, these cells were arranged in sheets or nests suspended in a fine fibrovascular stroma, formed palisades along capillaries, were oriented around small pools of eosinophilic proteinaceous fluid, or were surrounded by variably sized clear cysts. Larger cysts were lined by a thin layer of organized fibrin and surrounded by palisades of interstitial cells. In other areas, nests of interstitial cells were suspended in, and surrounded by, abundant fibrovascular connective tissue.

Interstitial cells had distinct cell borders and moderate amounts of finely vacuolated, eosinophilic cytoplasm. Nuclei were variable in size, round to oval in shape, and had a vesicular chromatin pattern; each nucleus contained a small nucleolus. A few larger cells with similar cytoplasmic and nuclear characteristics were detected. Mitotic figures were not observed during examination of 10 HPFs. In some areas, there were a few widely scattered seminiferous tubules (lined by 1 or 2 layers of sustentacular [Sertoli] cells) with rare spermatogenic activity. The histopathologic diagnosis was bilateral cystic interstitial cell tumors.

Discussion

Trauma-induced seroma or hematoma was strongly suspected as the cause of the enlargement in the boar reported here. The medical history included attempts by the boar to mate with a piece of polyvinyl chloride pipe, which could have resulted in injury to the inguinal region.

Results of the hematologic and serum biochemical analyses were not especially helpful in yielding a diagnosis but did aid in ruling out pathologic conditions of the kidneys and urinary tract. Results for the CBC reduced the likelihood of an infectious cause of the enlargement.

Ultrasonography is often extremely useful when attempting to identify enlargements or masses. An inguinal hernia was considered unlikely on the basis of the ultrasonographic appearance of the enlargement.

Normal testes have a characteristic ultrasonographic appearance. The parenchyma appears homogeneous with a hyperechoic mediastinum testis.¹ The enlargement did not have the typical testicular pattern, and although they were suspected to be testes, the lack of any characteristic testicular tissue made ultrasonographic confirmation difficult.

Fine-needle aspirates may sometimes be helpful in obtaining a definitive diagnosis. In this case, it was most useful in ruling out a hematoma or abscess. Bacterial culture and cytologic evaluation of the aspirate helped rule out bacterial causes of orchitis. Cytologic examination of the aspirate was somewhat misleading because the results were suggestive of a seroma but the fluid was clear, whereas the fluid of seromas typically is yellow.

Boars used in modern swine production typically have large, obvious testes. Testes of clinically normal sexually intact Vietnamese potbellied boars are not always noticeable and typically are much smaller than those of domestic production boars. In fact, even though the testes were greatly enlarged in the boar reported here, this was not especially obvious when the boar was standing because of the pendulous abdomen and numerous folds of skin typical of potbellied pigs.

Testicular neoplasia is a rare event in swine or is rarely reported.² In another report,³ investigators described a 9-year-old sexually intact male Vietnamese potbellied pig with bilateral testicular enlargement of 2 years' duration. Histologic examination revealed scant areas of normal testicular tissue with the bulk of both testes consisting of neoplastic tissue. Thus, the bulk of both testes consisted of neoplastic tissue in that 9-year-old boar, whereas the neoplastic tissue consisted of thin sheets surrounding the fluid-filled cavity in the 2-year-old boar reported here. Cystic cavities appear to be a characteristic of interstitial cell testicular tumors.^2,4

Interstitial cell neoplasms of the testes do not typically metastasize.² In 1 report,⁴ investigators described a Sertoli-Leydig cell tumor in a 6-month-old Landrace-Large White-Yorkshire boar in which the Sertoli portion did metastasize.

Outcome

The pig recovered uneventfully from anesthesia and was discharged to the owners on the same day. Two weeks after surgery, the owners reported that the pig appeared to have recovered fully.