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MALIGNANT SEMINOMA IN A HORSE

Kevin Sherman, ~ DVM; T. A. Turner, ~ DVM, MS; Maron B. Calderwood-Mays, 2 VMD, PhD; Atwood C. Asbury, ~ DVM

SUMMARY

An antemortem diagnosis of malignant seminoma was made on a 14-year-old Quarter Horse stallion. Castration was performed and histopathology showed evidence of vascular and lyumphatic metastasis. Ten months later the horse was off feed with diffuse swelling in the rear leg. Necropsy confirmed the diagnosis of malignant seminoma.

DIAGNOSIS

A 14-year-old Quarter Horse stallion was referred with a chief complaint of unilateral scrotal swelling of 6 months duration. There had been an outbreak of strangles on the farm shortly before the swelling was noticed in this horse, and a second stallion on the same farm with a similar problem responded to conservative therapy. On admission the stallion was alert, had normal vital signs and was in good flesh. The left testicle was firm, not painful and approxi- mately twice as large as the right. The parietal and visceral

Authors' addresses: 1Department of Large Animal Clinical Sciences, 2De- partment of Comparative and Experimental Pathology, College of Veterinary Medicine, University of Florida, Box J- 136, Health Science Center, Gainesville, FL 32610-0136. Acknowledgement: The authors wish to thank Dr. Walter Mulvihill for referral of this case. Published as journal series number R-00229 of the University of Florida. Re- print requests should be addressed to Dr. Sherman.

tunics were palpably adhered. The spermatic cord was not enlarged.

Ultrasonic examination of the left scrotum revealed a 2 cm uniform layer of densely echogenic soft tissue sur- rounding a core of less echogenic soft tissue. The echogenic pattern of the deeper tissues was consistent with normal tes- titular tissue. Semen evaluation was within normal limits. Complete blood count and fibrinogen values were within the normal reference ranges for our laboratory.

Unilateral castration utilizing a primary closure tech- nique was performed under general anesthesia. Recovery was uncomplicated. On the day following the orchiectomy the stallion was observed to be depressed and had decreased fecal output. Palpation of the abdominal and pelvic cavities per rectum revealed a mass in the ventral abdomen with four distinct lobules about 2 cm in diameter each. Transrec- tal ultrasonic images suggested the masses had fluid cen- ters.

The resected testicle was 15x8x9cm and weighed 980g. On cut section a pale tan, bulging multilobular mass measuring approximately 13x6x7 cm obliterated a substan- tial portion of the testicular parenchyma (Figure 1). In the center was a yellow caseous core partially surrounded by a reddened zone, the remainder was semi-fh-rn. Epididymis and spermatic cord were grossly normal. Microscopically the mass was composed of large neoplastic germinal ep- ithelial cells which filled many seminiferous tubules, infil- trated the testicular interstitium and obliterated the paren- chyma in sheets (Figure 2), inciting a desmoplastic re-

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Figure 1. Sagittally-sectioned enlarged left testicle of 14- year-old Quarter Horse, revealing bulging multilobular mass within the parenchyma.

sponse in some areas. The caseous core was necrotic and surrounded by a zone of granulation tissue. Emboli of neoplastic cells were recognized in vessels of the pampini- form plexus, and in thick walled structures thought to be lymphatics. A diagnosis of malignant seminoma with vas- cular and lymphatic metastasis was rendered.

A presumptive diagnosis of abdominal metastasis was made based on the histologic findings and palpable abdomi- nal masses. A guarded prognosis for recovery was given. The stallion was discharged with instructions to administer 12 million units of penicillin once daily for a month in the event the abdominal mass was an abscess. Following this course of antibiotic therapy a rectal examination to recheck the masses was suggested.

A month following discharge the referring veterinarian reported that the abdominal mass was not palpably enlarged and that the stallion was doing well and successfully settling mares.

Ten months after the initial diagnosis the stallion was readmitted with the complaint that the horse was off feed and had developed diffuse swelling in his left rear leg. Rectal examination revealed a large mass which prevented palpation beyond the brim of the pelvis. Due to the apparent advanced stage of the disease the owner elected euthanasia.

Necropsy confirmed diffuse edema through out the soft tissues of the hind limbs and ventral abdomen, espe- cially severe in the left hind leg. The peritoneal cavity contained approximately 2 liters of watery brown fluid. The mass palpated per rectum was approximately 50x25x25 cm and weighed 14 kg. It was multiobulated, friable, mottled tan red, and it obliterated the region of the medial iliac and lumbar aortic lymph nodes, surrounded the caudal aorta and vena cava, displaced the colon ventrally, and invaded the sublumbar musculature bilaterally. It filled the entrance to the pelvic canal, and surrounded the remains of the left

Figure 2. Photomicrograph of neoplasticgerminal epithelial cells with large vesicular nuclei obliterating the testicular parenchyma. H & E stain; bar=25g.

ductus deferens. A lobule of the mass extended into the right caudo-ventral abdomen to partially occlude the right ingui- nal ring as well. The right testicle was 8x5.6x4.7 cm, weighed 217g and was not directly involved. However, the right ureter was partially occluded as it passed through the mass into the pelvic inlet, resulting in severe hydronephro- sis of the fight kidney. In addition to the caudal abdominal mass, there were myriads of tan, semi-firm plaques and pedunculated tumor nodules, often coalescing, covering the ventral parietal peritoneum and diaphragm, and spreading throughout the omentum. These varied in size up to ap- proximately 7 em diameter (Figure 3). Nodules were also scattered on the capsule of the liver and spleen, and amassed along the hilus of the spleen. Microscopically the tumor cell characteristics were similar to those described 10 months earlier.

D I S C U S S I O N

Equine testicular tumors are rare with an estimated incidence of between 0.041 and 0.062 percent. Seminomas have been described as the most common 2 or second most common 1 testicular neoplasia in the horse with an estimated maximum incidence of 0.05 percent? The incidence of malignant seminomas in the horse is unknown.

Differential diagnosis for scrotal swelling in the horse includeorchitis,pcriorchitis,neoplasia, testicularhematoma, hematocoele, varicocele, testicular torsion and scrotal her- nia. 2

Although clinical examination and history can suggest a specific cause for scrotal swelling, a biopsy in indicated for definitive diagnosis especially in cases where testicular neoplasia is suspected. Fine needle aspirates, needle biop- sies 3 and exeisional biopsies (orchidectomy) have been

Volume 10, Number 4, 1990 273

Figure 3. Masses of metastatic seminoma nodules at- tached to the diaphragm adjecent to the liver.

reported as useful diagnostic techniques. Disadvantages of fine needle aspirate and needle biopsies include potentially severe hemorrhage and inability to diagnose vascular or lymphatic metastasis within the spermatic cord. Orchidec- tomy is simple and can be both diagnostic and therapeutic in some cases of testicular neoplasia. It is important to submit the entire testicle and spermatic cord for pathologi- cal examination iforchidectomy is performed, so that blood vessels and lymphatics along the epididymis and spermatic cord can be examined for metastatic tumor emboli.

There have been few reports 4'5 detailing the clinical course of malignant seminoma. The average age at the time of diagnosis is 16 years with a range of 9 to 22 years. ~,a11 The most common initial presenting sign in malignant seminomas is an enlarged testicle 4'5'7,8 or less frequently an inguinal or prepucial mass. 5,8

Of the previously reported cases that presented with an enlarged testicle 3 underwent orchidectomy and were dis- charged. 4,5,s Two were readmitted for weight loss (one with concurrent dyspnea) and one with recurrent colic. There have been no prior reports of horses readmitted with a chief complaint of hindlimb swelling.

The average life span with malignant seminoma fol- lowing orchidectomy is about 18 months (range 10-22 months).4,5, a

The most common clinical indication of metastasis is a palpable mass in the region of the caudal aorta. Thickening of the spermatic cord from an enlarged testicle is also supportive of metastasis. Metastasis occurs via lymphatics to the medial iliac and lumbar aortic lymph nodes, z4

Historically, treatment of malignant equine semino- mas has been limited to orchidectomy and euthanasia. Effective threapy has not been investigated, at least in part due to inability to differentiate benign from malignant masses. Chemotherapeutic regimens utilizing cis-dichloro- diammine platinum have resulted in a high rate of clinical remission in cases of malignant seminoma in manJ 2 The feasibility and efficacy of cis-dichlorodiammine platinum therapy in equines with malignant seminomas awaits inves- tigation.

REFERENCES

1. Peterson D: Equine testicular tumors. J Equine Vet Sci 4:25-27,1984.

2. Caron J, Barber M: Equine testicular neoplasia. Compend Contin Educ Pract Vet 7:$53-$59,1985.

3. Knudson O, Shantz B: Seminoma in a stallion. A clinical, cytological and pathologicoanitomical investigation. Come# Vet 53:395-403,1963.

4. Gibson G: Malignant seminoma in a Welsh pony stallion. Compend Contin Educ Pract Vet 6:$296-$298,1984.

5. Vaillancourt D, Fretz P: Seminoma in the horse: Report of two cases. J Equine Med Surg 3:213-218,1979.

6. Galofaro V, Giannetto S: Seminoma in a mule: An ultras- tructural investigation. J Equine Vet Sci 8~36-38,1981.

7. Becht J, Thacker H: Malignant seminoma in a stallion. J Am Vet Med Assoc 175:292-293,1979.

8. Trigo F, Miller R: Metastatic Equine Seminoma: Report of Two Cases. Vet Path 21:259-260,1984.

9. Benoit R: Contribution a I'etudes des Temeurs malignes. Revue de med vet Toulouse 76:502,1924.

10. Innes JRM: Neoplastic diseases in the testes in animals. J Path Bact 54:485-498,1942.

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