Melanoma

Keywords: melanoma, mare, equine, neoplasia

Focal melanomas are not unusual, especially in gray horses; this one occurring in an Arab mare.  The red arrows indicate the presence of raised melanomas on the perineal region; a common site for this neoplasm.

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Interestingly, although melanomas are often regarded as potentially malignant, those that occur in the perineal region are usually benign and seldom invasive. As a result, they may not even be treated but occasionally local resection or cryotherapy is used.

Squamous cells carcinomas

Keywords: squamous, neoplasia, carcinoma, equine, mare, stallion.

Images of squamous cell carcinoma on the penises of two different stallions. At left is a diffuse and erosive form of neoplasia, at right a more proliferative form.

Image size: 900 x 337 pixels. Copyright: Dr. Ram Kasimanickam, ramkasi@vetmed.wsu.edu

These old but unique images illustrate the severe destructive nature of locally invasive squamous cell carcinomas in mares.

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Interestingly, squamaous cell carcinomas in horses tumors do not usually metastasize and are most often treated using cryotherapy.

Used with permission from the Department of Theriogenology, Iowa State University, Ames Iowa. Chairperson; Dr Lawrence Evans. (levans@iastate.edu)

A leiomyosarcoma

Keywords: equine, neoplasia, leiomyosarcoma

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This tumor caused a chronic vulvar discharge in an aged Morgan mare. It had outgrown its blood supply and was partially necrotic; the source of the discharge.  The tumor was removed surgically and the mare conceived within two months of removal.

A leiomyosarcoma is a very unusual tumor in a mare; this case being the subject of a published case report.

Lofstedt, R. M., Spurlock, G., Williams, R., & Merriam, J. G. (1987). Leiomyosarcoma in the uterus of a mare. Compendium on Continuing Education for the Practicing Veterinarian, 9(1), 93–96.

A granulosa cell tumor

Keywords: GCT, neoplasia, equine, mare, ovary

Granulosa cell tumors (GCTs) such as this one are common forms of ovarian neoplasia in mares. Although they have been related to both male and female behavior in the affected animal they are also a common cause of pathological anestrus.

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Granulosa cell tumors produce a multitude of sex steroids that may cause negative feedback and suppress hypothalamic-pituitary function. High serum concentrations of testosterone are sometimes diagnostic of these tumors but GCTs often produce little testosterone. When they do produce testosterone, clitoral enlargement may be seen as shown in the inset at lower right.

Although their steroid production is variable, GCTs almost invariably produce the complex and closely related polypeptide hormones inhibin and mullerian inhibiting hormone (MIH). In fact, MIH is more consistently produced by these tumors than inhibin, so MIH assays have become the test of choice for the diagnosis of GCTs.

MIH, inhibin and androgens all suppress the production of FSH production. Therefore follicle growth on the contralateral ovary is usually suppressed as well (see inset image on the right). This is a useful diagnostic feature of the condition helping to differentiate GCTs from other forms of  neoplasia and hematomas as well.

Suppression of follicle growth on the contralateral ovary can continue for long periods of time after the removal of the tumor. Owners should be warned of this possibility.

The cut surface of a GCT usually has a honeycomb appearance as shown above. This is obvious on pre-operative ultrasonography as is suppression of activity on the contralateral ovary.

As shown below, GCTs can also be solid but this is less common than the honeycomb appearance.

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As shown elsewhere in LORI, GCTs may also consists of only one or two major cystic cavities.

Fortunately (unlike the situation in humans) GCTs are almost always benign in mares and surgical removal can be delayed for months if required. In aged mares, this author has elected not to remove the neoplastic ovary because operative risk can outweigh the value of treatment.

Lymphosarcoma

Keywords: equine, neoplasia, lymphosarcoma

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In this case, a lymphosarcoma developed between the legs of a gelding, ventral to and closely associated with, the penis. This is an unusual tumor in horses and an unusual site for its development.  The enlargement was readily visible and palpable as shown in the inset at lower left. Due to cost considerations, this animal was euthanized. The tumor was found to be well encapsulated and not locally invasive.

Squamous cell carcinoma requiring phallectomy

Keywords: neoplasia, equine, stallion, phallectomy, squamous, carcinoma

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As mentioned elsewhere, squamous cell carcinoma is a common neoplasm of the equine penis. A large squamous cell carcinoma developed on the glans of this stallion's penis, becoming locally invasive to a severe degree.  This required phallectomy (amputation of the penis).  Less severe cases of squamous cell carcinoma are often treated successfully with cryosurgery or local excision.

Due to the massive corpus cavernosum in a stallion, a major consideration during phallectomy is hemostasis. In that regard, note the large rubber tourniquet on the right side of the operative field.

Seminoma

Keywords: stallion, equine, seminoma, testicle, neoplasia

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An 18 year old stallion with a seminoma in his left testicle.  The stallion was presented because of remarkable enlargement (A) of the left testicle. Asymmetry due to the enlargement of this testicle was more evident in a lateral view than a caudal view. The appearance on ultrasound (B) of the seminoma (s) showed irregular masses of variable echodensity compared to normal (n) testicular parenchyma in the same testicle.

A needle biopsy was performed, providing a diagnosis of a seminoma and leading to hemicastration of the affected testicle.   The site of the needle biopsy (C) was obvious on the visceral surface of the tunica vaginalis of the testicle.  On cut surface of the removed testicle (D) the seminoma was obvious, as were areas of avascular necrosis (orange arrows). The normal tissue (n) seen on ultrasound and the seminoma (s) are clearly visible here as well.

Seminomas are the most common testicular tumors in stallions (Leydig cell and Sertoli cell tumors also occur) and should always be a differential diagnosis in older stallions with testicular asymmetry. As in other species, seminomas appear to have a higher prevalence in cryptorchid animals then normal animals. Fortunately, testicular neoplasms in stallions usually do not metastasize (although metastasis has been well documented) and they are rarely fatal; this, in contrast to the situation in humans.

Unusual granulosa cell tumor in a mare

Keywords: mare, equine, ovary, neoplasia, granulosa, tumor, GCT

These images were supplied by Dr A. Ortenburger, Dept of Surgery, AVC. Dr Ortenburger is the owner of the copyright for the images.

An 8 year old pony mare was presented for surgical resection of a mass on her right ovary. The mass was discovered incidentally during work-up for mild colic.  According to the owner, the mare had been "less good-natured" for the past several months, and had been observed mounting another mare on one occasion.  

On palpation, the mass was large (25 x 28 cm), ovoid, and very firm.  Transrectal ultrasonography revealed the mass to be comprised of a large fluid filled, cyst with intersecting strands of tissue. Two small follicles were present in the contralateral ovary. It was thought to be unlikely that this was a granulosa cell tumor (GCT) because in most of those cases, the contralateral is inactive and devoid of gross follicle development. Serum samples were drawn pre-operatively for the assay of estradiol 17 beta, testosterone, progesterone and inhibin.

The mass was surgically exteriorized and removed via a midline incision.

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Fluid was withdrawn from the tumor for hormone assay and to facilitate its removal. Then it was transected as shown in the inset above. The tumor structure was unusual because it consisted of a single large cyst rather that the common multicystic structure of a GCT.

This volume of fluid drained from the tumor was 2200 ml. The fluid was assayed for its estradiol 17 beta, testosterone, progesterone and inhibin concentrations.

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Serum steroid and inhibin concentrations were (followed by the normal range in each case):
Progesterone: 0.2 ng/ml (0.2 to 10 ng/ml)
Estradiol: 13.8 pg/ml (20 to 45 pg/ml)
Testosterone: 34.4 pg/ml (24 to 45 pg/ml)
Inhibin: 1.56 ng/ml (0.1 to 0.7 ng/ml)

Steroid and inhibin concentrations in the cyst were (no normal ranges available):
Progesterone: 0.5 ng/ml
Estradiol: 249.4 pg/ml
Testosterone: 149.0 pg/ml (24 to 45 pg/ml)
Inhibin: 73.8 ng/ml

The concentrations of serum progesterone, testosterone and estradiol  in the serum were consistent with those of a normal mare.  However, the inhibin concentration in the serum was approximately twice that of a normal mare. These values were consistent with a diagnosis of granulosa cell tumor. This diagnosis was verified by histopathology. The tumor itself was undoubtedly the source of the high concentration of inhibin: the inhibin concentration in the cyst was about a hundred times higher than its normal concentration in serum.

In view of the high concentrations of inhibin, it was not possible to explain the presence of the follicles in the contralateral ovary. Also, mounting of a herdmate could not be explained in terms of the pre-operative serum testosterone concentration.

Note: Low testosterone concentrations are often encountered in mares with GCTs. This underlines its questionable value in the diagnosis of GCTs. It is now (2013) becoming common to measure anti-mullerian hormone (AMH) as a diagnostic aid in these cases.

Malignant dysgerminoma in a mare 

Keywords: dysgerminoma, mare, equine, ovary, seminoma, neoplasia

  

Images by Dr Rob Lofstedt and Dr Shannon Martinson; case description by Dr Shannon Martinson, dept pathology, AVC.

An 8 year old Appaloosa X mares lost weight over 6-8 weeks and was inappetent for the last 2 weeks. She was presented with acute colic that could not be managed with analgesics. She was euthanized. 

As shown below, a firm lobulated tan mass measuring approximately 8 - 10 cm x 5 -6 cm was present in the neck at the thoracic inlet and continued as a chain of firm nodular masses in the cranial mediastinum.  These masses occupied a space of ~ 15 cm x 7 x 7 cm in total.  The masses were solid with central regions of necrosis.

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A large mass (shown below) obliterated the left ovary. It measured approximately 36 x 26 cm with a roughened/ruptured brown and red surfaces.  

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On cut section (as shown above) the mass was solid and tan colored with extensive regions of hemorrhage and necrosis. There were scattered areas of osseous metaplasia in the mass. It also contained several pockets of viscous tan to yellow exudate.  The right ovary (circled above) was active containing numerous follicles.  The uterus was unremarkable.  

The morphologic and histological diagnosis was that of a malignant dysgerminoma (details available on request).

Dysgerminomas are rare tumors of the ovaries in mares. They are of germ cell origin; the counterpart to seminomas in males.  In mares, these tumors appear to be more aggressive than in other species and metastasis is not uncommon. Metastases may occur to the regional lymph nodes or transcoelomically.  Interestingly, mares with disseminated dysgerminoma may develop hypertrophic osteopathy. This was not evident grossly in this case.