Haemangiosarcoma in two full sibling American Quarter Horse geldings

This case report describes two full sibling gelding American Quarter Horses that presented separately for evaluation of an external mass (Case 1) and signs of colic and epistaxis (Case 2). The horses had the same owner and resided on the same property for the majority of their lives. Both horses were definitively or presumptively diagnosed antemortem with haemangiosarcoma, and on necropsy, multicentric (Case 1) and primary renal (Case 2) haemangiosarcoma were confirmed. A unique finding on necropsy was extensive bilateral renal involvement. Due to the low incidence of haemangiosarcoma in horses, the unique organ involvement and common ancestry of these two horses, a genetic cause is suspected.     

Interstitial brachytherapy in the management of haemangiosarcoma of the rostrum of the horse: Case report and review of the literature

Sarcomas arising in the equine species are rare tumours, and treatment is generally surgical. Radiotherapy has been used in the management of malignancies of large animals; however, conventional external radiotherapy delivery is difficult. Interstitial brachytherapy has been used in the management of human sarcomas with reasonable success, although equine experience is minimal. We report a case of equine haemangiosarcoma treated with brachytherapy demonstrating the feasibility of the procedure and the highly malignant natural history of haemangiosarcoma. An 8‐year‐old American Saddlebred gelding presented for evaluation of a soft tissue mass on the forehead which had been present for at least 6 months. Initial surgical attempts at management were unsuccessful; therefore a radiation oncologist specialising in brachytherapy was consulted. The radiation oncologist and veterinary surgeon performed an interstitial implant of the tumour mass on the rostrum of the horse under general anaesthesia. The procedure was well tolerated by the horse. The tumour demonstrated immediate response and was noted to have completely regressed within 6 weeks of the implant removal. Unfortunately, the horse developed widespread metastatic disease and required euthanasia. At the time of necropsy, no visible tumour was identified at the implant site. Interstitial brachytherapy is feasible in soft tissue sarcomas of the horse; however, supportive demands are great with this procedure and we recommend it only be done at large speciality centres.     

Severe hindlimb lameness and pathological femur fracture in a horse secondary to haemangiosarcoma

An 18‐year‐old Warmblood stallion was presented for an acute onset nonweightbearing right hindlimb lameness following a mild lameness of 2 weeks' duration. Severe swelling was present in the right femoral area. Despite extensive diagnostic procedures, no definitive diagnosis could be made. Packed red cell volume was persistently low. The horse improved with supportive treatment and was discharged at the owner's request. The horse presented 4 days later for bleeding from a previously made incision on the lateral femoral area. Due to deterioration of his condition, the stallion was subjected to euthanasia. Diagnosis of disseminated haemangiosarcoma, affecting primarily the hindlimb musculature and leading to pathological fracture of the femur was made at necropsy and subsequent histopathology.     

Primary haemangiosarcoma in the proximal humerus of a Clydesdale gelding

An 11‐year‐old Clydesdale gelding was presented for investigation of left forelimb lameness of 2 weeks' duration. The use of scintigraphic imaging helped to localise the source of lameness to the left proximal humerus. In this report, the clinical and diagnostic imaging features of a primary osseous haemangiosarcoma in a horse are described, along with the challenges of establishing a definitive diagnosis ante mortem. In addition, neoplasia of the appendicular skeleton should be considered a differential cause of lameness in the horse.     

Paravertebral malignant peripheral nerve sheath tumour (MPNST) in a horse

A 10‐year‐old Lipizzaner gelding was presented with intermittent ataxia and hindlimb weakness. Ultrasonographic examination identified a mass cranial to the tuber sacrale. A provisional diagnosis of a soft tissue sarcoma was made based on a biopsy specimen. Owing to the extensive nature of the tumour and the associated poor prognosis, the horse was subjected to euthanasia on humane grounds. A post mortem examination revealed a locally infiltrative soft mass within the left lumbosacral epaxial musculature. Histologically, an infiltrative neoplasm predominantly composed of pleomorphic spindle or stellate‐shaped cells was identified. Neoplastic cells exhibited strong S‐100 protein and GFAP expression and variable vimentin, NSE, NGFR and myoglobin expression. They were uniformly negative for pan‐cytokeratin, melan A, laminin and desmin. The ultrastructural examination revealed pleomorphic cells with long cytoplasmic processes and an absence of melanosomes. Based on these results, a diagnosis of malignant peripheral nerve sheath tumour was made. This report contributes further information to assist in the diagnosis of these poorly defined neoplasms in animals, especially when they occur in uncommon locations.     

Osteosarcoma of the middle phalanx in a horse

An 11‐year‐old Thoroughbred gelding was presented for lameness investigation following acute onset hindlimb lameness, which developed during a period of paddock turnout. Clinical examination revealed a swelling over the dorsolateral aspect of the pastern that was painful on digital palpation. Radiography of this area was consistent with an aggressive bone lesion involving both joint surfaces of the middle phalanx with pathological fracture and distal collapse of this bone. On this basis, the horse was subjected to euthanasia. Post mortem histopathological examination revealed presence of an osteosarcoma without involvement of the articular cartilage. This bone tumour is extremely rare in horses and has not been reported in this anatomical location.     

Resection of a premaxilla and rostral portion of the maxilla in a horse

A 5‐year‐old, 520 kg Standardbred mare was admitted for an osteosarcoma of the right premaxilla. Two horizontal incisions of the labial mucosa and lingual surface were made 1 cm around the ulceration from the canine tooth to the premaxillary symphysis. The premaxilla and rostral portion of the maxilla were transected 1 cm caudal to the canine tooth with an oscillating saw. The maxillary symphysis was transected using an oscillating saw and a hammer. The wound was closed by primary intention and healed without complication. The cosmetic appearance of the mare was good. The mare was able to prehend hay and grain and grazed without difficulty and the tongue did not protrude. The neoplasm had not recurred 18 months after the surgery. A premaxilla and rostral portion of the adjacent maxilla can be resected to treat horses for a unilateral lesion of the premaxilla but care must be taken to avoid the palatine and incisive arteries which lie within the interincisive canal.     

Unilateral malignant melanoma of the adrenal gland with metastatic spread to the thorax in a horse

A 7-year-old grey horse that had a history of inappetence, weight loss, weakness, dyspnoea, coughing and intermittent colic was examined post-mortem. A melanoma, confirmed histologically, was found in the right adrenal gland and had eroded into the posterior vena cava. Thoracic metastases were also identified. The skin, including the legs, trunk and perineum was normal with no evidence of melanomas. This was considered to be a primary, malignant melanoma, a novel finding in the adrenal gland of the horse.     

Primary corneal malignant melanoma in a horse

A 13-year-old Missouri Fox Trotter gelding of chestnut colour was referred for a 6-week history of blepharospasm and epiphora of the left eye. Due to the presence of irregular corneal masses, superficial keratectomy was performed along with adjunctive strontium-90 beta irradiation and subsequent topical mitomycin C chemotherapy. A diagnosis of poorly melanised malignant melanoma was made based on histopathological examination and immunohistochemistry. There has been no recurrence of the neoplasm over 10 months of follow-up. To the authors' knowledge, this is the first documented case of a primary corneal melanocytic neoplasm in a horse.     

Primary sinonasal malignant melanoma with systemic metastasis in a non-gray horse

A 27-y-old Anglo-Arabian gelding with bay coat color was presented with a swelling of the left maxillary region. Fenestration on the left maxilla revealed that the left maxillary sinus was filled with black-red tissue. A portion of the tissue was excised and diagnosed histologically as malignant melanoma. Genotyping of the STX17 gene for gray coat color revealed that the horse did not have the “gray” factor. The horse was euthanized ~3 mo after first presentation. During autopsy, a black-to-gray mass extended from the left nasal cavity to the surrounding paranasal sinus and invaded the hard palate, cribriform plate, and the cranial portion of the left olfactory bulb. Moreover, identical black nodules were present in lymph nodes from the mandible to the larynx, and in the spleen, liver, kidney, and adrenal glands. However, masses were not found in the skin, perineal region, or pelvic cavity. All of the black-to-gray nodules were malignant melanomas that were histologically identical to the initial biopsy; tumor emboli were also found in the kidney. Sinonasal mucosal melanoma is a rare disease in horses.     

Resection of a ceruminous adenocarcinoma in a horse by a modified vertical ear canal ablation

A 13‐year‐old Swedish Warmblood mare was presented for evaluation of a mass on the medial aspect of the left vertical ear canal. The mass was initially resected using monopolar loop diathermy. Histopathological diagnosis of the excisional biopsy was a low‐grade malignant ceruminous adenocarcinoma. The clinical and histopathological features of this previously unreported neoplasm in the horse are described. A modified vertical ear canal ablation was performed in order to remove the base of the neoplasm with adequate free margins. The surgical technique is described. No recurrence was noted 2 years after surgery and the appearance and function of the pinna were retained.     

Episodic collapse in the horse

The term ‘collapse’ can be used to describe a variety of incidents in which a horse loses postural tone with or without progression to recumbency and with or without loss of consciousness. Depending on the aetiology of the condition the episode may be self‐limiting and may or may not recur. Alternatively the collapse may be secondary to serious injury or disease and require veterinary intervention. This article mainly discusses investigation of the former scenario of self‐limiting single or multiple episodes of collapse in apparently healthy horses. An overview of the various causes of collapse is followed by a suggested approach to the diagnosis of these challenging cases.     

Ocular angiosarcoma in a pony ‐ MRI and histopathological appearance

Ocular angiosarcomas are an infrequent aetiology of exophthalmus in the horse. In the case presented here, a pony was referred with a history of supraorbital swelling, exophthalmus and conjunctivitis of the right eye. Radiographic and ultrasonographic examinations were used for diagnosis; however, the exact definition of the retrobulbar changes could only be made by magnetic resonance imaging (MRI). MRI shows anatomic and physiological detail in both the osseous and soft tissue structures. Only 3 sequences were used in this case: a transverse T2‐weighted and a dorsal high resolution, T1‐weighted gradient echo with multiplanar reconstruction capability pre‐ and post contrast application. This case report suggests that MRI should be used more frequently in the diagnosis of head tumours in horses.     

Uveitic glaucoma in the horse

Glaucoma is a serious complication of anterior uveitis that can result in significant ocular discomfort and loss of vision. As glaucoma is insidious and mostly asymptomatic until late in the course of disease, it is often undiagnosed. Equine recurrent uveitis is the most common underlying disorder: it is a disease of high prevalence, characterised by recurrent‐remitting episodes of ocular inflammation. Here, the inflammatory cells and mediators they release alter the normal anatomic structure of the anterior chamber and aqueous drainage pathways of the eye. These changes alter the homeostatic mechanisms of intraocular pressure control. Management of glaucoma secondary to uveitis can be challenging due to the difficulties of managing the underlying disorder and its effects on the eye. This article reviews the pathogenesis of uveitic glaucoma in the horse and medical and surgical management options.     

Caffeine clearance in the horse

The pharmacokinetic properties of intravenously administered caffeine were studied in 10 horses using a commercially available automated enzyme immunoassay. The harmonic mean for the distribution half-life was 5.2 min (range 1.4–18.7). The harmonic mean for the elimination half-life was 10.18 h (range 6.82–20.92). The harmonic mean of the volume of distribution was 0.32 L/kg (range 0.22–0.53). There was no correlation between the dose of caffeine/kg body weight and the elimination half-life (Spearman's coefficient of rank correlation =0.19).Abbreviations AUC area under the serum concentration-time curve - AUMC area under the moment curve - BSP sulphobromophthalein - ICG indocyanine green - SD standard deviation - t _1/2 elimination half-life - V _c apparent volume of the central compartment - V _d(ss) apparent volume of distribution at steady state     

Ophthalmic antimicrobial therapy in the horse

Effective antimicrobial therapy of infectious ocular disease in the horse may be difficult to achieve. This paper reviews the routes of delivery, the pharmacokinetics and the bioavailability of the various antimicrobial agents used in the treatment of ocular infection in the horse. The modes of action and the criteria for selection of the common antibacterial, antimycotic and antiviral drugs used are described.