Diagnostic challenges: Equine thoracic neoplasia

The diagnosis of thoracic neoplasia in the horse can be difficult due to the nonspecific nature of the clinical signs and their overlap with other pulmonary diseases. Haematological and serum biochemical evaluation, thoracic ultrasonography, radiography, endoscopic examination, and, where appropriate, thoracocentesis and pleural fluid cytology may all be helpful in reaching a diagnosis. Granular cell tumours are the most frequently reported primary pulmonary tumours of horses. They occur as single or multiple masses adjacent to bronchi and bronchioles, and the mass typically extends into the airway, resulting in partial or complete occlusion of the lumen. Thymic tumours are classified as benign or metastatic, based on evidence of tissue invasiveness, even though they uniformly appear benign histologically. These tumours are derived from epithelial reticular cells of the thymus and are rare in horses. Other primary thoracic neoplasms originate from various pulmonary tissues and are primarily reported as single case reports: pulmonary and bronchial carcinoma and adenocarcinoma, bronchogenic squamous cell carcinoma, bronchial myxoma, pulmonary chondrosarcoma, pulmonary leiomyosarcoma and pleuropulmonary blastoma. Clinical signs of these primary pulmonary neoplasms are dependent on the tumour type and location, but commonly include chronic cough, weight loss, anorexia, fever and respiratory difficulty; ventral oedema, pleural effusion and epistaxis are also frequently observed. Mesothelioma is a rare primary pleural tumour arising from the mesothelium of the pleura, pericardium and peritoneum. The clinical presentation in horses includes weight loss, respiratory difficulty and large volume pleural effusion. The tumour appears ultrasonographically as multiple small nodules on a thick serosal surface and pleural biopsy is diagnostic. Lymphoma is the most common haematopoietic neoplasm in horses, which can present with 4 main manifestations of lesions: mediastinal, multicentric, alimentary and cutaneous. Common clinical features include chronic weight loss, lethargy, anorexia, subcutaneous oedema, lymphadenopathy, colic, bleeding tendency and diarrhoea. Coughing and laboured respiratory effort are often apparent in individuals suffering from mediastinal masses. In such instances, pleural effusion may result in severe pulmonary atelectasis and pulmonary function is significantly compromised. Haemangiosarcoma is the second most common metastatic thoracic neoplasm in horses. Disseminated haemangiosarcoma is aggressive and rapidly progressive. The clinical presentation often includes tachypnoea, pale or icteric mucous membranes, respiratory distress, epistaxis, and subcutaneous, cutaneous or intramuscular masses. Other tumour types that metastasise to the thoracic cavity include adenocarcinoma, squamous cell carcinoma, fibrosarcoma, metastatic melanoma, mastocytoma and undifferentiated sarcoma. The clinical features of these tumours are generally nonspecific and often relate more to the primary site of tumour formation.     

Parainguinal laparotomy as an alternative surgical approach for removal of an enterolith in the small colon of a horse

This report describes the use of a parainguinal approach to the abdomen to remove an obstruction in the small colon that could not be removed using an initial ventral midline approach. The use of a parainguinal approach should be considered for removal of an obstruction in the distal portion of the small colon.     

Paranasal sinus fibromatosis in a horse

A case of paranasal sinus fibromatosis in an 11‐year‐old Thoroughbred gelding is reported. At admission the gelding underwent a unilateral frontal sinusotomy and a paranasal sinus mass was extensively debulked. The mass was diagnosed via histopathology as a desmoid fibromatosis with bone invasion, reactive osteoclastic osteolysis and osteoproliferation. The gelding had radiographic evidence of slow recurrence of the mass 8 months post operatively. The histopathological appearance and short‐term outcome are presented for this previously undiagnosed condition of the horse. Recognition of paranasal fibromatosis and the resultant differentiation from other types of paranasal sinus neoplasia may allow for improved prognostication of equine sinus lesions.     

Parotid salivary gland carcinoma in a geriatric horse

This case report describes a geriatric gelding with a 2 month history of fast‐growing masses within the parotid and submandibular regions. The horse was dyspnoeic on presentation and upper airway endoscopy revealed partial airway obstruction at the level of the pharynx, secondary to a space‐occupying mass. Cytological evaluation of multiple fine‐needle aspirates obtained from the masses were suggestive of salivary gland neoplasia, therefore the horse was subjected to humane euthanasia. A computed tomographical scan was obtained post mortem and revealed a large multi‐lobulated mass involving both guttural pouches, resulting in 80% occlusion of the naso‐ and oropharynx. Histopathology confirmed a parotid salivary gland carcinoma (papillary‐cystic type). Salivary gland tumours are extremely rare in horses, with only a few cases reported in the literature. Treatment of these malignancies proves to be challenging, requiring complete parotidectomy or surgical debulkment, in combination with adjunctive therapy.     

Bilateral leiomyoma in the testes of a horse

A 19‐year‐old Hackney pony was referred to a veterinary teaching hospital for further investigation of left‐sided scrotal enlargement. Both testes were normally positioned within the scrotum and there was no pain on palpation. Ultrasonography revealed multiple masses of soft tissue echogenicity, located adjacent to the testicular parenchyma. They were hyperechoic when compared to the testicular parenchyma and affected both testes. Surgical excision was performed by closed castration. Gross examination revealed firm, white, nodular masses of varying size on the surface of both testes. The cut surface of individual masses had a dense, whorling, fibrous and somewhat shiny appearance. The histopathological diagnosis was bilateral, multicentric, well differentiated leiomyoma of the tunica albuginea. The smooth muscle origin was confirmed by immunohistochemical staining with an anti‐human monoclonal antibody reactive to smooth muscle actin. This is the first report of a bilateral, multicentric, leiomyoma in the testes of a horse confirmed by histopathology and immunohistochemistry. This case highlights that neoplasia should be considered as a differential for bilateral testicular enlargement.     

Osteosarcoma in the femur of a horse

A 27-year-old Arabian pony gelding presented for evaluation of weight loss, intermittent sheath oedema, persistent neutropenia and thrombocytopenia, and acute left hindlimb swelling and gait abnormality. Clinical findings included swelling, heat and sensitivity localised over the left greater trochanter, mild to moderate ventral and sheath oedema, a left hindlimb post-legged gait, and off-loading of weight from the left hindlimb at rest. Initially, neutropenia and thrombocytopenia were confirmed on bloodwork, but neutrophilia and thrombocytopenia persisted as the case progressed. Diagnostic imaging (radiography and percutaneous ultrasonography) of the left hindquarters revealed an aggressive, mixed proliferative and lytic bony lesion of the proximal left femur as well as associated muscle fibre disruption and a soft tissue mass. A percutaneous core biopsy of the lesion led to the diagnosis of osteoblastic osteosarcoma on histopathology. Pain and inflammation associated with the lesion was medically managed in the hospital with mild improvement. Additionally, palliative radiation was performed under general anaesthesia. Unfortunately, before a response to palliative radiation could be assessed, the patient was subjected to euthanasia due to development of acute neurological signs.     

Surgical resection of an osteoma of two thoracic spinous processes in a horse

This report describes the successful surgical removal of an osteoma of the thoracic dorsal spinous processes of a horse that presented with back pain. Osteomas of the spine are frequently reported in the literature in people, but have not been previously described in the horse.     

A retrobulbar meningioma as a cause of unilateral exophthalmos and blindness in a horse

This report describes the unusual diagnosis of a retrobulbar syncytial meningioma in a 16‐year‐old Thoroughbred gelding. The horse initially presented with unilateral left sided exophthalmos and apparent blindness characterised by unilaterally absent menace and pupillary light responses. Magnetic resonance imaging (MRI) identified a well‐defined soft tissue mass intimately associated with the optic nerve. Based on the characteristic MRI appearance, a meningioma was suspected. The eye was enucleated under general anaesthesia and partial excision of the mass was achieved. Histopathology confirmed the diagnosis and the horse underwent a course of adjuvant radiotherapy. Twelve months following surgery the horse is back in work, no neurological abnormalities have been detected and follow‐up computed tomographic imaging of the skull has revealed mild bone sclerosis with no remnants of the mass identified.     

Corneal invasion by hemangiosarcoma in a horse

A 15-year-old gray Arabian gelding presented for evaluation of a lateral limbal mass extending across approximately 30% of the cornea. Grossly, the raised mass appeared nonpigmented, smooth, and irregular in shape, with an area of central necrosis and serosanguinous discharge. The mass was removed via lamellar keratectomy and histopathologic evaluation revealed features characteristic of hemangiosarcoma (HSA), including irregular vascular channels lined by a plump spindle cell population. Immunohistochemistry results showed that the neoplastic cells lining the vascular channels present diffuse and strong cytoplasmic reaction with von Willebrand Factor and the perivascular spindle cells exhibit moderate cytoplasmic reaction for smooth muscle actin. A lack of cytokeratin staining definitively excluded a diagnosis of atypical squamous cell carcinoma. Smooth muscle actin staining of the perivascular cells adjacent to the neoplastic endothelial cells is not a feature commonly described in HSA and has not been reported in previous cases of equine HSA. The horse remained in good health 21 months postkeratectomy and has exceeded the survival time of previously documented equine ocular HSA cases where more extreme surgical excision was performed.     

Ocular manifestations of a metastatic adenocarcinoma in a horse

A 10‐year‐old German Warmblood gelding was referred to the Equine Department of the Vetsuisse Faculty, University of Zurich, Switzerland, for an iris mass OD, lethargy, intermittent fever, and coughing. Ophthalmic examination revealed a 7 × 9 mm raised, fleshy, whitish to pinkish, vascularized iris mass at the 2 o`clock position OD. Fundic examination showed multifocal round, brown to black, slightly raised lesions with indistinct margins and a surrounding hyperreflective zone OU. Physical examination revealed a temperature of 39.2 °C, sinus tachycardia, preputial and ventral edema, and an enlarged right mandibular lymph node. Results of a complete blood count and plasma biochemical profile showed mild anemia, leukocytosis, and thrombocytopenia. Severe splenopathy, moderate splenomegaly, and severe pulmonary pathology with nodules and large areas of consolidated lung parenchyma were observed on abdominal ultrasound and thoracic radiographs, respectively. Fine needle aspirates of the enlarged mandibular lymph node showed malignant epithelial neoplastic cells. The horse was euthanized because of the poor prognosis and subsequently underwent postmortem examination. Macroscopic necropsy and histopathology revealed an adenocarcinoma of suspected pulmonary origin with involvement of eyes, heart, liver, kidneys, spleen, diaphragm, skeletal muscles, mandibular, pulmonary, and internal iliac lymph nodes. Metastatic adenocarcinoma should be considered as a differential diagnosis in horses with iris masses, multifocal chorioretinal infiltrates, and clinical signs that conform to a paraneoplastic syndrome.     

Retrobulbar dermoid cyst in a horse: a case report

A 4-year-old Andalusian horse was presented for examination following a 3-month history of exophthalmos of the right eye and a soft swelling of the right supraorbital fossa noted after blunt head trauma. Ultrasonographic examination of the swelling showed an anecogenic mass of 5 cm in diameter involving the retrobulbar space. Centesis of the mass through the supraorbital fossa was performed and yielded a serous fluid with 7.2 g/dL of total protein and density of 1040. No cells were seen in the sample. A tentative diagnosis of cyst was made. The cyst was surgically removed and the definitive histologic diagnosis was retrobulbar dermoid cyst. No recurrence has developed 18 months following the complete removal of the cyst capsule. To the authors' knowledge, there are no previous reports of retrobulbar dermoid cysts in horses. Localization, causes and success of surgical treatment of dermoid cysts are discussed.     

An undifferentiated sarcoma in the cervical region in a horse

An Italian Saddle Horse mare was admitted for a hard, nonpainful mass localised in the cervical region. Clinical and diagnostic investigations were performed, which were suggestive of a multilobulated ossifying mass of neoplastic origin. Due to poor prognosis the horse was subjected to euthanasia. Post mortem computed tomography, anatomopathological examination and immunohistochemistry were used to make a definitive diagnosis of undifferentiated sarcoma in the cervical region.     

Sclerosing odontogenic carcinoma in the mandible of a horse

A 15-year-old Cob mare was presented for investigation of a mandibular mass. Radiography identified an oval-shaped mass occupying the intramandibular space, with a heterogeneous osseous opacity throughout the left hemimandible. Histopathology combined with immunohistochemistry was consistent with a diagnosis of sclerosing odontogenic carcinoma, which to date has only been described, rarely, in human patients. The mass was removed using a mandibular-sparing surgical technique allowing preservation of the dental arcade. Follow-up 5 years after surgery confirmed no signs of regrowth. This case report describes the successful treatment of a previously unreported mandibular neoplasm in the horse.     

Bilateral nodular lymphocytic conjunctivitis in a horse

A Russian jumper horse presented because of an ocular perilimbal conjunctival mass and, on clinical examination, two bilateral conjunctival masses were found, of different size and conformation. Attempts at complete excision of the left eye mass and excisional biopsy of the right eye mass were performed. The left eye mass recurred rapidly, but resolved completely after topical corticosteroid therapy. The two lesions had similar histopathologic features, characterized by focal, chronic, primarily lymphocytic conjunctivitis with follicular lymphoid hyperplasia. Special histopathologic staining techniques (Gomori methenamine silver and acid fast stains) and immunohistochemistry (for CD3, BLA36 and lysozyme) failed to reveal any etiologic agents and indicated an inflammatory lesion composed of a heterogeneous population of lymphocytes and macrophages (nodular lymphocytic conjunctivitis). The lesions were indistinguishable, clinically and behaviorally, from what has been reported as 'conjunctival pseudotumor' in the horse. Equine conjunctival pseudotumor/nodular lymphocytic conjunctivitis has been reported to be unilateral and have a good prognosis after partial or complete surgical excision. This is the first reported case of bilateral nodular lymphocytic conjunctivitis in a horse and for which surgical excision alone was not curative.     

Penile and preputial squamous cell carcinoma in the horse and proposal of a classification system

Squamous cell carcinoma (SCC) is the most common tumour of the penis and prepuce of the horse and is found mainly in older animals. Reports on breed predilection for penile tumour formation are equivocal but castration, coat colour, poor genital hygiene and various infectious agents have been suggested to predispose to the development of SCC. Careful assessment of the primary tumour is an important first step in the design of an optimal treatment protocol. Tumour size, invasiveness, differentiation grade and presence of metastases are relevant to the decision to pursue additional diagnostic procedures or specific treatment options. Complete elimination of the neoplasm and, therefore, risk of recurrence is highly dependent on the type of therapy chosen. However, the size and histopathological features of the primary tumour are also important factors with respect to prognosis. This review describes the clinical and pathological features of penile and preputial SCC in the horse and proposes a standard staging system.     

Orbital fibroma in a horse

An 11-year-old American Quarterhorse gelding presented for moderate periorbital swelling and exophthalmia of the left eye. The menace response, and direct and consensual pupillary light reflexes were absent in the left eye. Conjunctival hyperemia, blepharedema, a mydriatic pupil, resistance to retropulsion, and an increased intraocular pressure were present. A soft-tissue mass could be palpated in the left retrobulbar space by pressing onto the orbit over the supraorbital fossa. Incomplete surgical resection of the mass was performed and histopathologic evaluation was consistent with a fibroma. Normal pupillary light reflexes and vision returned following surgery. The mass has not recurred 14 months after surgery.     

Use of computed tomography angiography for the evaluation of a cutaneous haemangioma in a Standardbred horse

Cutaneous haeangiomas are benign vascular neoplasms that arise from endothelial cells of blood vessels. Haemangiomas account for 0.6%–4% of all equine cutaneous neoplasms and the fetlock is the most commonly affected site. We describe the use of computed tomography angiography (CTA) for the evaluation of a cutaneous haemangioma located on the plantarolateral aspect of the left hindlimb fetlock of a 9-month-old Standardbred colt. Computed tomography angiography of the affected fetlock was performed under general anaesthesia. The medial plantar artery was catheterised and a total volume of 50 ml of iodinated non-ionic contrast medium (Iopamidol, 300 mg I/ml, Bracco Imaging Canada) was injected at a rate of 2 ml/s. Following contrast medium administration, the dorsal metatarsal artery and branches including the lateral and medial digital arteries were well demarcated. Two smaller lateral and medial arteries were also identified, forming the vascular network of the metatarsophalangeal joint. At the level of the haemangioma, two tortuous arteries arising from the lateral digital artery were identified, in addition to multiple small branches from nearby cutaneous arteries. These vessels supplied the homogeneously strongly contrast-enhancing cutaneous mass. The initial goal of the CTA study was to map the vascular anatomy for arterial embolisation in conjunction with pharmacological therapy. Considering the involvement of multiple small arterial branches, complete surgical excision along with ligation of the two main supplying arteries was alternatively elected, resulting in a successful long-term outcome.