Mediastinal basaloid carcinoma arising from thymic cysts in two dogs

Mediastinal masses in dogs were diagnosed as basaloid carcinoma associated with multiple thymic cysts (MTCs). The masses were composed of MTCs and proliferating intracystic neoplastic basaloid cells, which immunohistochemically diffusely expressed p63 and cytokeratin 19. A gradual transition from the basal cell layers lining the cysts walls to the neoplastic cells was seen, and it was indicated that the neoplastic cells had originated from the basal cell layers of the cysts. To the best of our knowledge, this is the first report of basaloid carcinoma occurring in the mediastinal cavity in dogs. Although these tumors were demonstrated to be rare origins, basaloid carcinoma should be included in the differential diagnoses for canine mediastinal tumors.

Suspected bilateral phrenic nerve damage following a mediastinal mass removal in a 17-week-old pug

The anesthetic management of a pediatric pug for removal of a mediastinal mass is described. During recovery from anesthesia, the dog's respiratory pattern was compatible with bilateral diaphragmatic paralysis. Incidence, complications, possible treatments of phrenic nerve injury, problems of long-term mechanical ventilation, and alternative case management are discussed.

Concurrent cranial mediastinal Blastomyces granuloma and carcinoma with cranial vena caval syndrome in a dog

This report describes an unusual progression of blastomycosis in a dog with concurrent mediastinal carcinoma. The dog was evaluated for respiratory distress. Diagnostic results revealed chylothorax and a cranial vena caval thrombus. Histopathology of the cranial mediastinal mass diagnosed mediastinal carcinoma and fungal granuloma. Intercurrent disease may complicate the clinical presentation and clinical course of blastomycosis.

Respiratory distress due to retropharyngeal and neck swelling in a horse with mediastinal lymphosarcoma

A 9-year-old, 1494-lb (679-kg) Quarter horse gelding in good body condition was admitted to the Veterinary Teaching Hospital, Western College of Veterinary Medicine (WCVM), University of Saskatchewan, for evaluation and treatment of acute respiratory distress. On a trail ride 26 days before presentation, the gelding had been exposed to a horse with clinical signs of an upper respiratory tract infection. The gelding performed well on the trail ride but, 4 days later, developed a mild swelling in the retropharyngeal area and a slight bilateral mucoid nasal discharge. The gelding was examined at the farm by its primary veterinarian, who made a presumptive diagnosis of strangles. Treatment was initiated using a combination of trimethoprim/sulfamethoxazole (30 mg/kg PO q12h for 1 week) and phenylbutazone (6 mg/kg PO q24h for the first 2 days, followed by 3.5 mg/kg PO q24h for 5 more days). The gelding did not respond satisfactorily to antimicrobial and antiinflammatory therapy. During the following 2 weeks, the retropharyngeal swelling gradually became more pronounced and extended to the upper portion of the neck. Two days before presentation at WCVM, the gelding also developed a dry cough with difficult breathing, and the retropharyngeal and neck swelling extended to the pectoral region and ventral pectoral area extending to the cranial ventral abdomen. Because of progressing clinical signs and poor response to treatment, the horse was referred to WCVM for further evaluation.

Diagnosis of mediastinal masses in dogs by flow cytometry

BACKGROUND

Biopsy of mediastinal masses can be invasive, but the procedure may be necessary if cytology of a mass aspirate is inconclusive. The 2 most common mediastinal masses, lymphoma and thymoma, may both be comprised of small lymphocytes. We investigated the ability of flow cytometry to distinguish between these 2 neoplasms.

HYPOTHESIS

Flow cytometry of mediastinal mass aspirates may provide a definitive diagnosis of thymoma or lymphoma, reducing the need for biopsy.

ANIMALS

Dogs with mediastinal masses presenting to the Veterinary Teaching Hospital/Animal Cancer Center were included in the study.

METHODS

Aspirates obtained over 2 years that met the inclusion criteria (i.e. sufficient viable cells and a definitive diagnosis by means other than flow cytometry) were analyzed by flow cytometry to determine the percentage of cells expressing B- and T-cell markers, and co-expressing CD4 and CD8.

RESULTS

All cases of thymoma (n = 6) consisted of > or = 10% lymphocytes coexpressing CD4 and CD8, a phenotype that is characteristic of thymocytes, whereas 6 of 7 lymphomas contained <2% CD4+CD8+ lymphocytes. The CD4+CD8+ lymphoma could be readily distinguished flow cytometrically from thymoma by light scatter properties. The phenotypes of the remaining lymphomas were CD4+ T cell (4), CD34+ (1) and B cell (1).

CONCLUSIONS

Our studies demonstrate that flow cytometry is a useful tool for discriminating mediastinal masses. Lymphocyte-rich mediastinal masses could be unambiguously identified by flow cytometry in 13/13 cases.

Mixed thymoma in a cow

A neoplastic mass measuring 25 x 8 x 3 cm was found in the mediastinum of a 10-year-old Holstein cow. The neoplasm was encapsulated, multilobulated, and cystic. Several firm adhesions were present between the neoplasm and the right cranial lung lobe and the ipsilateral side of the pericardial sac. Under microscopic examination, the neoplasm was characterized by solid sheets of spindle epithelial cells (pancytokeratin and high molecular weight cytokeratin positive) subdivided by fibrous trabeculae. Numerous individualized or small aggregates of mature T-cell (CD3 positive) lymphocytes were scattered throughout the neoplastic cell population. Based on the gross, histologic, and immunohistochemical findings, the neoplasm was diagnosed as a mixed thymoma.

Mediastinal lymphoma in a young Turkish Angora cat

An 8-month old intact male Turkish Angora cat was referred to the Veterinary Medical Teaching Hospital (VMTH), Seoul National University, for an evaluation of anorexia and severe dyspnea. The thoracic radiographs revealed significant pleural effusion. A cytology evaluation of the pleural fluid strongly suggested a lymphoma containing variable sized lymphocytes with frequent mitotic figures and prominent nucleoli. The feline leukemia virus and feline immunodeficiency virus tests were negative. The cat was euthanized at his owner's request and a necropsy was performed. A mass was detected on the mediastinum and lung lobes. A histopathology evaluation confirmed the mass to be a lymphoma. Immunohistochemistry revealed the mass to be CD3 positive. In conclusion, the cat was diagnosed as a T-cell mediastinal lymphoma.

[Thorax examination by computed tomography: general aspects and presentation of clinical cases]

This article describes the application of the helicoidal tomography for the study of mediastinal and pulmonal affections by small animals. The global presentation is completed by clinical cases that show the interest in this technic. A thymoma, a chronic pleuresia due to thorns and a mediastinal cranio-dorsal neoplasia provoking only lameness signs will be presentated in details.

COMPUTED TOMOGRAPHIC EVALUATION OF CANINE AND FELINE MEDIASTINAL MASSES IN 14 PATIENTS

A 15-year retrospective analysis of histologically proven canine and feline mediastinal malignancies at the University of Minnesota was conducted to identify patients imaged by computed tomography (CT). The goal of the study was to characterize the CT appearance, to determine if there were any tumor type-specific appearances, and to clarify the role of CT in patients with mediastinal masses. Fourteen patients meeting these criteria were available for evaluation. The masses were characterized based on the presence or absence of contrast enhancement, internal architecture, size, extent of local invasion, the presence of pleural fluid, and the presence of regional vascular invasion. Within the limits of this study and the histopathologic information available, there appeared to be no clinically exploitable relationship between the CT appearance and the histologic characterization of the mass. However, CT does provide reasonably accurate local staging information.

Ultrasound-guided biopsy as a diagnostic aid in three horses with a cranial mediastinal lymphosarcoma

An ultrasound examination of the thorax of three horses which were performing poorly or had mild signs of colic showed that they had a cranial mediastinal mass and a pleural effusion. A cytological examination of the pleural fluid showed that it did not contain neoplastic cells. A histological examination of an ultrasound-guided core biopsy of the cranial mediastinal mass showed that in each of the three horses it was a lymphosarcoma.

Pleural fluid from a dog with marked eosinophilia

A 12-year-old neutered male Shar-Pei was presented to the North Carolina State University Veterinary Teaching Hospital cardiology service with a 2-week history of coughing and a 2-day history of lethargy and anorexia. Pleural effusion and a mediastinal mass were detected with thoracic radiographs. Ten mL of fluid were removed via thoracocentesis, and cytologic examination of the fluid revealed marked eosinophilic inflammation and few atypical mast cells. Mast cell neoplasia was suspected. Aspirates of the mediastinal mass, abdominal lymph nodes, and bone marrow contained similar pleomorphic mast cells and increased numbers of eosinophils. The dog was diagnosed with systemic (visceral) mastocytosis, a rare form of neoplasia in dogs, and was euthanized. These tumors carry a poor to grave prognosis and the etiology is uncertain.

Mediastinal Lymphoma in a Badger (Meles meles)

A case of mediastinal lymphoma in a free-living, adult male European badger (Meles meles), from Trento Province (northern Italy) is described. A yellow-red mass delimited by a thick fibrous capsule completely occupied the anterior mediastinum. Based on the histologic and immunohistochemical findings, a diagnosis of mediastinal lymphocytic lymphoma was made. Documentation of neoplasms in free-living species is important for comparison with domestic animals and humans and may give insight into epidemiology of these diseases. To the authors' knowledge, this is the first report of a mediastinal lymphoma in a badger.

Thoracic teratoma in a white Pekin duck (Anas platyrhinchos domesticus)

Teratomas are infrequent tumors in domestic fowl and have been rarely reported in ducks. It appears that the only case of mediastinal teratoma in a Pekin duck was observed by Alezais and Cotte in 1908. A lobulated, firm mass occupied the thorax of a 7-mo-old male white Pekin duck (Anas platyrhinchos domesticus). The tumor was composed of squamous epithelium, feather follicles, glandular epithelium, bone and cartilage, and thymus and was classified as tridermic, thoracic teratoma.

Clinicopathologic and electron microscopic study of cutaneous neuroendocrine (Merkel cell) carcinoma in a cat with comparisons to human and canine tumors

Malignant neuroendocrine carcinoma of the skin (Merkel cell tumor) was diagnosed in an 18-year-old spayed female Maine Coon Cat. The diagnosis was made on the basis of morphologic and electron microscopic findings. The cat was euthanatized 321 days after surgical excision of the tumor. The tumor's malignancy contrasted with the benign nature of Merkel cell tumors reported in dogs and was consistent with the malignancy of Merkel cell tumors reported in humans.

Giant cell hepatitis in two young cats

A very rare case of the liver lesion characterized by formation of multinucleated giant hepatocytes with inflammatory cell infiltration were observed in two young (1.5 years and 2 years old) cats bearing thymic malignant lymphoma. Histopathological features of this liver lesion were very similar to giant cell hepatitis (GCH) in human neonates and infants. Therefore, the lesion was diagnosed as feline GCH.

Mediastinal plasma cell tumor in a sheep

An extramedullary plasmacytoma was found in a 10-year-old sheep. The tumor involved the mediastinum, where a 25 x 15 x 10-cm encapsulated mass was found. The lungs had multiple metastases ranging from 0.5 to 2 cm in diameter, and the portal vein contained a 10-cm-long mass. The cytologic and histopathologic analyses were consistent with a moderately differentiated plasmacytoma. The immunophenotype of the tumor cells was lambda light chain IgG+, CD79a-, and CD3-. Occasional granulomas were observed at the periphery of the mediastinal and pulmonary tumors. Microbiologic culture yielded growth of Corynebacterium from these granulomas. This is the first report of plasmacytoma in sheep. The tumor most likely arose from mediastinal lymph nodes and metastasized to the lungs and portal vein.

Myeloblastic leukemia with massive neoplastic infiltration of the skin and mediastinum in a cow

An acute myeloblastic leukemia was found in a 3.5-year-old Holstein cow. The neoplasm was characterized by massive tumor growths, and there were multiple tumor nodules in the dermis or subcutis and a large tumor mass in the mediastinum. This tumor showed negative reactivity for CD3, CD79a, major histocompatibility complex class II and myeloid/histiocyte antigen. Ultrastructural features such as dispersed cytoplasmic granules and poorly developed organelles were compatible with those of early promyelocytes.

Concurrent multicentric hemangiosarcoma and ovarian teratoma in an aged Père david's deer (Elaphurus davidianus)

A 20-yr-old female Père David's deer (Elaphurus davidianus) died following a 3-wk history of depression, anorexia, and progressive respiratory distress. At necropsy, numerous soft to firm, tan or blood-filled nodular structures, 1-6 cm in diameter, were noted in the lung and the visceral and parietal pleura and within the mediastinum. Similar nodules were also found in the liver, spleen, kidney, and lymph nodes. Histologically, the nodules were diagnosed as hemangiosarcoma. A benign teratoma was present in the left ovary.

Thymic carcinoma of the thymic hormone secretory type in a cow

An 8-year-old Holstein cow had tumor nodules and enlarged lymph nodes in the mediastinum, and metastatic tumor masses in the pelvic cavity. The neoplastic cells were characterized by squamous features and intracytoplasmic vacuoles carrying microvilli, some of which contained periodic acid Schiff-positive globular cores, but tubular structures or goblet cells were absent. Many neoplastic cells stained positively for keratin, and occasional cells were positive for thymosin. The presence of secretory granules in the cytoplasm was confirmed by electron microscopy. This neoplasm was considered to be of thymic hormone-secreting epithelial cell origin.

Unusual metastatic behavior and clinicopathologic findings in eight cats with cutaneous or visceral hemangiosarcoma

Eight cats with visceral or cutaneous hemangiosarcoma were evaluated, and unusual metastatic and clinicopathologic behavior was evident in each. Cutaneous hemangiosarcoma is generally believed to be locally aggressive and slow to metastasize. These 8 cats with cutaneous hemangiosarcoma, however, developed metastatic disease after initial surgical resection; only 1 had local regrowth of the tumor. All cats with visceral hemangiosarcoma had metastasis at the time of diagnosis, which is consistent with cats of other reports. Three of 8 cats had evidence of disseminated intravascular coagulation, including increased prothrombin time and partial thromboplastin time, decreased number of platelets, and anemia. These potential complications need to be considered when planning diagnostic and treatment protocols.

Pulmonary embolism and cor pulmonale in a cat

A 14-year-old male neutered cat experienced pulmonary embolism 15 days following surgical debridement of a recurrent dorsolumbar abscess. Clinical signs were dominated by respiratory distress. Pulmonary embolism was suggested from the lateral thoracic radiograph by the presence of an abruptly attenuated lobar artery and a contiguous oligaemic area in the caudal lung lobe. Pulmonary hypertension was demonstrated on Doppler echocardiography by right pulmonary artery dilation and tricuspid regurgitation raising the pulmonary arterial pressure to 56 mmHg. Chronic pulmonary hypertension, assumed from right ventricular wall hypertrophy, and hypokinesia, indicating chronic cor pulmonale, was suggestive of chronic rather than acute pulmonary embolism. Postmortem histological evidence of pulmonary arteriolar occlusion confirmed the diagnosis of pulmonary embolism.

Immunophenotypic characterization of lymphomas from the mediastinum of young ferrets

OBJECTIVE

To determine the phenotype of naturally developing lymphomas in young ferrets.

ANIMALS

10 ferrets with lymphoma.

PROCEDURE

Neoplastic tissues were graded histologically according to the National Cancer Institute's Working Formulation for non-Hodgkin's lymphoma and phenotype was determined by means of immunohistochemical staining. A polyclonal anti-human CD3 and a monoclonal anti-human CD79 antibody were used to classify the lymphomas in situ as T-cell or B-cell origin. Specificity of antibodies was determined by evaluating lymphoid tissue from normal ferrets in situ, which was confirmed by western blot analyses.

RESULTS

All 10 ferrets had clinically aggressive tumors, irrespective of the phenotype. Nine ferrets had T-cell lymphoma that extensively involved the mediastinum. Remnants of thymic tissue, indicative of thymic origin, were identified in lymphoma of these 9 ferrets. One ferret had a B-cell multicentric lymphoma without involvement of the mediastinum.

CONCLUSIONS

The majority of lymphomas in these young ferrets involved the mediastinum and were of T-cell phenotype. Impact for Human Medicine-There are many similarities between the lymphoma syndrome of ferrets and the condition documented for cats and children with lymphoma of the mediastinal area.

CLINICAL RELEVANCE

Differential diagnoses for young ferrets with clinical signs of lethargy or respiratory distress should include T-cell lymphoma of the mediastinum.

Cranial vena caval thrombosis secondary to invasive mediastinal lymphosarcoma in a cat

A 12-year-old female cat was diagnosed with a cranial vena caval thrombosis in association with a mediastinal lymphosarcoma. The cause of the cranial vena caval thrombosis was thought to be invasion of the venous wall by neoplastic lymphoid cells. Clinical signs of cranial vena caval thrombosis, such as swelling and oedema of the submandibular area, the ventral part of the neck and the forelimbs, were related to a space-occupying mediastinal lymphosarcoma, which also induced respiratory distress and cyanosis. Non-selective angiocardiography demonstrated the occlusion of the cranial vena cava and abnormal venous collateral vessels feeding the heart which are accepted as the venographic hallmark of clinically overt cranial vena caval syndrome. At postmortem examination, an intracaval thrombus, 5 cm in length, was seen extending from the costocervical vein to the sulcus terminalis of the right atrium.

Primary adenocarcinoma of the gland of the nictitating membrane in a cat

An 11-year-old, neutered, male domestic shorthair was presented with a five-month history of recurrent, unilateral, seromucoid discharge from the right eye. A verrucous mass extended from the posterior aspect of the nictitating membrane. Adenocarcinoma of the gland of the nictitating membrane (GNM) was diagnosed upon biopsy. The cat subsequently developed metastases to the lungs, pleura, mediastinum, liver, and kidneys and died six months after clinical signs first were observed. Little is known about the biological behavior of adenocarcinoma of the GNM in cats. This is the first report that describes the natural progression of this disease.

Retrospective study of 60 cases of feline lymphosarcoma

OBJECTIVE

To characterise epidemiological and clinical findings, and diagnostic procedures undertaken, in cats with lymphosarcoma at a veterinary teaching hospital.

DESIGN

Retrospective case study.

PROCEDURE

Hospital records were reviewed for 7159 cats, sick or healthy, examined during a 10-year period (1984 to 1994). Sixty cats with lymphosarcoma were identified and classified by anatomical location of the tumor. Data on breed, age, sex, clinical signs and diagnostic procedures were collated.

RESULTS

The prevalence of feline lymphosarcoma in the hospital population was 0.84%. Siamese cats appeared predisposed to lymphosarcoma but other purebreds were not. Males were somewhat overrepresented amongst affected cats. Similar numbers of cases (12 to 18) were seen in each of the four anatomic categories (multicentric, mediastinal, alimentary and extranodal). Cats with mediastinal lymphosarcoma were mostly young and Siamese. Clinical signs in affected cats were varied, usually multiple and often nonspecific. Two of 22 cases tested positive for feline leukaemia virus antigen in blood and 6 of 13 were positive for feline immunodeficiency virus antibody.

CONCLUSIONS

Extranodal lymphosarcoma seemed more prevalent in this study than reported elsewhere. Siamese cats in the study population may have had a genetic predisposition to lymphosarcoma. Limited evidence suggested feline leukaemia virus may be less important, and feline immunodeficiency virus more important, in the local population than indicated in overseas reports. Additional studies are needed to investigate breed predisposition and feline leukaemia virus and feline immunodeficiency virus status in Australian cats with lymphosarcoma.

A cluster of cases of juvenile mediastinal lymphoma in a ferret colony

Three cases of juvenile mediastinal lymphoma developed in a laboratory colony of ferrets. Two ferrets became acutely moribund, and one was found dead with no preceding signs of illness. Splenomegaly, hepatomegaly, and a large thoracic mass were the primary features in each case. All three ferrets had multiorgan metastasis of the tumor. Two ferrets were tested for feline leukemia virus and Aleutian disease virus with negative results.

Chylothorax and chylous ascites in a dog with mediastinal lymphangiosarcoma

A 10-year-old, male toy poodle presented for evaluation of a progressively worsening, harsh, nonproductive cough. Chylous pleural effusion, lymphopenia, thrombocytopenia, normoblastemia, and recurrent subcutaneous bruising were diagnosed. Surgical exploration of the cranial mediastinum revealed extensive, redundant connective tissue which was confirmed by histopathology to be mediastinal lymphangiosarcoma (LAS). During surgical placement of a fenestrated silastic mesh for passive pleuroperitoneal drainage, chylous ascites also was diagnosed. The patient was euthanized two days postoperatively due to persistent chylothorax. The etiopathogenesis of chylothorax and chylous ascites are discussed. Previous case reports of lymphatic endothelial neoplasia are reviewed.

Metastatic thymoma in a goat

Images

Focal myasthenia gravis as a paraneoplastic syndrome of canine thymoma: improvement following thymectomy

A 10-year-old, neutered male cocker spaniel-cross experienced regurgitation, dry retching, and weight loss. A large, mediastinal mass and dilatation of the esophagus were seen on thoracic radiographs. Cytological, histopathological, immunohistochemical, and serological findings were consistent with a lymphoepithelial thymoma and focal, esophageal myasthenia gravis. Surgical removal of the mass resulted in rapid resolution of the megaesophagus and a decrease in serum acetylcholine-receptor antibody concentration. The dog was clinically normal until the thymoma recurred six months postoperatively. Clinical signs, diagnostic evaluation, management, and treatment of a dog with thymoma and megaesophagus are described.

Posterior mediastinal paraganglioma involving the spinal cord of a dog

A posterior mediastinal paraganglioma is described in a five-year-old female collie showing paralysis of the hindlimbs. The mass was observed radiographically and a myelogram confirmed a spinal cord compression at the thoracic level. Histological examination of the mass diagnoses a paraganglioma which was confirmed by histochemical and immunohistochemical studies. This is compared with paraganglioma found in man.

Sonographic findings in horses with mediastinal lymphosarcoma: 13 cases (1985-1992)

Sonographic findings correlated with necropsy findings in 8 of 9 horses in which the cranial portion of the mediastinum was evaluated by use of both methods. Cranial mediastinal masses were imaged as multilobular and homogeneously hypoechoic; a complex echogenic pattern was observed with necrosis within the mass. Pleural effusion was a common finding in horses with mediastinal lymphosarcoma. Cytologic evaluation of pleural fluid samples was useful in diagnosis of lymphosarcoma in 10 of 12 horses that had thoracentesis. Sonographic examination of the thorax and cranial portion of the mediastinum can aid in the diagnosis of mediastinal lymphosarcoma in horses. Such examination should be performed in horses with clinical signs of cranial vena cava obstruction in which pleural effusion is detected, or when thoracic lymphosarcoma is suspected.

Lymphoplasmacytic lymphoma in a stallion

Lymphoplasmacytic lymphoma found in a 6-year-old Anglo-Arabian stallion was investigated histologically, immunohistochemically and ultrastructurally. The animal showed a large mediastinal mass and generalized lymph node involvement. The neoplastic cells were in various differentiation stages of small lymphocyte, centrocyte, centroblast, immunoblast and plasma cell. Some neoplastic cells showed positive cytoplasmic reactivity for mu and lambda chains. There were well developed rough endoplasmic reticulum (RER) and Golgi complexes in plasmacytoid cells, and slightly developed RER or a few long strands of RER in medium-sized to large lymphoid cells. These findings suggest that this neoplasm is of B-cell origin.

Antemortem diagnosis of cholangiocellular carcinoma in a horse

A 10-year-old Tennessee Walking Horse gelding was admitted to the veterinary teaching hospital for evaluation of intermittent fever, lethargy, and anorexia. Initial laboratory analyses revealed anemia and hyperfibrinogenemia. Abdominocentesis and thoracentesis yielded fluid samples with high nucleated cell counts and total protein concentrations. The tentative diagnosis was nonseptic peritonitis. The horse did not improve after 4 days of antimicrobial treatment, and pitting edema of the ventral midline developed. Thoracic radiography and ultrasonography revealed consolidation of the ventral aspect of the lung fields and pleural effusion. Pleuroscopy of the right hemithorax revealed pleural effusion and a soft-tissue mass in the caudal portion of the mediastinum. Findings on biopsy of the liver and mediastinal mass led to a presumptive diagnosis of metastatic cholangiocellular carcinoma. The horse was euthanatized, and the diagnosis was confirmed at necropsy.

Chemotherapy for intrathoracic cancer in dogs and cats

The thoracic cavity contains numerous tissue types from which tumors may arise. Broadly speaking, the cavity is comprised of the pleural surfaces, the mediastinum and its enclosed viscera, and the lungs. Neoplasms arising from these structures are frequently advanced at the time of diagnosis, and surgery is rarely curative for malignant processes. Although reports describing anticancer chemotherapy use in dogs and cats for tumors of the thoracic cavity largely have been anecdotal, as advances are made in the chemotherapeutic management of comparable tumors in human cancer patients and as veterinarians become familiar with these compounds, use of antineoplastics as an adjunct to, or in place of, local treatment modalities should increase. This article reviews the epidemiology, clinical features, and diagnosis of pulmonary neoplasia; mediastinal neoplasia, particularly thymoma; and pleural neoplasia, with emphasis on mesothelioma. In addition, options for chemotherapy, derived from both the human and veterinary literature, are given for each tumor type.

Mediastinal squamous cell carcinoma and thyroid carcinoma in an aged horse

A mediastinal squamous cell carcinoma and thyroid carcinoma were found in an aged horse. Clinical signs consisted of bilateral thyroid gland enlargement, chronic cough, and mild respiratory distress. The neoplasms were not treated. Squamous cell carcinoma is a common neoplasm in horses, but not in the cranial portion of the mediastinum. Thyroid carcinomas in horses are uncommon. This combination of neoplasms is rare and may have been associated with a defect in the immune system.

Acquired myasthenia gravis in a cat with thymoma

A 4-year-old castrated Abyssinian cat was evaluated for profound neuromuscular weakness. Results of electromyography and repetitive nerve stimulation tests were normal. Thoracic radiography revealed a cranial mediastinal mass, which was excised and identified as a thymoma. Serum acetylcholine receptor antibodies were detected at high concentration, supporting a diagnosis of acquired myasthenia gravis. Clinical signs of disease responded to treatment with pyridostigmine and corticosteroids.

Hypercalcaemia and soft tissue mineralisation associated with lymphosarcoma in two horses

Two horses with deposits of lymphosarcoma, one in the spleen, the other in the mediastinum, several lymph nodes and kidneys, lost weight rapidly and became depressed and weak. They were hypercalcaemic and post mortem examination revealed extensive calcification of the heart and major vessels. There was no evidence of bone marrow metastases in the one horse whose marrow was examined, and the thyroid and parathyroid glands of both horses were grossly normal.

Bizarre lymphoid cells in serous effusion of a dog with mediastinal lymphoma

An 8-year-old collie dog was examined because of dyspnoea. Thoracocentesis revealed a modified transudate containing a predominance of large (10 to 15 microns diameter) unusual-appearing mononuclear cells showing cloverleaf-shaped nuclei. These cells were categorized as lymphoid in origin on the basis of ultrastructural and cytochemical methods. Subsequent necropsy examination revealed lymphoma, localized primarily to the cranial mediastinum, but also infiltrating tissues surrounding the thyroid, parathyroid and adrenal glands.

Neoplastic diseases of the thorax

Thoracic neoplasia comprises a heterogeneous group of diseases, many of which are distinctly uncommon in veterinary medicine. These diseases often present the clinician with diagnostic and therapeutic challenges. Careful diagnostic work-up and staging are essential for consideration of therapeutic options and formulation of prognosis. Neoplastic diseases of the thorax are classified here as tracheal tumors, primary lung tumors, nonrespiratory intrathoracic tumors, and thoracic wall tumors.

Pleural effusion secondary to metastasis of an ovarian adenocarcinoma in a horse

An 11-year-old Quarter Horse mare was presented with ventral edema and pleural effusion, secondary to a disseminated ovarian adenocarcinoma. Bilateral thoracocentesis yielded 30 L of thin, blood-tinged fluid, which was a modified transudate. Cytologic examination of the fluid revealed large atypical cells, suggestive of carcinomatous neoplasia. Similar cells were found in the peritoneal fluid. The mare was euthanatized. Necropsy revealed a 35-cm diameter mass in the cranial mediastinum, ventral to the trachea. The left ovary was 25 cm in diameter and most of the parenchyma was replaced by red or brown friable tissue, containing numerous 1-to 3-mm cysts. Papillary adenocarcinoma of the ovary was diagnosed, based on the appearance and arrangement of tumor cells in the ovary, sublumbar and tracheobronchial lymph nodes, and mediastinal mass. Ovarian neoplasia should be considered in the differential diagnosis of pleural effusion in the horse.