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.     

THORACIC RADIOGRAPHIC CHARACTERISTICS OF CANINE INFLUENZA VIRUS IN SIX DOGS

Canine influenza virus is an emerging, highly contagious, respiratory pathogen that has not previously been radiographically described. In this retrospective case series study, we describe the thoracic radiographic appearance of confirmed canine influenza virus in six dogs. Radiographic findings varied, but included abnormal unstructured interstitial (one) and unstructured interstitial and alveolar (five) pulmonary patterns, which were distributed cranioventral (four), diffuse (one), and caudodorsal (one). The right middle (five), left cranial (five), and right cranial (four) lung lobes were most commonly affected. Additionally, mild pleural effusion was present in one dog. Intrathoracic lymphadenopathy and cranial mediastinal widening/fluid accumulation were not detected in any dog. Canine influenza virus should be considered as a differential diagnosis for canine patients with respiratory signs and a cranioventral unstructured interstitial to alveolar pulmonary pattern.     

Radiographic, computed tomographic, and ultrasonographic findings with migrating intrathoracic grass awns in dogs and cats.

The purpose of this study was to describe the clinical, radiographic, and computed tomographic findings in dogs and cats with migrating intrathoracic grass awns. Thirty-five dogs and five cats with visual confirmation of a grass awn following surgery, endoscopy or necropsy, and histology were assessed. The medical records and all diagnostic imaging studies were reviewed retrospectively. Labrador Retrievers or English Pointers < 5 years of age, with a history of coughing and hyperthermia, were the most common presentations. Seventeen animals had an inflammatory leukogram of which 14 had a left shift or toxic neutrophils. Radiographs were performed in 38 animals and computed tomography (CT) in 14. Thoracic radiographs were characterized by focal pulmonary interstitial to alveolar opacities (n = 26) that occurred most commonly in the caudal (n = 19) or accessory lobes (n = 8). Additional findings included pneumothorax (n = 9), pleural effusion (n = 8), and pleural thickening (n = 7). Pulmonary opacities identified on radiographs correlated to areas of pneumonia and foreign body location. CT findings included focal interstitial to alveolar pulmonary opacities (n = 12) most commonly in the right caudal lung lobe (n = 9), pleural thickening (n = 11), mildly enlarged intrathoracic lymph nodes (n = 10), soft tissue tracking (n = 7) with enhancing margins (n = 4), pneumothorax (n = 6), pleural effusion (n = 4), and foreign body visualization (n = 4). Histologic diagnoses included pulmonary and mediastinal granulomas or abscesses, bronchopneumonia, and pleuritis. Migrating intrathoracic grass awns should be considered as a differential diagnosis in coughing, febrile animals with focal interstitial to alveolar pulmonary opacities, pleural effusion, pleural thickening, and/or pneumothorax on radiographs or CT.     

Radiographic differentiation of mediastinal versus pulmonary masses in dogs and cats can be challenging

The ability to differentiate thoracic masses of mediastinal and pulmonary origins is often confounded by their complex spatial relationship. The objectives of this retrospective, observational cross‐sectional study were to assess radiographic differentiation of mediastinal versus pulmonary masses, and to determine if there are any correlations with specific radiographic findings. Thoracic radiographs of 75 dogs and cats with mediastinal and/or pulmonary masses identified on CT were reviewed. Radiographic studies were anonymized, randomized, and reviewed twice by three reviewers. Reviewers categorized the origin of each mass(es) as mediastinal, pulmonary, or both. On the second review, the presence or absence of 21 different radiographic findings was recorded for each mass. Agreement between the radiographic and CT categorization of mass origin, as well as inter‐ and intraobserver agreement, was calculated. Overall agreement between radiographs and CT was moderate for both mediastinal (68.6%) and pulmonary masses (63%). Overall, interobserver agreement was moderate (κ = 0.50‐0.74), with moderate to strong intraobserver agreement (κ = 0.58‐0.93). Masses within the mediastinum were significantly more likely to displace other mediastinal structures. Alternatively, masses lateral to midline and in the caudal thorax were found to be significantly positively correlated with a pulmonary origin. The results of this study highlight the limitations of radiography for differentiation of mediastinal and pulmonary masses, with mass location and displacement of other mediastinal structures potentially useful for radiographic findings that may help improve accuracy.     

RADIOGRAPHIC APPEARANCE OF CONFIRMED PULMONARY LYMPHOMA IN CATS AND DOGS

Herein we describe the thoracic radiographic appearance of confirmed pulmonary lymphoma. Patients with thoracic radiographs and cytologically or histologically confirmed pulmonary lymphoma were sought by contacting American College of Veterinary Radiology members. Seven cats and 16 dogs met the inclusion criteria, ranging in age from 4 to 15 years. Method of diagnosis was via ultrasound‐guided cytology (four), surgical biopsy (two), ultrasound‐guided biopsy (one), and necropsy (16). Radiographic findings varied but ranged from normal (one) to alveolar (six) and/or unstructured interstitial infiltrates (11), nodules and/or masses (eight), and bronchial infiltrates (four). Additional thoracic radiographic findings included pleural effusion and lymphadenopathy. The results of this evaluation indicate a wide variability in thoracic radiographic abnormalities in cats and dogs with pulmonary lymphoma.     

CT features of pleural masses and nodules

Pleural space masses and nodules are rarely described on computed tomography (CT) in veterinary medicine and have only been described in patients with neoplasia. Our purpose was to describe the CT findings and diagnoses in seven patients with pleural masses and nodules. Two patients had broad-based, plaque-like pleural masses, both of which were due to neoplasia (primary pleural carcinoma, metastatic thymoma). Two patients had well-defined pleural nodules and nodular pleural thickening, one of which had mesothelial hypertrophy, and another of which had metastatic hemangiosarcoma. Three patients had ill-defined pleural nodules to nodular pleural thickening, one of which had metastatic pulmonary carcinoma, while the other two had bacterial infection with mesothelial proliferation (n = 2), fibrinous pleuritis (n = 1), and severe mediastinal pleuritis/mediastinitis (n = 2). Five of the seven patients had focal, multifocal or diffuse smooth, and/or irregular pleural thickening. Five of seven patients had pleural effusion, and postcontrast CT was useful in several patients for delineating the pleural lesions from the effusion. All patients except one had additional lesions identified on CT besides those in the pleural space. CT is useful in identifying and characterizing pleural space lesions and could be used to guide further diagnostic procedures such as thoracoscopy or exploratory thoracotomy. Both neoplastic and nonneoplastic diseases should be considered in the differential diagnoses for pleural space masses and nodules found on CT.     

Pleural effusion secondary to thoracic metastatic mammary adenocarcinoma in a mare

A 17-year-old Quarter Horse mare was examined nearly 3 years after excision and cryotherapy of a papillary mammary gland adenocarcinoma. The mare had been used for pleasure riding since surgery, but had recently developed progressive dyspnea. The mare had clinical evidence of pleural effusion, but died before further clinical examination and treatment were instituted. Necropsy revealed deep mammary masses with similar nodules in the deep inguinal, renal, and mediastinal lymph nodes and in the lungs, pericardium, visceral and parietal pleurae, and left ovary. The masses were identified as papillary mammary gland adenocarcinoma. Large volumes of free pleural and peritoneal fluid were detected. The pleural fluid contained similar neoplastic cells that could have been readily detected by exfoliative cytologic examination had the mare survived.     

IMAGING CHARACTERISTICS OF INTRATHORACIC HISTIOCYTIC SARCOMA IN DOGS

In this retrospective study, two observers independently reviewed thoracic imaging studies of 39 dogs with confirmed histiocytic sarcoma. The most common findings were intrathoracic lymphadenopathy, identified by the first and second observers in 82.1% and 87.2% of dogs, respectively, and pulmonary masses (74.4% and 82.1%). Right middle lung lobe masses were significantly more common than masses in any other lung lobe (P<0.0013), with the majority having a ventral distribution. Sternal and tracheobronchial lymphadenopathy were significantly more common than cranial mediastinal lymphadenopathy (P‐values of 0.0002 and 0.012, respectively). Interobserver agreement regarding distribution of lymphadenopathy and pulmonary masses was good (κ=0.64 and 0.75, respectively). Other findings included pulmonary nodules, pleural effusion, and abnormal pulmonary patterns. In patients with CT examinations, the majority of masses were mildly to moderately enhancing and heterogeneous, poorly marginated, and bronchocentric. Lymphadenopathy and pulmonary masses are the most common intrathoracic findings in dogs with histiocytic sarcoma, and the strong predilection for the ventral aspect of the right middle lung lube may help to differentiate it from other types of neoplasia.     

Primary cranial mediastinal hemangiosarcoma in a young dog

Primary cranial mediastinal hemangiosarcomas are uncommon tumors. A 30-kg, 2-year-old, intact female German shepherd was presented for evaluation of cachexia and respiratory distress of a few days’ duration. Lateral radiographic projection of the thorax revealed significant pleural effusion. Computed tomography revealed a cranial mediastinal mass effect adjacent to the heart. On surgical exploration, a pedunculated mass attached to the esophagus, trachea, brachiocephalic trunk, left subclavian artery and cranial vena cava without attachment to the right atrium and auricular appendage was removed and debrided by use of blunt dissection and dry gauzes, respectively. Histopathology results described the cranial mediastinal mass as hemangiosarcoma. At 8 months and 5 days post-operatively, the patient died. Primary cranial mediastinal hemangiosarcomas, although a seemingly rare cause of thoracic pathology in young dogs, should be considered in the differential diagnosis for pleural effusion and soft tissue mass effect in the cranial mediastinum. This is the first case report in a dog to describe primary cranial mediastinal hemangiosarcoma.     

LUNG LOBE COLLAPSE

The radiographic changes caused by collapse of lung lobes in pulmonary disease, pneumothorax, and pleural effusion depend on the lobar recoiling force and local pleural pressure. Differences in the tendency of normal lung lobes or regions to collapse depend on the relative surface-to-volume ratio, determined by shape and size of the region or lobe. This ratio affects the physiologic parameters of pulmonary interdependence, compliance, and collateral air flow. Pulmonary surfactant increases compliance, particularly at low volumes, maintains alveolar stability, and assists in maintaining capillary patency and preventing pulmonary edema. Its loss due to lung injury increases collapsing forces. In the presence of pneumothorax or pleural effusion, diseases that cause lobar collapse produce localized air or fluid entrapment that is a diagnostic sign of the presence of the underlying pulmonary disease.     

THE RHESUS MONKEY

Transbronchoscopic inoculation of five serotypes of Streptococcus pneumoniae was used to produce pneumonia in five rhesus monkeys. The development and resolution of the pneumonia were followed radiographically and clinically. The initial inoculation determined the lung lobes that would become involved. The acute state was accompanied by a febrile response, leukocytosis, and bacteremia. Resolution of the pneumonia occurred in six weeks. The radiographic features of spontaneous streptococcal pneumonia in rhesus monkeys were similar but not identical to those found in man. However, extension to other lobes, mediastinal lymphadenopathy, and extensive pleural effusion, as often noted in the human, were not identified. The rhesus monkey is thought to be a good animal model for the radiographic evaluation of streptococcal pneumonia.     

Multimodality imaging characteristics of tension pyopneumothorax secondary to pulmonary carcinoma in a cat

A 3‐year‐old Himalayan cat was presented with respiratory distress. Radiography showed multiple gas opacity foci, with the locations dependent on patient positioning, and severe pleural effusion with a contralateral mediastinal shift. A large volume of fluid and air was aspirated, and the fluid components were consistent with a nonseptic exudate. A pulmonary mass, pleural nodules, and an air–fluid interface with air bubbles trapped in fibrous septations were identified using thoracic ultrasonography and CT. The cat died 2 days after imaging studies. Necropsy revealed tension pyopneumothorax caused by pulmonary carcinoma and multiple pleural metastases.     

Successful medical treatment of 15 dogs with pyothorax

OBJECTIVES: To review the success of non-surgical management, which included antibiotics and a single thoracocentesis, in 15 dogs presenting with pyothorax. METHODS: Sixteen dogs were selected retrospectively from case files at the Veterinary Cardiorespiratory Centre. RESULTS: One dog was diagnosed with a mass suspected to be a pulmonary abscess on ultrasound examination and was referred for surgery. Fifteen dogs were treated medically. Springer spaniels were the most commonly presented breed (six cases) followed by Labrador retrievers (three cases). Under sedation or general anaesthesia, thoracocentesis was performed unilaterally and as much purulent effusion as possible was removed. Lavage of the thorax was not undertaken. In most dogs, antibiotic treatment was ampicillin at a mean dose of 33 mg/kg administered three times daily and 25 mg/kg metronidazole administered twice daily. Antibiotics were provided for a minimum of six weeks. All dogs recovered completely and did not show relapse on prolonged follow-up. This included one dog, which had very widespread pleural adhesions and minimal effusion. CLINICAL SIGNIFICANCE: In dogs that do not have evidence of pulmonary masses or consolidations and no evidence of granular pleural effusion, medical therapy may be curative even in chronic cases of pyothorax with pleural adhesions.     

Medical and surgical treatment of pyothorax in dogs: 26 cases (1991-2001)

OBJECTIVE: To compare outcomes of dogs with pyothorax treated medically versus surgically and to identify prognostic indicators for dogs with pyothorax. DESIGN: Retrospective study. ANIMALS: 26 dogs. PROCEDURE: Medical records were reviewed to obtain information regarding signalment, results of physical and laboratory evaluations at the time of initial examination, results of bacterial culture of pleural fluid, radiographic abnormalities, treatment (surgical vs medical), complications, whether the disease recurred, disease-free interval, survival time, and cause of death. RESULTS: Calculated proportions of dogs free from disease 1 year after treatment were 25 and 78%, respectively, for dogs treated medically and surgically. Treatment was 5.4 times as likely to fail in dogs treated medically as in dogs treated surgically. Two regression models relating treatment group (medical vs surgical) to disease-free interval were found to be significant. The first contained terms for medical treatment and isolation of Actinomyces spp from pleural fluid; the second contained terms for medical treatment and radiographic detection of mediastinal or pulmonary lesions at the time of initial examination. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that surgical treatment is associated with a better outcome than medical treatment in dogs with pyothorax. In addition, surgery should be considered if radiographic evidence of mediastinal or pulmonary lesions is detected or if Actinomyces spp is isolated from the pleural fluid.     

Localised radiotherapy for a ferret with possible anal sac apocrine adenocarcinoma

A seven-year-old, neutered male ferret was referred to our hospital with two perianal masses (2.4x3.0 and 2.4x3.5 cm, respectively) that had recurred after initial surgical excision. Complete resection of the masses was impossible as there was deep invasion along the rectum. On histopathology, the masses were diagnosed as apocrine adenocarcinoma possibly of anal gland origin based on tumour location. There was marked response to localised radiotherapy using an orthovoltage unit at 4 Gy, twice weekly. No visible mass was detectable after six doses of radiation. However, at that time, pleural effusion was diagnosed and radiotherapy was discontinued. Cytology of a sample of the pleural effusion suggested mesothelioma, and no obvious pulmonary metastasis of anal sac adenocarcinoma were identified on thoracic radiography. The ferret died at home on day 71 after the first admission.     

Malignant melanoma in a grey horse: case presentation and review of equine melanoma treatment options

A 15 year-old grey Thoroughbred gelding presented for investigation of chronic weight loss and recent onset of respiratory difficulty. Clinical examination confirmed tachypnoea with increased respiratory effort. Thoracic ultrasound examination detected pleural effusion. The dyspnoea was related to the large volume of pleural effusion and, following post-mortem examination, to the presence of a large mediastinal mass. Multiple pigmented masses, likely melanomas, were detected peri-anally. Thoracic radiography, cytological examination of the pleural fluid and a fine needle aspirate of a thoracic mass led to a presumptive diagnosis of malignant melanoma and this was confirmed at post mortem examination. Further metastatic spread to the central nervous system and right guttural pouch was also identified. In conclusion this case manifests the potential malignant behaviour of equine melanomas, and a review of proposed therapies for melanoma treatment highlights the therapeutic options and current areas of research.     

Neoplastic pleural effusion and intrathoracic metastasis of a scapular osteosarcoma in a dog: a multidisciplinary integrated diagnostic approach

A 10‐year‐old, female spayed mixed‐breed or cross‐bred dog was referred to the Small Animal Teaching Hospital of the University of Liverpool due to tachypnea, dyspnea, and pleural effusion not responding to diuretics and antibiotics. The chest was drained and cytology of the pleural fluid was consistent with a modified transudate with presence of atypical cells initially attributed to mesothelial hyperplasia and dysplasia. Computed tomography detected, in addition to the bilateral pleural effusion, diffuse pleural thickening, multiple pleural and pulmonary nodules, and a mineralized and lytic mass in the left scapula. Imaging findings were suggestive of a primary bone tumor with intrathoracic metastasis. Cytology of the left scapular and pleural masses revealed a malignant neoplasm highly suggestive of osteosarcoma. The diagnosis was confirmed by demonstration of a positive cytochemical reaction for alkaline phosphatase on prestained cytology slides. This finding prompted review of the initial interpretation of the pleural effusion cytology. The presence of neoplastic osteoblasts in the thoracic fluid was identified by a combination of cytochemistry, cell pellet immunohistochemistry, and transmission electron microscopy findings. In this report, a multidisciplinary integrated diagnostic approach was used to diagnose and confirm a neoplastic pleural effusion due to osteosarcoma metastasis in a dog.     

Thoracic Radiographic Features of Silicosis in 19 Horses

Clinical records and thoracic radiographs of 19 horses with a confirmed pathologic diagnosis of silicosis were reviewed. These horses had histories of varying degrees of chronic weight loss, exercise intolerance, and respiratory distress. At the time of presentation, two horses were asymptomatic. Ten horses were geldings and nine were female. The mean age of the 19 horses was 10.7 +/- 5.5 years. Fourteen horses were identified as being from the Monterey-Carmel Peninsula of midcoastal California. An abnormal, structured interstitial pulmonary pattern was identified on thoracic radiographs in each horse. The interstitial pulmonary changes were classified as miliary (13 horses), reticulonodular (4), or linear interstitial (2), and were best visualized dorsally and caudodorsally. In addition to the abnormal interstitial pulmonary pattern, areas of pulmonary consolidation were evident caudodorsally in seven horses. Other thoracic radiographic features included: hilar lymphadenopathy (4 horses), pleural effusion/thickening (4), cranial mediastinal lymphadenopathy (2), hyperinflation (1), and a discrete pulmonary mass (1). Necropsy findings in eight horses and results of lung biopsies in an additional five horses showed a diffuse, multifocal, granulomatous pneumonia with areas of pulmonary fibrosis. Cellular infiltrates included predominantly macrophages with intracellular and/or extracellular crystalline material, occasional lymphocytes, and giant cells. Similar cellular changes were also identified, during necropsy, in the hilar and tracheobronchial lymph nodes in each of the eight horses, although gross enlargement of the lymph nodes was present in only six horses. The radiographic and pathologic findings of these 19 horses are consistent with chronic or the accelerated forms of silicosis that are recognized in humans.     

Nodules and masses are associated with malignant pleural effusion in dogs and cats but many other intrathoracic CT features are poor predictors of the effusion type

Thoracic CT may be used in the workup of patients with pleural effusion. In humans, certain pleural features on CT aid in diagnosing an underlying cause for pleural effusion, whereas this is not well studied in veterinary medicine. This retrospective cross‐sectional analytical study assessed pleural and other intrathoracic abnormalities on CT in dogs and cats with pleural effusion and explored potential discriminatory features between effusion types. Eighty‐nine dogs and 32 cats with pleural cytology and/or histopathology were categorized into malignant pleural disease (15 dogs and 11 cats), pyothorax (34 dogs and 7 cats), chylothorax (20 dogs and 11 cats), transudative (11 dogs and 2 cats), and hemorrhagic effusion (9 dogs and 1 cat). Multivariable logistic regression analysis comparing malignancy to other effusions found that older patient age (dogs: odds ratio 1.28, P = 0.015; cats: odds ratio 1.53, P = 0.005), nodular diaphragmatic pleural thickening (dogs: odds ratio 7.64, P = 0.021; cats: odds ratio 13.67, P = 0.031), costal pleural masses (dogs: odds ratio 21.50, P = 0.018; cats: odds ratio 32.74, P = 0.019), and pulmonary masses (dogs: odds ratio 44.67, P = 0.002; cats: odds ratio 18.26, P = 0.077) were associated with malignancy. In dogs, any costal pleural abnormality (odds ratio 47.55, P = 0.002) and pulmonary masses (odds ratio 10.05, P = 0.004) were associated with malignancy/pyothorax, whereas any costal pleural abnormality (odds ratio 0.14, P = 0.006) and sternal lymphadenopathy (odds ratio 0.22, P = 0.040) were inversely associated with transudates. There were, however, many overlapping abnormalities between effusion types, so further diagnostic testing remains important for diagnosis.