Diseases of the Thoracic Wall and Cavity

Amelia R. Woolums

Pleuritis and Pleural Effusions

■ Definition and Etiology Acute, primary pleuritis is rare in ruminants. It is almost always a secondary condition. The most common primary cause is most likely bronchopneu­monia caused by M.

■ Clinical Signs The signs depend on and may be over­shadowed by the primary disease process. Pleuritis is a painful, septic process, whereas the signs associated with nonseptic effusions depend largely on the cause. Signs referable to pleuritis itself include anorexia, depression, fever, weight loss, decreased milk production, progressive dyspnea, and a characteristic stance and respiratory pattern, with the head and neck extended, elbows abducted, restricted excursion of the thorax, abdominal breathing, tachypnea, and a grunting or groaning with respira­tion. The animal may be reluctant to move. If a cough is present, it is often soft and suppressed because of pain. Jugular distention and pulsation may result from interference with venous return. Auscultation may reveal creaking or rubbing noises in dry pleuritis or a cranial-ventral masking of sounds caused by effusion. Percussion may reveal dullness ventral to the fluid line and may elicit pain. Differential diagnoses for dyspnea with abnormally quiet lung fields may include acute interstitial pneumonia, pneumothorax, and space-occupying lesions such as large abscesses, tumors, and diaphragmatic hernia.

■ Diagnosis A CBC helps separate infectious causes from noninfectious causes and distinguish relatively acute condi­tions (with significant left shifts) from those of a more chronic nature (with mature neutrophilia, hyperglobulinemia, and nonregenerative anemia of chronic disease). Serum chemical determinations and urinalysis identify hypoproteinemia and azotemia. A thoracocentesis should be performed and submitted to cytologic and cultural examination for bacteria, mycoplasma, and chlamydia. Nonseptic transudates indicate conditions such as neoplasia, heart failure, hypoproteinemia, and uremia. Septic exudates high in both cells and protein occur with pleuropneumonia, hardware, peritonitis, abscesses, penetrat­ing trauma, and septicemias. A transtracheal wash is usually indicated because of the common association with pneumonia. Pericardiocentesis, abdominocentesis, and radiographs may indicate the primary source of an infection. Tuberculosis tests, leukemia virus titers, electrocardiography, echocardiographic examinations, ultrasonographic examination of the liver, and exploratory laparotomy may also help detect other primary processes.

■ Treatment The primary problem should be treated. Effusions should be drained, either periodically or continuously through a Heimlich valve or a suction device fashioned from a syringe with the plunger transfixed with a pin. Effective drainage can be difficult in ruminants because of their propensity for fibrin formation and loculation of the fluid. Intermittent drainage is as effective as continuous drainage and simpler to maintain. Attempts at lavage have rarely been successful because of adhesions. Appropriate antibiotics are indicated in the presence of sepsis. NSAIDs (flunixin meglumine, 1.1 to 2.2 mg/ kg IV or divided twice daily) are useful to relieve pain, ease respiration, and improve appetite.

Pneumothorax

Pneumothorax is not common in ruminants. Most cases result from the rupture of an emphysematous bulla associated with pneumonia, straining, or coughing or from puncture of the lung by a fractured rib. The bullae that occur in BRSV-induced pneumonia are a common source. Trauma to the pharynx or larynx can also lead to pneumothorax, presumably caused by air traveling from the cranial cervical regions through soft tissues and into the thoracic cavity. Penetration from the exterior is possible but less common. A case has been described in a postparturient cow with no other underlying cause found.⁸ A retrospective study of 30 cattle with pneumothorax presented to a referral hospital found that 18 of the cases (60%) were associated with bronchopneumonia, 7 cases were associated with interstitial pneumonia, 3 cases were associated with laryngeal or pharyngeal trauma, and 2 cases were associated with neonatal respiratory distress.⁹ Of interest was the finding that 13 of the 18 cases with bronchopneumonia were chronic, based on history and diagnostic findings; an association between pneumothorax and chronic bronchopneumonia had not been previously reported. The rate of survival for cattle with pneu­monia and pneumothorax was lower than for cattle presented with pneumonia without pneumothorax, with an overall survival rate of 60% for cattle presented with pneumothorax.

Clinical signs of pneumothorax include inspiratory dyspnea, sometimes severe, with open-mouth breathing sometimes present. One side of the thorax may be relatively collapsed and immobile, with a compensatory increase in the size and excursion of the other side; however, this latter finding is often subtle and difficult to appreciate. Ruminants have a complete mediastinum; thus when pneumothorax occurs it is usually unilateral, and the animal is able to ventilate adequately using the opposite lung.

If the affected animal shows signs of significant distress, the air in the pleural space should be evacuated. Evacuation can be accomplished by aseptically placing a teat cannula into the thoracic cavity at the dorsal aspect of the thorax at the tenth intercostal space and withdrawing air by use of an exten­sion set, three-way stopcock, and syringe.

Diaphragmatic Hernia

■ Definition and Etiology Diaphragmatic hernias are uncommon in ruminants. Hernias may be congenital, but most appear to be acquired, including those occurring in neonates. A congenital weakness in the diaphragm may predispose to some cases. Causes include difficult parturition, external trauma, and, by far the most common cause, traumatic reticuloperitonitis (TRP).

■ Clinical Signs and Differential Diagnosis Affected animals can be asymptomatic for a prolonged period.¹¹ Most affected cattle are in late gestation or have calved recently. The history may include decreased milk production, weight loss, capricious appetite, difficulty in swallowing or regurgita­tion, previous signs of abdominal pain (possibly associated with acute TRP), vomiting, and abnormal posturing of the head and neck on swallowing or regurgitation. Respiratory signs are actually fairly uncommon, with the exception of large congenital hernias, in which there is obvious severe dyspnea and abdominal respiration from birth. Occasional cough and dyspnea have been reported, and auscultation may reveal asymmetric sounds, with lack of lung or heart sounds in the affected area, or splashing sounds similar to those heard with pericarditis. GI signs are actually more common and include bloat, signs consistent with TRP, difficulty or pain on passage of a stomach tube, diarrhea, constipation, and ruminal hypo­motility.

■ Diagnosis Radiographs can be used to confirm the diagnosis. The normal outline of the diaphragm and heart may be obscured, and the honeycombs or foreign objects in the reticulum may be seen in the thorax because this organ is most commonly involved. Oral barium may also aid in the radiographic interpretation, particularly in early small hernias that will be missed on plain films. Pleuritis and other masses such as tumors and abscesses can also mimic hernias on plain films. If TRP is involved, the CBC, pleural effusions, and abdominocentesis may reflect the septic process. In cases not associated with TRP, the pleural effusion may be hemorrhagic in acute cases and normal in chronic cases.

■ Necropsy The hernial ring is usually located at the junction of the musculotendinous portion of the diaphragm, about 12 cm ventral to the vena cava and slightly lateral to the midline. The ring is usually round to oval, with a diameter of 7 to 20 cm. The reticulum is usually herniated, most fre­quently to the right side of the chest. The liver, spleen, rumen, omasum, abomasum, intestine, and omentum may also be involved. Extensive adhesions usually develop between the herniated organs and the thoracic organs, and evidence of hardware can often be found.

■ Treatment and Prognosis Treatment is surgical. A two-stage approach is usually used. First, a standing left flank laparotomy and rumenotomy are performed; the defect is identified, foreign bodies are removed, and the ruminoreticulum is emptied. Because of the complete mediastinum, ventilatory assistance is rarely needed during this stage. Next, the animal is placed under general anesthesia with positive pressure ventilation. Various approaches have been used for this portion, including ventral midline, paramedian, semilunar postxiphoid, paracostal, and transthoracic with rib resection. The hernia is reduced, and the rent is repaired with sutures or mesh grafts. Mesh grafts are contraindicated if infection is present.

Pleural Mesothelioma

Mesotheliomas have been reported in cattle and goats,¹² includ­ing a congenital form in calves.¹³ Most are peritoneal, but pleural mesotheliomas also occur.¹⁴ Mesotheliomas result in the accumulation of large amounts of fluid in the involved body cavity; signs of pleural mesothelioma are therefore related to pleural effusion. They include dyspnea, tachypnea, decreased lung and heart sounds (sometimes unilateral, with a concomitant increase in sounds on the normal side), dullness on percussion, exercise intolerance, cyanosis, tachycardia, anorexia, weight loss, decreased production, cough, and weak pulses. If peritoneal lesions are also present, as is common but not universal, ascites is also present. Radiographs confirm the pleural effusion, and thoracocentesis yields a serous, sometimes blood-tinged or gelatinous fluid. Cytologic examination may reveal reactive mesothelial cells. At necropsy the pleura is thickened and contains multiple nodules of gray to yellowish-white tissue measuring several millimeters to several centimeters in diameter. Metastasis is uncommon. The tumor can be difficult to diagnose histologically and may resemble inflammation, pleural tuber­culosis (“pearl disease”), or metastasis of another tumor.¹³ There is no treatment.