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Melissa A. Bisesi Tufts Veterinary Emergency & Treatment Specialties, Walpole, MA 02081.

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Tara N. Hammond Tufts Veterinary Emergency & Treatment Specialties, Walpole, MA 02081.

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Trisha J. Oura Tufts Veterinary Emergency & Treatment Specialties, Walpole, MA 02081.

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History

A 12-year-old 4.3-kg (9.5-lb) spayed female domestic shorthair cat was evaluated for an acute episode of collapse and dyspnea. The cat had been previously healthy with no known underlying medical conditions and historically had negative serologic test results for FeLV and FIV infections.

On physical examination, the cat was open-mouth breathing with increased abdominal effort and short, shallow respirations. Thoracic auscultation revealed muffled heart sounds and dull bronchovesicular sounds bilaterally. The cat was tachycardic with pale mucous membranes and weak femoral pulses.

Evaluation of a fluid sample obtained by diagnostic thoracocentesis revealed a nonclotting hemorrhagic effusion with a PCV of 18% and total solids concentration of 5.0 g/dL. A peripheral blood sample was obtained for comparison of values between the thoracic fluid and blood. The blood sample had a PCV of 21% (reference range, 30% to 45%), total solids concentration of 6.0 g/dL (reference range, 6.0 to 7.5 g/dL), and lactate concentration of 6.2 mmol/L (reference range, 1.1 to 3.5 mmol/L). These findings were consistent with hemothorax.

Measurements of 1-stage prothrombin time and activated partial thromboplastin time were within reference ranges. The cat was placed in an oxygen cage. A bolus of 100 mL of sterile saline (0.9% NaCl) solution was given IV, followed by transfusion of 40 mL (10 mL/kg [4.5 mL/lb]) of type-specific (type-A) packed RBCs during a 1-hour period. The dyspnea improved, and the cat was able to tolerate further handling. At 1 hour after completion of the transfusion, the cat had a peripheral blood PCV of 30% and total solids and lactate concentrations of 7.0 g/dL and 1.7 mmol/L, respectively.

Therapeutic thoracocentesis removed 55 mL of nonclotting hemorrhagic fluid from the left hemithorax and 75 mL of nonclotting hemorrhagic fluid from the right hemithorax. Following therapeutic thoracocentesis, thoracic radiographs were obtained (Figure 1).

Figure 1—
Figure 1—

Lateral (A) and ventrodorsal (B) thoracic radiographs of a 12-year-old spayed female domestic shorthair cat with an acute onset of respiratory distress and hemothorax. Images were acquired after therapeutic thoracocentesis.

Citation: Journal of the American Veterinary Medical Association 248, 6; 10.2460/javma.248.6.609

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →

Diagnostic Imaging Findings and Interpretation

On radiographic evaluation, a large soft tissue opacity mass is evident within the cranial aspect of the thorax extending to the level of the ninth intercostal space. This mass results in marked dorsal deviation of the trachea, and the carina is displaced caudally to the level of the eighth intercostal space, indicating caudal displacement of the cardiac silhouette. The caudal aspect of the mass results in border effacement of the cardiac silhouette, limiting detailed assessment of the cardiovascular structures. The right cranial and middle lung lobes and the cranial segment of the left cranial lung lobe are not visualized, likely because of atelectasis. The caudal segment of the left cranial lung lobe is markedly reduced in size, and the left and right caudal lung lobes are small but have normal opacity. There is a small volume of bilateral pleural effusion identified by increased opacity within the pleural space and retraction of the lung lobes (Figure 2).

Figure 2—
Figure 2—

Same radiographic images as in Figure 1. A large soft tissue opacity causes dorsal deviation of the trachea (arrows). There is caudal displacement of the carina (arrowhead) consistent with caudal displacement of the heart itself. There is a small volume of pleural effusion (asterisk).

Citation: Journal of the American Veterinary Medical Association 248, 6; 10.2460/javma.248.6.609

The observed dorsal deviation of the trachea and caudal displacement of the carina and heart are most consistent with a large cranial mediastinal mass. On the basis of the radiographic findings, differential diagnoses included thymoma and lymphoma. Given the hemothorax, there was concern for vascular effacement or invasion by the mediastinal mass.

Thoracic ultrasonography revealed a > 8.0-cm-diameter, heterogenous, cavitated, moderately vascular mass within the cranial aspect of the thorax that caused marked caudal displacement of the heart and pulmonary parenchyma. The mass extended from the level of the thoracic inlet to approximately the 11th intercostal space and spanned the entire width of the thorax.

Routine fine-needle aspirates of the mass were obtained while the cat was under sedation and submitted for cytologic analysis. Cytologic findings were consistent with thymoma. Computed tomography was recommended to evaluate surgical resectability, but was declined by the owner.

Treatment and Outcome

Overnight, the cat was maintained on a continuous rate IV infusion of lactated Ringer solution (containing 20 mEq of potassium chloride/L) at a rate of 100 mL/kg/d (45.5 mL/lb/d). The respiratory rate and effort increased 7 hours after transfusion of packed RBCs and continued to progressively worsen. The peripheral blood PCV decreased overnight. The peripheral blood PCV and total solids concentration at 14 hours after transfusion were 23% and 6.0 g/dL, respectively, and at 24 hours after transfusion were 19% and 6.6 g/dL, respectively. Oxygen saturation at 26 hours after transfusion was 86%. Given the cat's rapid clinical decline, the owner elected to have the cat euthanized.

Comments

In the cat of the present report, thoracic radiography helped determine that the cause of the clinical signs was a large cranial mediastinal mass. A cranial mediastinal origin was thought most likely, as the mass was located on midline, caused marked dorsal but no left or right deviation of the trachea, and caused caudal displacement of the carina and heart. Mediastinal masses are uncommon in cats, but the most common are lymphoma and thymoma, with branchial cysts, ectopic thyroid, chemodectoma, and other neoplasms occurring less frequently.1 Results of cytologic evaluation of the mass were consistent with thymoma. Although histologic evaluation would have likely led to a more conclusive diagnosis, a retrospective study2 evaluating the correlation between cytologic and histologic diagnosis of mediastinal masses in dogs and cats found complete agreement in 12 of 17 (71%) cases of feline thymoma.

Thymic disease is uncommonly reported in cats.1,3 In a report3 of 30 cats with histopathologically confirmed thymic disease, thymic lymphoma was most common (n = 19 cats), followed by thymoma (5), thymic hyperplasia (2), thymic branchial cysts (1), thymic hypoplasia (1), thymic hemorrhage (1), and thymic amyloidosis (1). In that report, thymoma occurred in an older patient population (mean age, 9.1 years), compared with thymic lymphoma (mean age, 4.07 years). Of the 19 cats with confirmed thymic lymphoma, 8 were tested for FeLV status and 4 of these had positive results.3 Thymomas are classified as benign versus malignant on the basis of their clinical resectability rather than classic histologic features.1 Approximately 65% of thymomas are benign (noninvasive) and resectable.1 The remaining 35% are malignant (invasive) with adhesions to surrounding tissues including major nerves, veins, trachea, pericardium, and esophagus, making resection difficult.1 The prognosis for surgically resectable thymoma is good, whereas the prognosis for nonresectable thymoma is generally considered poor.1 The use of preoperative advanced imaging (CT or MRI) is recommended to predict resectability, although this ultimately remains an intraoperative decision.4

The most unusual feature of the cat of the present report was a hemothorax detected on initial examination, which is more often associated with trauma or coagulopathic disease as opposed to mediastinal neoplasia. In most healthy dogs and cats, the mediastinal pleura isolates the mediastinal space from the pleural space; however, the pleural tissue is extremely fragile and may break down to allow communication between the 2 spaces.

A search of the literature produced 2 case reports of thymoma in humans resulting in spontaneous hemothorax. One case report describes a malignant thymoma with local invasion into the pericardium and right atrium,5 and the second case report describes rupture of a benign thymoma that had been presumably present for many years without causing clinical signs.6 To the authors' knowledge, spontaneous hemothorax secondary to thymoma in a cat has not been previously reported. Given the evidence of vascularity on thoracic ultrasonography, the authors hypothesize that invasion of adjacent mediastinal vascular structures resulted in mediastinal hemorrhage with subsequent extension into the pleural space.

References

  • 1. Withrow SJ, Vail DM. Miscellaneous tumors: thymoma. In: Withrow SJ, Vail DM, eds. Withrow and MacEwen's small animal clinical oncology. 4th ed. St Louis: Saunders, 2007;795799.

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  • 2. Pintore L, Bertazzolo W, Bonfani U, et al. Cytological and histological correlation in diagnosing feline and canine mediastinal masses. J Small Anim Pract 2014; 55:2832.

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  • 3. Day MJ. Review of thymic pathology in 30 cats and 36 dogs. J Small Anim Pract 1997; 38:393403.

  • 4. Zitz JC, Birchard SJ, Couto GC, et al. Results of excision of thymoma in cats and dogs: 20 cases (1984–2005). J Am Vet Med Assoc 2008; 232:11861192.

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  • 5. Templeton PA, Vainright JR, Rodriguez A, et al. Mediastinal tumors presenting as spontaneous hemothorax, simulating aortic dissection. Chest 1988; 93:828830.

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  • 6. Caplin JL, Gullan RW, Dymond DS, et al. Hemothorax due to rupture of a benign thymoma. Jpn Heart J 1985; 26:123125.

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