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Meghan L. Collins 1Veterinary Specialty Hospital, 2055 Montiel Rd 104, San Marcos, CA 92069

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Sarena K. Sunico 1Veterinary Specialty Hospital, 2055 Montiel Rd 104, San Marcos, CA 92069

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History

A 10-year-old 4.8-kg (10.6-lb) sexually intact male domestic shorthair cat was taken to its primary care veterinarian because when the owners returned home from a 9-day trip, they found the cat markedly dyspneic with open-mouth breathing and underweight with an estimated body weight loss of 0.5 to 0.9 kg (1.1 to 2 lb). During the owners’ absence, a pet sitter periodically cared for this and other cats of the household, and the cats had indoor and outdoor access on a large property in southern California. The primary care veterinarian administered flow-by oxygen, performed thoracic radiography (not shown), and attempted thoracocentesis without real-time imaging guidance. Thoracocentesis yielded no fluid, and the cat was then transferred to the emergency department of a referral hospital for further evaluation.

On initial referral examination, the cat was bright, alert, responsive, tachycardic (240 beats/min; reference range, 120 to 140 beats/min), and tachypneic (> 100 breaths/min; reference range, 16 to 40 breaths/min) and had a rectal temperature of 38.4°C (101.2°F; reference range, 37.8° to 39.2°C [100.0° to 102.6°F]), pink mucous membranes, and a capillary refill time of < 2 seconds. No cardiac murmurs were heard on auscultation, and the cat's femoral pulses were strong and synchronous bilaterally. The cat's lung sounds were quiet with decreased bronchovesicular sounds in all lung fields. No abnormalities were detected on palpation of the abdomen and peripheral lymph nodes. Flow-by oxygen was administered through a face mask, and thoracic radiography was performed (Figure 1).

Figure 1—
Figure 1—

Right lateral (A) and dorsoventral (B) thoracic radiographic images of a 10-year-old 4.8-kg (10.6-lb) sexually intact male domestic shorthair cat from southern California referred for evaluation of severe dyspnea.

Citation: Journal of the American Veterinary Medical Association 256, 1; 10.2460/javma.256.1.43

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

Radiographic Findings and Interpretation

A mass effect was evident in a large area of the cranial aspect of the thorax and caused circumferential soft-tissue opacification around the trachea, which was deviated slightly dorsally in the cranial aspect of the thorax and substantially ventrally in the caudal aspect, most prominently at the level of the tracheal bifurcation (Figure 2). This ventral deviation of the tracheal bifurcation also indicated that the heart, the silhouette of which could not be seen, had been deviated ventrally. In addition, the tracheal bifurcation was displaced caudally to the level of the seventh intercostal space (reference location, fifth intercostal space), and the cranial margins of the lungs were also displaced caudally. Although the trachea was mildly deviated to the left, it remained close to midline. The mediastinum was widened, and the lungs had a marked loss of pulmonary volume, mildly worse on the right side. Given the severity and character of the displacement of the trachea, a solid mass in the mediastinum was more likely than diffuse mediastinal effusion. Coursing dorsal to the trachea was a thin lucent line, consistent with a dorsally displaced esophageal lumen. It was unclear whether deviation of the esophageal lumen was solely because of extraluminal compression or because there was a concurrent mural component. The diaphragm was caudally displaced, and diaphragmatic flattening was evident, consistent with increased thoracic volume and, as clinically observed in this cat, severe dyspnea.

Figure 2—
Figure 2—

Same radiographic images as in Figure 1. A mass effect is evident in a large area of the cranial aspect of the thorax and obscures the cardiac silhouette. The trachea deviates slightly dorsally in the cranial aspect of the thorax and substantially ventrally in the caudal aspect, most prominently at the level of the tracheal bifurcation (wide arrow; A). There is mediastinal widening (arrowheads; B) and loss of pulmonary volume combined with caudal displacement of the cranial margins of the lungs and caudal displacement and flattening of the diaphragm, consistent with increased thoracic volume and the clinically evident dyspnea. The pulmonary parenchyma has a patchy interstitial pattern with a peribronchovascular distribution, and in the perihilar to centrilobar regions of the caudal lung fields, the pulmonary infiltrates coalesce to alveolar infiltrates that silhouette with the presumed mediastinal mass. The caudodorsal tips of the lung fields (white dashed outline; A) have greater lucency, without apparent pulmonary infiltrates or recognizable vascular detail, consistent with emphysema, a bulla or bleb, or a small pocket of pneumothorax. There are 2 rounded areas of increased lucency (black dotted outline; A), consistent with variably inflated lung, cavitary lesions in the pulmonary parenchyma or mediastinum (eg, secondary to neoplasia, granulomatous disease, or abscess formation), or small pockets of pneumothorax. The larger of these 2 areas of increased lucency is superimposed over the dorsally displaced esophageal lumen (thin arrows; A).

Citation: Journal of the American Veterinary Medical Association 256, 1; 10.2460/javma.256.1.43

The pulmonary parenchyma had a patchy interstitial pattern with a peribronchovascular distribution. In the perihilar to centrilobar regions of the caudal lung fields, the pulmonary infiltrates coalesced to alveolar infiltrates that silhouetted with the mediastinal mass. On the lateral radiographic view, nearly the entire area of aerated pulmonary parenchyma in the caudodorsal region was occupied by small rounded lucencies with thick-walled, soft-tissue margins, consistent with areas of heterogenous pulmonary infiltrates, thickened and dilated bronchi, or cavitary lesions. The caudodorsal tip of the lung fields had greater lucency without apparent pulmonary infiltrates or recognizable vascular detail, consistent with an area of emphysema, a bulla or bleb, or a small pocket of pneumothorax. Alternatively, oligemia from thromboembolic disease could have resulted in similar focal radiographically abnormal reduction in vasculature. However, thromboembolic disease was less likely owing to the well-demarcated cranial margin of the highly lucent region seen on the lateral radiographic view.

Additionally, there were 2 rounded lucencies in the thorax evident on the lateral radiographic view but not the dorsoventral view. The larger of these lucencies was dorsal to the tracheal bifurcation in the seventh to the ninth intercostal spaces, and the smaller of these lucencies was ventral to the trachea in the fifth to sixth intercostal spaces. This dorsal lucency was not consistent with an esophageal origin because the lucency extended more dorsally than expected for the esophagus and appeared superimposed over a thin lucent line suspected to represent the esophageal lumen. Considerations for these 2 lucencies included regions of variably inflated lung; cavitary lesions in the pulmonary parenchyma or mediastinum secondary to neoplasia, granulomatous disease, or abscess formation; or small pockets of pneumothorax. Although iatrogenic pneumothorax from the thoracocentesis performed before referral and radiography was considered unlikely, spontaneous pneumothorax from infiltrative erosion into the pleural space could not be ruled out.

On the basis of physical and radiographic examination findings, a large mediastinal mass with concurrent pulmonary infiltrates was diagnosed, and either cavitary lesions or small pockets of pneumothorax were suspected. The primary differential diagnosis list included multicentric neoplasia (eg, round cell neoplasia), severe granulomatous disease (eg, cryptococcosis, actinomycosis, nocardiosis, or other fungal infections), or a primary infiltrative mediastinal mass with concurrent pulmonary metastasis (eg, thymic carcinoma or either an esophageal or paraesophageal tumor). However, many of the differential diagnoses for a solitary mediastinal mass were less likely to extend caudally into the dorsal mediastinum or cause such a complex pulmonary pattern.

Treatment and Outcome

Although flow-by oxygen delivered through a face mask continued, the cat's condition rapidly declined with progressive dyspnea and development of cyanotic mucous membranes. The differential diagnoses and likely poor prognosis were discussed with the owners, who then elected to have the cat euthanized without further treatment or diagnostic procedures, including thoracic CT or ultrasonography. However, immediately after euthanasia and with the owners’ permission, ultrasonographically guided fine-needle aspirate samples of the intrathoracic mass were obtained. On ultrasonography, the mass was heterogeneous, with a predominantly hypoechoic appearance and small hyperechoic areas. Cytologic examination of the aspirated samples revealed high cellularity with few scattered RBCs, a low number of activated macrophages, rare nondegenerate neutrophils, but a very high number of medium to large encapsulated yeast structures consistent with Cryptococcus spp (Figure 3).

Figure 3—
Figure 3—

Photomicrograph of the postmortem, ultrasonographically guided fine-needle aspirate sample obtained from the mediastinal mass in the cat in Figures 1 and 2 showing a high number of medium to large encapsulated yeast structures, consistent with Cryptococcus spp. Near the center of the image, the largest single organism in this particular field is surrounded by a thick nonstaining capsule (arrowheads). Wright-Giemsa stain; bar = 20 mm.

Citation: Journal of the American Veterinary Medical Association 256, 1; 10.2460/javma.256.1.43

Comments

Cryptococcosis is a systemic mycotic disease that affects humans and animals and is caused by Cryptococcus spp, a genus of encapsulated yeast with worldwide distribution.1 Dogs are more likely to develop systemic dissemination of infection, whereas cats more commonly develop localized nasal or cutaneous disease.2 Cryptococcosis is the most common systemic mycosis reported in cats.3

Although pulmonary manifestation of cryptococcosis is less common, thoracic lesions ranging from interstitial infiltrates, pleural effusion, mediastinal widening, and pulmonary nodules or masses have been reported.3 Similarly, mediastinal widening and interstitial infiltrates were indicated among other abnormal results of the thoracic radiographic examination of the cat in the present report. Findings on postmortem ultrasonography, although not diagnostic, facilitated our accurate sampling of the cat's mediastinal mass, which then led to the diagnosis of cryptococcosis.

Other reported sites of cryptococcosis involvement include the skin, CNS (more common in dogs than cats), lymph nodes, kidneys, liver, eyes, pancreas, gastrointestinal tract, myocardium, and urinary bladder.3 As such, a baseline hematologic evaluation combined with complete ophthalmic and neurologic examination should be performed in all patients stable enough for these procedures. In addition, fungal cultures and Cryptococcus antigen testing of CSF samples can be performed in patients with abnormal neurologic signs.4 Definitive diagnosis of a suspected thoracic cryptococcal mass can be made with cytologic or histologic examination of samples obtained. Serum Cryptococcus antigen testing is also available, and additional diagnostic procedures may include a search for specific causes of a potentially underlying immunodeficiency, such as FIV, concurrent infection, or pneumonia.3

Prognosis for animals with cryptococcosis depends on lesion localization (eg, pulmonary, CNS, or systemic) and severity, comorbidities, host immunocompetence, and owner willingness to pursue treatment. Typically, antifungal treatment must be continued for at least 6 months and in some cases, for life. Treatment should not be discontinued until after resolution of clinical signs and documentation of undetectable Cryptococcus antigen titers.2

Acknowledgments

The authors thank Dr. Andy Loar for cytologic review.

References

  • 1. Duncan CG, Stephen C, Campbell J. Evaluation of risk factors for Cryptococcus gattii infection in dogs and cats. J Am Vet Med Assoc 2006;228:377382.

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  • 2. Vorathavorn VI, Sykes JE, Feldman DG. Cryptococcosis as an emerging systemic mycosis in dogs. J Vet Emerg Crit Care (San Antonio) 2013;23:489497.

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  • 3. Trivedi SR, Sykes JE, Cannon MS, et al. Clinical features and epidemiology of cryptococcosis in cats and dogs in California: 93 cases (1988-2010). J Am Vet Med Assoc 2011;239:357369.

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  • 4. Sykes JE, Sturges BK, Cannon MS, et al. Clinical signs, imaging features, neuropathology, and outcome in cats and dogs with central nervous system cryptococcosis from California. J Vet Intern Med 2010;24:14271438.

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