What Is Your Diagnosis?

Joseph T. Sweeney Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, Grafton, MA 01536.

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Trisha J. Oura Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, Grafton, MA 01536.

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Kathryn B. Wulster Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, Grafton, MA 01536.

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Stacie Aarsvold Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, Grafton, MA 01536.

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History

A 5-year-old 3.4-kg (7.5-lb) neutered male Munchkin-Minskin crossbred cat was evaluated because of an acute onset of respiratory distress of 12 hours’ duration. The cat had been adopted 2 years ago and, at the time of adoption, had a 2-year history of chronic rhinitis that had been treated with long-term oral administration of antimicrobials and corticosteroids. After adoption, medications were discontinued and the cat underwent surgical turbinate reduction and periodic nasal flushes that were reportedly well tolerated. The day prior to hospital admission, the cat had recovered uneventfully from a nasal flush procedure performed under general anesthesia; however, the owner noticed that the cat's breathing was more labored than normal at the time of hospital discharge, which progressed throughout the night.

Physical examination revealed that the cat was tachypneic (60 breaths/min) with a marked respiratory effort. Heart rate and rectal temperature were within reference limits. Hematologic findings revealed respiratory acidosis with metabolic compensation (pH, 7.236 [reference range, 7.337 to 7.467]; Pco2,61.4 mm Hg [reference range, 36.0 to 44.0 mm Hg]; bicarbonate, 26.3 mmol/L [reference range, 18.0 to 24.0 mmol/L]) and a lower-limit serum chloride concentration (104.0 mmol/L [reference range, 104 to 109 mmol/L]). The PCV and serum total protein concentration were at the lower limit of the reference ranges (PCV, 28% [reference range, 28% to 40%]; total protein, 6.6 g/dL [reference range, 5.7 to 8.0 g/dL]). Leukocytosis (36.4 × 103 leukocytes/µL [reference range 4.5 × 103 leukocytes/µL to 15.7 × 103 leukocytes/µL]), neutrophilia (33.12 × 103 neutrophils/µL [reference range, 2.1 × 103 neutrophils/µL to 10.1 × 103 neutrophils/µL]), and a lymphocyte count at the lower limit of the reference range (1.43 × 103 lymphocytes/µL [reference range, 1.1 × 103 lymphocytes/µL to 6.0 × 103 lymphocytes/µL]) were found on the CBC; findings were considered most consistent with a stress leukogram.

On the basis of the cat's signalment, history, clinical signs, and laboratory findings, the primary differential diagnoses included pneumonia or occult heart disease with congestive heart failure induced by recent anesthesia and hospitalization. Right lateral and dorsoventral thoracic radiographs were acquired (Figure 1).

Figure 1—
Figure 1—

Right lateral (A) and dorsoventral (B) radiographic views of the thorax of a 5-year-old 3.4-kg (7.5-lb) neutered male Munchkin-Minskin crossbred cat that was evaluated because of an acute onset of respiratory distress of 12 hours’ duration after receiving a nasal flush while sedated. Because of patient conformation and respiratory distress, proper positioning for thoracic radiography was difficult, resulting in thoracic limbs superimposed on the thorax.

Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1235

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

Diagnostic Imaging Findings and Interpretation

Bilaterally, an increase in soft tissue opacity is found in the cranial lung lobes. Within the left cranial lung lobe, multiple punctate gas opacities are evident and are consistent with a vesicular gas pattern (Figure 2). The remaining pulmonary parenchyma is radiographically normal. The thoracic trachea appears to have mild dorsal displacement. A small volume of bilateral pleural effusion and mild retraction of the caudal lung lobes are apparent. Evaluation of the cranial margin of the heart is limited by silhouetting with the soft tissue opacity of the cranial lung lobes and pleural effusion; however, the cardiac silhouette appears to be radiographically normal in size. The pulmonary vessels also appear normal in size.

Figure 2—
Figure 2—

The same radiographic images as in Figure 1 (A and B) and a magnified view of the lateral image (C). Bilaterally, an increase in soft tissue opacity within the cranial aspect of the thorax is evident. Within the left cranial lung lobe, numerous punctate gas foci (arrows) are visualized on both projections (A and B) but are best appreciated (circle) in the right lateral view when magnified (C). These findings are consistent with a vesicular gas pattern. The thoracic trachea is dorsally displaced (black arrowheads) on the lateral projection (A), and there is a small volume of pleural effusion as evidenced by increased opacity within the pleural space. Retraction of the right cranial and middle lung lobes (white arrowheads) on the dorsoventral projection is evident (B).

Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1235

On the basis of the lack of cardiomegaly and the normal appearance in pulmonary vessel size, congestive heart failure was considered unlikely. Given the pleural effusion and vesicular gas pattern, the differential diagnoses were revised to left cranial lung lobe torsion or necrotizing pneumonia. Computed tomography of the thorax was recommended to confirm suspected lung lobe torsion prior to surgery.

Thoracic CT (Figure 3) revealed that the left cranial lung lobe is moderately enlarged with rounded margins. The lung lobe is characterized by increased soft tissue attenuation and innumerable, small, gas-attenuating foci consistent with a vesicular gas pattern. The enlarged left lung lobe causes right displacement of the heart and mediastinal structures and dorsal displacement of the partially atelectatic right cranial lung lobe. The left cranial principal bronchus is abruptly attenuated. Increased soft tissue attenuation and decreased size of the right cranial lung lobe are consistent with atelectasis, and a small volume of bilateral pleural effusion is evident. On the basis of these CT findings, particularly the abrupt attenuation of the left cranial principal bronchus, the diagnosis was left cranial lung lobe torsion and thoracotomy was recommended.

Figure 3—
Figure 3—

Postcontrast transverse (A) and oblique dorsal plane reformatted (B) CT images of the thorax of the cat in Figure 1. A—The transverse image is at the level of the sixth intercostal space. The left cranial lung lobe is enlarged, resulting in right displacement of the heart (arrowhead) and dorsal displacement of the smaller right cranial lung lobe. In the same view, the left cranial lung lobe is heterogenous because of an increase in soft tissue attenuation with dispersed gas, compared with the right lung cranial lung lobe (double-headed arrow). This heterogeneity represents the vesicular gas pattern identified radiographically (sharp algorithm; window width, 1,600 Hounsfield units; window level,–500 Hounsfield units; slice thickness, 2.0 mm). B—The dorsal plane reformatted image highlights abrupt attenuation of the left cranial lung lobe bronchus (arrow) consistent with lung lobe torsion.

Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1235

Treatment and Outcome

A left-sided intercostal thoracotomy and left cranial lung lobectomy were performed, and a thoracostomy tube was placed. Histologic evaluation of the excised lung lobe revealed diffuse hemorrhage, congestion, and necrosis consistent with a lung lobe torsion.

The cat recovered from surgery uneventfully, remained in hospital, and received IV administration of analgesics and antimicrobials. Two days after surgery, the patient was discharged from the hospital with a prescription for oral administration of antimicrobials and a fentanyl patch for analgesia. The cat was reportedly doing well at home 3 months after surgery.

Comments

Lung lobe torsion occurs when a lobe rotates axially around its pedicle and is a rare occurrence in small animals, particularly in cats, with few reported cases in the literature.1–4 The most commonly affected lung lobes in dogs and cats are the right middle and left cranial lung lobes, with the latter seen more commonly in small-breed dogs.1–6 Often, the exact cause of lung lobe torsion is unknown; however, some precipitating causes include trauma, pleural effusion, neoplasia, and chronic lower respiratory tract disease.3,5,6 The exact mechanism of torsion in the cat of the present report is unknown.

The cat of the present report had several of the nonspecific clinical manifestations of lung lobe torsion, including tachypnea and increased respiratory effort that may also be seen with other causes of respiratory distress. Other reported clinical signs associated with lung lobe torsion include coughing, hematemesis, epistaxis, crackles on thoracic auscultation, and tachycardia.1,3,5,6 On initial physical examination, it can be difficult to differentiate lung lobe torsion from other causes of respiratory distress including pneumonia, pleural effusion, pulmonary thromboembolism, diaphragmatic hernia, pulmonary abscess, necrotizing pneumonia,1 or congestive heart failure; thoracic radiography and CT are helpful in differentiating these disease processes.

Imaging characteristics of lung lobe torsions have been documented for several modalities. Radiographic characteristics of lung lobe torsion include increased lobar opacity, often with a concurrent pattern of dispersed small gas bubbles, also known as a vesicular gas pattern.1 On the basis of histologic findings, this radiographic pattern is thought to be due to emphysema, although the pathophysiology underlying the development of emphysema is unclear. Bronchial tears resulting in trapped gas or rapid increased alveolar pressure following torsion with subsequent alveolar rupture and interstitial gas accumulation have been proposed mechanisms.1 In addition to a radiographic vesicular pattern, venous congestion secondary to torsion causes expansion of the lung lobe that may result in displacement of normal mediastinal structures. Deviation of the trachea dorsally on lateral radiographic images combined with the deviation of the heart and cranial mediastinum structures to the contralateral side helps support the diagnosis of lung lobe torsion.1 Pleural effusion is seen inconsistently with lung lobe torsion,1,2 and its presence may obscure visual detection of pulmonary disease. Thoracic CT, ultrasonography, bronchoscopy, or multidetector CT-generated virtual bronchoscopy can help confirm the diagnosis of lung lobe torsion prior to surgical intervention.1,2,4 Common CT findings with lung lobe torsion include an abruptly attenuating bronchus and a noncontrastenhancing emphysematous lung lobe. Often, enlargement of the affected lobe with compression of the surrounding lung lobes and a contralateral mediastinal shift is found.2

In conclusion, lung lobe torsions are rare in cats and are difficult to differentiate from other causes of respiratory distress by physical examination alone. The case described in the present report had several classic radiographic and CT findings expected with lung lobe torsion.

References

  • 1. d'Anjou MATidwell ASHecht S. Radiographic diagnosis of lung lobe torsion. Vet Radiol Ultrasound 2005;46:478484.

  • 2. Seiler GSchwarz TVignoli M, et al. Computed tomographic features of lung lobe torsion. Vet Radiol Ultrasound 2008;49:504508.

  • 3. Dye TLTeague HDPoundstone ML. Lung lobe torsion in a cat with chronic feline asthma. J Am Anim Hosp Assoc 1998;34:493495.

  • 4. Schultz RMPeters JZwingenberger A. Radiography, computed tomography and virtual bronchoscopy in four dogs and two cats with lung lobe torsion. J Small Anim Pract 2009;50:360363.

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  • 5. Mclane MJBuote NJ. Lung lobe torsion associated with chylothorax in a cat. J Feline Med Surg 2011;13:135138.

  • 6. Millard RPMyers JRNovo RE. Spontaneous lung lobe torsion in a cat. J Vet Intern Med 2008;22:671673.

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