History
A 9-year-old castrated male Shih Tzu with a body weight of 5.5 kg (12.1 lb) and a body condition score of 7 of 9 was evaluated at the internal medicine service because of a 2-month history of irregular intervals of panting. The dog had no history of coughing, sneezing, vomiting, or diarrhea but would pant excessively at rest, to the point of waking the owner. On initial evaluation, the dog was quiet, alert, and responsive. No abnormal respiratory sounds were detected, aside from referred upper airway noises secondary to the dog's conformation. No cardiac murmurs or arrhythmias were detected.
Abnormal laboratory findings included mildly high alanine aminotransferase activity (137 U/L; reference range, 10 to 100 U/L). Arterial blood gas analysis was performed (pH, 7.599; Pao2, 122 mm Hg; Paco2, 17.7 mm Hg; oxygen saturation as determined by pulse oximetry, 99%). Findings on an echocardiogram were unremarkable, with no valvular insufficiency, regurgitation, or evidence of pulmonary hypertension noted. Results of a low-dose dexamethasone suppression test were within reference range both before and after cortisol administration. No abnormalities were detected on urinalysis. Thoracic radiography was performed (Figure 1).
Left lateral (A) and ventrodorsal (B) radiographic views of a 9-year-old castrated male Shih Tzu with a 2-month history of panting.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.487
Left lateral (A) and ventrodorsal (B) radiographic views of a 9-year-old castrated male Shih Tzu with a 2-month history of panting.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.487
Left lateral (A) and ventrodorsal (B) radiographic views of a 9-year-old castrated male Shih Tzu with a 2-month history of panting.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.487
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
The cardiac silhouette and pulmonary vasculature are normal in appearance (Figure 2). Two linear to fusiform soft tissue opacities are evident on the orthogonal projections. On the lateral projection, a sharply demarcated linear soft tissue opacity can be observed extending in a cranial to caudal direction from the third to fifth rib space ventral to the trachea. On the ventrodorsal projection, a well-marginated linear soft tissue opacity is observable between the fifth and sixth ribs extending in a craniolateral to caudomedial direction within the right cranial lung lobe.
Same radiographic images as in Figure 1. On the lateral (A) and ventrodorsal (B) views, notice the linear radiopaque areas within the cranial lung fields (arrows). Mild to moderate hepatomegaly and a redundant dorsal tracheal membrane (primarily of the extrathoracic trachea; arrowheads) are evident on the lateral view and an incidental fusiform fat opacity (asterisk) is seen between the right cranial and middle lung lobes on the ventrodorsal view.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.487
Same radiographic images as in Figure 1. On the lateral (A) and ventrodorsal (B) views, notice the linear radiopaque areas within the cranial lung fields (arrows). Mild to moderate hepatomegaly and a redundant dorsal tracheal membrane (primarily of the extrathoracic trachea; arrowheads) are evident on the lateral view and an incidental fusiform fat opacity (asterisk) is seen between the right cranial and middle lung lobes on the ventrodorsal view.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.487
Same radiographic images as in Figure 1. On the lateral (A) and ventrodorsal (B) views, notice the linear radiopaque areas within the cranial lung fields (arrows). Mild to moderate hepatomegaly and a redundant dorsal tracheal membrane (primarily of the extrathoracic trachea; arrowheads) are evident on the lateral view and an incidental fusiform fat opacity (asterisk) is seen between the right cranial and middle lung lobes on the ventrodorsal view.
Citation: Journal of the American Veterinary Medical Association 245, 5; 10.2460/javma.245.5.487
Mild to moderate hepatomegaly and a redundant dorsal tracheal membrane (primarily of the extrathoracic trachea) are evident on the lateral view and an incidental fusiform fat opacity is seen between the right cranial and middle lung lobes on the ventrodorsal view.
The most likely differential diagnosis for the radiographic findings within the lung fields was plate-like atelectasis. Other differential diagnoses included linear pleural fibrosis, fluid within a pleural fissure, thickened interlobular septa, thickened bronchial walls, or chest wall structures projected onto the lung.
Treatment and Outcome
In addition to the differential diagnoses for radiographic findings, primary endocrinopathy, such as hyperadrenocorticism, hypothyroidism, or even obesity hypoventilation syndrome, could account for the clinical signs. Results of the low-dose dexamethasone suppression test and total thyroxine concentration were within reference range, making these possibilities less likely. Atypical hyperadrenocorticism was a possibility, but was not tested for. This patient was overweight, but not morbidly obese, making it less likely that obesity hypoventilation syndrome alone could cause the signs noted.
The clinical signs of the patient described in this report resolved spontaneously in 4 to 6 weeks with no pharmacological intervention. No additional endocrine testing was allowed by the owner. Repeated radiography was not performed to evaluate for resolution of the presumed plate-like atelectasis.
Comments
Atelectasis is the acquired reduction in volume of all or part of a lung.1 Multiple types of atelectasis exist, which have different mechanisms and etiologies. One form is termed plate-like or discoid atelectasis. Radiographically, plate-like atelectasis appears as a linear opacification, limited to either a bronchial segment or a subsegment, or can involve an entire lung lobe or extend across fissures to affect several lung lobes.2 When correlated pathologically, this form of atelectasis is not associated with bronchiolar or vascular obstruction.3 Plate-like atelectasis is intimately associated with congenital pleural clefts, indentations, scars, and incomplete fissures, which can either be a developmental anomaly or be caused by some disease foci. The subpleural lung folds inward along these pleural invaginations, although the exact mechanism is unknown at this time.3 Gravity-dependent collapse, surfactant deficiency, and hypoventilation are suspected to be the primary predisposing factors to this radiographic finding.3,a
Conditions known to be associated with plate-like atelectasis in people include pulmonary thromboembolism, pneumonia, pulmonary edema, prolonged shallow breathing, diaphragmatic dysfunction, pain, and morbid obesity. In humans,3 plate-like atelectasis can indicate more widespread peripheral atelectasis than is radiographically apparent and can be associated with hypoxemia. Evaluation for an underlying cause is suggested if plate-like atelectasis is found. Serial radiographic evaluation can be performed. In many cases, as was true for the dog of the present report, plate-like atelectasis spontaneously resolves.4
Berry CR, Giglio RF, Winter MD, et al. Radiographic characterization of presumed plate-like atelectasis in 37 dogs and 13 cats (abstr). Vet Radiol Ultrasound 2010;51:227.
1. Woodring JH, Reed JC. Types and mechanisms of pulmonary atelectasis. J Thorac Imaging 1996; 11: 92–108.
2. Gurney JW. Atypical manifestations of pulmonary atelectasis. J Thorac Imaging 1996; 11: 165–175.
3. Westcott JL, Cole S. Plate atelectasis. Radiology 1985; 155: 1–9.
4. Boucher H. Delmas J, Mieral R. A little-known radio-clinical syndrome, Fleischner's plate-like atelectasis. Presse Med 1952; 60: 1437–1440.
