What Is Your Diagnosis?

Hock Gan Heng Department of Radiological Health Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.

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 DVM, MVS, MS, DACVR
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Tim Holt Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.

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History

A 3-year-old Suffolk ram was evaluated for decreased appetite, chronic weight loss, and severe wool loss on the dorsal and lateral aspects of the thorax and abdomen for an unknown duration. The sheep also had a history of an unknown duration of intermittent fever ranging from 40° to 41.5°C (104° to 106.7°F). The sheep's condition had not improved despite treatment with numerous antimicrobials.

On physical examination, the sheep was lethargic and had a body condition score of 1 (scale of 1 to 5). Thoracic auscultation revealed increased lung sounds in the right cranial and ventral lung fields. The wool was patchy and brittle on the dorsal and lateral aspects of the thorax and abdomen. The sheep's rectal temperature was 41.0°C (105.8°F). A lateral radiographic view of the thorax was obtained while the sheep was standing (Figure 1).

Figure 1—
Figure 1—

Right lateral radiographic view of the thorax of a standing 3-year-old Suffolk ram evaluated for chronic weight loss.

Citation: Journal of the American Veterinary Medical Association 230, 7; 10.2460/javma.230.7.993

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

Figure 2—
Figure 2—

Same radiographic view as in Figure 1. Notice the soft tissue mass in the caudoventral lung fields, which displaces the cardiac silhouette cranially and ventrally. Gas (arrows) can be seen at the most dorsal aspect of the mass. CVC = Caudal vena cava.

Citation: Journal of the American Veterinary Medical Association 230, 7; 10.2460/javma.230.7.993

Radiographic Interpretation and Diagnosis

A large, well-defined soft tissue mass (approx 20 cm in diameter) with a distinct linear gas-fluid interface is visible in the caudoventral portion of the thorax (Figure 2). The distance between the cardiac silhouette and the diaphragmatic outline is greater than normal, indicating that the cardiac silhouette is displaced slightly cranioventrally. The caudal vena cava (CVC) is evident, indicating that the mass is located lateral to the CVC. An incidental finding of spondylosis deformans is evident along the ventral aspect of the thoracic vertebrae.

Comments

Detection of a large thoracic mass with a gas-fluid interface in the lateral radiographic view indicated a cavitary mass. Differential diagnoses included abscess, granuloma, neoplasia, and septic infarct. In this sheep, the cavitary mass was most likely of lung origin (located lateral to the CVC) and less likely to have originated from the caudal mediastinum and esophagus because of lack of a distended or gas-filled esophagus. Because the sheep had a history of intermittent fever, pulmonary abscess was the most likely diagnosis.

A ventrodorsal or dorsoventral radiographic view is useful in determining the lobar distribution of lung lesions. A left lateral radiographic view obtained while the sheep was standing may also have been used to localize the mass. A lesion at the side closest to the film cassette will be smaller because it is less magnified; however, further radiographic examination was not performed. Instead, thoracic ultrasonography was performed to characterize and determine the location of the mass. A hyperechogenic rim mass with homogeneous echogenic content was detected in the left thoracic cavity extending from the 3rd to the 11th intercostal space. No reverberation artifacts were detected. Approximately 2 L of brown mucopurulent fluid was removed from the mass via ultrasound-guided fine-needle aspiration. The sheep's respiratory rate and demeanor improved following the aspiration procedure.

The sheep was euthanatized the following day because of poor prognosis. At necropsy, an approximately 35-cm-diameter cavitary mass was detected in the left caudal lung lobe. The pericardium was firmly adhered to the left lung. The right cranial lung lobe was adhered firmly to the right thoracic wall. The thoracic cavity contained approximately 30 mL of serosanguinous fluid. Because of financial constraints, bacterial cultures of the serosanguinous fluid and mass content were not performed. Microscopic evaluation of the mass revealed numerous degenerative neutrophils and a mixed population of bacteria.

Antemortem diagnosis of a pulmonary abscess without the use of diagnostic imaging modality is difficult. Ultrasonographic investigation of pleural and pulmonary disease has been reported in dogs, horses, and a sheep.1–3 Although the risk of complications encountered with ultrasound-guided fine-needle aspiration and biopsy, such as hemorrhage and seeding of neoplastic cells along the needle tract, are low, we believe that the serosanguinous fluid in the thorax most likely resulted from leakage of purulent material from the abscess because pleural effusion was not detected during radiography or ultrasonography before the fine-needle aspirate was obtained.

  • 1

    Stowater JL, Lamb CR. Ultrasonography of noncardiac thoracic diseases in small animals. J Am Vet Med Assoc 1989;195:514520.

  • 2

    McClellan PD. Diagnostic thoracic ultrasound. J Equine Vet Sci 1991;11:7677.

  • 3

    Braun U, Flückiger M, Sicher D, et al. Suppurative pleuropneumonia and a pulmonary abscess in a ram: ultrasonographic and radiographic findings. Schweiz Arch Tierheilkd 1995;137:272278.

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