Computed tomographic evaluation of a bronchogenic cyst in a German shepherd dog

Abstract

A German shepherd dog was referred for further evaluation of a cavitary pulmonary lesion. Computed tomography identified a well-defined rounded radiolucent area in the left cranial lung lobe in continuity with the bronchial lumen. These findings were consistent with a bronchogenic cyst.

Case description

A 2-year-old spayed female German shepherd dog was referred to the Veterinary Teaching Hospital of the University of Montreal for further evaluation of an unusual pulmonary lesion. One month earlier the dog had been presented to the referring veterinarian for coughing, dyspnea, lethargy, bilious vomiting, and anorexia. The patient was first treated with cephalexin, tolfenamic acid, and fenbendazole. The owner reported a mild improvement of the clinical signs but the dog still remained lethargic. Two weeks after initial presentation, thoracic radiographs done by the referring veterinarian revealed a round, well-defined, radiolucent lesion measuring about 5 cm in diameter in the left cranial lung lobe surrounded by an alveolar pulmonary pattern. Radiographic diagnosis at that time was a cavitary pulmonary lesion complicated by atelectasis or infection. Thoracic ultrasound of this region revealed a hypoechoic area in the ventral portion of the left cranial lung lobe, corresponding to the region of alveolar pattern seen previously on radiographs. Ultrasound-guided fine-needle aspiration led to a cytologic diagnosis of mild suppurative and lymphoplasmocytic inflammation. Treatment was therefore changed to enrofloxacin.

The dog was referred for further investigation regarding the cavitary pulmonary lesion. At the time of the referral, there were no abnormal physical findings. Thoracic radiographs (Figures 1A and 1B) were repeated on the day of admission.

Figure 1.

Right lateral (A) and ventrodorsal (B) thoracic radiographs of a 2-year-old spayed female German shepherd dog on the first day of hospitalization showing a radiolucent structure (arrows) with a thin wall in the cranial part of the left cranial lung lobe.

Radiographs (Figures 1A and 1B) revealed a large, thin-walled radiolucent spherical structure around 5 cm in diameter in the left cranial lung lobe. The alveolar pattern was no longer evident. Radiographic diagnoses for such a lesion should include a bulla, possibly congenital or resulting from alveolar wall rupture secondary to an unknown trauma, a congenital bronchogenic cyst, a pneumatocele, healed abscess or a parasitic cyst (less likely in Quebec) (1–3).

A computed tomography (CT) scan was performed to better characterize this lesion and to assess the lungs (Figures 2A, 2B, and 2C). The well-defined rounded radiolucent area was identified at the most cranial portion of the left cranial lung lobe and was approximately 4.6 cm high, 5.8 cm long, and 3.2 cm wide. A thin wall of soft tissue attenuation delineating this lesion was in continuity with the lumen of the left cranial lobar bronchus. There was no contrast enhancement of this lesion. These findings were consistent with a bronchogenic cyst.

Figure 2.

Computed tomographic images of the thorax of the same dog as in Figure 1. (A) Transverse image of the thoracic cavity at the most cranial part of the lungs. A well-defined and rounded radiolucent area is present in the left cranial lung lobe; it is approximately 4.6 cm high, 5.8 cm long, and 3.2 cm wide. A thin wall of soft tissue attenuation delineated this area. Dorsal (B) and sagittal (C) reformatted images show the communication between the left cranial bronchus lumen and the cyst (arrows).

The patient underwent a partial lobectomy of the left cranial lung lobe by thoracoscopy. Histopathologic diagnosis was a bronchogenic cyst with mild atelectasis of the surrounding lung parenchyma. Aerobic and anaerobic bacterial cultures of the surrounding lung tissue yielded negative results. The cyst wall consisted of smooth muscle fibers and fibrous tissue and it was lined by ciliated pseudostratified epithelium. There were no complications in the post-operative period and the patient was discharged the following day. Follow-up radiographs at 3 months showed a left-sided mediastinal shift due to the partial lobectomy with no evidence of pulmonary lesions.

Discussion

This is the first report of a bronchogenic cyst diagnosed by CT in a dog. Differential diagnoses for radiolucent structures in the lung parenchyma surrounded by a thin wall include: pulmonary blebs, bullae, pneumatoceles, or cysts (1–3). These conditions are difficult to distinguish radiographically. Cysts are uncommon in dogs and can be congenital or acquired lesions (1,3,4) that contain air or fluid. Bronchogenic cysts may communicate with a bronchial lumen (1) and are lined with respiratory epithelium (2). Because of the appearance of the lesion and the communication with a bronchial lumen on the CT-scan images, a diagnosis of a bronchogenic cyst was made in this case. A retrospective study reported 5 dogs including 1 German shepherd dog, with a radiographic diagnosis of a pulmonary congenital cyst (1). In 2 cases that had a concurrent pneumothorax, the diagnosis of congenital cyst was confirmed histopathologically. One of them had a definite communication between the cyst and a bronchial lumen demonstrated with bronchography and was likely of bronchogenic origin.

A bronchogenic cyst was recently reported on thoracic radiographs in a two-and-a-half-year-old male German shepherd dog that had intermittent episodes of fever, severe dyspnea, and cyanosis (4). The dog had concurrent bronchitis and peri-bronchitis at the time of the diagnosis and the cyst was thought to have developed secondarily to bronchiectasis. In the human literature, bronchogenic cysts are described as lesions of congenital origin (5). Most frequently unilocular, they contain clear fluid or, less commonly, hemorrhagic secretions or air. They are lined by columnar ciliated epithelium, and their walls often contain cartilage and bronchial mucous glands. Patent connection with the airway is unusual in humans, but when present, such a communication may promote infection of the cyst by allowing bacterial entry (5). Use of CT-scan has been advocated in the diagnosis of bronchogenic cysts in humans (6). Dyspnea or chest pain or both are the most common symptoms (6) and complete surgical resection is often recommended to establish a diagnosis, alleviate symptoms, and prevent complications (7). Interestingly, the dog reported here had been diagnosed with a suspicion of pneumonia that had responded to antibiotic therapy. Thus, a secondary bacterial infection of a congenital cyst secondary to patent communication with the bronchial lumen was retrospectively suspected. Unfortunately, the absence of a positive bacterial culture of bronchoalveolar lavage fluid prevents us from confirming this hypothesis. Moreover, development of a cyst secondary to focal bronchiectasia following pulmonary infection cannot be ruled out. However, the dog had no evidence of pulmonary inflammation or infection on histology making a congenital origin more likely.

In conclusion, bronchogenic cysts should be included in the differential diagnosis of a rounded thin-walled radiolucent pulmonary lesion seen on thoracic radiographs of young dog with signs of pulmonary inflammation, particularly if it is a German shepherd dog. Although more advanced imaging technologies can aid in differentiating between possible causes, histopathology is necessary to obtain a final diagnosis. CVJ