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Lateral thoracic radiograph

VD thoracic radiograph

History

Last week ate a bone. The day following the dog was very unwell, painful and lethargic. Now pyrexic. Unproductive retching. Still drinking. Endoscopy showed the caudal esophagus appeared to be externally obstructed extramurally and it could not be distended. The esophagus itself looked normal.

Radiography: A large, oblong soft tissue opacity structure is present in the caudal thorax between the carina and the diaphragm, dorsal to the caudal vena cava. In the VD view the soft tissue opacity structure is situated on midline in the region of the caudal mediastinum. Slight gas is present in the esophagus at the level of the base of the heart. Pulmonary parenchyma and vasculature appear normal.

A barium study shows a linear focus of contrast media in the caudal esophagus displaced towards the left of midline by the caudal mediastinal mass.

Differential diagnoses from radiography could include either a fluid-filled structure or soft tissue mass in the caudal mediastinum to the right side of the oesophagus. Dilation of the caudal oesophagus is unlikely based on the barium study.

Thoracic CT, soft tissue window

Thoracic CT, ST+C

Thoracic CT +C, lung window

CT (follow-up to radiographic study): A relatively homogeneous soft tissue density is present in the right middle lung lobe and the more ventral/dependent aspect of the right caudal lung lobe. There is a slight hazy increase in attenuation in the caudal aspect of the left cranial lung lobe. There is no evidence of mediastinal shift.

Caudal to the heart there is a fluid-filled, encapsulated structure with a dorsally/non-dependently situated gas-cap running along the right side of the esophagus. The esophagus itself is minimally distended. The gastro-esophageal junction appears within normal limits.

Metallic opacities are present in the mid-abdomen, likely representing barium within the small bowel.

Differential diagnosis

Paraesophageal fluid-filled structure, abscess/ diverticulum would be most likely. Aspiration pneumonia (from CT study).

Diagnosis

The referring veterinarians report that she did have a paraesophageal abscess causing severe fibrosis and adhesion of the lung to the esophagus as well. The surgeon tore a small hole in the lung in the process of getting the abscess sorted. They did not remove any lung. The patient has recovered well.

Discussion

This CT case was referred to our teleradiology service. Radiographs were obtained at a later date and were requested for use as teaching material. The clinical history, endoscopy findings and imaging studies were highly suggestive of a paraesophageal abscess or diverticulum resulting in external compression of the esophagus. The barium study shows the caudal mediastinal mass does not fill with contrast media and the caudal oesophagus is deviated more towards the left of midline. These findings are consistent with a paraesophageal structure (mass/cyst/abscess) rather than esophageal dilation.

In a recent paper (Brissot et al., Caudal Mediastinal Paraesophageal Abscesses in 7 Dogs. 2012) published in Veterinary Surgery the clinical, imaging, and surgical findings associated with caudal mediastinal paraesophageal abscesses was reported. Radiography showed caudal mediastinal enlargement in all cases. In some cases there was pulmonary consolidation and pleural effusion. CT showed a large fluid-filled structure in the midline extending from the caudal aspect of the heart to the diaphragm. This structure was closely associated with the esophageal wall. The esophagus was displaced dorsally and toward the left of midline, with flattening of the esophageal lumen. In one patient there were also changes consistent with cranial mediastinitis and inflammation of the ventral paraspinal cervical and thoracic muscles. None of the dogs had abnormalities of the oesophageal mucosa on endoscopic examination.

Nota: since publication of this case, this pathology has been described as paraesophageal empyema of the mediastinal serous cavity.

Gendron, K., McDonough, SP., Flanders, JA., et al. The pathogenesis of paraesophageal empyema in dogs and constancy of radiographic and computed tomography signs are linked to involvement of the mediastinal serous cavity. Vet radiol ultrasound 2018; 59(2), 169-179.