Accessory lung lobe carcinoma mimicking a caudal mediastinal paraoesophageal abscess in a dog

Abstract This case highlights an accessory lung lobe carcinoma with radiographic and computed tomography characteristics similar to mediastinal paraoesophageal abscessation. Initial radiographs suggested an increased soft tissue opaque structure within the caudal thorax. Thoracic computed tomography suggested the presence of a caudal mediastinal paraoesophageal abscess; however, an accessory lung lobe mass with adherence to surrounding structures was identified following a lateral thoracotomy. This patient recovered well from surgery, but ultimately continued to have clinical signs related to the diagnosed neoplasia, and was humanely euthanased approximately 8 weeks after surgery.