Two cases (a cat and a dog) illustrating computed tomographic features distinguishing an accessory lung lobe mass from a caudal mediastinal origin

Abstract

A seven-year-old female Chinchilla cat and a 13-year-old male Cocker Spaniel were presented to Dick White Referrals for respiratory difficulties and cough, respectively. Based on radiographic and CT findings, including the midline location of the lesion and its mass effect on mediastinal structures, a caudodorsal mediastinal mass was considered more likely than a pulmonary origin in both cases. However, further investigations in the form of thoracic ultrasound and ultrasound-guided fine needle aspirates in the first case and histopathology in the second, revealed the presence of an accessory lobe pulmonary carcinoma in both cases. Retrospective review of these cases allowed identification of CT features that can be used to distinguish mediastinal and accessory lung lobe masses in future cases, including absence of part or all of the accessory lobe and its lobar bronchus, presence of gas in the lesion and the shape of the lesion mimicking a lung lobe.

Primary mediastinal spindle cell sarcoma in a dog

“…Similarly, some pulmonary masses can be misidentified as mediastinal on imaging. For example, a recent case report described two cases of caudal thoracic masses originating from the accessory lung lobe, which were originally thought to be most likely mediastinal in origin on CT imaging 20 …”

“…For example, a recent case report described two cases of caudal thoracic masses originating from the accessory lung lobe, which were originally thought to be most likely mediastinal in origin on CT imaging. 20 It is likely that the acute decompensation and subsequent euthanasia of the patient was due to either regrowth of the original mass or pulmonary metastasis resulting in the soft tissue mass identified on thoracic radiographs. The original mass displayed several characteristics that could be suggestive of a shorter median survival time, such as a high mitotic count, high histological grade and poor cell differentiation.…”