Congenital segmental absence of tracheal cartilaginous rings in two cats.

Tracheal disorders are uncommon in animals. Among congenital anomalies, segmental or complete absence of tracheal rings is described rarely in humans and in animals even less frequently. This report describes the clinical, gross and histopathological features of two cases of segmental absence of tracheal rings in cats and briefly reviews tracheal disorders. Cat 1 was a 1-year-old male mixed breed (Domestic Shorthair) that presented with a history of trauma and pneumothorax, followed by persistent respiratory distress and death despite treatment. Cat 2 was a 3-year-old male stray mixed breed (Domestic Shorthair) admitted with severe dyspnoea that died before therapy could be initiated. At necropsy, both cats showed an absence of cartilaginous rings in the distal third of the trachea, approximately 2 cm cranial to the carina. The affected segments measured 1 cm (cat 1) and 2 cm (cat 2) in length, with moderate to marked narrowing of the lumina. Cat 1 also had marked emphysema in the perirenal adipose tissue. Histologically, the cartilaginous rings were completely absent and replaced by vascularized fibrous connective tissue infiltrated by a small number of mixed inflammatory cells and loss of the respiratory epithelium in the affected segments. Pulmonary lesions included alveolar emphysema, congestion, haemorrhage and oedema in cat 1, and atelectasis, congestion and alveolar oedema in cat 2. Segmental absence of tracheal rings in cats appears to occur predominantly in the distal third of the trachea. Although rare, it should be considered as a differential diagnosis in cats presenting with respiratory distress.