Abnormal tracheal morphology Anomalous tracheal cartilage An abnormality of the C-shaped rings of hyaline cartilage, normally 16 to 20 in number, that occupy the anterior two-thirds of the circumference of the trachea (the posterior portion of the ring is completed by fibrous and smooth muscle tissue). UMLS:C1863406 Abnormal tracheal cartilaginous ring HP:0004468