Finally, fibroblast proliferation, scar formation, and contracture can occur and result in stenosis. Congenital stenosis has two main types, membranous and cartilaginous. In membranous stenosis, fibrous soft-tissue thickening is caused by increased connective tissue or hyperplastic dilated mucus glands with absence of inflammation. Membranous stenosis usually is circumferential and may extend upward to include the true vocal folds. In cartilaginous stenosis, a thickening or deformity of the cricoid cartilage most commonly occurs, causing a shelflike plate of cartilage and leaving a small posterior opening.
Cartilaginous stenosis is less common than membranous stenosis.
Acquired subglottic stenosis is secondary to localized trauma to subglottic structures. Usually, injury is caused by endotracheal intubation or high tracheostomy tube placement. If irritation persists, the original edema and inflammation progress to ulceration and granulation tissue formation. This may or may not involve chondritis with destruction of the underlying cricoid cartilage and loss of framework support. When the source of irritation is removed, healing occurs with fibroblast proliferation, scar formation, and contracture, leading to stenosis or complete occlusion of the airway.