The quadrangular membrane is a sheet of fibroelastic tissue forming the lateral walls of the supraglottic larynx, extending from the lateral epiglottis and aryepiglottic folds to the arytenoid and thyroid cartilages. Its inferior free border forms the vestibular ligament (false vocal cord ligament), which is the structural framework of the vestibular fold (false vocal cord). It defines the supraglottic compartment between the laryngeal inlet and the glottis.
Forms the lateral wall of the supraglottic larynx and vestibule, provides structural support for the aryepiglottic folds and vestibular folds (false cords), and contributes to the fibroelastic framework that maintains laryngeal shape.
The quadrangular membrane and its inferior vestibular ligament border are relevant in supraglottic laryngectomy, where the procedure preserves the true glottis below while removing the supraglottic structures above including the quadrangular membrane, epiglottis, and vestibular folds. Laryngocoeles arise from dilatation of the laryngeal saccule (appendix of the laryngeal ventricle) that lies between the quadrangular membrane and the thyroid cartilage, producing a soft fluctuant swelling at the anterior neck that increases with the Valsalva manoeuvre.
Dilatation of the laryngeal ventricle saccule between the quadrangular membrane and the thyroid cartilage produces an internal laryngocele visible as a supraglottic submucosal swelling causing muffled voice and dyspnoea, or an external laryngocele presenting as a neck swelling through the thyrohyoid membrane, managed by endoscopic or external surgical excision.
