I would like to congratulate Tsuiki and his colleagues on their recent publication examining the upper airway imbalance of airway soft tissue and craniofacial size.1They have postulated a caudal expansion of excessive soft tissue from the maxilla-mandibular enclosure downwards into the submandibular space. This leads to a caudal displacement of the hyoid and an increase in the mandibulo-hyoid distance. Previously, some of these authors2have focused on an increased submandibular angle leading to difficult tracheal intubation.

Tsuiki’s work is in agreement with Chou and Wu’s work3,4which proposed that a relatively short mandibular ramus and a caudally positioned hyoid causes a large “hypopharyngeal tongue.” This in turn is associated with both obstructive sleep apnoea and difficult tracheal intubation.

Tsuiki stated that one of the limitations of their study was that it involved only Japanese patients. The study by Lam and workers5that is referenced by Tsuiki described a crowded posterior oropharynx and a steep thyromental plane (that is an increased submandibular angle) in Hong Kong Chinese and Caucasians predicts obstructive sleep apnoea though the Chinese group had a higher Mallampatti score, shorter thyromental distance and increased thyromental angle.

Horton and workers in 1990 described a “peardrop” phenomenon seen with x-ray where the laryngoscopy blade causes compression of the tongue and its postero-inferior displacement results in airway obstruction. The epiglottis is also displaced posteriorly against the posterior wall of the pharynx causing difficult tracheal intubation.

It would therefore appear that there is a now a link between an anatomical relationship of a low lying hyoid, increased submandibular angle and difficult tracheal intubation.

Royal Brisbane and Women’s Hospital, Brisbane, Australia. french9a@yahoo.co.uk

Tsuiki S, Isono S, Ishikawa T, Yamashiro Y, Tatsumi K, Nishino T: Anatomical balance of the upper airway and obstructive sleep apnea. Anesthesiology 2008; 108:1009–15
Suzuki N, Isono S, Ishikawa T, Kitamura Y, Takai Y, Nishino T: Submandible angle in nonobese patients with difficult tracheal intubation. Anesthesiology 2007; 106:916–23
Chou HC, Wu TL: Mandibulohyoid distance in difficult laryngoscopy. Br J Anaesth 1993; 71:335–9
Chou HC, Wu TL: Large hypopharyngeal tongue: a shared anatomic abnormality for difficult mask ventilation, difficult intubation, and obstructive sleep apnea? Anesthesiology 2001; 94:936–7
Lam B, Ip MS, Tench E, Ryan CF: Craniofacial profile in Asian and white subjects with obstructive sleep apnoea. Thorax 2005; 60:504–10