Where is the glottis? 29 April 2012 Sir, We have noted the continuing controversy of the clinical definition of the glottis with interest. Reviewing the litera- ture, descriptions of the glottic region are confusing, which is problematic as it negatively impacts on the diag- nosis and staging of laryngeal neoplasia, thus preventing the development of standards of care for their treatment. The current edition of TNM guidelines contain no clear definitions of accepted boundaries. 1 The division of the larynx into supraglottis and glottis is logical on clinical and pathological grounds. Embryo- logically, the ventricle separates the upper parts of the larynx, derived from the lower pharynx, from the glottic and subglottic regions, developed from the upper tra- chea. 2 The upper limit of the glottis is therefore widely accepted as the apex of the ventricle. 2 Some argue that a separate classification of the glottis and subglottis is not indicated. 2 Moreover, there is no consensus as to the transition point between the glottis and subglottis. Various bodies demarcate 5 mm below the free edge of the true vocal folds (TVFs) or 10 mm below the apex of the ventricle. 1,2 The National Cancer Institute in conjunction with the American Joint Com- mittee on Cancer (AJCC) and American Association of Otolaryngology advise that the subglottis ‘begins 10 mm below the vocal cords.’ Anatomists describe the boundary as that of the infe- rior arcuate line (the border between the squamous epi- thelum of the vocal fold and high columnar epithelium of the subglottis) which is of variable distance from the vocal folds. 3 Historically, in 1975, Bryce demarcated the border his- tologically by the conus elasticus, which originates from the upper margin of the cricoid and extends to the vocal ligaments of the true vocal folds. 4 The elastic laminae insert posteriorly on the vocal processes of the arytenoids and fuse anteriorly to form the cricothyroid membrane. The posterior vocal folds are about 5 mm thick, tapering to 1 mm at the anterior commissure. This zone of vari- able thickness inferior to the upper free margin consti- tutes the undersurface of the true vocal folds and, despite Bryce’s work, has been excluded from definitions by most authors, instead using either 5 mm or 10 mm imaginary circles below the level of the true vocal folds. 4 The controversy is further deepened by the lack of research into the lymphatics of this oft-neglected region inferior to the vocal folds. Studies have elucidated that the supraglottic and subglottic portions of the larynx have very rich lymphatic networks; there is no lymphatic vessel in the free margin of the vocal cord; the superior surface of the vocal cord has several lymphatic vessels running paral- lel to the free margin of the cord; the inferior surface of the vocal cord has a rich lymphatic network and that the lymphatic networks in the superior and inferior surfaces of the vocal cord appear as two different patterns. 5 It has also been reported that the posterior commissure serves as an important interconnection site between supraglottic and subglottic lymphatic networks, implying that using lym- phatics as a source of definition is less robust. 5 More work is required in this area as appreciating lymphatic drainage is essential for clinicians to diagnose, grade, prognosticate and surgically manage laryngeal cancer. It is important to differentiate between sites as tumours behave differently therein, in part due to differing lym- phatics. Employing a standard definition would enable better planning and comparisons of research looking at the behaviour of laryngeal cancers, their spread and response to treatments. Any description of the boundaries of the glottis must take into account the needs of the radiologist, pathologist and surgeon. Modern high-definition CT imaging can determine the apex of the laryngeal ventricle alongside the medial limit of the vocal fold and as a result, mea- surements can be made caudally from these landmarks. There has to be an agreement internationally on the lower border of the glottis and it will be one of the first tasks of the newly formed British Laryngological Associa- tion (BLA) to present a view on the subject to the other international Laryngological and Head and Neck Associa- tions so that a consensus can be reached. Virk, J.S. & Sandhu, G. ENT Department, Charing Cross Hospital Imperial College Healthcare NHS Trust London, UK. E-mail: j_v1rk@hotmail.com References 1 Sobin L., Gospodarowicz M.K. & Wittekind C. (2009) Head and Neck Tumours. In TNM Classification of Malignant Tumours, 7th edn, pp. 22–62. Springer, New York, NY 2 Buckley J.G. & Maclennan K. (1999) Cancer spread in the larynx: a pathologic basis for conservation surgery. Head Neck 22, 265–274 CORRESPONDENCE: LETTERS Correspondence 253 Ó 2012 Blackwell Publishing Ltd • Clinical Otolaryngology 37, 245–255