Very rare. It can present as a mirror (but non-functional) structure of the actual larynx, a duplication of the epiglottis or the presence of laryngeal remants (duplication of the vocal cords, for example).

Anesthetic implications:

difficult identification of the effective laryngeal lumen

References : 

-        Wong TLW, Baki MM, Ishak S, See GB.
A bizarre case of accessory larynx in an infant with OEIS syndrome.
Int J Pediatr Otorhinolaryngol Extra 2018 ; 114 : 143-7

Updated: November 2018