[Computerized morphometric analysis of the fiber composition of the upper and lower laryngeal nerves in humans].

Phonation troubles often arise after surgical operations on the antero-lateral region of the neck in which the recurrent laryngeal ILN), was respected. This fact allows to consider the possibility that the superior laryngeal nerve (SLN), contains also fibres responsible of the motor innervation of some intrinsic muscles of the larynx. According to the suggestion that the fibre-analysis may permit to distinguish a motor from a sensory nerve (Tomasch and Schwarzacher), a computerized morphometric analysis on the fibres of the superior and inferior laryngeal nerves in the man was carried out. The nerves investigated were taken away from five patients subjected to a total laryngectomy. The fibre perimeter and the maximum diameter were evaluated in 1500 fibres in each nerve. The histograms of the obtained data shows that: 1) Two groups of fibres are distinguishable in the SLN: the first is composed by small diameter fibres that show one spike for both the parameters considered. The second group of larger fibres shows a lower spike with a larger basis. 2) In the ILN only a spike corresponding to the greatest fibres we observed for both the parameters considered. In conclusion it seems that the number of fibres of large diameter present in the SLN can justify a motor function of this nerve for some intrinsic muscles of the larynx other than the cricotiroideus.