Laryngeal anatomical variants and their impact on the diagnosis of mechanical asphyxias by neck pressure.

The aims of this investigation were to determine the characteristics and prevalence of anatomical variants of the larynx apparatus and to evaluate the impact of these variants on the accurate diagnosis of laryngeal fractures. A population-based study was carried out, analyzing a series of 207 consecutive autopsied cases in the Institute of Legal Medicine of Galicia (Northwestern Spain). The prevalence of triticeal cartilage was 52.7% and that of agenesis of thyroid horns 10%. Calcification of the stylo-hyoid ligament accounted for 1.4%. We identified three new anatomical variants: the terminal segmentation of the thyroid horns (11.6%), ectopic superior thyroid horns (8%) and lateral thyrohyoid ossification (5.3%). These three names, based on anatomical criteria, are the author's proposal to solve the lack of uniformity in the designation of these variants. Agenesis of thyroid horns were related to the presence of ectopic superior thyroid horns in 93% of cases, either uni or bilateral. The combination of variants was present in 6.8% of the cases, being the terminal segmentation of the thyroid horns in association with triticeal cartilage the most frequent (3.8%). The probability of misdiagnosis due to the presence of anatomical variations in deaths by pressure on the neck was high in this population (71.5%). The prevalence of triticeal cartilage in more than half of the sample, determined an important rate of potential errors (46.4%), followed by the mistaken diagnoses induced by terminal segmentation of thyroid horns (7.3%) and by ectopic superior thyroid horns (6.3%). The likelihood of a misdiagnosed laryngeal fracture was greater if the thyroid cartilage was affected, with a higher proportion of false positives comparing to the hyoid bone (p<0.001). The higher frequency of thyroid fractures in neck pressure together with the prevalence and location of triticeal cartilage on the lower third of the lateral thyrohyoid ligament are the main reasons for these results. Further studies should be done with larger samples to expand epidemiological data and consolidate these results and their influence on the diagnosis of mechanical asphyxias.