Radioanatomy of upper airways in flexion and retroflexion of the neck.

Ten flexion-retroflexion radiographs of the cervical spine (in lateral projection) were utilized to study anatomical configuration and topography of the upper air passages in these two positions. Measurement of AP diameters revealed narrowing in flexion and widening in retroflexion, being maximal at the region of the epiglottis, and minimal at the regions of larynx and trachea. The distance from the pharyngeal attachment of the skull-base, to the upper chest aperture proved to be markedly greater in retroflexion than in flexion. As the pharynx virtually does not change its length during these movements, it is drawn up (with respect to the upper chest aperture) in retroflexion, and pushed down in flexion, over a mean distance of 42 mm. The up and down movement of the upper part of the trachea is slightly less: 38 mm. No correction for radiological magnification of 15-20%.