Abstract â–¡ 169

Several studies have asserted that asphyxia is the cause of death in SIDS. The seemingly silent death of SIDS victims suggests that the larynx is the probable site of obstruction conducive to the asphyxia.

Our recent studies have focused on the oldest theory regarding SIDS, namely that the upper airway obstruction is the fatal terminal event in this sudden, unexpected and tragic occurrence. The upper airways and especially the larynx in SIDS and non-SIDS infants dying suddenly and unexpectedly were thoroughly examined by us. No macroscopic changes were detected in the upper airways of our SIDS cases, yet the microscopic examination showed pronounced thickening in the basement membrane of the stratified squamous epithelium of the vocal cords. Invariably BMT was absent in the vocal cords of infants dying suddenly from known causes other than SIDS. BMT itself cannot be the direct cause of death, for it is probably a chronic, slowly developing process without clinical symptomatology. We suggest death may result from chronic recurrent episodes of respiratory insult developing into a laryngeal obstruction, e.g. vocal cord spasm or laryngeal collapse. It is likely that BMT is the outcome of this recurrent irritation which is reflected by our immunohistologic findings of elevated Coll.IV in the thickened BM and fibronectin depositions in the sub-mucosa.

In the absence of morphological pathology in the upper airways of our studied SIDS cases, we resorted to an investigation of the relative position of their anatomical structures in mid-sagittal sections and lateral head and neck radiographs obtained from human infants and fetuses. We have demonstrated that cervical lordosis opens the veloepiglottic 'sphincter' and enables oral ventilation by reducing oral airway resistance.

Findings of these studies offer a strong case for focusing further attention on the upper airways. While the posture of the infant in the crib may be strongly contributory to the fatality in SIDS - the histological findings in the 'vocal' cords (resembling the heavy smoker's cords) suggest it should prove fruitful to investigate the larynx as the possible site for clinically unexpected obstruction leading to sudden fatality in SIDS.