Sudden and Unexpected Death in A 2-Month-Old Infant with Congenital Tracheal Stenosis and Bilateral Arcuate Nucleus Agenesis

Background: Congenital tracheal stenosis (CTS) caused by complete tracheal rings and absence of the pars membranacea is rare and potentially lethal in infancy. Agenesis or hypoplasia of the medullary arcuate nucleus (ARC), a chemosensitive component of the ventral medullary surface, has been implicated in disordered respiratory control in sudden perinatal and infant deaths. The coexistence of these two abnormalities is uncommon. Case: A 2-month-old male infant, apparently healthy, was found unresponsive on his parents’ bed in the early morning. The pregnancy was uncomplicated, aside from maternal obesity and tobacco use. Given a context compatible with either sudden natural death or accidental overlay/suffocation, a full forensic autopsy was ordered. An external examination showed diffuse cyanosis and minor superficial abrasions without significant trauma. An internal examination revealed heavy, congested lungs with petechiae and cerebral edema. The heart and great vessels were anatomically normal, and the ductus arteriosus was closed. Histological examination demonstrated congenital tracheal stenosis characterized by complete cartilaginous rings with absent pars membranacea and bilateral agenesis of the medullary arcuate nucleus. The overall findings supported an acute hypoxic–ischemic event during sleep. Conclusions: This case documents a rare, isolated CTS with complete rings and absent pars membranacea coexisting with bilateral ARC agenesis, providing a plausible organic substrate (“cum materia”) for sudden unexpected death in infancy (SUDI). It underscores the importance of standardized neuropathological examination with serial brainstem sections in SUDI investigations and of distinguishing explained SUDI from sudden infant death syndrome (SIDS), which remains unexplained after complete investigation (“sine materia”).