Abstract
Unexpected infant deaths often present complex diagnostic challenges, where clinical histories alone may not reveal the underlying etiology. Autopsy examination remains essential in identifying uncommon neuropathologic findings that contribute to mortality. A two-month-old male infant was found unresponsive in his car seat (day 0) and succumbed four days later despite intensive medical intervention. His medical history included neonatal respiratory distress with two prior admissions to the neonatal intensive care unit. Autopsy was conducted one day after death (approximately five days postictus), revealing ectopic lymphoid tissue within the medulla of the brainstem, accompanied by subacute infarction and early necrosis. Additional systemic findings included acute splenic infarction, colonic inflammation, and focal acute bronchiolitis. Genetic analysis (collected two days postictus) identified a heterozygous SLC4A3 missense variant, though it was not deemed contributory to death. This case describes a rare neuropathologic finding of ectopic lymphoid tissue within the brainstem of an infant, suggesting an underrecognized cause of death. It underscores the indispensable role of autopsy in elucidating rare pediatric neuropathologies and broadening the understanding of infant mortality mechanisms.