Trimyelia with divergent cord pathways and three foramina magni.

ABSTRACT

OBJECT We report the rare finding of trimyelia with divergent cord pathways in a 33 5/7-week-old fetus who died shortly after spontaneous vaginal delivery. METHODS: The main autopsy findings were three separate and distinct spinal cords, arising from the medulla and exiting through three separate foramina magni. The two lateral cords coursed toward each upper extremity and the medulla split into two halves that rejoined to form a central cervical cord. Further evaluation of this anomaly revealed agenesis of the cerebellar vermis and cystic dilation of the fourth ventricle. Microscopic cross-sections of the two lateral cords demonstrated well-formed central canals, white matter, and central gray with motor neurons. Sections of the abnormal mid-cervical cord demonstrated abnormally structured cord parenchyma without central canals. CONCLUSIONS: Some features were consistent with iniencephaly; however, defects of the occipital bone, anterior spina bifida, and shortening of the spinal cord were absent. Although agenesis of the cerebellar vermis and cystic dilation of the fourth ventricle indicate Dandy-Walker syndrome, other features such as hydrocephalus, agenesis of the corpus callosum, infundibular hamartomas, and malformations of the inferior olives or an occipital encephalocele were absent. The possible pathogenesis of this intriguing pathological entity is briefly discussed.