Dual white matter pathology in fetal holoprosencephaly featuring concurrent malformative and destructive features: A...

Holoprosencephaly (HPE) is a classic brain malformation involving defective forebrain induction and patterning. Cases of HPE bearing white matter abnormalities have not been well documented, with only rare cases exhibiting hypoxic-ischemic damage. However, neuroradiologic studies of HPE using diffusion tensor imaging have suggested the presence of white matter architectural disarray. Described in this case series are the clinicopathologic features of 8 fetuses with HPE who underwent autopsy at BC Children's Hospital. All 8 cases exhibited subacute to chronic, periventricular leukomalacia (PVL)-like white matter pathology, with 7 of 8 cases also demonstrating aberrant white matter tracts, one of which manifested as a discreet bundle crossing the midline within the ventral aspects of the fused deep gray nuclei. In 6 of these 7 cases, the PVL-like pathology resided within this aberrant white matter tract. Original workup, alongside an additional HPE-focused next-generation sequencing panel identified a likely etiologic cause for the HPE in 4 cases, with an additional 2 cases exhibiting a variant of unknown significance in genes previously suggested to be involved in HPE. Despite our in-depth clinicopathologic and molecular review, no unifying etiology was definitively identified among our series of fetal HPE bearing this unusual pattern of white matter pathology.