2025 – Abstract 13

Presenter

Dr. Stephanie Beldick is neuropathology resident at Western University in London, Ontario. She completed her Master’s at the University of Toronto, followed by medical training in the United States. Her research interests include basic and clinical investigations of neurodevelopmental processes.

Stephanie R. Beldick¹, Andrew Gao^2,3, Yael Fisher⁴, & Patrick Shannon^2,4

¹Department of Laboratory Medicine and Pathology, Western University, London, ON
²Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON
³University Health Network, Toronto, ON
⁴Mount Sinai Hospital, Toronto, ON

CanMEDS:
Medical Expert (the integrating role), Scholar

Brainstem cap dysplasias: pathology and novel descriptions

Abstract

Brainstem cap dysplasias are characterized by heterotopic axonal tracts coursing peripherally in the brainstem, identified by magnetic resonance imaging. However, there is a paucity of neuropathological descriptions of cap dysplasias. We therefore aimed to review the histopathology and expand the morphological spectrum of cap dysplasias. Three forms are described, including pontine tegmental cap dysplasia (PTCD), medullary tegmental cap dysplasia (MTCD), and anterior mesencephalic cap dysplasia (AMCD; a component of the Joubert syndrome). We describe a series of seven brainstem dysplasias with “cap” features from our autopsy practice: Two PTCD, one MTCD, two AMCD, and two undescribed forms. Both PTCD cases demonstrated hypoplasia of rhombic lip derivatives and a dorsal pontine tegmental tract. The MTCD case demonstrated hypoplastic rhombic lip derivatives, large axonal tracts in the medullary fourth ventricle and coursing along the ventrolateral medulla, post-necrotic tegmental calcifications, and spinal cord anomalies. The two AMCD cases demonstrated Joubert syndrome features with axonal bundles crossing the interpeduncular fossa as leptomeningeal heterotopias. The two additional cases of undescribed “cap” forms have a prominent tectal cap. In one case, this is formed by aberrancy in the pathway of the inferior colliculi brachia, and in the other it is formed by incomplete duplication and fusion of midbrain with cerebellar elements, and heterotopic dorsal and lateral medullary tracts, in the context of a complex supratentorial malformation. In summary, “cap dysplasia” should be considered a morphological descriptor rather than limited to axonal pathology or a particular disease entity, as a diversity of pathological developmental processes are evident.