Semilobar holoprosencephaly with midline 'seam': a topologic and morphogenetic model based upon MRI analysis

Area of Science:

• Neuroanatomy
• Developmental Neuroscience
• Medical Imaging

Background:

• Holoprosencephaly (HPE) is a spectrum of brain malformations due to failed forebrain division.
• Semilobar HPE represents an intermediate form with specific midline structural anomalies.
• Understanding the precise anatomic features is crucial for diagnosis and research.

Purpose of the Study:

• To describe the common MRI-based anatomic features of semilobar holoprosencephaly.
• To define a consistent pattern of topological anomaly in affected human brains.
• To correlate specific structural abnormalities with overall telencephalic growth.

Main Methods:

• Magnetic Resonance Imaging (MRI) analysis of seven human brains with semilobar holoprosencephaly.
• Detailed description of midline gray matter structures and ventricular morphology.
• Correlation analysis between the extent of midline anomaly and total telencephalic volume.

Main Results:

• A rostro-caudally aligned midline gray matter 'seam' was consistently observed, extending from the telencephalic-suprachiasmatic region to the callosal commissure.
• This seam formed the ventricular roof, comprising conjoined caudate/accumbens nuclei rostrally and bridging neocortex caudally.
• Absence of fornix and septal nuclei, with open septal choroid fissures, contrasted with normal temporal hippocampal formation and closed temporal choroid fissures.
• Total telencephalic growth strongly correlated with the length of the abnormal midline segment.

Conclusions:

• The observed topological anomaly in semilobar HPE is confined to the midline telencephalic evagination region.
• Findings suggest a graded failure of rostral to caudal specification in the midline rostral telencephalon.
• The study provides a detailed anatomic framework for understanding semilobar holoprosencephaly.