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Neuroradiology Case of the Week

Case 403

April 2009

Hisao Nakamura, MD

Clinical Presentation: Ultrasound performed of a newborn of 31th weeks gestation revealed the absence of the corpus callosum and an MRI was requested for the further evaluation.

Imaging Findings: Middle interhemispheric holoprosencephaly and lissencephaly.

Diagnosis: Middle interhemispheric holoprosencephaly

Discussion: The holoprosencephalies are a group of disorders characterized by a failure of differentiation and cleavage of the prosencephalon. DeMyer has divided holoprosencephaly into three subcategories: alobar, semilobar, and severities. These categories are useful for classifying holoprosencephalies of different severities. The embryogenesis of holoprosencephaly has been not clearly elucidated. The disorder is postulated to result from a deficient or defective cranial mesenchyme with subsequent lack of induction and differentiation of basal midline structures. The deficiency of mesenchyme may be responsible for the hypoplasia of the premaxillary segments of face and the falx cerebri, the lack of differentiation of the telencephalon from diencephalon, the lack of separation of the telencephalon from the diencephalon, the lack of separation of the telencephalon into two hemispheres, and the common lack of cortical organization in those regions where the cortex is formed. This condition that the interhemispheric fissure is formed frontally and occipitally, but the hemispheres are fused in the posterior frontal and parietal regions is termed holoprosencephaly with middle interhemispheric fusion, or syntelencephaly. It is classified as semilobar holoprosencephaly. Concerning the lissencephaly, the relationship is uncertain at this time.

References:

1. Barkovich AJ. Pediatric Neuroimaging. Philadelphia, Lippincott Williams and Wilkins, 2000:318-323.
2. DeMyer W, Zeman W, Palmar CG. The face depicts the brain: Diagnostic significance of median facial anomalies for holoprosencephaly (arhinencephaly) with median cleft lip and palate. Pediatrics. 1964 Aug;34:256-63. [PubMed]