Agenesis of the corpus callosum

Brian H Le MD (Dr. Le of Reading Hospital has no relevant financial relationships to disclose.)
Harvey B Sarnat MD FRCPC MS, editor. (Dr. Sarnat of the University of Calgary has no relevant financial relationships to disclose.)
Originally released July 5, 1994; last updated September 1, 2017; expires September 1, 2020

This article includes discussion of agenesis of the corpus callosum, callosal agenesis, agenesis of the corpus callosum, hypoplasia of the corpus callosum, and agenesis and hypoplasia of the corpus callosum. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Agenesis of the corpus callosum may occur as an isolated event or as part of dozens of developmental and dysmorphic syndromes. Although affected patients may exhibit few obvious neurologic functional deficits, the absence of the corpus callosum, a structure responsible for interhemispheric connections, does carry consequences with respect to information processing and language functions. In this article, the author discusses attempts to classify and characterize agenesis of the corpus callosum based on morphologic and molecular findings.

Key points

 

• In patients with primary or isolated agenesis of the corpus callosum, the intelligence quotient (IQ) may be normal, but impaired processing between the hemispheres can be demonstrated by detailed psychometric testing and may manifest as deficits in learning and recall; associations with autism spectrum disorder have been of particular interest in recent years.

 

• In cases where agenesis of the corpus callosum occurs as part of a syndrome or larger malformative cluster, the clinical scenario is usually dominated by the primary condition.

 

Hypertelorism is the most common recognizable facial abnormality in patients with agenesis of the corpus callosum who have abnormal facial features.

 

• Hypoplasia of the corpus callosum exists when all the components of the callosum are present, but structure is thinner than normal. This represents a global defect of brain development, whereas agenesis of the corpus callosum may be an isolated abnormality.

 

• Agenesis of the corpus callosum can be diagnosed or suspected in the antenatal period based on axial view ultrasound findings; careful examination of imaging findings and, if applicable, of brains from autopsy are essential in characterizing the specific callosal abnormality.

 

• Many genetic alterations have been etiologically linked to agenesis of the corpus callosum, both as an isolated developmental event as well as in the context of a syndromic cluster.

Historical note and terminology

The corpus callosum, the largest fiber tract in the brain, connects to the 2 cerebral hemispheres in order to facilitate the integration of motor and sensory information from the 2 sides of the body. Agenesis of the corpus callosum has been recognized pathologically for over 160 years, and descriptions of the various clinical manifestations continue to accumulate (Parrish et al 1979). Studies on the behavioral aspects of this condition have been reported since 1912 (Lassonde et al 1995; Jancke et al 1997).

The recognition and diagnosis of agenesis of the corpus callosum in the living patient, however, was not possible with any degree of certainty until the development of pneumoencephalography in the early part of the 20th century (Davidoff and Dyke 1934). Newer neuroimaging techniques used to demonstrate agenesis of the corpus callosum include cranial ultrasonography, CT, and MRI. With the advent of even newer MRI techniques such as diffusion tensor imaging and tractography (Wahl and Mukherjee 2009), the recognition of various forms of partial agenesis and hypoplasia of the corpus callosum has also become possible (Barkovich 1988; Schaefer et al 1991a).

The term "agenesis of the corpus callosum" is as old as the early pathologic descriptions. The use of the term "partial agenesis of the corpus callosum" is relatively new to the clinical literature, and the delineation of the diagnostic criteria for "hypoplasia" of the corpus callosum has only recently been accomplished concurrent with the use of computer-assisted analysis of MRI images (Schaefer et al 1990).

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