By Rahul V. Pawar, MD

History

A 10-year-old boy underwent neuroimaging after suffering a single (witnessed) seizure while at school; a brief episode of “staring” was followed by generalized convulsions.

Past medical history was significant for pervasive developmental disorder with autistic features. The patient was born prematurely (36 weeks) secondary to fetal distress.

On exam, he was alert but nonverbal, demonstrated poor eye contact, and was unable to obey commands. Mood and affect also were abnormal.

Findings

Compared with an age-matched, normal-appearing corpus callosum (Figure B), midline sagittal T1-weighted imaging of this patient’s brain demonstrated diminutive caliber of the posterior thirds corpus callosal body and splenium (Figure A). On careful inspection, a clearly definable callosal rostrum was absent. Axial T2-weighted imaging (Figure C) and coronal T1-weighted imaging (Figure D) both confirmed thinning of the posterior callosal body and splenium, secondary enlargement of the superior vermian cistern, and relatively parallel orientation of the lateral ventricles.

Diagnosis

Partial agenesis of the corpus callosum

Discussion

Formation of the corpus callosum—the largest commissural white matter structure in the brain—is complex. Rakic and Yavovlev concluded that “development of the corpus callosum is preceded by the infolding of the dorsal part of the lamina reuniens of His (1904) in the region of the prospective hippocampus into a median groove, and by fusion of its banks into a massa commissuralis which becomes the bed for corpus callosum.”1

Agenesis of the corpus callosum has been defined as the most common cerebral malformation.2 It is generally accepted that the corpus callosum forms anterior to posterior, beginning with the genu, followed by the body, splenium, and finally the rostrum.3 Interestingly, Kier and Truwit have postulated the converse, reporting that the corpus callosum actually develops bidirectionally.4

Pediatric neuroimaging plays a seminal role in a comprehensive semiologic workup. With particular respect to the corpus callosum, MRI has a distinct advantage over CT since the intrinsic T1 hyperintensity of callosal myelin enables identification of subtle abnormalities.5 Images depicted were generated on the Philips Intera 1.5T MRI system.

Clinically, the presentation of corpus callosum agenesis is variable; the spectrum includes those who may be (relatively) asymptomatic as well as patients who suffer from severe mental retardation. A constellation of associated behavioral and psychiatric disorders have been reported, including mood disturbances, attention-deficit/hyperactivity disorder, and autistic features. Epilepsy is a frequent manifestation that presents during early childhood and is generally controllable with antiepileptic medications.6

— Rahul V. Pawar, MD, is a diagnostic neuroradiologist at Saint Barnabas Medical Center in Livingston, New Jersey, and a consultant for Philips Healthcare North America.