Introduction
Corpus callosum malformation includes complete agenesis, partial agenesis (hypogenesis), thin corpus callosum (hypoplastic) and thick corpus callosum. It can occur as an isolated finding, but is more commonly associated with central nerve system (CNS) anomalies. The prognosis varies considerably depending on the presence of associated anomalies, therefore it is needed to evaluate of combined anomalies. Diffusion tensor imaging (DTI) is a useful tool to visualize the altered anatomical fiber connections. We report a case of corpus callosum hypoplasia that was evaluated by DTI and tractography.
Case report
A 17-month-old baby visited our clinic for developmental delay, who was found to have callosal abnormality at prenatal sonography. He was born full-term (39weeks) and had no specific perinatal history accounted for the callosal abnormality. Brain magnetic resonance imaging (MRI) study performed at 3 months of age demonstrated that thin underdeveloped corpus callosum and asymmetric mild dilatation of left lateral ventricle. He needed one hand support during gait with poor trunk balance and was tilted to right side while sitting on a bench. In addition to gross motor function, expressive and receptive language function was also mildly delayed. He saw left side more frequently with tilting head to right side and he was left handed. Owing to suspected visuo-motor problem, we referred him to ophthalmologist; however, there was no definite structural abnormalities. DTI was performed to reveal abnormalities in white matter fiber structures. In tractography based on DTI, there is no fiber to connect primary motor cortex and anterior pons. We assumed that the fiber tracking from primary motor cortex was corticospinal tract (CST), that was descending in the location of reticular formation at the pontine level (Fig.1). Arcuate fasciculus was poorly reconstructed in both sides, a connection between Broca’s area and Wernicke area was not well visualized (Fig.2). And left uncinate fasciculus was poorly reconstructed compared to right side. For the retro-geniculate visual pathway, Bilateral optic radiation had decreased tract volume and a poor integrity. The temporal part of left optic radiation was poorly reconstructed compared to contralateral side. Bilateral inferior longitudinal fasciculus (ILF) was also poorly reconstructed, especially in the left side (Fig.3).
Conclusion
Above-mentioned DTI findings were correlated with clinical features of delayed development in the gross motor and language, and asymmetric visuo-motor functions. Corpus callosal hypoplasia might not the only abnormality though plain MRI shows this finding. We revealed several abnormalities in white matter fiber structures which are informative to explain his clinical symptoms. |
