Term of the day: HIMAL-Hippocampal Malrotation

Temporal lobe epilepsy is the most common form of partial epilepsy, and hippocampal sclerosis is a common radiologic finding. It is also possible that developmental abnormalities of the hippocampus may predispose or otherwise contribute to epileptogenesis. In normal fetal development, the hippocampus inverts within the medial temporal lobe. In cases of hippocampal malrotation (HIMAL), hippocampal inversion fails to occur.  Further reading : AJNR 2009 30: 1571-1573 . If anyone has a characteristic image and wants to share here, please email me the images and we will acknowledge the contributor on this blog.

Described by Barsi et al, the criteria for HIMAL include :

Ø  Unilateral involvement and incomplete rotation of a hippocampus that is normal in size and signal intensity, but abnormally rounded in shape so that the dimensions in either direction are equal, with blurred inner structure.

Ø  In addition, ipsilateral findings of an atypical collateral sulcus angle and atypical position and size of the fornix were noted.

Ø  The normal collateral sulcus angle is flat at the level of the body and tail of the hippocampus. In cases of HIMAL, the collateral sulcus angle is more vertical.

Ø  The normal position of the fornix is symmetrical. In cases of HIMAL, the fornix can be unilaterally downwardly displaced.

Ø  The corpus callosum is normal, and the temporal lobe remains normal in size, though the temporal horn may appear enlarged.