FINDINGS Figure 262-1. Coronal T2WI of the hippocampus obtained perpendicular to the long axis of the hippocampus. There is a rounded appearance of the left hippocampus (vertical arrow) compared with the transverse lie of the right hippocampus (chevron). The left collateral sulcus is verticalized (transverse arrow) compared with the transverse position of the right collateral sulcus (line arrow). Both hippocampi are of similar signal intensity.
DIFFERENTIAL DIAGNOSIS N/A.
DIAGNOSIS Left hippocampal malrotation (HIMAL).
DISCUSSION The major prerequisites for the diagnosis of HIMAL or as some would like to call it incomplete hippocampal inversion (IHI) on coronal T2WI obtained perpendicular to the long axis of the hippocampus are unilaterality of the lesion, abnormal round shape of the hippocampus, normal size and intensity of the hippocampus, verticalization of the ipsilateral collateral sulcus, and atypical position and size of the fornix with or without apparent enlargement of the ipsilateral temporal horn. All these findings are usually not fulfilled in every case. The two most constant findings are the round configuration of the hippocampus and the verticalization of the collateral sulcus. In our patient, the unilaterality and similar signal intensity criteria are also fulfilled. HIMAL is most often unilateral and left-sided. It is found in all ages without gender preference.
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