Isolated Fornix Infarction with Damage to the Limbic System as a Cause of Persistent Amnesia: A Case Report

BACKGROUND The fornix is a white matter tract bundle that acts as the major output of the hippocampus and is an important component of the Papez circuit. We present an instructive imaging case of sudden onset of persistent amnesia due to selective ischemic damage of the anterior fornix. CASE REPORT A 54-year-old Japanese male came to our attention for a sudden onset of retrograde amnesia, associated with severe anterograde amnesia. The brain magnetic resonance imaging demonstrated a bright diffusion restriction, which was associated with swollen fornices bilaterally. His symptoms gradually improved, but episodic memory impairment still persisted after 1 month. The coronal T1-weighted MPRAGE (magnetization-prepared rapid acquisition with gradient echo) sequence clearly showed disruption of the left anterior fornix. Diffusion tensor tracking showed decrease in the density of entire fiber tracts on the Papez circuit as well as location of the left fornix. CONCLUSIONS When dealing with sudden, persistent amnesia associated with small fornix infarction, it is prudent to consider the possibility of tract damage along with limbic system damage using MPRAGE sequence.