Transient Amnesia Episodes Due to Isolated Unilateral Fornix Infarction

A 72-year-old man developed fluctuating episodes of confusion, apathy, and transient memory disturbance on the third postoperative day following an emergency splenectomy for splenic rupture. He had no focal neurological deficits but experienced recurrent confusional states lasting from 10 minutes to 4 hours, accompanied by anxiety, reduced speech output, and retrograde amnesia. Between the episodes, the patient was fully alert and oriented. Laboratory tests revealed postoperative leukocytosis and thrombocytosis related to an underlying myeloproliferative disorder. Brain magnetic resonance imaging (MRI) revealed a small diffusion-restricted lesion in the right column of the fornix, consistent with acute lacunar infarction, and chronic periventricular ischemic changes [Figure 1]. Low-molecular-weight heparin was administered. Follow-up MRI performed 10 days later showed complete resolution of diffusion restriction, and at the 1-month follow-up, his neurological and cognitive examinations were entirely normal.Figure 1: Acute right fornix lacunar infarction in a 72-year-old man with transient amnesia episodes. The lesion appears slightly hypointense compared to the gray matter on the T1-weighted image (arrow) (a) and hyperintense on the T2-weighted image (arrow) (b). Diffusion-weighted imaging (DWI) shows hyperintensity (arrow) (c) with a corresponding hypointense signal on the apparent diffusion coefficient (ADC) map (arrow) (d), consistent with restricted diffusionIsolated infarction of the fornix is exceedingly rare and typically involves both columns, resulting in acute and persistent amnestic syndromes. The fornix, a key white matter tract connecting the hippocampus and hypothalamus within the Papez circuit, plays a pivotal role in episodic memory formation and retrieval.[1] Its vascular supply arises from the subcallosal artery, a perforating branch of the anterior communicating artery that also nourishes the genu of the corpus callosum and the bilateral subcallosal regions. Unilateral involvement is rare and remains poorly defined in the literature. The clinical presentation in this case differs from the classical amnestic syndrome of subcallosal artery infarction, which usually causes bilateral fornix involvement and persistent memory loss.[2] To date, only a few unilateral cases have been reported, all on the left side, presenting with either prolonged anterograde amnesia or transient global amnesia.[3,4] The brief and reversible nature of the symptoms in our patient suggests that partial disruption of the Papez circuit may lead to transient cognitive dysfunction without permanent memory impairment. Hemodynamic instability following hemorrhage and emergency surgery likely contributed to the ischemic injury. In conclusion, this case highlights an exceptionally rare example of isolated unilateral fornix infarction with an unusual but reversible clinical course. While isolated fornix infarction typically presents bilaterally with acute amnestic syndrome, unilateral involvement may result in transient and diverse cognitive disturbances. Awareness of this entity and its imaging features is crucial because early recognition can prevent misdiagnosis and unnecessary investigations. Declarations The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.