Amnestic syndrome of the subcallosal artery describes an acute amnestic syndrome secondary to ischemic stroke affecting the subcallosal artery which leads to infarction of the bilateral fornices.
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Epidemiology
The exact incidence of amnestic syndrome of the subcallosal artery is not known, but it is likely to be very rare.
Clinical presentation
The typical clinical presentation is that of acute and severe anterograde amnesia, with particular impairment of episodic, rather than semantic, memory 1,2.
Pathology
Amnestic syndrome of the subcallosal artery is caused by infarction in the territory of the subcallosal artery 1-5. The subcallosal artery is a branch from the anterior communicating artery, and infarction of its territory typically results in bilateral forniceal infarction, with particular involvement of the bilateral columns, although nearby structures may also be affected 1-5.
The fornices are part of the Papez circuit, which has a key role in memory storage 2. Thus, infarction of the fornices disrupts this circuit, leading to amnesia which characterizes the clinical presentation of amnestic syndrome of the subcallosal artery 2.
Ischemic stroke of the subcallosal artery can be caused by the typical mechanisms of ischemic stroke (e.g. thrombotic, cardioembolic), but also iatrogenically after certain neurosurgical interventions (e.g. surgical trapping of anterior communicating artery aneurysms) 1-5.
Radiographic features
MRI
MRI brain is the imaging investigation of choice, and reveals ischemic stroke in the territory of the subcallosal artery, affecting the bilateral fornices and other nearby structures such as the anterior corpus callosum, septal nuclei, and septum pellucidum 1,2,5. See ischemic stroke for a detailed description of the expected MRI findings.
A number of radiological signs have been proposed to describe the appearance of high signal on axial DWI affecting the bilateral fornices and genu of the corpus callosum 2:
'goblet sign': describing the appearance of a goblet 5
'watch out sign' or 'warning sign': describing the appearance of an exclamation mark (or exclamation point) 6
MR angiography may reveal occlusion (or a filling defect) of the subcallosal artery, particularly on sagittal views 5, but this may be difficult to visualize given the small caliber of the subcallosal artery.
Treatment and prognosis
Management does not differ from other causes of ischemic stroke.
History and etymology
Amnestic syndrome of the subcallosal artery was first described in 2005 3, although there were case reports prior to this describing amnesia in the setting of forniceal infarction 7.
Differential diagnosis
Clinical differential diagnoses include:
transient global amnesia, has DWI high signal affecting the CA1 area of the hippocampus
other strategic ischemic stroke (e.g. hippocampal infarct)
transient epileptic amnesia, typically present upon waking
psychogenic amnesia, more-so affects semantic memory compared to episodic memory
drug-related amnesia, typically has features of encephalopathy
post-traumatic amnesia, has a history of trauma
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