Amnestic syndrome of the subcallosal artery

Amnestic syndrome of the subcallosal artery describes an acute amnestic syndrome secondary to ischaemic stroke affecting the subcallosal arteries which leads to infarction of the bilateral fornices.

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 arteries ^1-5. The subcallosal arteries are branches from the anterior communicating artery, and infarction of their 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, explaining the clinical presentation of amnesia when the fornices are infarcted ².

This location of ischaemic stroke can be caused by the typical mechanisms of ischaemic 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 ischaemic stroke in the territory of the bilateral subcallosal arteries, affecting the bilateral fornices and other nearby structures such as the anterior corpus callosum, septal nuclei, and septum pellucidum ^1,2,5. In one case report, the appearance on axial DWI of high signal affecting the bilateral fornices and genu of the corpus callosum has been likened to a goblet, and thus termed the 'goblet sign' ⁵. See ischaemic stroke for a detailed description of the expected MRI findings.

MR angiography may reveal occlusion (or a filling defect) of the subcallosal artery, particularly on sagittal views ⁵, but this may be difficult to visualise given the small calibre of the subcallosal artery.

Treatment and prognosis

Management does not differ from other causes of ischaemic 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 ⁶⁷.

Differential diagnosis

Clinical differential diagnoses include:

• transient global amnesia, has DWI changes affecting the CA1 area of the hippocampus

• other strategic ischaemic 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