What type of stroke causes inability to form short-term memories?

Posterior Cerebral Artery Stroke Most Commonly Causes Short-Term Memory Impairment

Strokes affecting the hippocampus, particularly those in the posterior cerebral artery (PCA) territory, are the primary cause of inability to form short-term memories. 1, 2

Anatomical Basis of Memory Impairment After Stroke

Hippocampal Involvement

• The hippocampus plays a crucial role in the formation of new memories and is supplied primarily by the posterior cerebral artery (PCA)
• Bilateral hippocampal damage typically results in more severe and persistent memory deficits than unilateral damage 3
• Four distinct patterns of hippocampal infarction have been identified on diffusion-weighted MRI:
  1. Complete hippocampal involvement
  2. Lateral parts of hippocampal body and tail
  3. Dorsal parts of hippocampal body and tail
  4. Circumscribed lesions in the lateral hippocampus 1

Clinical Presentation

• Memory deficits may present as:
  • Anterograde amnesia (inability to form new memories)
  • Impaired retention of new information
  • Deficits in short-term memory with relative preservation of long-term memory 4
  • Verbal episodic memory deficits in left hippocampal infarcts
  • Non-verbal episodic memory deficits in right hippocampal infarcts 1

Diagnostic Considerations

Imaging

• MRI is the preferred imaging modality for detecting hippocampal infarcts 5, 6
• Diffusion-weighted imaging (DWI) is particularly sensitive for acute infarcts
• CT scans may show hypodense areas in the hippocampus but are less sensitive than MRI 4

Neuropsychological Assessment

• Careful neuropsychological examination is essential as memory deficits may not be clinically apparent in all cases 3
• Assessment should include:
  • Short-term memory
  • Working memory
  • Episodic long-term memory (both verbal and non-verbal) 1

Clinical Course and Prognosis

• Memory impairment may be:
  • Transient in unilateral hippocampal infarcts
  • Persistent in bilateral hippocampal infarcts 2
• Good recovery is possible in some cases, with improvement in short-term memory and ability to retain new information 4
• Distinguishing features from vascular dementia include better outcomes and more specific memory deficits 4

Management Approaches

Cognitive Rehabilitation

• Patients should be assessed for cognitive deficits and given appropriate cognitive retraining 5
• Recommended strategies include:
  • Training to develop compensatory strategies for memory deficits 5
  • Use of internal strategies (visual imagery, semantic organization)
  • External memory assistive technology (notebooks, electronic reminders) 5

Environmental Modifications

• Enriched environments to increase engagement with cognitive activities 5
• Structured routines to compensate for memory deficits

Exercise and Physical Activity

• Exercise may be considered as adjunctive therapy to improve cognition and memory after stroke 5

Important Caveats

• Memory deficits may not be the presenting symptom in hippocampal stroke; other symptoms from lesions outside the hippocampus often dominate the clinical picture 1
• Bilateral PCA infarcts causing hippocampal damage result in more severe and persistent memory deficits than unilateral lesions 2
• Careful neuropsychological testing is necessary to detect memory deficits that may not be apparent on routine examination 3
• Post-stroke cognitive impairment occurs in up to 60% of stroke survivors, with the highest rate seen shortly after stroke 5

Understanding the specific pattern of hippocampal involvement can help predict the type and severity of memory deficits, guiding appropriate rehabilitation strategies to improve outcomes.