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MRI volumetry of medial temporal lobe structures in amnesia following herpes simplex encephalitis
Y Yoneda1, E Mori, H Yamashita
1Neurology Service, Hyogo Brain and Heart Center, Himeji, Japan.
Abstract:
Using a magnetic resonance imaging-based volumetry, we quantified the volumes of the hippocampal formation (HF), parahippocampal gyrus (PHG), amygdaloid body (AMB), and anterior temporal neocortex (ATN) in 5 post-herpes simplex encephalitic (post-HSE) patients with temporal lobe damage and memory impairment at 12-52 months after the onset, and in 10 age-matched control subjects. In the post-HSE patients, the HF (p < 0.001) and PHG (p < 0.005) were significantly atrophic, while the AMB (p = 0.155) and ATN (p = 0.102) were smaller but not significantly. Performances on the verbal learning memory tests correlated highly with the HF volume, and length of dense retrograde amnesia with the PHG atrophy. Two patients with severe lasting amnesia had a marked atrophy of the HF and PHG, while 3 patients with good recovery from initial amnesia had temporal lobe structures larger than 50% of the control mean volumes. These results suggest that anterograde and retrograde memory functions involve different neural structures; the former is related to the HF and the latter to the PHG. For producing lasting amnesia, either severe HF damage or a combined damage of the HF and PHG might be necessary.
Insights
Herpes simplex encephalitis can cause significant atrophy in the hippocampal formation (HF) and parahippocampal gyrus (PHG), impacting memory. HF volume relates to anterograde memory, while PHG atrophy is linked to retrograde amnesia.
Area of Science:
- Neuroscience
- Neurology
- Radiology
Background:
- Herpes simplex encephalitis (HSE) can lead to temporal lobe damage and persistent memory deficits.
- Quantifying structural brain changes is crucial for understanding the neurological basis of memory impairment after HSE.
Purpose of the Study:
- To investigate the relationship between temporal lobe structural changes and memory deficits in post-HSE patients.
- To differentiate the roles of specific brain structures in anterograde and retrograde memory.
Main Methods:
- Magnetic resonance imaging (MRI)-based volumetry was used to measure the volumes of the hippocampal formation (HF), parahippocampal gyrus (PHG), amygdaloid body (AMB), and anterior temporal neocortex (ATN).
- Structural volumes were compared between 5 post-HSE patients and 10 age-matched controls.
- Memory performance, including verbal learning and retrograde amnesia, was assessed and correlated with brain structure volumes.
Main Results:
- Post-HSE patients showed significant atrophy in the HF (p < 0.001) and PHG (p < 0.005).
- Verbal learning memory performance correlated strongly with HF volume, while retrograde amnesia length correlated with PHG atrophy.
- Patients with severe amnesia exhibited marked HF and PHG atrophy, whereas those with good recovery had larger temporal lobe structures.
Conclusions:
- Anterograde memory is associated with the hippocampal formation (HF), while retrograde memory is linked to the parahippocampal gyrus (PHG).
- Lasting amnesia following HSE may result from severe HF damage or combined HF and PHG damage.