Yoshitaka Ishiguro, Naoto Jingami, Tomohisa Okada, Sachi Okuchi, Yasutaka Fushimi, Yuji Nakamoto, Ryosuke Takahashi, Riki Matsumoto, Shigeru Ohtsuru
Serial 7 T MRI demonstrates that hippocampal T2WI lesions in TGA are consistently visible acutely and uniformly disappear by 2 weeks, providing high-field structural evidence that typical TGA is a transient phenomenon. These findings refine the temporal profile of hippocampal signal evolution and contribute to mechanistic understanding of CA1 vulnerability in TGA.
BACKGROUND: Transient global amnesia (TGA) often shows tiny punctate hippocampal CA1 lesions on diffusion-weighted imaging (DWI). Whether these lesions represent truly transient structural alterations remains unsettled. Ultra-high-field 7-tesla (7 T) MRI increases spatial resolution and lesion conspicuity. However, the evolution of hippocampal T2 signal at 7 T from the acute phase through short-term follow-up has not been systematically examined.
OBJECTIVE: To determine, using serial 7 T MRI, whether hippocampal T2-weighted imaging (T2WI) abnormalities visible in acute TGA are consistently detectable acutely and completely disappear by approximately 2 weeks.
METHODS: Single-center consecutive case series of six patients with clinically defined TGA and DWI-confirmed CA1 lesions who underwent serial 7 T MRI, including acute imaging and follow-up at 14-18 days. The primary outcome was complete resolution of hippocampal T2 hyperintensity. Secondary outcomes were acute T2 detection rate, lesion distribution, and concordance with DWI.
RESULTS: Six patients (4 men), median age 69 years (range 50-76), all fulfilled the diagnostic criteria of TGA and no neurological deficits. Acute 7 T MRI was performed at a median of 37 h after symptom onset. Acute phase: All 6/6 showed focal hippocampal CA1 hyperintensity on 7 T T2WI, colocalizing with DWI/ADC abnormalities. Follow-up (day 15-18): T2 hyperintensity resolved in 6/6 with no visible residual signal abnormality or structural atrophy. Follow-up 7 T DWI demonstrated complete disappearance of the previously identified diffusion abnormalities in all patients. Interpretation: Even at ultra-high field, hippocampal T2 abnormalities are fully reversible within approximately 2 weeks.
CONCLUSION: Serial 7 T MRI demonstrates that hippocampal T2WI lesions in TGA are consistently visible acutely and uniformly disappear by 2 weeks, providing high-field structural evidence that typical TGA is a transient phenomenon. These findings refine the temporal profile of hippocampal signal evolution and contribute to mechanistic understanding of CA1 vulnerability in TGA.