## Why Alzheimer disease with medial temporal lobe atrophy is right Bilateral symmetric hippocampal atrophy (marked **A**) with enlarged temporal horns is the hallmark MRI finding in Alzheimer disease. The hippocampus is critical for memory formation and spatial navigation, and its atrophy on coronal MRI at the temporal lobe level is a key diagnostic and prognostic marker (Scheltens grade assessment). The clinical presentation of progressive memory loss and spatial disorientation combined with this imaging pattern is pathognomonic for AD. This finding is used for diagnosis, disease monitoring, and clinical trial enrollment (Sutton Radiology). ## Why each distractor is wrong - **Temporal lobe epilepsy with hippocampal sclerosis**: While hippocampal pathology is present, sclerosis presents with T2 hyperintensity and loss of internal architecture on MRI, not simple bilateral symmetric atrophy. Seizures are the primary presentation, not progressive dementia. - **Herpes simplex virus encephalitis**: HSV encephalitis shows bilateral temporal lobe T2 hyperintensity involving the insular cortex and cingulate gyrus, with acute presentation and fever/altered mental status, not chronic progressive atrophy. - **Frontotemporal dementia with semantic variant**: Semantic FTD shows asymmetric anterior temporal atrophy (left > right), not bilateral symmetric hippocampal atrophy. Language deficits and semantic loss predominate over memory loss. **High-Yield:** Bilateral symmetric hippocampal atrophy on coronal MRI = Alzheimer disease until proven otherwise; enlarged temporal horns reflect the atrophy. [cite:Sutton Radiology — Coronal MRI Brain Temporal Lobe Level; Scheltens grading for hippocampal atrophy in AD]
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