Cerebral Amyloid Angiopathy-Related Inflammation Mimicking Leptomeningeal Metastasis After Resected Lung Adenocarcinoma: A Case Report Highlighting Dynamic Diagnostic Reassessment.

Cerebral amyloid angiopathy-related inflammation (CAA-ri) is a rare inflammatory subtype of cerebral amyloid angiopathy that may present with leptomeningeal enhancement on magnetic resonance imaging (MRI), thereby mimicking leptomeningeal metastasis (LM) in patients with cancer. We report the case of an 82-year-old woman with a recently resected lung adenocarcinoma who underwent brain MRI following a fall. MRI revealed bilateral asymmetric white matter hyperintensities and multifocal leptomeningeal enhancement, which initially suggested LM. However, preserved neurological function, negative cerebrospinal fluid cytology, and the subsequent identification of numerous cortical and subcortical microbleeds on targeted reassessment with susceptibility-weighted MRI prompted diagnostic reassessment. Brain biopsy demonstrated vascular amyloid deposition with perivascular inflammatory infiltrates, confirming CAA-ri. Because the patient remained neurologically stable, she was managed conservatively, and spontaneous radiological improvement was observed during follow-up. This case highlights the fact that leptomeningeal abnormalities in patients with lung cancer do not invariably represent leptomeningeal metastasis. When clinicoradiological findings are discordant, prompt reassessment using appropriately selected MRI sequences should be integrated with cerebrospinal fluid analysis and multidisciplinary evaluation, with pathological confirmation considered when clinically consequential alternative diagnoses cannot be excluded. This approach may help avoid inappropriate LM-directed therapy.