Case Report: extensive leptomeningeal metastasis from gastric cancer presenting with hearing impairment.

Leptomeningeal metastasis (LM) from gastric cancer is a rare but devastating manifestation of advanced disease. Early diagnosis can be difficult when neurological symptoms are atypical and cerebrospinal fluid (CSF) cytology is negative. We report a 71-year-old man with gastric cardia adenocarcinoma who initially developed hearing impairment, dizziness and gait instability approximately 11 months after radical total gastrectomy, followed by rapidly progressive bilateral hearing loss at presentation. Neurological examination initially showed no meningeal signs or pathological reflexes. Contrast-enhanced brain magnetic resonance imaging (MRI) demonstrated extensive, multifocal linear and patchy leptomeningeal enhancement over the bilateral cerebral hemispheres and cerebellar surfaces. CSF analysis showed marked hypoglycorrhachia, elevated protein, and mild mononuclear pleocytosis, whereas cytology did not identify malignant cells. After alternative infectious and immune-related diagnoses were considered clinically less likely, the findings supported a diagnosis of probable type IIA LM according to the EANO-ESMO criteria. Immunohistochemistry of the primary gastric tumor showed CK7 positivity, diffuse CAM5.2 positivity, partial CDX-2 nuclear positivity, HER2 immunohistochemistry (IHC) 2+ membranous staining, mutant-pattern p53 expression, and a Ki-67 proliferation index of approximately 90%. The disease progressed rapidly to impaired consciousness, and the family chose best supportive care after a multidisciplinary team (MDT) discussion. This case highlights that leptomeningeal metastasis from gastric cancer may initially present with hearing impairment; integrated assessment of MRI findings, CSF biochemistry, clinical course, and careful consideration of alternative diagnoses is essential.