Leptomeningeal Carcinomatosis Arising 29 Years After Gastrectomy: A Report of a Rare Autopsy Case.

Leptomeningeal carcinomatosis (LMC) is extremely rare in gastric cancer, as is recurrence >10 years after gastrectomy. Herein, we report an autopsy case of LMC that developed 29 years after gastrectomy for gastric signet ring cell carcinoma. A 74-year-old man presented with multiple progressive cranial neuropathies involving cranial nerves III, V, VI, VII, IX, X, and XII. CSF analysis revealed pleocytosis and markedly elevated protein levels; however, cytological examination of five consecutive samples was negative for malignant cells. Multiplex PCR analysis excluded infectious etiologies. MRI demonstrated contrast enhancement of cranial nerves III, V, VII, and XII. Despite antiviral, antituberculous, and corticosteroid therapy, the patient's condition deteriorated, and he ultimately died three months after symptom onset. Autopsy revealed extensive infiltration of signet ring cell carcinoma in the leptomeninges and cranial nerves. Immunohistochemical analysis of this tissue revealed cytokeratin 7 positivity and cytokeratin 20 negativity, identical to the gastric carcinoma resected 29 years earlier. No recurrence was observed in the remnant stomach or other organs. This case suggests reactivation of microscopic leptomeningeal metastases following an exceptionally prolonged period of tumor dormancy. Signet ring cell carcinoma is thought to be prone to dormancy owing to its weak intercellular adhesion, leading to reduced proliferative signaling and activation of stress response pathways. This experience suggests that LMC should be considered when meningitis-like neurological symptoms develop, even in patients who remain recurrence-free for decades postoperatively.