Fate of Brain metastasis with Cerebrospinal fluid space invasion based on MRI findings: Clinical features and factors affecting progression to overt leptomeningeal metastasis

Purpose Parenchymal brain metastasis (BM), its extended growth into cerebrospinal fluid (CSF) pathways or surgical spillage could result in leptomeningeal metastasis (LM). We defined BM with epipial spread or dural attachment on MRI as BM with CSF space invasion (BM-CSFi), regardless of CSF cytology results, and evaluated its clinical course after BM resection. Methods We retrospectively reviewed 297 patients who underwent craniotomy for BM excluding patients followed for < 6 months or without follow-up MRI. Primary outcomes were proportion of patients progressing to overt LM and time to progression. We also evaluated clinical and radiologic variables to identify risk factors for LM progression. Results Total of 91 patients (30.6%) developed overt LM, with median time to progression of 7.9 months during 18.3 months follow-up after the craniotomy. On multivariable analysis, preoperative MRI evidence of dural attachment with enhancement (hazard ratio [HR], 5.59; p  = 0.002), primary small cell lung cancer (HR, 4.92; p =  0.026), infratentorial BM location (HR, 2.14; p  = 0.019), and postoperative cumulative CSF cytology positive rate ≥ 50% (HR, 7.13; p  = 0.012) were independent risk factors for LM progression. Intraoperative findings, the mode of resection, and postoperative radiotherapy or systemic chemotherapy were not significantly associated with LM progression. Conclusion BM-CSFi, defined by preoperative MRI findings, may represent a clinically important precursor of LM. Our findings highlight the need for close monitoring of patients with BM-CSFi and the development of management protocols to minimize the risk of LM progression.