P11.20.A RETROSPECTIVE ANALYSIS OF LEPTOMENINGEAL METASTASES FROM SOLID TUMORS: A DIAGNOSTIC STRATIFICATION

Abstract BACKGROUND Leptomeningeal metastasis (LM) is the spread of tumor cells to the arachnoid mater, pia mater or subarachnoid space by either hematogenous spread, direct extension from a contiguous intraparenchymal brain metastasis, or through systemic involvement along the perineural or perivascular spaces. LM has a poor prognosis and is characterized by non-specific neurological symptoms which require early diagnosis by neuroimaging and CSF analysis. Presence of malignant cells on CSF cytology provides the gold standard for diagnosing LM. The 2017 EANO-ESMO guidelines proposed diagnostic criteria with levels of certainty for diagnosing LM to guide treatment decisions. With this background, we aim to classify LM into Type I (confirmed) and Type II (Probable, Possible) categories by capturing the broad spectrum of LM presentations. MATERIAL AND METHODS This is a retrospective observational study of a four-year period (2020-2023). Cases for which CSF analysis was performed due to neurological symptoms suspected to be caused by metastasis or with some radiological suspicion of LM were included. Primary central nervous system tumors, hematolymphoid neoplasms, head and neck neoplasms (direct extension) were excluded. The Pathology search engine was used to retrieve CSF positive, negative and equivocal cases. The clinico-pathology and radiology details were accessioned from the Electronic Medical Record. Furthermore, subtyping was done on Radiology into linear (type A); nodular (type B); both linear and nodular (type C); hydrocephalus only (type D-hydrocephalus) or no neuroimaging evidence of LM (type D-normal). Based on the level of evidence, cases were categorized as Confirmed LM (Positive CSF cytology), Probable LM (Equivocal/ Negative CSF cytology with presence of typical MRI features of LM and typical clinical features) and Possible LM (Equivocal/ Negative CSF cytology with absence of typical MRI features but with typical clinical features). RESULTS Of the 265 cases, 95 were CSF cytology positive (Type I, confirmed LM; Type IA=37, IB=23, IC=15, ID-Hydrocephalus=4 and ID-Normal=16). In 170 cases, CSF cytology was Negative/ equivocal (Type II; Type IIA=19, IIB=13, IIC=4, IID-Hydrocephalus=None and IID-Normal=134) which in conjunction with clinical characteristics were further characterized as probable (n=36) or possibly (n=134) due to LM. The primary sites were lung (n=160), breast (n=80), gastro-intestinal tract (GIT) (n=23), urogenital (n=1) and soft-tissue(n=1). CONCLUSION In all, there were 95 Type I (confirmed cases) and 170 Type II (36 probable, 134 possibly due to LM) cases. Lung was the most common primary site followed by breast and GIT. Rare sites included urogenital and soft tissues.