Utility of CSF Cytology Study in Pediatric Parameningeal Rhabdomyosarcoma at Initial Diagnosis - Is this an essential staging investigation in all?

Introduction: Parameningeal Rhabdomyosarcoma (PM-RMS) has a tendency for leptomeningeal spread and hence cerebrospinal fluid (CSF) analysis has been an integral part of staging.Evidence for the utility of this invasive investigation at first presentation is scarce with a reported incidence of 0 (n=0/192)-7.5% (n=2/26) in the available studies.This study analyses the utility of CSF analysis at initial diagnosis. Methodology:A retrospective analysis of treatment-naive patients with PM-RMS, aged 15 years, from January 2013 to October 2024 was performed.The staging was by FDG-PET CECT scan and CSF cytology with MRI brain wherever required.Patients were treated with the IRS-IV protocol.Descriptive statistics were used for data analysis. Results:Of 127 patients with PM-RMS, 97 patients were eligible for analysis.The median age was 5.5 years.The most common site of the primary tumor was the nasopharynx (n=32, 33%) followed by the nasal cavity and paranasal sinuses (n=29, 30%) with embryonal histology being the commonest (n=59, 61%).Fusion negatives were 75% (n=56/75).Staging details were: stage 2-13% (n=13), stage 3-72% (n=70), stage 4-15% (n=14).Cranial Bone Erosion (CBE) was seen in 73% (n=71), and Intracranial Extension (ICE) in 49% (n=48).None of the 97 patients tested positive for CSF involvement.92 patients of this cohort completed treatment, of which 40 progressed/relapsed.Of these 40 patients, 19 had relapse/progression in the central nervous system (16/19 had baseline ICE) as follows: mass lesion-14, leptomeningeal enhancement-8, alone or combined).CSF analysis was positive for involvement at relapse/progression in 5/13 tested, all of whom had high-risk features at first diagnosis (ICE).