P14.15.B PURE CYSTIC LESIONS OF THE CONUS MEDULLARIS: A SINGLE CENTRE STUDY AND SYSTEMATIC REVIEW

Abstract BACKGROUND Pure cystic lesions at the conus medullaris comprising ventriculus terminalis (VT), intramedullary arachnoid cyst (IMAC) and neurenteric cyst (NEC) are rare benign cysts. Compared to IMAC and NEC requiring often surgery, the VT is considered as a normal anatomic development phenomenon rarely needing more than MRI surveillance. However, the literature is limited and there exist no uniform guidelines. The aim was to present our experience from a cohort with these lesions and discuss management strategies as compared to the existing literature. MATERIAL AND METHODS A retrospective review was conducted identifying patients (>16 years) from our institutional archive from 2013 to 2024. Demographic factors, presenting symptoms using the established Classification by de Moura Batista et al., and therapeutic management were recorded. Previous history of spinal trauma or surgery, or radiological evidence of adjacent tumour tissue or malformations e.g. Chiari malformation, tethered cord or spinal dysraphism were excluded. A literature search was performed using PubMed/Medline, EMBASE and Cochrane until December 2024 to identify cases with pure cysts at the conus medullaris using same inclusion criteria. Non-parametric Fisher exact or Kruskal-Wallis tests were used. RESULTS Twenty-two patients (F/M ratio 2: 1; median age 42 years) were included. All patients but two presented with back pain with/without sciatica where six had sensorimotor disturbances and two with also urinary dysfunction. No association was found between the cyst size and the symptoms, p=0.572. Ten patients underwent microsurgical cyst fenestration via laminectomy while two had additional a cyst-subarachnoid shunt inserted. Histology was available for eight patients revealing VT in one case, IMAC in three and NEC in four while it was inconclusive in the rest. Complete recovery was observed in four patients while partial in three with no association with the cyst size, p=0.707. Patients with NEC showed a tendency of recurrence, p=0.465. Twelve patients underwent annual MRI surveillance and remained stable with a median follow-up of 49 months. The literature yielded case studies and small series of VT (n=99), IMAC (n=10) and NEC (n=6) whereas 77 patients (VT 77.8%, IMAC and NEC 100%) had undergone surgery, most commonly microsurgical cyst fenestration. Complete recovery was seen in 36.5% and partial in 37.4%. CONCLUSION Our results shows that the VT rarely requires surgery, compared to IMAC and NEC. However, the literature mainly reports surgical treated VT cases and may not be representative for all VT cases as conservatively managed and asymptomatic cases are less likely to be published. We believe that the VT is an expression of persistent malformation of 5th ventricle without necessary having a progressive evolution, and surgery should be avoided unless expansion of the cyst per se and exclusion of other causes.