Isolated filar cyst on lumbar spine sonography in infants: a case-control study

Background: Simple cysts found within the filum terminale of infants on lumbar spine sonography are relatively common, but no study has established their clinical significance. Objective: To obtain information on the sonographic features of isolated filar cysts and determine their clinical significance in comparison with age- and sex-matched controls. Materials and methods: We performed a retrospective review of 644 consecutive spine sonograms in patients younger than 8 months. Gestational age- and sex-matched controls with normal lumbar sonograms were taken from the same period. We obtained short-term clinical follow-up of motor milestones for each group. Results: The incidence of filar cyst was 78 of the 644 (11.8%) and was inversely related to age. Developmental follow-up of the study patients compared with control population showed no statistically significant difference in the ages at which the infants were able to turn over, crawl and walk. Follow-up MR imaging of 13 study patients (19%) failed to demonstrate filar cysts previously identified on sonography. Conclusion: No significant difference was found in the short-term outcome of infants with isolated filar cysts on lumbar sonography compared with that of a control population. Filar cysts should be considered a normal variant when found in isolation on lumbar sonography.