Natural history of filum terminale lipoma and low-set conus medullaris

Filum terminale lipoma and low-set conus medullaris may cause tethered cord syndrome; however, the natural course of these lesions has not yet been fully elucidated. In this study, the authors investigated the natural history of filum terminale lipoma and low-set conus medullaris.

The authors retrospectively analyzed the data of patients who were diagnosed with filum terminale lipoma or low-set conus medullaris and followed without untethering surgery. Cases with a follow-up period of < 12 months were excluded.

From 2010 to 2021, 1070 cases were diagnosed with filum terminale lipoma and/or low-set conus medullaris on initial lumbar MRI at our hospital. Of these, 960 cases underwent untethering surgery after initial diagnosis. One hundred ten cases were followed without untethering surgery. Of these cases, 92 were evaluated, excluding those with a follow-up period of < 12 months. Among those, 12 cases had abnormal findings on initial cystography or abdominal ultrasound and were considered symptomatic, while 80 cases were asymptomatic. Of the 12 symptomatic cases, 3 (25%) developed worsening or new symptoms. These 3 cases underwent untethering surgery, with 2 (67%) showing improvement in symptoms and 1 remaining unchanged. During follow-up, 21 of 80 asymptomatic cases (26%) developed symptoms. Among these, 14 cases had filum terminale lipoma and 8 cases had low-set conus medullaris (1 case had both). Of these, 19 cases underwent untethering surgery; 10 cases (53%) improved, 2 cases remain unchanged, and the results of 7 cases are unknown.

In this study, 26% of asymptomatic patients with filum terminale lipoma or low-set conus medullaris eventually developed symptoms, and 25% of symptomatic patients had worsening or new symptoms. These incidence rates should be considered when discussing preventive surgery for these lesions.