Abstract

Knowing where the dural sac (DS) ends is important, especially when placing the portal fields during craniospinal irradiation (CSI) and performing caudal anesthesia. The purpose of this investigation was to determine the level of termination of the DS in relation to the spine in a group of South African patients using magnetic resonance imaging (MRI). We retrospectively reviewed the lumbosacral MR Imaging of 309 patients in each case identifying the tip of the DS. This level was recorded in relation to the adjacent vertebral body i.e. upper-, middle- and lower third and adjacent intervertebral disc. The overall mean of the DS position was at the middle third of S2. A notable percentage (13.9%) of patients had a DS level lower than the lower third of S2 and (15.2%) patients had a DS level higher than the S1-S2 intervertebral disc. This study failed to demonstrate a difference in the DS termination level, compared to the levels reported in various international studies; nor is there a statistical difference between gender, race and age. Our study shows that routine placement of the portal field at the lower border of S2 adequately treats the majority of CSI patients. However some patients (13.9%) will be undertreated and some patients (15.2%) will be overradiated. Using spinal MRI to establish the lower border of the CSI portal field will however benefit patients by ensuring adequate coverage of the entire neuroaxis as well as minimizing late gonadal toxicity due to overradiation.

Thecal Sac; Dural Sac; Termination Level; Craniospinal Irradiation; Magnetic Resonance Imaging