The Termination Level of the Dural Sac Relevant to Caudal Epidural Block in Lumbosacral Transitional Vertebrae: A Comparison between Sacralization and Lumbarization Groups

Abstract

Background: Lumbosacral transitional vertebrae (LSTV) are a relatively common variant and have been considered as one of the reasons for back pain. It is not unusual for clinicians to encounter patients with LSTV who require caudal epidural block (CEB) for pain management. Objective: We investigated the termination level of the dural sac (DS) and anatomical features of the lumbosacral region relevant to CEB in patients with LSTV and compared these findings between sacralization and lumbarization groups. Study Design: A retrospective evaluation. Setting: A university hospital with inpatient and outpatient LSTV cases presenting low back pain. Methods: Four hundred ninety-four LSTV patients were included and categorized into sacralization (n = 201) or lumbarization groups (n = 293). Magnetic resonance imaging (MRI) of all of the LSTV patients were reviewed to determine the level of DS termination, the shortest distance between the apex of the sacral hiatus and DS, and the presence and the caudal level of sacral perineural cysts. Each lumbosacral vertebra column was divided into 3 equal portions (upper, middle, and lower thirds). The MRI findings in both of the groups were compared and analyzed. Results: The distribution frequency of the levels of DS termination demonstrated a significant difference between the 2 groups. The mean caudal DS level in the lumbarization group was significantly lower than the sacralization group (lower third of the S2 [131 {44.7%} of 293 patients] vs. lower third of the S1 [78 {38.8%} of 201 patients]). The DS terminated at the S3 in more than 19% of the lumbarization group, whereas in only one case of the sacralization group. Although the incidence of perineural cysts was not significantly different between the 2 groups, the mean level of caudal margin of perineural cysts in the lumbarization group was significantly lower than the sacralization group (middle third of the S3 [10 {35.7%} of 28 cases] vs. middle third of the S2 [11 {44%} of 25 cases]). Limitations: This study reveals several limitations including the practical challenge of accurate enumeration of the transitional segment and the constraints on generalizability posed by the single-country study. Conclusion: When planning CEB for patients with LSTV, pre-procedural MRI to check the anatomical structures, including the level of DS termination and caudal margin of perineural cysts, would be of great use for lowering the risk of unexpected dural puncture during the procedure, especially in the lumbarization cases. Key words: Termination of the dural sac, dural sac termination, lumbosacral transitional vertebrae, transitional vertebra, caudal epidural block

Early Dural Sac Termination with Lumbar Disc Herniation: A Mimic of Nerve Root Anomalies

“…The frequency distribution of level of dural sac termination as determined by MRI. Three previous studies reported that the S2 was the most frequent point of termination for the dural sac 8,11,16) . vel 1,6,12) , while the most frequent level of DS termination was at the middle one-third of S2 (Fig.…”

“…Although earlier studies on the level of termination of the spinal cord and DS have been confined to cadavers and myelography, MRI has become a more accurate and convenient method by which to confirm early termination of the DS 16) . A study on the caudal epidural block demonstrated a significant difference in level of DS termination on MRI scans between sacralization and lumbarization groups 8) . Here, the mean caudal DS level in the lumbarization group (lower one-third of S2; 44.7%) was significantly lower than that in the sacralization group (lower one-third of the S1; 38.8%), and it has been reported that knowing the DS termination point could prevent injury to the dura or surrounding structures during caudal block 8) .…”

“…For determination of the exact level, a horizontal line was drawn from the end of dural convergence to the posterior margin of the corresponding vertebrae, and early DS termination is defined as the DS ending above the sacrum, with a reported prevalence of 0.8% to 6.4% (Fig. 3) [6][7][8][9]11,13,16) . Notably, surgical problems related to early DS termination have not been reported, because it is rarer to have both early DS termination and to experience a problem requiring surgery.…”

“…Spine surgeons are not often interested in the location of DS termination, but radiotherapists have investigated it before craniospinal irradiation for cerebrospinal (CSF) seeding and leptomeningeal metastasis, while anesthesiologists have focused on DS termination before caudal anesthesia 5,7,16) . A caudal epidural block is widely adopted for intraoperative and postoperative analgesia, and caudal anatomy and DS termination could have implications not only for the anesthesiologist, but also for spine surgeons for preventing neural injury during spine surgery or procedures 8,13) . Disc herniation is one of the most common diseases requiring surgical interventions, and minimally invasive discectomy with endoscopy has been increasing.…”

Infiltraciones epidurales: caudales, interlaminares o transforaminales. Algo más que una inyección

“…El aspecto de seguridad de las técnicas es otro aspecto a tener en consideración. La vía caudal es una vía segura para evitar la punción dural (salvo en los hipotéticos casos de punción de quistes de Tarlov o un saco tecal descendido más allá de S2) y evitar posibles lesiones neurológicas derivadas de punciones de arterias espinales (31). La vía interlaminar es una vía segura para evitar lesiones neurológicas provocadas por punción de arterias radiculares e inyección de material embolígeno, aunque la punción dural y la subdural sigue constituyendo un riesgo (32).…”