Primary spread of caudal blockade in children: the possible limiting role of the lumbar spinal cord enlargement (tumenescence) in combination with the cerebrospinal fluid rebound mechanism.

BACKGROUND: Despite being the most frequently used pediatric nerve block, certain aspects of the initial intraspinal spread of local anesthetics when performing a caudal block need further elucidation. The fact that injected volumes of 0.7-1.3 mL kg-1 initially only reach the thoraco-lumbar junction, with only a few vertebral segments difference despite the huge difference in injected volume, still has no apparent explanation. We hypothesize that the narrowing of the epidural space caused by the lumbar spinal enlargement may provide an anatomical barrier causing this restriction of initial spread, alone or in combination with increased intrathecal pressure caused by the "cerebrospinal fluid rebound mechanism." The aim of this observational study was to find support for or refute this hypothesis.

METHODS: Twenty nine MRI scans of the vertebral column, performed in children 0-6 years of age, was identified from the radiographic imaging computer system and analyzed for the vertebral level of the maximum of the lumbar spinal enlargement (Associated anatomical data related to the spinal canal, the dura mater, and the spinal cord were also recorded.

RESULTS: The maximum of the lumbar spinal enlargement was found at a median vertebral level of Th 11 (IQR 11-11).

CONCLUSION: The maximum of the lumbar spinal enlargement is located at the Th 11 vertebral level. Although not entirely conclusive, the findings of the present study do support the notion that the lumbar spinal enlargement, in combination with the CSF rebound mechanism, may be the factors limiting the initial spread of a caudal block to the thoraco-lumbar junction.