Estimation of the depth of the thoracic epidural space in children using magnetic resonance imaging

BACKGROUND The estimation of the distance from the skin to the thoracic epidural space or skin to epidural depth (SED) may increase the success rate and decrease the incidence of complications during placement of a thoracic epidural catheter. Magnetic resonance imaging (MRI) is the most comprehensive imaging modality of the spine, allowing for the accurate determination of tissue spaces and distances. The present study uses MRI-derived measurements to measure the SED and define the ratio between the straight and inclined SEDs at two thoracic levels (T6-7 and T9-10) in children. METHODS The T2-weighed sagittal MRI images of 109 children, ranging in age from 1 month to 8 years, undergoing radiological evaluation unrelated to spine pathology were assessed. The SEDs (inclined and straight) were determined, and a comparison between the SEDs at two thoracic levels (T6-7 and T9-10) was made. Univariate and multivariate linear regression models were used to assess the relationship of the inclined thoracic T6-7 and T9-10 SED measurements with age, height, and weight. RESULTS Body weight demonstrated a stronger association with the SED than did the age or height with R2 values of 0.6 for T6-7 and 0.5 for T9-10. The formulae describing the relationship between the weight and the inclined SED were T6-7 inclined (mm) = 7 + 0.9 × kg and T9-10 inclined (mm) = 7 + 0.8 × kg. CONCLUSION The depth of the pediatric thoracic epidural space shows a stronger correlation with weight than with age or height. Based on the MRI data, the predictive weight-based formulas can serve as guide to clinicians for placement of thoracic epidural catheters.