The lumbosacral spinal cord is a critical component of the central nervous system. Performing functional MRI (fMRI) to analyze neural activity in this region is challenging due to its size, local anatomy, and motion artifacts [1]. However, exploring the lumbosacral neural circuits at this level is crucial because it represents the level of control for lower urinary tract. Furthermore, the integrity of the S2-S4 spinal cord levels can be assessed with the bulbocavernosus reflex (BCR), a reproducible and practical clinical test. A gentle squeezing of the penis glans or the clitoris usually triggers the BCR. A similar and more convenient method is to tap on the midline of the suprapubic region[2]. Therefore, we sought to evaluate the feasibility of spinal cord activity with BCR-triggered fMRI in healthy individuals.

We included healthy males and females without any history of neurological disease or urological symptoms. They were asked to drink 500ml of water and empty their bladder before entering the MRI room. To elicit the BCR, we developed a dedicated tool to perform a mechanical suprapubic tapping over the bladder. First, we performed a 3T MRI sagittal anatomical sequence, followed by a task block fMRI protocol defined by: 20s of tapping and 20s of rest, repeated four times at empty and full bladder state. Data were processed in the subject space (denoising and co-registration to anatomical) with the Spinal Cord Toolbox [3] after manual delineation of the spinal cord area; then, statistical analysis was performed with FSL. A Z score thresholded >3.1 was used with a p>0.05.

Ten individuals (6 females and 4 males), with an average age of 27.6 years, participated in the study. One subject had a technical issue with the functional MRI acquisitions and was removed from the analysis. Over the nine remaining patients, a significant signal was present for empty and full bladder in 7 subjects (Figure 1). Two individuals showed no activation in the spinal cord during the two-bladder states. The activated areas covered the spinal cord's terminal part with additional activations at higher levels.

The BCR elicited neural activity in 7/9 healthy participants, in the lumbosacral spinal cord, whatever the vesical filling, at the T12-L1 vertebral level. The areas involved are pretty similar, localized, and present in the expected regions with interindividual variations (T8 to L1 vertebral levels). The bladder-sphincter control could be located in the same key areas and will be easier to target.

We show here for the first time that the neuronal signal generated by the BCR is visible in fMRI at the expected location in the lumbosacral cord. Our results open the door to other analyses of this area with dedicated stimulation of pelvic organs such as the lower urinary tract.

Powers J, Ioachim G, Stroman P. Ten Key Insights into the Use of Spinal Cord fMRI. Brain Sciences. 2018 Sep 10;8(9):173.
Amarenco G, Bayle B, Ismael SS, Kerdraon J. Bulbocavernosus muscle responses after suprapubic stimulation: Analysis and measurement of suprapubic bulbocavernosus reflex latency. Neurourology and Urodynamics. 2002;21(3):210–3.
De Leener B, Lévy S, Dupont SM, Fonov VS, Stikov N, Louis Collins D, et al. SCT: Spinal Cord Toolbox, an open-source software for processing spinal cord MRI data. Neuroimage. 2017 Jan 15;145(Pt A):24–43.

Continence 7S1 (2023) 100756
DOI: 10.1016/j.cont.2023.100756