Somatotopy of corticospinal tract fibres of the intercostal muscles : report of a case and review of literature

This study aimed at describing the first case of subcortical stimulation of the corticospinal tract leading to selective contraction of the intercostal muscles during surgery for removal of a tumour centred in the right central lobule/supplementary motor area. A 53-year-old male presented with partial motor seizures. Imaging demonstrated a low-grade glioma affecting the posterior aspect of the superior and middle frontal gyri and invading the precentral gyrus. Preoperative motor Transcranial Magnetic Stimulation and advanced diffusion tractography were performed to establish the relationship of the tumour with the motor cortex and corticospinal tract. Intraoperative motor mapping and monitoring were performed with monopolar stimulation (“train of 5” technique). At the posterior margin of resection, subcortical stimulation demonstrated a selective response from intercostal muscles, medial to responses from the lower limb and lateral to responses from the upper limb. PubMed literature search was performed to identify any case reporting similar findings. There were no cases previously reported in the literature. The location of the subcortical response for intercostal muscles confirms the somatotopy of the corticospinal tract. Intercostal muscles are controlled by selective fibres within the corticospinal tract. Damage to these fibres can lead to paralysis of voluntary respiratory muscles. Further studies are needed to define the cortico-subcortical network controlling voluntary respiratory muscles.