Bold fMRI and fcMRI in the Pediatric Brachial Plexus Injury Population: Evaluating Cortical Sensory Network Plasticity

PURPOSE:  Brachial plexus birth palsy is a debilitating injury.¹ Nerve root avulsions may occur; these cannot be repaired primarily.  Previous work using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) in the rat model has demonstrated a high degree of brain remodeling following peripheral nerve injury and repair.^2,3 We present our initial findings using air-puffer somatosensory stimulation for 3T BOLD fMRI assessment in a pre-operative pediatric brachial plexus injury patient.

METHODS: An 11-month-old female with left brachial plexus birth palsy was evaluated. The patient was noted to have injury to the C5-C6 nerve roots resulting in 0/5 shoulder external rotation and posterior deltoid function. This pathology was confirmed via pre- and intra-operative EMG and during post-scan surgical exploration. 3T BOLD fMRI imaging was performed prior to surgery. EPI imaging was obtained in duplicate while a timed air-puff mechanism delivered somatosensory stimulus to the C5-C6 dermatome on the injury and healthy side. The primary somatic sensory cortex in the post central gyrus (S1) was the region of principal evaluation.^4,5 These functional images were utilized to contrast the injury side cortex to the non-injury side cortex. The injury patient’s S1 cortical function was then compared to a healthy adult using the same protocol. Functional connectivity MRI (fcMRI) was also performed.

RESULTS: The BOLD fMRI investigation demonstrated a significant difference between the injury side primary somatic sensory cortex function when compared to the non-injury side in a brachial plexus birth palsy patient. This variance is also illustrated when compared to a healthy adult subject undergoing the same functional imaging parameters. fcMRI demonstrated significant intra-cortical connectivity differences.

CONCLUSIONS: This novel application of BOLD fMRI and fcMRI has demonstrated inter-cortical somatosensory differences in a high brachial plexus birth palsy patient. The 3T BOLD fMRI model proposed is applicable to demonstrate cortical sensory pathology in the pre-operative patient with nerve root injuries. Ultimately, this model will be utilized to prospectively investigate cortical sensory plasticity after nerve transfer for brachial plexopathy treatment.