Intramuscular distribution of botulinum toxin--visualized by MRI.

•MRI scans were performed to study the spaciotemporal distribution of BoNT.•In the muscle, BoNT distributes in a thin and long layer parallel to muscle fibers.•In spastic muscle, layers are shorter.•To reach more endplate zones, different muscle levels should be targeted.•In spastic muscle, additional sites along muscle fibers should be considered.