title: Sensory neurons of the human brachial plexus:  a quantitative study employing optical fractionation and in vivo volumetric magnetic resonance imaging.
abstract: BACKGROUND
  Extensive neuron death following peripheral nerve trauma is implicated in poor sensory recovery. Translational research for experimentally proven neuroprotective drugs requires knowledge of the numbers and distribution of sensory neurons in the human upper limb and a novel noninvasive clinical measure of neuron loss.
  
  
  OBJECTIVE
  To compare optical fractionation and volumetric magnetic resonance imaging (MRI) of dorsal root ganglia (DRG) in histological quantification and objective clinical assessment of human brachial plexus sensory neurons.
  
  
  METHODS
  Bilateral C5-T1 DRG were harvested from 5 human cadavers for stereological volume measurement and sensory neuron counts (optical fractionator). MRI scans were obtained from 14 healthy volunteers for volumetric analysis of C5-T1 DRG.
  
  
  RESULTS
  The brachial plexus is innervated by 425,409 (standard deviation 15,596) sensory neurons with a significant difference in neuron counts and DRG volume between segmental levels (P < .001), with C7 ganglion containing the most. DRG volume correlated with neuron counts (r = 0.75, P < .001). Vertebral artery pulsation hindered C5 and 6 imaging, yet high-resolution MRI of C7, C8, and T1 DRG permitted unbiased volume measurement. In accord with histological analysis, MRI confirmed a significant difference between C7, C8, and T1 DRG volume (P < .001), interindividual variability (CV = 15.3%), and sex differences (P = .04). Slight right-left sided disparity in neuron counts (2.5%, P = .04) was possibly related to hand dominance, but no significant volume disparity existed.
  
  
  CONCLUSIONS
  Neuron counts for the human brachial plexus are presented. These correlate with histological DRG volumes and concur with volumetric MRI results in human volunteers. Volumetric MRI of C7-T1 DRG is a legitimate noninvasive proxy measure of sensory neurons for clinical study.
authors.affiliation: Department of Integrative Medical Biology, Section for Anatomy, Umeå University, Umeå, Sweden. drchristianwest@gmail.com
authors.forename: Christian Alexander
authors.initials: CA
authors.lastname: West
authors.forename: Andrew
authors.initials: A
authors.lastname: McKay Hart
authors.forename: Giorgio
authors.initials: G
authors.lastname: Terenghi
authors.forename: Mikael
authors.initials: M
authors.lastname: Wiberg
mesh_terms: D000328:Adult; D001917:Brachial Plexus / Q000166:cytology*; D002102:Cadaver; D002452:Cell Count; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011984:Sensory Receptor Cells / Q000166:cytology*