Contribution of the pudendal nerve to sensation of the distal rectum.
BACKGROUND
Anal and rectal sensory mechanisms and pudendal nerve function are important in the control of faecal continence. The contribution of the pudendal nerve to sensation of the distal rectum was investigated.


METHODS
Heat thresholds in the anal canal, distal and mid rectum were measured using a specially designed thermoprobe. Rectal sensory threshold volumes were measured using the balloon distension method. Needle electrodes were inserted into the external anal sphincter. Pudendal nerve block was performed through a perineal approach, and completeness assessed by loss of electromyographic activity. Heat and rectal volume thresholds were measured again following unilateral and bilateral pudendal nerve block.


RESULTS
The technique was successful in four of six volunteers. Bilateral pudendal nerve block produced complete anaesthesia to heat in the anal canal (P = 0.029), but had no effect on heat thresholds in the distal or mid rectum. Rectal sensory threshold volumes were also unaffected by pudendal nerve anaesthesia.


CONCLUSIONS
Anal canal sensation is subserved by the pudendal nerve, but this nerve is not essential to nociceptive sensory mechanisms in the distal or mid rectum. The transition between visceral control mechanisms in the lower rectum and somatic mechanisms in the anal canal may have functional importance in the initiation of defaecation and the maintenance of continence.
Chan
C L H
CL
Centre for Academic Surgery, Barts and the London School of Medicine and Dentistry, UK. christopherlhchan@yahoo.co.uk
Ponsford
S
S
Scott
S M
SM
Swash
M
M
Lunniss
P J
PJ
D000328:Adult; D001003:Anal Canal / Q000294:innervation / Q000502:physiology; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male; D009407:Nerve Block; D012007:Rectum / Q000294:innervation / Q000502:physiology*; D012677:Sensation / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology