The purpose of this study is to determine whether Sacral Nerve Stimulation (SNS) for idiopathic faecal incontinence affect cortical and deep brain activity in an acute and chronically stimulation model. Furthermore the association between brain activity and unilateral/bilateral SNS will be studied in each patient. Brain activity will be studied by use of positron emission tomography.

Faecal incontinence is a devastating condition affecting daily living and quality of life. A new treatment Sacral Nerve Stimulation (SNS) has over the last decade given new hope to these patients. In Europe SNS is routinely offered to patients not archiving satisfactory continence result with standard non-surgical treatments. SNS is electrical stimulation of the sacral nerve root(s2,3 or 4). Stimulation of this nerve roots results in improved continence. The mechanism of action is at present not well described. Recent studies have shown that the effect of SNS is by means a neuromodulation in the central nervous system, whereas direct stimulation of efferent nerves to the anal sphincter and the pelvic floor has less significance.

The aim of this study is to describe changes in regional cerebral blood flow (RCBF), with positron emission tomography (PET), in patients implanted bilaterally with sacral neuromodulators with the indication idiopathic faecal incontinence.

RCBF in three deferent stimulations settings will be compared. PET will be performed before and one hour after changes in the activity status of the pacemakers. Four weeks prior to the first scan, patients are informed to switch both neurostimulator off. PET will be performed with the pacemaker settings: OFF/OFF (Stimulation status of left/right pacemaker), On/Off and On/On. The order of the On/OFF and On/On period will be random. Unilateral stimulation will be performed with the pacemaker there has the best efficacy, determined prior to study enrolment. The interval between these three pacemaker settings is four weeks. Four weeks prior to each PET scan the patients fill in bowel habit diaries, bowel habit questionnaires and quality of life assessments.

The association between continence and changes in RCBF will be studied. Additional RCBF and quality of life will be compared.

Inclusion Criteria:

• 18 years or older
• Informed consent
• Idiopathic fecal incontinence or Fecal incontinence due to small sphincter defect(≤60 o)
• Permanent neuromodulator (medtronic InterStim II) bilateral implanted
• Reduction in fecal incontinence episodes of at least 50% between baseline and latest follow up with unilateral stimulation(Bowel diary card)
• Willing and competent to fill out diary cards
• MR-cerebrum before implantatation of neuromodulator
• Right-handed dominant

Exclusion Criteria:

• Colorectal/proctological surgery since IPG-implant
• Pregnancy
• Neurological diseases including spinal cord injury.
• Use of medication with known alternation of gastrointestinal motilitet (thyroid, diabetes, neuroleptica)
• Claustrofobia
• Latex allergy