Purpose: Sacral neuromodulation is a new treatment for refractory voiding disorders such as urge incontinence, urinary retention, frequency-urgency syndromes and faecal incontinence. The current approach to sacral nerve stimulation consists of a two-stage procedure. The first is a PNE test (Percutaneous Nerve Evaluation) by a provisional electrically stimulated spinal needle, placed percutaneously in the S3 foramina for four to ten days. If successful, the second stage, permanent implantation, is carried out. The PNE test is performed under fluoroscopic control using the palpable bony sacral foramina as referral points. This technique can show some limitations, such as operator Rx exposure, poor visualization of sacral foramina because of bowel gas artefacts or sacral malformation. In order to reduce these inconveniences and to improve efficiency of the test we tried an alternative technique. The purpose of our study was to test the use of CT as an alternative technique in order to evaluate its advantages and possible routine use.
Materials and methods: We tested 30 patients with the PNE test under CT guidance (16 males and 14 females) suffering from serious pelvic disorders and not responding to the normal therapeutic regime. Twenty-seven patients showed relative anatomical integrity of the pelvis and the sacrum, the remaining 3 patients presented morphological anomalies of the sacral foramina. With the patient in the prone position the sacral foramina were identified with CT volumetric scanning using a spiral CT scanner equipped with a second console for the three-dimensional reconstructions. Having identified the location of the S3 foramina, a sterile field was prepared and the spinal needle introduced checking correct positioning with a CT control scan. An electrode was then inserted after having checked correct muscular contractile response and the precise position with a further CT scan.
Results: Thirty patients were subjected to PNE under CT guidance for a total of 38 centerings. Eight patients underwent the PNE procedure on both the S3 foramina. The sacral foramen was centred at the first attempt in 36 out of 38 cases. Two cases required several attempts to centre correctly the foramen. In 4 patients out of 30 a second electrode was implanted. In one patient who had a nonconsolidated sacral fracture, CT guidance enabled insertion of the electrode inside the only practicable foramen, a manoeuvre that would have been impossible with fluoroscopical guidance. Only once was the electrode placed in a wrong location but promptly repositioned after a CT control. During the whole trial period we had a positive response to the PNE test in 18 out of 30 patients (60%), a partial response in 4 out of 30 patients and a negative response in the remaining 8 patients. None of the patients who underwent the PNE test had infectious complications and the procedure was well tolerated by all. The procedure lasted about 45 minutes.