Anal incontinence

 

Aetiology

Aetiology of incontinence

Descent

Destruction

Debility

Deficiency

Damage

Denervation

Dementia

The origins of anal incontinence may derive from causes relating to:

  descent:

    perineal descent,

   rectal prolapse;

  destruction:

    malignant tumours,

    irradiation;

  debility:

    illness,

   old age;

deficiency:

    congenital abnormalities;

  damage:

    wounds,

    surgical procedures,

    childbirth;

 denervation:

   spinal injuries,

    neurosurgical procedures,

   spina bifida,

    neurological disorders, e.g. multiple sclerosis;

  dementia:

    senility,

    psychological abnormality.

Of these causes, geriatric, traumatic and obstetric cases predominate  with anal surgical procedures an important contributor to the traumatic group. Another major cause in women is pudendal nerve neuropathy which results from chronic straining, perineal descent and a traction injury to the nerve. This type of incontinence used to be termed idiopathic but neurophysiological studies have determined its true nature. In particular, the latency of pudendal nerve transmission can now be measured by stimulating the pudendal nerve per rectum and measuring the time taken for an electromyographic (EMG) response to be detected in the external and sphincter. A latency above 2 ms is usually diagnostic of pudendal nerve neuropathy.

Once the cause of the incontinence has been precisely defined by a careful history and meticulous examination, supported by special investigations as indicated (see above), treatment may be possible. Surgical procedures have been developed to repair and support damaged or weak sphincter muscles. These may be classified as follows.

Operations to reunite divided sphincter muscles

The sphincter muscles may have been divided as a result of direct trauma, operations for fissure and flstula or by obstetrical injury. The ends of the divided muscle are found and reunited by a double overlap repair (Fig. 61.19).

Operations to reef the external sphincter and puborectalis muscle

If the sphincter muscles are stretched and patulous (as they often are in old age and cases of rectal prolapse) they may be tightened by a postanal repair. These operations use darns of absorbable material to narrow down and plicate the external sphincter and the puborectalis sling (Fig. 61.20). They restore length to the anal canal, strength to the anal sphincter and angulation to the anorectal junction. The approach is usually through the intersphincteric plane.

Operations to support the anal canal

If the anal canal is gaping and has feeble muscles that cannot be strengthened by direct means, support can be given by encircling stitches or Mersilene strands after the Thiersch operation pattern (Chapter 53). However, these techniques are not popular since the sutures may erode into the, anal canal or cause an impediment to satisfactory evacuation and have now been abandoned. Recently, attempts have been made to create a new anal sphincter by transposing the gra­cilis muscle around the anal canal and stimulating it electri­cally by a pacemaker (Williams) (Fig. 61.21). This appears a promising technique and is effective in approximately 60 per cent of patients who have previously had more conventional operations.

More recently an artificial sphincter has been developed from that used in urology. It consists of a silastic cuff which is inflated around the anal canal and occludes it. When evacuation is required, the cuff is deflated by squeezing a small balloon attached to a reservoir (Fig. 61.22). Since this device is a foreign body which exerts pressure on the bowel wall, there is concern that erosion and infection will be a common problem.

All of these procedures achieve best results if the bowel habit is regulated and a normal defecatory pattern established over the preoperative and postoperative periods. The opera­tions should be covered by antibiotics active against both aerobic and anaerobic organisms to reduce the risk of septic complications. If any of these procedures fail or are contraindicated, the patient may require a permanent colostomy.