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.