It runs from the anal margin up to where the bowel is gripped by the pubo-rectalis sling of the pelvic floor.
It is a specially adapted part of the lower bowel (endoderm), where it joins embryological ectoderm.
The circular muscle of the bowel is adapted to form a complex sphincter muscle.
An internal sphincter consisting of smooth muscle.
An external sphincter consisting of striped muscle.
The external sphincter relaxes away from the operating field and is not encountered here.
The longitudinal muscle has degenerated into a thin fascial layer.
The anal canal’s lining of columnar epithelium merges with the squamous epithelium of the anal skin.
Between the epithelium and the internal sphincter lie prominent vascular cushions. These soft cushions help maintain continence.
Two lines are commonly mentioned running round the lining of the anal canal.
One line marks the lower end of lax columnar epithelium.
Above this, the mucosa is folded longitudinally by underlying veins into the “anal columns”.
The line itself is irregular, hence its name dentate (tooth-like) or pectinate (like the teeth of a comb).
It is not an important feature in haemorrhoid surgery.
The second line (Hilton’s white line), marking the lower end of the longitudinal muscle/ fascia, is a rarely prominent line.
It is more significance for lymphatic drainage in cancer surgery than in haemorrhoid surgery.
However, two other “lines” are useful landmarks in haemorrhoid surgery.
The anal margin and the internal sphincter (anal ring)
Piles are localised enlargements of the normal fibro-vascular cushions.
They are named piles after the Latin pila meaning a ball.
Piles bleed easily, hence the alternative name haemorrhoids, from the Greek meaning to pour blood.
They are divided into:
External haemorrhoids lying under the sensitive squamous anal skin.
They may thrombose and be painful.
“Hot marble syndrome”.
They usually settle down and form one type of skin tag.
Internal haemorrhoids lie under the insensitive transitional epithelium higher up in the anal canal.
Transitional means a thinned squamous layer between columnar and squamous proper.
(Not to be confused with the specific transitional epithelium of the urothelium.)
Piles prolapse through the internal and external anal sphincters with varying levels of effort.
In their most severe form, they can be strangulated by the anal sphincters and become very congested and infected.
External and internal haemorrhoids merge together in severe cases.
One, two, or three piles may be seen, or the whole lining of the anal canal may be prolapsed – a mucosal prolapse.
A mucosa prolapse is different from a rectal prolapse:
In the latter, not just the mucosa, but the whole muscular wall of the rectum prolapses out of the anal canal.
As seen by the surgeon facing the patient placed in the lithotomy position, typically 3, 7 and 11 o’clock piles can be identified.
This is conveniently, but incorrectly, explained by the arterial blood supply from the left superior rectal artery (3 o’clock pile) and two terminal branches of the right superior rectal artery (7 and 11 o’clock piles).
Nevertheless, the arterial blood supply to the piles is vigorous.
The vessels need to be ligated securely with strong sutures to prevent bleeding at the time of operation and afterwards.
The veins of the piles, draining into the superior rectal veins, require similar secure ligation.
When there is a mucosal prolapse, the individual “piles” coalesce.
The operation consists of excising tissue at the 3, 7 and 11 o’clock sites, just as for haemorrhoids.
Haemorrhoids are very common and may coexist with other diseases in the large bowel.
These other diseases must be excluded before assuming that the patient’s symptoms, especially rectal bleeding or anaemia are due to the haemorrhoids.
Chapter 5. POSTOPERATIVE HAZARDS. [Back to top]
The operation is often classified as “minor”, but unless correctly performed in every detail it can lead to serious complications.
Incontinence of faeces, fluid, or flatus.
Recurrence of haemorrhoids.
Chapter 6. OPERATION OVERVIEW. [Back to top]
The operation consists of:
Identifying the haemorrhoids (or prolapsed mucosa).
Dissecting the haemorrhoids free from the surrounding internal anal sphincter.
Transfixing and excising the haemorrhoids.
Leaving the skin wounds open to heal by secondary intention.