Anus

  د مهند الشاله

Lecture 1

The Anus and Anal canal 

Describe applied anatomy and histology of the anal canal 

Describe the clinical features, investigations and principles of 
management of common anorectal diseases

Learning objectives 

Surgical anatomy

 The anal canal commences at the

 level where the rectum passes

 downwards and backwards for

 around 4 cm through the pelvic

 diaphragm  and ends at the anal

 verge.

The internal sphincter is a condensation 

of the circular muscle of the bowel wall. 

The external sphincter is a composite 

striated muscle. Its lower fibres encircle 

the anal canal and they can be subdivided 

into deep, superficial and subcutaneous 

portions. 

The dentate line represents the site 

of fusion of the proctodaeum and 

post- allantoic gut.

Superiorly, the external sphincter 

blends with the puborectalis portion 

of the levator ani muscle of the 

pelvic floor. 

The puborectalis muscle sling does 

not encircle the anus and is 

deficient anteriorly.

The anal glands lie partly in the submucosal plane and partly between the 

sphincters in the intersphincteric plane; infection in these glands is thought to 

be the main cause of peri- anal sepsis and fistulae. The orifices of the glands 

open just above the anal valves and this is therefore the commonest site of 

the internal opening for a fistula.

Vascular plexi lie beneath the mucosa of the anal canal. 

The main arterial inflow is from the terminal branches of the superior 

rectal artery, which classically divides into a left lateral, a right 

anterolateral and a right posterolateral branch; they anastomose with 

branches of the inferior rectal artery. Three small swellings, or anal 

cushions, are associated with the underlying vascular plexi. 

Blood supply to the anal canal is via superior, middle and inferior rectal vessels

The epithelium of anal canal 

The lining of the anal canal above 

the dentate line is  similar to the 

columnar epithelium of the colon 

and rectum, except that there is a 

junctional zone extending for about 

1 cm above the dentate line. 

Below this line it is modified skin, 

or anoderm, consisting of 

squamous epithelium.

 This change in the mucosa is important, as malignant lesions

 arising in the distal anal canal are more likely to be squamous cell

 carcinomas than adenocarcinomas.

 The dentate line also marks the watershed for lymphatic drainage.

 The upper anal canal drains to the inferior mesenteric nodes and

 the lower anal canal to the inguinal nodes.

 The dentate line is also the division between somatic and visceral

 sensation. Distal pathology in the anal canal may thus be

extremely painful.

EXAMINATION OF THE ANUS 

Careful clinical examination will be diagnostic in the vast majority of 

patients complaining of anal symptoms, but it requires a relaxed patient 

who is informed of what the examination will entail, a private environment, a 

chaperone (for the security of both parties) and good light. 

A rectal examination is essential for any patient with anorectal and/or 

bowel symptoms – ‘If you don’t put your finger in, you might put your 

foot in it’

A proctosigmoidoscopy is essential in any 

patient with bowel symptoms, and particularly 

if there is rectal bleeding

ANAL FISSURE 

An anal fissure is a longitudinal split in the anoderm of the distal 

anal canal which extends from the anal verge proximally towards, 

but not beyond, the dentate line.

Symptoms

: 

•

Pain on defaecation 

•

Bright-red bleeding 

•

Mucous discharge 

•

Constipation

Anal fissure typically located in the Posterior midline of anus. 

~10% of women have anterior midline lesions—weakest muscular 

support

Classically, acute anal fissures arise from the trauma caused by the 

strained evacuation of a hard stool or, less commonly, from the 

repeated passage of diarrhoea.

Chronicity may result from repeated 

trauma, anal hypertonicity and vascular 

insufficiency, either secondary to 

increased sphincter tone or because 

the posterior commissure is less well 

perfused than the remainder of the anal 

circumference.

Treatment of an anal fissure

■

Conservative initially, consisting of stool-bulking agents and 

softeners, and chemical agents in the form of ointments designed 

to relax the anal sphincter and improve blood flow

■

Conservative management should result in the healing of almost 

all acute and the majority of chronic fissures.

Such agents include glyceryl trinitrate (GTN) 0.2 per cent applied four times per 

day to the anal margin (although this may cause headaches) and diltiazem 2 per 

cent applied twice daily.

■ Surgery if above fails, consisting of lateral internal sphincterotomy or 

anal advancement flap

Hemorrhoids are cushions of submucosal tissue containing venules, 

arterioles, and smooth muscle fibers that are located in the anal canal. 

Three hemorrhoidal cushions are found in the left lateral, right anterior, 

and right posterior positions. 

Cushions are thought to function as part of the continence mechanism 

and aid in complete closure of the anal canal at rest. Because 

hemorrhoids are a normal part of anorectal anatomy, treatment is only 

indicated if they become symptomatic.

Haemorrhoids (Greek: haima, blood; rhoos, flowing; synonym: 

piles, Latin: pila, a ball)

External haemorrhoids relate to venous channels of the inferior 

haemorrhoidal plexus and located distal to the dentate line and are 

covered with anoderm. 

Because the anoderm is richly innervated, thrombosis of an external 

hemorrhoid may cause significant pain. 

Internal hemorrhoids are located proximal to the dentate line and 

covered by insensate anorectal mucosa.

Combined internal and external hemorrhoids straddle the dentate 

line and have characteristics of both internal and external 

hemorrhoids.

Causes of hemorrhoid  

Engorged anal cushions and vessels from increased pelvic/

abdominal pressures: 

•

Constipation/straining

•

Pregnancy

•

Ascites/abdominal tumors 

•

Portal hypertension

Symptoms of haemorrhoids: 

•

Bright-red, painless bleeding  

•

Mucous discharge 

•

Prolapse 

•

Pain only on prolapse

Internal hemorrhoids may prolapse or bleed, but rarely become painful 

unless they develop thrombosis and necrosis (usually related to severe 

prolapse, incarceration, and/or strangulation). 

■ First degree – bleed only, no prolapse 

■ Second degree – prolapse, but reduce spontaneously 

■ Third degree – prolapse and have to be manually reduced 

■ Fourth degree – permanently prolapsed

Internal hemorrhoid are graded according to the extent of 

prolapse into four degree:

Complications of haemorrhoids 

■ Strangulation and thrombosis  
■ Ulceration 
■ Gangrene 
■ Portal pyaemia 
■ Fibrosis

Management 

Exclusion of other causes of rectal bleeding, especially colorectal 

malignancy, is the first priority. 

Important measures include attempts at normalising bowel and defaecatory 

habits: only evacuating when the natural desire to do so arises, adopting a 

defaecatory position to minimise straining, and the addition of stool soften- 

ers and bulking agents to ease the defaecatory act. 

Various creams can be inserted into the rectum from a collapsible tube fitted 

with a nozzle, at night and before defaecation. Suppositories are also useful.

Sclerotherapy 

A submucosal injection of 5 per cent phenol 

in almond oil causes both thrombosis of the 

feeding vessels and fibrosis, which tethers 

the lax mucosa, thus reducing prolapse.

Infrared photocoagulation 

With infrared photocoagulation (IRPC) an infrared radiation 

source is applied immediately proximal to the upper 

margin of the haemorrhoid.

The aim is to create fibrosis, cause obliteration of 

the vascular channels and hitch up the anorectal 

mucosa.

In those with first- or second-degree piles whose symptoms are not 

improved by conservative measures,

Banding 

For more bulky piles, banding has been 

shown to be efficacious, but it is 

associated with more discomfort. 

The Barron’s bander is a commonly 

available device used to slip tight elastic 

bands onto the base of the pedicle of each 

haemorrhoid.

The bands cause ischaemic necrosis of the 

piles, which slough off within 10 days; this 

may be associated with bleeding, about 

which the patient must be warned. 

Operation management  

The indications for haemorrhoidectomy include: 

Third- and fourth-degree haemorrhoids 

Second-degree haemorrhoids that have not been cured by 

non-operative treatments 

Fibrosed haemorrhoids 

Interoexternal haemorrhoids when the external 

haemorrhoid is well defined.

Surgical treatment of haemorrhoids

MILLIGAN–MORGAN HAEMORRHOIDECTOMY 

In this classical operation involves resection of 

hemorrhoidal tissue.

Adequate bridges of skin and mucosa must be left 

intact between the excisions to prevent anal 

stenosis developing during healing. 

Closed Submucosal Hemorrhoidectomy.  

The Parks or Ferguson hemorrhoidectomy involves resection of 

hemorrhoidal tissue and closure of the wounds with absorbable 

suture. 

Procedure for prolapse and hemorrhoids 

(PPH) removes a short circumferential segment 

of rectal mucosa proximal to the dentate line 

using a circular stapler. 

This effectively ligates the venules feeding the 

hemorrhoidal plexus and fixes redundant mucosa 

higher in the anal canal. 

Transanal haemorrhoidal dearterialisation 

In this procedure, a Doppler probe is used to identify the artery or arteries 

feeding the hemorrhoidal plexus. These vessels are then ligated. 

Complications of haemorrhoidectomy 

Early  

•

Pain

•

Acute retention of urine

•

Reactionary haemorrhage 

Late 

•

Secondary haemorrhage 

•

Anal stricture

•

Anal fissure

•

Incontinence

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