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Anatomy Of The Anal Canal

  1. The anal canal is 3-4cm in length and runs from the anorectal junction to the anus verge. The line of the anal valves, often called the dentate line, is approximately half way along the anal canal. Anal columns extend upwards from this line.
  2. The columnar epithelium of the rectum is replaced by mixed columnar and squamous epithelium in the upper anal canal, corresponding to the zone of fusion between the embryological hindgut and the proctodeum.
  3. Between the line of the anal valves and the lower border of the internal sphincter, the epithelium is str squamous and often referred to as the pecten.
  4. At the anal margin, the epithelium becomes hair-bearing skin.
  5. Sphincters: Two sphincters surround the anal canal: the internal sphincter, which is the expanded distal portion of the circular smooth muscle; and the external sphincter, which is derived from the striated muscle of the pelvic floor and becomes continuous with the puborectalis and the levator ani muscles.
  6. Spaces: There are three important spaces in the area. The intersphincteric space contains the terminal fibres of the longitudinal muscle of the gut and the anal intermuscular glands.
  7. These anal glands are important in the pathogenesis of abscesses and fistulae. The ischiorectal fossa lies outside the external sphincter, and the supra-levator space is between the rectum and the levator ani muscles.
Carcinoma Anal Canal
  • MC type of CA anal canal: SCC >BCC >Melanoma
  • Median age at diagnosis: 60 years
- MC symptom: Bleeding PR
- MC site of metastasis: Lung
- MC site of LN metastasis: Inguinal LNs
Risk Factors for Carcinoma Anal Canal
• HPV infection (16, 18, 31, 33)
• HIV or Immuno-suppression      
• Smoking
• anal receptive intercourse
• Sexual promiscuity
• Chronic inflammation
• Anal intra-epithelial neoplasia
• History of vulvar or cervical cancer
  1. Congenital Anorectal Anomalies
    1. It occurs in 1:5000 births with a slight male predominence. Anorectal anomalies, varies from anal stenosis and imperforate anus to complete ano-rectal agenesis.
    2. Agenesis accounts for over 75% of anorectal atresias and is often complicated by vaginal, vesical or urethral fistula. Anal stenosis is usually manifest at birth with the presence of a small anal aperture containing a dot of meconium.
    3. The abdomen may be distended, and defaecation - if possible - results in a ribbon-like stool.
    4. Anorectal anomalies are one component of the VACTERL association (Vertebral, Anal, Cardiac, Tracheal, Esophageal, Renal, and Limb abnormalities).
    5. The diagnosis of anorectal anomalies is clinical by inspection of the perineum. Rectal atresia presents clinically  with abdominal distension and failure to pass meconium.
    6. Anorectal malformation classified into low type and high type.
    7. Low type include –
      1. Membranus type – treatment is by excision of membrane
      2. Anal stenosis –  treatment is by anal dilatation upto the age of 1-2 year.
      3. Anal atrasia – treatment is by Posterior sagital anorecto plasty. 
    8. The outlook following surgery is good if the bowel has passed through the puborectalis sling. However, high abnormalities are usually associated with a rectourethral fistula in the male or rectovaginal fistula in the female.
    9. The terminal bowel may be blind but commonly is associated with a fistula to the bladder, prostate, perineum  or vagina. Meconium may be passed per vaginam or urethram. Initial surgery is a colostomy with definitive surgery being delayed.
    10. During this the fistula is closed and a pull through operation is performed.
  • Imaging
  1. A lateral decubitus radiograph (Prefer) or Invertogram is taken, the anal dimple being marked with barium. The film should not be taken before 12 hours to allow sufficient passage of air distally. In a low lesion air reaches the perineum.
  2. In a high lesion the bowel ends above the pelvic sling and lies above the M line, a line running horizontally through the junction of the lower 1/3 and upper 2/3 of the ischia and the sacrococcygeal junction.
  3. Ultrasound of the renal tract should be performed to rule out renal anomalies.
  4. The exact site of the blockage is better determined by running contrast medium into the distal loop of the colon after a colostomy has been performed (distal colonogram).
  5. Treatment of choice for high type of anorectal malformation include closure of fistula and Posterior Sagittal Anorectoplasty, pelvic floor repair with colostomy and colostomy closure after 2-3 Months.
  6. If facility of surgery is not available or neonate is not fit for surgery, minimum 1st surgical procedure for anorectal malformation is transverse colostomy.Q
  1. Hemorrhoids
    1. Hemorrhoids are masses of mucosa, submucosa, venule and arteriol in the anal canal. The prevalence of hemorrhoids is equal in both sexes. They arise from a plexus of dilated veins originating from the superior and inferior hemorrhoidal veins, are located in the submucosal layer.
    2. Hemorrhoids are classified as internal and external, based on whether they arise above or below the dentate line, and often coexist.
    3.  Internal hemorrhoids arise from the superior (internal) hemorrhoidal vascular plexus, and their primar locations are the 3, 7, and 11 o'clock positions corresponding to the end branches of the middle and superior hemorrhndal veins.
    4. External hemorrhoids are dilations of the inferior (external) hemorrhoidal plexus and lie below the dentate line, covered with squamous epithelium that contains numerous somatic pain receptors. External skin tags represent residual excess skin associated with prior thrombosis of external hemorrhoids,
    5. Internal and external hemorrhoids communicate with each other and drain into the internal pudendal veins.Hemorrhoids may reside in proximity to rectal varices in patients with cirrhosis but are more common in patients with portal hypertension.
    6. Hemorrhoids has been associated with increasing age, chronic diarrhea, pregnancy, pelvic tumors, prolonged sitting and straining, and possibly chronic constipation.
    7. Haemorrhoids usually present with the passage of bright red blood. Bleeding is usually self-limited but may be associated perianal pain, prolapse, mucous discharge and pruritus.
    8. Thrombosis may affect external or internal components.
    9. A small area of involvement of the external plexus is often referred to as a perianal haematoma. These are painful and may progress to ulceration and/or haemorrhage.
    10. It is classified into primary and secondary:
Primary:                                              Secondary:
  1. Idiopathic (Most common)            a. CA rectum
  2. Constipation                                     b. Portal hypertension
  3. Fecolith formation                             c. Pregnancy
Classification of Internal hemorrhoids
1st degree  Painless bleeding, no prolapse
2nd degree  Prolapse through the anus, on straining but reduce spontaneously
3rd degree  Prolapse through the anal canal and require manual reduction
4th degree  Permanently prolapsed and cannot be manually reduced
Extra Edge:
Clinical Features:
• More common when intra-abdominal pressure is raised, e.g. in obesity, constipation and pregnancy?
• Symptoms: bright-red, painless bleeding, mucus discharge and prolapse
• Hemorrhoids cannot be palpated, best diagnosed by proctoscopy"
Internal Hemorrhoids External Hemorrhoids
·  Located proximal to the dentate Iine
·  Painless, can be Iigated
·  Banding is preferred
·  Located distal to dentate Iine
·  Also known as 5-days painful self curing lesion
·  Painful, not Iigate
·  Excision is done
· Repeated thrombosis leads to semi-ripe black current appearance
Management of Hemorrhoids
  1. Treatment is for primary hemorrhoid only.
  2. Conservative treatment for 1o and 2o which includes proper diet, use of bulk-forming agents, warm sitz baths and avoidance of prolonged sitting.
  3. Minimally invasive interventions are rubber band ligation or sclerotherapy (only for interntal hemorrhoid), infrared or laser photocoagulation, bipolar diathermy, cryosurgery, and dilation of the internal anal sphincter, wich are usually, reserved for 1o and 2o hemorrhoids (When not responding with conservative treatment).
  4. Surgical management required for 3o and 4o .
  5. The most common technique is a closed hemorrhoidectomy in which an elliptical incision is made on the external hemorrhoidal tissue and all 3 hemorrhoidal columns are treated at a time, and the defect is closed with a continuous absorbable suture.
  6. This procedure has a 95% success rate and a low rate of wound infection. Open hemorrhoidectomy involves excision and ligation of internal hemorrhoids without mucosal closure.
  7. Stapler anopexy or hemorrhoid pexy is latest surgical option for 3o and 4o hemorrhoid.
Complications of hemorrhoidectomy
- Pain (MC)
- Acute retention of urine (2nd MC)
- Reactionary hemorrhage
- Secondary hemorrhage
- Anal stricture
- Anal fissure
- Incontinence
  1. Abscess And Fistula
    1. Abscesses and fistulae begin as a nonspecific infection of the anal crypts glands which may produce an abscess between the two sphincters - the so-called intersphincteric abscess, (Most common)
    2. Infection may then spread, to the anal margin gives rise to a perianal abscess.
    3. Upward spread produces either an intermuscular abscess or a supralevator abscess.
    4. Horizontal spread carries infection back into the anal canal across the internal sphincter.
    5. Across the striated muscle into the ischiorectal fossa forming an ischiorectal abscess.
    6. If the primary track passes through the external sphincter, it is termed trans-sphincteric, but if above the puborectalis, supra sphincteric.
    7. Circumferential spread carries infection in the intersphincteric space, supralevator space or the ischiorectal fossa to the opposite side
    8. Fistulae are classified according to the position of the primary track - intersphincteric if it lies between the sphincters, trans-sphincteric when it crosses the external sphincter and suprasphincteric when it crosses above the puborectalis muscle.
    9. Perianal fistulae are a major feature of Crohn's disease and are usually associated with rectal involvement; rarely do they represent spread from more proximal bowel disease.
    10. Anorectal fistulas can develop in other medical disorders such as anorectal malignancy, lymphogranuloma venereum, radiation proctitis, actinomycosis, tuberculosis, and leukemia.
    11. Classification of fistula in ano given by park / standard classification:
      1. Low type        
      2. ​High type (Supra levator / Pelvi rectal)
Classification of anorectal fistulas
Fistula Type Description
Intersphincteric Travels along intersphincteric plane to the perianal skin
Transsphincteric Encompasses a portion of the internal and external anal sphincters and terminates on the skin overlying the buttock
Suprasphincteric Encompasses the entire anal sphincter
Extrasphincteric Extends from an internal opening in the bowel proximal to the anus, encompasses the entire anal sphincter, and opens onto the skin overlying the buttocks
  1. The goal of surgical management is to eradicate the fistula while preserving fecal continence. Intersphincteric fistulas are managed by a primary fistulotomy; the base of the wound is then curetted and left open to heal by secondary intention.
  2. Transsphincteric fistulas are divided into low and high fistulas. Low fistulas are managed by a fistulotomy.
  3. High transsphincteric and supra levator fistulas are managed with a cutting seton.
  4. This procedure involves placing a reactive suture or elastic through the fistulous tract and tightening it sequentially until it cuts through the tract. A relatively new therapy involves the injection of fibrin glue.
  1. SOLITARY RECTAL ULCER SYNDROME (Mucosal prolapse syndrome)
    1. Most common site is anterior rectal wall.
    2. SRUS is a benign condition and usually presents in women during the third and fourth decades of life.
    3. SRUS pursues a chronic course of constipation, mucorrhea-associated rectal prolapse, rectal bleeding, and tenesmus.
    4. It is characterized by an indolent, shallow, whitish ulcer surrounded by hyperaemic mucosa on the anterior wall of the rectum, typically 7-10 cm from the margin.
    5. There is usually some degree of intussusception of the anterior rectal wall into the anal canal, and the ulceration is probably caused by trauma to the mucosa during excessive straining against an actively contracting puborectalis.
    6.  Once clinical symptoms are elucidated flexible recto-sigmoidoscopy & biopsy is performed to confirm the diagnosis and exclude malignant ulcer.
    7. Histopathology examination of SRU: Proliferation of muscular layer with devoid of inflammatory cells.Q
    8. Management of SRUS is based on the presence of symptoms.
    9. Usually conservative therapy with bulk laxatives, application of local steroids or 5-acetylsalicylic acid (ASA) and  bowel retraining is attempted before considering surgical options.
    1. Rectal prolapse represents an intussusception of the rectum from a point typically some 8cm above the anus.
    2. Prolapse is usually associated with generalized laxity of the pelvic floor and defective sphincter function
    3. It also occurs with conditions in which intra-abdominal pressure is raised, such as cystic fibrosis, and should be distinguished from prolapse of an adenoma or other neoplasm
  • Types -          
  1. Partial - only the mucosa protrudes out. This is the most common type.
    1. It is seen at the extremes of age.
    2. Treatment in children is digital reposition after each and every defecation.
    3. Rarely sub-mucosal injections of a mixture of phenol & almond oil causing aseptic inflammation and later on fibrosis & adherence of mucosa to muscle.
    4. Operative treatment in children is required only in the severe & recurrent cases where repstein (preferred) or thiersch's operation can be performed.
  2. Total (procidentia)- entire wall of rectum protrudes out. This is less common.
    1. It is actually a hernia - en - glissade of the rectum, where it slides down, & may bring along the surrounding structures or a peritoneal pouch along with it.
    2. Commonly starts in anterior wall, where the support is weakest, especially in women. Anal sphincter is  patulous & gapes widely on straining. It is usually >4 cm in length. Concentric folds can be seen on mucosa  (radial in partial).
    3. Definitive treatment is for complete prolapse is surgery.
Trans anal approach -
  1. Thiersch's operation
  2. Delorme's operation - Stripping of redundant mucosa + plication of muscle wall to create a ring + re-suturing of anal mucosa to rectal mucosa
  3. Altmeirs operation
Abdominal approach –
Laproscopic mesh rectopexyQ is the option of choice for rectal prolapse.
Repstein operation "sling" procedures to hold rectum to a fixed structure.
Gold berg operationQ include resection rectopexy (anterior resection with suture rectopexy)
  • It is a surgical option of choice in complete rectal prolapse with severe constipation and redundent sigmoid colon. 
Well's operation - rectum held to sacrum by polyvinyl alcohol sponge - evokes a fibrotic reaction.
  1. Pilonidal sinus
    1. A pilonidal sinus is a subcutaneous sinus containing hair
    2. Lined by granulation tissue rather than epithelium
    3. Usually occur in the natal cleft
    4. Also seen in interdigital clefts, face and axilla
    5. Usually seen in young & hairy adults. 
    6. Rare after the age of 40 years
    7. Male : female ratio is 4:1
  1. It is an acquired condition
  2. Inflamed hair follicles in the cleft result in abscess or sinus formation
  3. Hair becomes trapped in cleft and enters sinuses
  4. Results in a foreign body reaction and perpetuates sinus formation
  5. 80% present with recurrent pain    
  6. 80% present with a purulent discharge
  • Treatment
  1. Consider methylene blue injection to identify all of the tracts
  2. Antibiotic prophylaxis may be of benefit
  3. Options available included:
    1. Excision and healing by secondary intention
      1. Requires regular wound dressing and shaving
      2. Produces 70 - 90% healing at 70 days
      3. 5-15% recurrences rate
    2. Excision and primary closure
      1. Produces 70% healing at 2 weeks
      2. 20% develop wound infection
    3. Phenol injections
      1. Produces 60 - 70% healing
    4. Skin flap procedures (e.g. Karydakis procedure)
      1. Aim to flatten natal cleft and keep scar from midline
      2. In expert hands produces good results
      3. Failure rates as low as 5% have been reported
      4. Bascom procedure
  1. Anal Canal- cancer of the anal canalQ
    1. M.C. type squamous cell carcinoma (Epidermoid type)
    2. M.C. site of occurence is from anorectal ring to halfway between dentate line & anal verge (w 55% are distal to the pectinate line)
    3. Occurs in 6th/7th decades of life.
    4. M:F = 1:2 (i.e. female dominance)
    5. Etiology/Risk factors
      1. Sexually transmitted HPV infection (can lead to condyloma acumiñata progress to carcinoma)
      2. Homosexual males due to anal intercourse
      3. In AIDS patients
      4. Renal transplant recipients (Remembers hemorrhoids, fissures, fistulae & abscesses in the anal region were considered risk factors best studies have failed to support the association).
      5. Clinical manifestations are usually late & nonspecific, can lead to bleeding, pain, sensation of perianal mass & pruritis.
      6. Investigation of choice is biopsy from anal growth.
      7. Definitive diagnosis by biopsy (forceps, needle or excisional biopsy)
      8. CT, MRI, EUS (endoanal Ultrasonography) are useful to assess the spread.
      9. Lymph node metastasis
        1. Below dentate line —> inguinal lymphnodes
        2. Above dentate line —> Superior rectal, internal pudendal, hypogastric or obturator lymph nodes.
        3. M.C. site of distant spread —* Liver.
  • Treatment
  1. Treatment of choice is Nigro regimen which include concurrent chemoradiation (chemotherapy – 5Fu with mitomycin).
  2. Radical surgery (abdomino perineal resection with lymph node sampling and a permanent colostomy) is reserved for those having
    1. Residual tumor
    2. Sphicter involvement
    3. Adenocarcinoma of anal canal
    4. Malignant melanoma of anal canal
    5. GIST of anal canal

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