ANAL CANAL, ANAL

TRIANGLE AND

ISCHIORECTAL FOSSA

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Perineum

Lower most part of the trunk.

Below the pelvic diaphragm.

It carries the external genital organs

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PerineumIn anatomical position it is a narrow area between the 2 thighs

When the thighs are abducted, it is a diamond-shaped area extending from pubic symphysis anteriorly to the tip of the coccyx posteriorly

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BoundariesPerineum is bounded by: Pubic symphysis Inferior pubic rami Ischial rami Ischial tuberosity Sacrotuberous

ligaments Coccyx

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DivisionsFor descriptive purposes,

It is divided by an imaginary line joining the two ischial tuberosities, into two triangles:

Urogenital triangle anteriorly

Anal triangle posteriorly

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Anal TriangleBounded: Anteriorly: by the

imaginary line Behind: by the tip of

coccyx On each side: by the

ischial tuberosity and the Sacrotuberous ligament

Overlapped by the lower border of the gluteus maximus musclesContains: Anal canal, External anal sphincter Ischiorectal fossa

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Anal Triangle The perianal skin is: Pigmented, &

corrugated Has many sweat

and sebaceous glands

Is supplied by inferior rectal nerve and vessels

Its lymphatics drain into medial group of superficial inguinal lymph nodes

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Anal CanalAbout 4 cm long

Passes downward and backward from the rectal ampulla, at the level of the sling of the puborectalis part of levator ani

Remains contracted and forms an antero-posterior slit, except during defecation.

The walls are kept in apposition by the levator ani muscle and the anal sphincter.

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Relations of the Anal CanalAnteriorly: Perineal body Urogenital

diaphragm Membranous

urethra & bulb of penis in male, and lower part of vagina in female

Posteriorly: Anococcygeal body

Laterally: Ischiorectal fossa

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Development of The Anal Canal

Embryologically the anal canal is developed from two sources: • Upper half is derived

from hindgut (Endodermal)

• Lower half is derived from the proctodeum (Ectoderm).

The junction of the two parts is indicated by the pectinate line

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The part of anal canal superior to pectinate line differs from the part inferior to pectinate line in its:• Epithelial lining• Arterial supply• Venous drainage• Innervation• Lymph drainage

The white line (below the pectinate line) indicates the site of mucocutaneous jnction

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Mucous MembraneUpper Half Lined by columnar

epithelium Thrown into vertical

folds called anal columns, which are

joined together at lower ends by semilunar folds

called anal valves (semilunar folds are remnants of the anal

membrane)

Lower Half: Lined by stratified

squamous epithelium No columns

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MusclesTwo distinct layers: outer longitudinal & inner circular layer of smooth muscleThickening of the smooth muscles of the circular layer at the upper end of anal canal forms the involuntary internal sphincterThe internal sphincter is enclosed by a sheath of skeletal muscle that forms the voluntary external sphincter

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External Anal SphincterVoluntary

Composed of skeletal muscle

Surrounds the inferior 2/3rd of anal canal

Divided into three parts: Subcutaneous part:

encircles the lower end of the anal canal, has no bony attachment

Superficial part: attached to perineal body anteriorly, and coccyx posteriorly

Deep part: encircles the upper end of the anal canal, has no bony attachment

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Anorectal RingA distinct muscular ring formed at the junction of rectum and anal canalFormed by the internal sphincter, deep part of the external sphincter and the puborectalisCan be felt at rectal examinationHelps in increasing the anorectal angle

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Blood Supply Arteries: Upper half: superior rectal artery (continuation of the inferior mesenteric artery)Lower half: inferior rectal artery from internal iliac artery.

Venous Drainage:Upper half: superior rectal vein drained into the inferior mesenteric veinLower half: inferior rectal vein drained into the internal pudendal vein• Important site of

portal-systemic anastomosis

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Nerve Supply

Mucous membraneUpper half: Sensitive only to

stretching Supplied by

inferior hypogastric plexus

Lower half: Sensitive to pain,

temperature, touch and pressure

Supplied by inferior rectal nerve

Involuntary internal sphincter supplied by inferior hypogastric plexus (sympathetic) & pelvic splanchnic nerves (parasympathetic) Voluntary external sphincter supplied by inferior rectal nerve (branch of internal pudendal nerve) and peineal branch of the S4 nerve

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LymphaticUpper half: pararectal nodes & then to inferior mesenteric lymph nodes

Lower half: medial group of the superficial lymph nodes

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Ischiorectal Fossa

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Ischiorectal FossaA large fascia-lined wedge-shaped space on each side of the anal canalLocated between the skin of the anal region and the pelvic diaphragmThe two fossae are communicated with each other behind the anal canal 20

BoundariesBase of the wedge is superficial and formed of skin and fascia

Apex lies superiorly, at the junction of medial and lateral walls

Medial wall is formed by sloping levator ani muscle and the anal canal

Lateral wall is formed by ischial tuberosity and the lower part of obturator internus muscle and its fascia

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ContentsDense fat

Pudendal canal and its contents (internal pudendal vessels & nerves)

Inferior rectal vessels & nerve

Perforating branches of S2-S3

Perineal branch of S4

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Pudendal CanalA fascial canal formed by the splitting of the obturator fascia

Located on the lateral wall of the ischiorectal fossa, on the medial side of the ischial tuberosity

Contains pudendal nerve and internal pudendal vessels

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Pudendal NerveBranch of sacral plexusLeaves pelvic cavity through the greater sciatic foramenEnters perineum through the lesser sciatic foramenPasses forward in the pudendal canalGives branches: Inferior rectal nerve Dorsal nerve of penis

or clitorus Perineal nerve

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Internal Pudendal ArteryBranch of Internal iliac arteryLeaves pelvic cavity through the greater sciatic foramenEnters perineum through the lesser sciatic foramenPasses forward in the pudendal canal with the pudendal nerve.

Gives the following branches: Inferior rectal artery Branches to penis

or to clitoris and to labia

Accompanied veins are tributaries of the internal pudendal vein

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CLINICAL NOTES

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Pudendal Block

Pudendal nerve as it runs in the pudendal canal, it is blocked by an anaesthetic to produce analgesia of the perineum in forceps deliveryThe anaesthetic can be injected around the nerve by: Transvaginal method Perineal method

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Rectal ProlapseNormally, the rectum is attached to the pelvis with the help of ligaments and muscles. This attachment firmly holds the rectum in place. Various factors (age, long-term constipation, the stress of childbirth) may cause these ligaments and muscles to weaken.This causes the rectum to prolapse (it slips or falls out of place)May be A. incomplete (mucosal) B. complete involving the rectal

wall

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HemorrhoidsA condition in which the veins around the anus or lower rectum are swollen and inflamed.

May result from straining to move stool, chronic constipation or diarrhea, pregnancy, aging

Hemorrhoids are either inside the anus (internal) or under the skin around the anus (external).

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Internal HemorrhoidsVaricosities of the tributaries of superior rectal vein covered by mucous membrane Tributaries which lie in anal columns at 3, 7, 11 o’clock position are more prone to become varicosed.3 degrees:– 1st degree: contained

within the anal canal– 2nd degree: protrude

out of anal canal during defecation but return back after it

– 3rd degree: protrude in defecation and remain outside

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External HemorrhoidsVaricosities of the tributaries of inferior rectal vein covered by skin

Varicosed tributaries may rupture due to coughing or straining and form a perianal hematoma in the subcutaneous tissue around anus

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Anal FissureIt is an elongated wound produced by tearing of anal valves due to passage of hard fecal mass

Occurs most commonly in the midline posteriorly or anteriorly

Is extremely painful condition and is usually examined under anaesthesia

Anal fissure in the lower part of anal canal results in reflex spasm of external anal sphincter

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Perianal abcessesProduced by fecal trauma and infection to anal mucosaMay be: Submucosal Subcutaneous Pelvirectal Ischiorectal

Spread or inadequate treatment of abscess may lead to the formation of anal fistula and anal sinus

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Ischiorectal AbscessFossa is filled with fat

Is poorly vascularized

Is vulnerable to infection from anal canal

Abscess of one side may spread to opposite fossa across the midline behind the anal canal

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