ANAL CANAL, ANAL TRIANGLE AND ISCHIORECTAL FOSSA

1. ANAL CANAL, ANAL TRIANGLE AND ISCHIORECTAL FOSSA

2. Perineum • Lower most part of the trunk. • Below the pelvic diaphragm. • It carries the external genital organs

3. Perineum • In 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

4. Boundaries • Perineum is bounded by: • Pubic symphysis • Inferior pubic rami • Ischial rami • Ischial tuberosity • Sacrotuberous ligaments • Coccyx

5. Divisions • For descriptive purposes, • It is divided by an imaginary line joining the two ischial tuberosities, into two triangles: • Urogenital triangle anteriorly • Anal triangle posteriorly

6. Anal Triangle • Bounded: • 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 muscles • Contains: • Anal canal, • External anal sphincter • Ischiorectal fossa

7. Anal Triangle • The perianalskin 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 inguinallymph nodes

8. Anal Canal • About 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.

9. Relations of the Anal Canal • Anteriorly: • Perineal body • Urogenital diaphragm • Membranous urethra & bulb of penis in male, and lower part of vagina in female • Posteriorly: • Anococcygeal body • Laterally: • Ischiorectal fossa

10. 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

11. 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 mucocutaneousjnction

12. Mucous Membrane • Upper 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

13. Muscles • Two distinct layers: outer longitudinal & inner circular layer of smooth muscle • Thickening of the smooth muscles of the circular layer at the upper end of anal canal forms the involuntaryinternal sphincter • The internal sphincter is enclosed by a sheath of skeletal muscle that forms the voluntary external sphincter

14. External Anal Sphincter • Voluntary • 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

15. Anorectal Ring • A distinct muscular ring formed at the junction of rectum and anal canal • Formed by the internal sphincter, deep part of the external sphincter and the puborectalis • Can be felt at rectal examination • Helps in increasing the anorectal angle

16. 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 vein Lower half: inferior rectal vein drained into the internal pudendal vein Important site of portal-systemic anastomosis Blood Supply

17. Mucous membrane Upper 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 Nerve Supply

18. Lymphatic • Upper half: pararectal nodes & then to inferior mesenteric lymph nodes • Lower half: medial group of the superficial lymph nodes

19. Ischiorectal Fossa

20. Ischiorectal Fossa • A large fascia-lined wedge-shaped space on each side of the anal canal • Located between the skin of the anal region and the pelvic diaphragm • The two fossae are communicated with each other behind the anal canal

21. Boundaries • Base 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

22. Contents • Dense fat • Pudendal canal and its contents (internal pudendal vessels & nerves) • Inferior rectal vessels & nerve • Perforating branches of S2-S3 • Perineal branch of S4

23. Pudendal Canal • A 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

24. Pudendal Nerve • Branch of sacral plexus • Leaves pelvic cavity through the greater sciatic foramen • Enters perineum through the lesser sciatic foramen • Passes forward in the pudendal canal • Gives branches: • Inferior rectal nerve • Dorsal nerve of penis or clitorus • Perineal nerve

25. Internal Pudendal Artery • Branch of Internal iliac artery • Leaves pelvic cavity through the greater sciatic foramen • Enters perineum through the lesser sciatic foramen • Passes 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

26. CLINICAL NOTES

27. 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 delivery • The anaesthetic can be injected around the nerve by: • Transvaginal method • Perineal method

28. Rectal Prolapse • Normally, 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

29. Hemorrhoids • A 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).

30. Internal Hemorrhoids • Varicosities 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

31. External Hemorrhoids • Varicosities of the tributaries of inferior rectal vein covered by skin • Varicosed tributaries may rupture due to coughing or straining and form a perianalhematoma in the subcutaneous tissue around anus

32. Anal Fissure • It 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

33. Perianalabcesses • Produced by fecal trauma and infection to anal mucosa • May be: • Submucosal • Subcutaneous • Pelvirectal • Ischiorectal • Spread or inadequate treatment of abscess may lead to the formation of anal fistula and anal sinus

34. Ischiorectal Abscess • Fossa 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