1. AND ISCHIORECTAL FOSSA
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 Urogenital triangle anteriorly Anal triangle posteriorly
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 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

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 mucocutaneous jnction

12. Mucous Membrane Upper Half Lower 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 involuntary internal 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. 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 vein
Lower half: inferior rectal vein drained into the internal pudendal vein
Important site of portal-systemic anastomosis

17. Nerve Supply
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
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

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
Internal Pudendal Artery

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. 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).
Hemorrhoids

30. 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
Internal Hemorrhoids

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 perianal hematoma in the subcutaneous tissue around anus

32. 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
Anal Fissure

33. Perianal abcesses
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