Where are ischiorectal fossae located ?
Ischiorectal fossae are located in the lateral part of the anal triangle on either side of the anal canal. They are pyramida/wedge shaped , with apex directed upwards and base downwards. they are fat filled spaces that help in dilatation of anal canal during defecation. They are approximately 5cm. long, 5cm. wide and 5cm deep.
Name the structures that form boundaries of ischiorectal foss.
Boundaries of Ischiorectal fossa
- Anteriorly: Posterior free border of urogenital diaphragm.
- Posteriorly: Lower border of gluteus maximus and sacrotuberous ligament.
- Medially: Levator ani above and sphincter ani externus below.
- Laterally: Obturator internus with obtrurator fascia above and ischial tubrosity below.
- Superiorly: Is the apex- where the fascia lining the perineal surface of levator ani (inferior fascia of pelvic fascia) meets the obturator fascia.
- Inferiorly : is the floor : Perineal skin.
Posteriorly the two ischiorectal fossae communicate with each other behind the anal canal.
What are the contents of Ischio-rectal fossa?
Following are the contents of ischio-rectal fossa:
- Ischiorectal pad of fat.
- Inferior rectal nerve and vessels.
- Perineal branch of S4.
- Branches of posterior cutaneous nerve of thigh (S2,S3).
Describe briefly the perianal fascia, fascia lunata and the spaces associated with the Ischio-rectal fossae.
Perianal fascia:Is formed by the lateral most septum from the lower end of the conjoint longitudinal tendon of anal canal.
Lunate fascia: The subcutaneous fat raises the deep fascia in the region of ischiorectal fossa to form a dome shaped lunate fascia.
Spaces around ischio-rectal fossae:
- Perianal space: Is between skin below and perianal fascia above. It is divided into numerous small fat filled compartments by fibroelastic septa derived from the longitudinal coat of anal canal. The infection in this space causes perianal abscess, which is very painful.
- Ischioananal space proper: Is between perianal fascia below and lunate fascia above.
- Suprategmental space: Is above the lunate fascia.
Describe briefly location, formation and contents of Pudendal canal.
Pudendal canal is an elongated fascial canal located along the lateral wall of ischiorectal fossa. It Is formed by separation of fascia lunata medially from the obturator fascia laterally. It extends from the lesser sciatic foramen to the to the anterior end of the ischiorectal fossa . It contains :
- Pudendal nerve (S2, S3, S4) divides in the canal into its terminal branches.
- Dorsal nerve of penis/clitoris
- Perineal nerve
- Internal pudendal vessels.
Inferior rectal nerve and vessels (branches of pudendal nerve and internal pudendal vessels arise in the pudendal canal and pierce the fascia lunata to reach the anal canal.
Applied Aspects
Pudendal nerve Block
Pudendal nerve can be blocked in the pudendal canal by
- Injecting local anaesthetic agent via perineal route. The needle is inserted along the medial side of the ischial tuberosity and the anaesthetic solution is injected in the canal about 2.5cm from the surface.
- Injecting local anaesthetic agent where it crosses ischial spine. Ischial spine is palpated through the vagina and the needle in inserted through the vaginal wall and guided by a finger to the ischial spine.
Ischiorectal abscess
Ischiorectal fossae are prone to infection due to its location. It is common because the fat in the fossa is poorly vascularized and may get infected from the infections from anal canal or from infections in the perianal skin. The infection from one ischiorectal fossa may pass to other behind the anal canal forming horseshoe shaped abscess.
Herniation of pelvic viscera
Herniation of pelvic viscera into the ischio-rectal fossa may occur if there is a gap due to separation of levator ani muscle from the obturator fascia. The gap is called Hiatus of Schwalbe.
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