Download The Ischiorectal fossa

THE ISCHIORECTAL FOSSA
LEARNING OBJECTIVES
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At the end of the lecture the student should be able to:
Know the details of ischiorectal fossa
Identify the boundaries and recessess of ischiorectal fossa
Know the contents of ischiorectal fossa.
ISCHIORECTAL FOSSA
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Wedge shaped spaces between skin of anal region and pelvic diaphragm
Base directed downwards to the surface of the perineum
Apex at the line of meeting of the obturator and anal fascia
5 to 6 cm deep,
anterioposteriorly 5 cm,
2.5 cm side to side
Lie below the levator ani muscles and on either side of anal canal
ISCHIORECTAL FOSSA
Post anal space connects the two fossae posteriorly by a horse shoe path.
The space is filled with loose areolar tissue and loosely arranged large loculi
of fat. The infection of this space leads to abscess formation and are least
painful because swelling can occur without tension.
BOUNDARIES
Base is formed by the skin.
Apex - Is formed by meeting of Obturator fascia with the inferior fascia of the pelvic
diaphragm (anal fascia). The line corresponds to the origin of levator ani from the lateral
pelvic wall.
Anterior wall - The fossa is limited by the posterior border of perineal membrane.
Posterior wall- (a) lower border of the gluteus maximus and (b) Sacro tuberous ligament
Lateral wall is vertical and is formed by
(a) Obturator internus with Obturator fascia,
(b) Medial surface of ischial tuberosity below the attachment of Obturator fascia.
Medial wall - Slopes upwards and laterally and is formed by
(a) External anal sphincter with fascia covering it in the lower part and
(b) levator ani with anal fascia in the upper part.
RECESSES
These are narrow extension of the fossa beyond its boundaries.
1. Anterior recess - Extends forwards above the urogenital diaphragm almost up to
the posterior surface of the body of pubis.
2. Posterior recess - It is smaller than anterior recess. It extends deep
to sacrotuberous ligament.
3. Horse shoe recess (deep post anal space/Post Sphincteric space) Connects the two fossae behind the anal canal
CONTENTS OF ISCHIORECTAL FOSSA
Inside Alcock's canal, on the lateral wall
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Internal pudendal artery
Internal pudendal vein
Pudendal nerve
Outside Alcock's canal, crossing the space transversely
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Perineal branch of fourth sacral nerve
Perforating cutaneous branch of S2, S3 nerve
Inferior rectal artery
Inferior rectal vein
Inferior anal nerves
Fatty tissue across which numerous fibrous bands extend from side to side
PUDENDAL CANAL
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It is a fascial tunnel present in the lower part of the lateral wall of the
Ischiorectal fossa, just above the sacrotuberous ligament
Pudendal canal is formed by splitting of the fascia lunata.
The fascial wall of the canal is fused laterally to the Obturator fascia,
medially to the perineal fascia and inferiorly with the sacrotuberous
ligament. It contains pudendal nerve and the internal pudendal vessels.
LUNATE FASCIA
It arches over the Ischiorectal fat, begins laterally at the pudendal canal and after
arching the Ischiorectal fat fuses medially with the fascial covering of external anal
sphincter.
The fascia divides the Ischiorectal space into
(a) Supra tegmental space above
(b) Tegmental space below
PUDENDAL NERVE
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S2, S3, S4.
In the posterior part of the pudendal canal the pudendal nerve gives off inferior
rectal nerve and then it divides into to terminal branches –
Perennial nerve
Dorsal nerve of penis.
The inferior rectal nerve pierces the medial wall of pudendal canal, crosses the
Ischiorectal fossa from lateral to medial side and supplies the external sphincter,
the skin around the anus and the wall of the anal canal below the pectinate line.
PUDENDAL NERVE S2-S4
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Supplies skin, organs and muscles of perineum
Distribution similar in males and females
Route: (travels with internal pudendal vessels)
Passes through GSF inferior to piriformis
Enters the perineum by passing around the ischial spine and
sacrospinous ligament
Passes through LSF
Functions:
Micturition
Defecation
Erection
Ejaculation
Parturition
INTERNAL PUDENDAL ARTERY
It is smaller of the two terminal division of the anterior trunk of internal iliac
artery. It gives off a branch in the posterior part of the pudendal canal - inferior
rectal artery, and then it divides in two terminal branches
(a) Perineal artery and (b) Artery to penis.
APPLIED ANATOMY
Both the Perianal and Ischiorectal spaces are common site of abscesses.
Poor blood supply and coarse lobulated fat predispose it for infection.
Abscesses in this region are –
(a) Perianal abscess
(b) Ischiorectal abscess
(c) Supra levator abscess
(d) Sub mucous abscess.
Fournier's Gangrene - An uncommon but potentially lethal complication of Ischiorectal
abscess
PUDENDAL NERVE
(a) SPHINCTERIC INCONTINENCE - Injury to the inferior rectal branch of the pudendal
nerve causes Sphincteric incontinence.
(b) PUDENDAL BLOCK - The pudendal nerve is infiltrated with local anaesthetic
solution where it crosses the ischial spine.This means that when complete perineal
anesthesia is required an injection of local anaesthetic must be given around the anus.
Through the inter-sphincteric longitudinal fibers the inter-sphincteric abscess tracks
down and gives rise to Perianal abscess.
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