The perineum includes all structures below the pelvic diaphragm and occupies the pelvic outlet. The ischio-rectal fossa is a space on each side of the anal canal bounded above by the pelvic diaphragm and below by the ischium bone. It contains fat which acts as a cushion for the rectum and anal canal during defecation. The fossa has several recesses and is divided by fascia into supra-tegmental, ischio-rectal, and perianal spaces containing fat, vessels, and nerves. Diseases that can affect the fossa include hernias, abscesses, fistulas, and infections due to its anatomical structure

1. PERINEUM

2. INTRODUCTION
• It includes all structures which occupy the
pelvic outlet and lie below the Pelvic
Diaphragm.
• Pelvic outlet is diamond shaped space.

3. SUPERFICIAL BOUNDARIES
• In front :
• Behind :
• Antero-laterally :
• Postero-laterally :

6. DEEP BOUNDARIES
• In front :
• Behind :
• Antero-laterally :
• Postero-laterally :

10. DIVISIONS
1. Anal triangle
2. Urogenital triangle

12. ISCHIO-RECTAL
FOSSA

13. INTRODUCTION
 It’s a space on each side of Anal Canal
between inferior surface of the Pelvic
Diaphragm and Pelvic surface of Ischium.
 Filled with fat acting as elastic cushion to
allow expansion of the Rectum and Anal canal
during defaecation.

14. DIMENSIONS
• Wedge shaped
• Apex directed upwards
• Lateral wall – vertical
• Medial wall – slopes downwards and medially.
• Dimensions :
• Vertically : 5 cm
• Antero-posteriorly : 5 cm
• Transversely : 2.5 cm.

15. BOUNDARIES
• Laterally :
• Medially :
• In front :
• Behind :
• Apex / Edge :
• Base :

18. RECESSES OF FOSSA
1. Anterior recess :
 Each fossa presents a forward extension along
the pubic arch and above the Deep Perineal
pouch.
 Its triangular in cross section.
 Its situated between Pelvic Diaphragm and
Urogenital Diaphragm.

19. RECESSES OF FOSSA
2. Posterior recess :
 Each fossa presents a backward extension to
the side of coccyx between Sacrotuberous and
Sacrospinous ligaments.
3 Horseshoe recess :
 It connects the two ischio-anal fossae behind
the anal canal.

21. FASCIAL DISPOSITION OF THE FOSSA
 Lunate fascia :
 Its arranged in an arched manner and lines
deepest part of the fossa.
 Laterally :
 It covers Obturator fascia
 Forms medial wall of Pudendal canal
 Medially :
 It covers Anal fascia
 Blends with Anal fascia at Hilton’s line.

23. FASCIAL DISPOSITION OF THE FOSSA
 Alcock’s / Pudendal canal :
 It’s a fascial tunnel situated in lateral wall of
the fossa about 2.5 cm above Ischial tuberosity.
 It extends from Lesser Sciatic Foramen to the
posterior limit of Deep Perineal Pouch.
 It is formed by splitting of Obturator fascia /
separation between Lunate and Obturator
fascia / splitting of the Perianal fascia.

24. FASCIAL DISPOSITION OF THE FOSSA
 Perianal space :
 Perianal fascia separates shallow subcutaneous
perianal space from deep Ischio-anal space.
 Fat in perianal space is tightly arranged in
small loculi formed by complete septa.
 Infections here are very painful.
 Ischio-anal space : Large and Deep.
 Fat here is loosely arranged in large loculi
formed by incomplete septa. Least painful.

25. CONTENTS OF PUDENDAL CANAL
1. Internal Pudendal vessels
2. Pudendal nerve which divides within the
canal into Perineal nerve and dorsal nerve of
penis /clitoris.

27. DIVISIONS OF ISCHIO-RECTAL FOSSA
 Supra-tegmental space :
 Its situated between the apex of the fossa and
the Tegmentum of Lunate fascia.
 It contains loose fat.
 Ischio-rectal space :
 Its bounded above by Lunate fascia and below
by Perianal fascia.
 Its filled with fat which is traversed by fibrous
tissue.

28. DIVISIONS OF ISCHIO-RECTAL FOSSA
 Perianal space :
 Its bounded above by Perianal fascia and
below by Perianal skin.
 Its subdivided into numerous compartments
by fibro-elastic septa and contains loculated
fat.

29. CONTENTS
1. Internal Pudendal vessels and nerve :
2. Inferior Rectal vessels and nerve
3. Posterior Scrotal / labial vessels and nerve
4. Perineal branch of 4th Sacral nerve
5. Perforating branches of 2nd and 3rd Sacral
nerves.
6. A pad of fat.

30. 1. Internal Pudendal vessels and nerve :
2. Inferior Rectal nerve – External anal
sphinctor, skin around anus, lining of the anal
canal.
• Inferior Rectal vessels – skin, muscles and
mucous membrane of the anal region.
3 Posterior Scrotal / labial vessels and nerve –
4 Perineal branch of 4th Sacral nerve –
 It pierces Coccygeus and appears in fossa by
the side of tip of coccyx to supply external
anal sphinctor and adjoining skin.

31. 5 Perforating branches of 2nd and 3rd Sacral
nerves –
• They carry fibres from dorsal branches of
ventral rami of S 2,3, pierces Sacrotuberous
ligament to supply the skin over lower part of
buttock.
6 A pad of fat.

33. APPLIED ANATOMY
1. Allows distention of Rectum and Anal canal.
2. Ischio-rectal Hernia through Hiatus of
Schwalbe
3. Ischio-rectal abcess
4. Peri-anal abcess
5. Fistula in Ano
6. Anal sinus
7. Horse shoe shaped abcess
8. Ischio-anal fat acts as a cushion like support
to Rectum and Anal canal.