1. Learning Objectives
Perineum 1 Lecture
Anal Triangle
1. Perineum and Pelvis- Define the boundaries of the anatomical regions known as the perineum and pelvis.
2. Anal Triangle
a. Define the boundaries of the ischio-anal fossae.
b. Describe the course of the pudendal nerve and internal pudendal vessels through the gluteal region and anal triangle.
c. Define the location and contents of the pudendal canal.
d. Describe the course and distribution of the inferior rectal nerve and vessels.
e. Describe the location of the internal and external anal sphincter muscles.
f. Define the location and importance of the perineal body.
g. Define the types of hemorrhoids and the vessels involved in each.
h. Describe the sensory nerve supply for the anal canal.
i. Describe the blood supply and lymphatic drainage for the anal canal and peri-anal skin.
j. Understand the importance of the fat in the ischio-anal fossae.
Define boundry between perineium and pelvis
-Posterior part – anus
-Anterior part – external genitalia

2. Netter 334 Pelvis—space bounded by the pelvic bones (male pelvis shown
Bones of the pelvis:
1. Sacrum 2. Ilium 3. Ischium 4. Pubic bone 5. Pubic symphysis 6. Acetabulum 7. Foramen obturator 8. Coccyx
Pubic Symphysis – anterior articulation in midsaggital plane
Inguinal ligament goes from ASIS to pubic tubricle
Pelvic brim – ridge of bone that extends from the upper edge of the pubic symphysis around the inner aspect of the pelvic girdle.
Superior to this is the false pelvis (greater pelvis), which is part of the abdominal cavity
Inferior to this is thetrue pelvis (lesser pelvis)
Pregnant uterus and urinary bladder occupy both the false and true pelvis
GI tract is in the false pelvis, and the false pelvis is part of the abdomenal cavity.
Obturator foramen faces anteriorly.
Ischial spine on posterior side.
Ischial spine
Obturator foramen
Netter 334

3. Shown is a female pelvis
Shown is a female pelvis. the subpubic arch in the female is much more obtuse, since the transverse dimension of the pelvis is larger than in male.
Netter 334

4. Male subpubic arch should close to angle between index and middle finger.
Female subpubic arch should be close to angle between the thumb and index finger.
Moore et al; Fig. 3.3

5. Netter 334 Inlet to true pelvis  pelvic brim
Outlet to true pelvis formed by
1) Tip of coccyx
2) To ischial tuberosities
3) Inferior edge of the pubic symphysis
Gluteus maximus covers ischial tuberosities when hip is extended.
When you sit, the hip is flexed and the gluteus maximus exposes the ischial tuberosities, which are used to rest weight
Netter 334

6. Acetabulum – depression to receive the femur
Acetabulum – depression to receive the femur. It is also the juncture of the following bones, which fuse during teenage years:
1)Red= pubis
2)Blue=ischium
3)Ilium=yellow
(Ileum = small bowel)
Netter 474

7. Medial view of hip bone
Netter 474

8. The anatomical orientation of the pelvis is tipped significantly interiorly to what’s shown in atlases.
ASIS and pubic tubercle are in the same coronal plane if the pelvis is in the same anatomical position.
Two ligmanets extending from sacrum:
1) Sacral spinous ligament – sacrum to ischial spine
2) Sacral tuberous ligament – sacrum to tuberosity of ischium
These two ligaments helps us to form two foramina, which house the structures passing to the lower limb
The Greater sciatic foramen
The Lesser sciatic foramen
Greater sciatic nerve travels throuch the greater sciatic foramen
Netter 335

9. Netter 336

10. Netter 335

11. Obturator membrane – closes most of obturator; exists to decrease the overall weight of the hip bone
Netter 336

12. Netter 334 View of female pelvis.
Posterior wall (sacrum) is much longer than anterior wall (pubic symphysis)
Sacral promontory – upper end of s1 vertebral body
Conjugate diameter – distance from superior border of pubic symphysis to sacral promontory (average is 11 cma safe number to pass a baby though).
The transverse dimensions will increase during pregnancy as a result of oxytocin causing cartilage of pubic symphysis to gelatinized. The conjugate diameter, however is constant.
Diagonal conjugate – Distance from the inferior border of the pubic symphysis to sacral promentory. This is what can be measured during a pelvic exam.
Diagonal conjugate
Netter 334

13. Moore et al, Fig B3.2

14. Urethral hiatus
Puborectalis m.
Anorectal hiatus
Iliococcygeus m.
Tendinous arch
Obturator internus m.
Shown is a male pelvic diaphragm with the contents removed.
The pelvic outlet is closed by a diaphragm. The diaphragm is concave looking at it from above.
Oturator internus doesn’t have anything to do with pelvic diaphragm.
Piriformis has nothing to do with pelvic diaphragm.
In male two hiatus -- one for anus and one for urethra
Pubococcygeus m.
Piriformis m.
Plate 340
(Ischio)coccygeus m.

15. Urethra
Puborectalis m.
Male Pelvic diaphragm from inferior prospective.
Gluteus maximus coming into field or right.
Pubococcygeus m.
Iliococcygeus m.
(Ischio)coccygeus m.
Gluteus maximus m.
Plate 341

16. Pubococcygeus m.
Urethra
Iliococcygeus m.
Vagina
Rectum
Female pelvic diaphragm. Vagina is between rectum and urethra
Tendinous arch
Piriformis m.
(Ischio)coccygeus m.
Plate 338

17. Urethra
Vagina
Pubococcygeus m.
Obturator internus m.
Puborectalis m.
Iliococcygeus m.
Plate 339
(Ischio)coccygeus m.
Sacrotuberous ligament

18. Piriformis m.
Obturator internus m.
Tendinous arch
This is female
Thickening of fascia on later pelvic wall
Iliococcygues m.
(Ischio)coccygues m.
Rectum
Pubococcygeus m.
Urethra
Vagina
Plate 338

19. Inferior to pelvic diaphragm is the perineum
Inferior to pelvic diaphragm is the perineum. Pelvic diaphragm is the transition from pelvis to perineum
Moore et al, Fig. 3.8

20. Seen from posterior, perineum a little cleft from the proximal end of the thigh. To get a good view of the perineum, you must abduct the thighs. Perineum is covered by skin.
Backhouse & Hutchings, Plate 435

21. Dermatomes to remember: S2,S3, and S4 – supply skin of perineum
Netter 159

22. Scrotum and penis are diverticuli of perineum—don’t fit within bony landmarks, but are part of them.
Snell, Fig 4-3
Snell, Fig. 4-3

23. Lithotomy position – patient is laid on the back with knees bent, positioned above the hips, and spread apart through the use of stirrups.
Snell, Fig 4-4
Snell, Fig 4-4

24. Urogential triangle – pubic symphysis to ischial tuberosities
Anal triangle – ischial tuberosities to coccyx
There are no sexual differences in the anal triangle
Plate 360

25. Sacral tuberous ligament (green posterior ligament)
Snell; Fig 23-2

26. Perineal body
Anus – aperture (aka external opening)
Anal canal – Last 3-4 cm of digestive tract
External anal sphincter – skeletal muscle circulating anus. Attached to tip of coccyx posteriorly and wrap around anus to attach to parineal body interiorly. Action is to close anal canal.
Perineal body – subcutaneous collection of dense connective tissue where several muscles attach in center of perineum
Ischioanal fossa – recess on either side of anus that is packed full of fat
External anal sphincter m.
Levator ani m.
Gluteus maximus m.
Plate 362

27. Perineal body
Levator ani m.
Episiotomy – increase size of vaginal opening
External anal sphincter m.
Plate 358
Gluteus maximus m.

28. Perineal n.
Dorsal n. of clitoris
Pudendal nerve – is the nerve of the perineum containing S2, S3, and S4 spinal cord levels. It has sensory and motor components. It traverses in a fascial sleeve formed by the obturrator internus muscle on wall of ischioanal fossa. It does NOT pierce the pelvic floor. Comes from sacral plexus and out of the greater sciatic foramen.
Inferior rectal nerve – Branch of pudendal. Sensory and motor. Supplies the external anal sphincter and the skin over the angle triangle
Pudendal nerve
Inferior rectal nn.
Plate 393

29. Perineal a.
Internal pudendal a.
Internal pudendal artery travels with the pudendal nerve.
The inferior rectal artery is a branch of the internal pudendal artery.
Inferior rectal a.
Plate 384

30. Fascia of obturator internus m. forming pudendal canal
Posterior scrotal n
Perineal n.
Pudendal n.
Inferior rectal a
Inferior rectal nn.
Fascia of obturator internus m. forming pudendal canal
Plate 391

31. Perineal a. and v.
Inferior rectal v.
Pudendal canal
Inferior rectal a.
Plate 385

32. Shown is a coronal section in posterior triangle
Shown is a coronal section in posterior triangle. This shows that the ischioanal fossa is filled with fat. Rectum becomes anal canal and pierces the diaphragm.
Not shown are branches of pudendal artery and nerve supplying the external sphincter.
Pudendal canal – tunnel formed by the fascia of obturrator internus, through which the internal pudental artery and nerve traverse.
Specilization of obteruator internus:
Fibers of pelvic diaphragm take their origin from the thickened fascia on the superior part (thus part of obturrator internus is in the true pelvis and part is in the perineum).
Fascia of obturator internus splits to form the pudendal canal
Rectum
Obturator internus m.
Anal canal
Fat in ischioanal fossa
Levator ani m.
Pudenal canal with pudendal n, internal pudendal a. and v.
Plate 372

33. Anal columns
Deep fibers of external anal sphincter are right up against pelvic diaphragm.
Internal anal sphincter – smooth muscle sphincter of the anal canal
There are two communicating venus plexuses of the anal canal—an internal and external
Anal columns (Columns of Morgagni) – vertical folds produced by infolding of the mucous membrane and some muscular tissue in the upper half of the lumen of the anal canal.
Anal valves– folds of mucosa connecting adjacent anal columns.
Anal canal has two embryological origins
Upper
Derived from endoderm
Vieseral innervation – distension is the only associated receptor
Blood drains into the inferior rectal artery
Lymph drains into pelvis
Lower
Derived from ectoderm (proctodeum)
Somatic innervation – from pudendal nerve, highly sensitive to pain
Blood drains into the inferior vena cava
Lymph drains into superficial inguinal nodes
There are no valves in either the internal or external plexus, and are a portacaval anastomosis (aka portal systemic anastomosis)
Produced mucous to lubricate feces.
RECTUM
Levator ani m.
Internal venous plexus
External anal sphincter m.
External venous plexus
Plate 373

34. Internal venous plexus
Anal columns
Internal anal sphincter m.
If these veins get torn and bleed (e.g. from constipation or stool) the blood is red because there are arterial venus anastamoses in this region
External anal sphincter m.
Anal valves
External venous plexus
Plate 374

35. Superior rectal a.
There are three anal canal arteries (that are called rectal arteries
Superior
Middle
Inferior rectal arteries
There are anastamoses here
Internal pudendal a.
Obturator internus m.
Inferior rectal a.
Middle rectal a.
Plate 378

36. Superior rectal v.
The two venus plexuses of the anal canal drain as follows:
Inferior venus plexus  portal vein
External venus plexus  IVC
Middle rectal v.
Levator ani m.
Internal pudendal v.
Obturator internus m.
Inferior rectal v.
Internal venous plexus
Plate 379
External venous plexus

37. Anal Fissure Anal fissure – tear in epithelium lining of anal canal.
In the anal canal there is an epithelium change from simple columnar epithelium (like rest of gut) to stratified squamous to keratinized epithelium
Anal fissures almost always occur along anal canal. Commonly caused by hard stool that tears epithelium lining. Highly innervated, so painful.
Ramsayhealth.co.uk

38. Hemorrhoids Two types of hemorrhoids based on two venus plexuses.
Internal hemorrhoids
intrude into lumen of anal canal
Will prolapse and protrude through anus.
Often will get torn and bleed when making a bowel movement.
Submucosal
Not painful – usually itch
Pregnancy or chronic constipation can cause  increased intrabdominal pressure causes venus backflow
External hemmorhoids
Subcutaneous
Due to clot

39. Anal Fistula
Fistula – abnormal communication between two cavities. Begins as abrasion to anal canal. Often becomes infected, may form an abcess.