Clinical Anatomy of Abdomen & Pelvis - Complete Notes

1. ASCITES (Pages 2)

• Ascites is free fluid accumulating in the peritoneal cavity (potential space between visceral and parietal peritoneum).
• Normal peritoneal fluid: ~50 mL. Ascites = pathological accumulation (can be litres).
• Fluid gravitates to the rectouterine pouch (of Douglas) in females and rectovesical pouch in males - the lowest parts of the peritoneal cavity in the erect position.
• In the supine position, fluid collects in the hepatorenal pouch (Morrison's pouch) - the lowest point.

2. CAPUT MEDUSAE (Page 3)

• Results from portal hypertension (usually liver cirrhosis).
• The paraumbilical veins (running in the falciform ligament) connect the portal vein to the anterior abdominal wall veins.
• In portal hypertension, blood is diverted through the paraumbilical veins into the thoracoepigastric veins (draining to SVC) and superficial epigastric veins (draining to femoral vein - IVC).
• Note: In IVC obstruction or impaired IVC drainage, the blood can travel via thoracoepigastric veins to the SVC. In pure portal hypertension, flow is away from umbilicus in all directions.

1. Lower oesophagus (oesophageal varices)
2. Anal canal (haemorrhoids)
3. Paraumbilical region (Caput Medusae)
4. Retroperitoneal (veins of Retzius)
5. Bare area of liver

3. HERNIAS (Pages 4-5 & 16)

Inguinal Hernia

• Pushes directly through the posterior wall of the inguinal canal (Hesselbach's triangle).
• Medial to the inferior epigastric artery.
• Does NOT have a sac derived from processus vaginalis.
• More common in older men (weakened posterior wall).
• Hesselbach's triangle: bounded by inferior epigastric artery laterally, rectus abdominis medially, inguinal ligament inferiorly.

• Passes through the deep inguinal ring (lateral to inferior epigastric artery), travels through the inguinal canal.
• Enters via a persistent processus vaginalis.
• Can descend into the scrotum.
• More common; can occur at any age.

Femoral Hernia

• Passes through the femoral ring (medial compartment of femoral canal).
• Below and lateral to the pubic tubercle (vs. inguinal hernia which is above and medial).
• More common in women.
• High risk of strangulation because the femoral ring is rigid.

Umbilical Hernia

• Congenital: due to failure of gut to return to the abdominal cavity after physiological herniation (week 6-10).
• Acquired (paraumbilical hernia): pushes through a weakness near (but not through) the umbilical scar; more common in multiparous women.

Epigastric Hernia

• Through defects in the linea alba between xiphoid and umbilicus.

Spigelian Hernia

• Through the semilunar line (lateral edge of rectus abdominis).

Richter's Hernia

• Only part of the circumference of the bowel wall is in the hernial sac (not the entire lumen).

4. COSTOVERTEBRAL ANGLE & KIDNEY EXAMINATION (Page 6)

• The costovertebral angle (CVA) is formed between the 12th rib and the lateral border of the vertebral column.
• Percussion here elicits pain in pyelonephritis, renal calculi, perinephric abscess.

• Right kidney: T12-L3 vertebral levels, lower than left (due to liver).
• Left kidney: T11-L2.
• The right kidney is palpated bimanually (ballottement) in the right lumbar/iliac region.

5. PARACOLIC GUTTERS & PERITONEAL FLUID FLOW (Pages 7-8)

• Right paracolic gutter: between the ascending colon and the right lateral abdominal wall - communicates freely with the hepatorenal pouch (Morrison's pouch) superiorly and the pelvic cavity inferiorly.
• Left paracolic gutter: between the descending colon and the left lateral abdominal wall - limited superiorly by the phrenocolic ligament (blocks communication with the spleen); communicates freely inferiorly with the pelvis.

• In peritonitis (e.g., perforated duodenal ulcer), fluid flows from the site of perforation DOWN the right paracolic gutter into the pelvis.
• In the supine position, inflammatory exudate collects in the right posterior subhepatic space (Morrison's pouch) and the right posterior subphrenic space.
• Pus also collects in the pelvic cavity as this is the most dependent site in the supine/semi-recumbent patient.

• Right anterior subphrenic space
• Right posterior subphrenic space (hepatorenal/Morrison's pouch)
• Left anterior subphrenic space
• Left posterior subphrenic space (lesser sac)

6. PORTAL SYSTEM & PORTAL HYPERTENSION (Page 9)

• Formed by union of superior mesenteric vein (SMV) + splenic vein behind the neck of the pancreas at the L1/L2 level.
• The inferior mesenteric vein (IMV) usually drains into the splenic vein.

• Right and left branches to the liver.
• Carries nutrient-rich blood from the GIT, spleen, pancreas to the liver.

1. Lower oesophagus: Left gastric vein (portal) <-> oesophageal veins (azygos - systemic) → oesophageal varices
2. Anal canal: Superior rectal vein (portal) <-> middle and inferior rectal veins (IVC) → haemorrhoids
3. Paraumbilical veins: Portal <-> thoracoepigastric/superficial epigastric (systemic) → Caput Medusae
4. Retroperitoneal veins (Retzius): Colic veins (portal) <-> lumbar/renal veins (systemic)
5. Bare area of liver: Portal tributaries <-> phrenic veins

7. PERITONEAL POUCHES (Page 10)

• Between the liver (right lobe, visceral surface) and the right kidney.
• The lowest part of the peritoneal cavity in the supine position.
• Site of collection of blood after trauma, pus in peritonitis, and malignant ascites.

• Between the uterus/posterior vaginal fornix and the rectum.
• The lowest part of the peritoneal cavity in the erect position in females.
• Accessible clinically via posterior vaginal fornix (culdocentesis) or rectum.

• Between the bladder and the rectum.
• The lowest point in males.

8. URACHUS & PATENT URACHUS (Pages 11-12)

• Remnant of the allantois (fetal connection between the bladder apex and umbilicus).
• Normally obliterates before birth to form the median umbilical ligament.

1. Patent urachus (urachal fistula): Complete failure to close → urine drips from the umbilicus at birth. Often associated with bladder outlet obstruction (posterior urethral valves in males).
2. Urachal cyst: Both ends close but the middle remains patent → cyst forms in the midline between bladder and umbilicus. Can become infected.
3. Urachal sinus: Only the umbilical end remains open → discharge from umbilicus.
4. Vesicourachal diverticulum: Only bladder end remains open.

9. DEVELOPMENT OF PANCREAS (Page 12)

• Pancreas develops from two buds arising from the caudal part of the foregut (duodenum):
  1. Dorsal pancreatic bud (larger): forms body, tail, and part of head.
  2. Ventral pancreatic bud (associated with bile duct): forms part of head and uncinate process.
• As the duodenum rotates to the right (D-loop rotation), the ventral bud rotates posteriorly and to the left, fusing with the dorsal bud.
• The main pancreatic duct (Wirsung): formed by the ventral bud duct + caudal part of the dorsal bud duct.
• Accessory duct (Santorini): proximal part of the dorsal bud duct.

• Annular pancreas: ventral bud fails to rotate properly → ring of pancreatic tissue encircles the duodenum → duodenal obstruction.
• Pancreas divisum: failure of dorsal and ventral ducts to fuse → most common pancreatic developmental anomaly.

10. DEVELOPMENT OF CAECUM & APPENDIX (Page 13)

• Physiological herniation of the midgut loop into the umbilical cord occurs at week 6 (gut too large for the abdominal cavity).
• Returns to the abdomen at week 10 and undergoes 270° anticlockwise rotation around the superior mesenteric artery.
• The caecal bud appears at the junction of the cephalic and caudal limbs of the midgut loop.
• The appendix develops from the tip of the caecal bud.

• Base is at the confluence of the three taeniae coli (useful surgically).
• McBurney's point: 1/3 of the way from the anterior superior iliac spine (ASIS) to the umbilicus - marks the base of the appendix.
• Position: retrocaecal (most common, ~65%), pelvic, subcaecal, pre-ileal, post-ileal.

11. HERNIA ANATOMY IN DETAIL (Pages 16-17)

1. Hernial orifice: the opening through which hernia passes.
2. Hernial sac: diverticulum of peritoneum (neck, body, fundus).
3. Coverings of the sac: layers of abdominal wall through which it passes.
4. Contents: omentum, small bowel (most common), large bowel, bladder (sliding hernia).

1. Extraperitoneal fat
2. Internal spermatic fascia (from transversalis fascia at deep ring)
3. Cremasteric fascia & muscle (from internal oblique at deep ring)
4. External spermatic fascia (from external oblique at superficial ring)
5. Skin of scrotum

• Protrudes through the linea alba just above or below (not through) the umbilicus.
• Not the same as true umbilical hernia (which passes through the umbilical scar/ring).
• Common in obese, multiparous women.
• Sac often contains omentum or transverse colon.

12. EPISIOTOMY (Pages 17-18)

1. Mediolateral episiotomy (most common in UK): Cut is made at 45° posterolaterally from the midline of the posterior fourchette → avoids the external anal sphincter and ischiorectal fossa.
2. Median (midline) episiotomy (common in US): Cut along the perineal body in the midline → easier to repair but higher risk of extension into the anal sphincter (3rd/4th degree tear).

• Bulbospongiosus
• Superficial transverse perineal
• Deep transverse perineal
• External anal sphincter (posteriorly)
• Levator ani (pubococcygeus)

13. SURFACE ANATOMY OF LIVER & GALLBLADDER (Page 17)

• Upper border: right side - 5th intercostal space (tip of 9th costal cartilage level anteriorly); left side - 5th intercostal space left of sternum.
• Lower border: follows the right costal margin from the 9th rib to the 8th rib.
• The right lobe extends to the right midclavicular line at the 5th ICS.

• Located at the tip of the right 9th costal cartilage (where the lateral border of the right rectus abdominis crosses the right costal margin) - the linea semilunaris.
• Murphy's sign: pain on deep inspiration when palpating below the right costal margin at this point → acute cholecystitis.

14. KIDNEY ANATOMY & RETROPERITONEAL SPACE (Pages 18-19)

• Posterior: 12th rib, quadratus lumborum, psoas major, transversus abdominis.
• The 12th rib crosses the posterior surface of both kidneys.
• Pleura may extend down to the 12th rib level → surgeons must be careful during posterior approach (loin incision) not to open the pleura.

• Surrounds the kidney and adrenal gland.
• Three layers of fat:
  1. Perirenal fat (between kidney capsule and renal fascia)
  2. Renal fascia (Gerota's fascia)
  3. Pararenal fat (external to renal fascia)

• Suprarenal glands, Aorta/IVC, Duodenum (2nd & 3rd parts), Pancreas (body/tail), Ureters, Colon (ascending & descending), Kidneys, Esophagus, Rectum.

15. HORSESHOE KIDNEY & URETERIC BUD DEVELOPMENT (Pages 20-21)

• Kidneys develop from metanephric mesoderm (metanephros).
• The ureteric bud grows out from the mesonephric duct and induces the metanephric mesoderm to differentiate into nephrons (glomeruli, tubules).
• Kidneys ascend from the pelvis to the lumbar region; during ascent they rotate 90° medially (so the hilum faces medially).

• Most common renal fusion anomaly (1 in 400).
• The two kidneys fuse at their lower poles during ascent, connected by an isthmus of renal tissue (usually parenchyma, occasionally fibrous).
• The isthmus lies anterior to the aorta, IVC, and is trapped below the inferior mesenteric artery, preventing normal ascent.
• Location: at L3-L4 level (lower than normal).
• Often asymptomatic; associated with PUJ obstruction, increased risk of renal calculi, UTIs, and Wilms tumour.

16. ANAL CANAL ANATOMY (Pages 22-23)

• Length: ~4 cm.
• Divided by the pectinate (dentate) line into upper and lower halves.

• Epithelium: columnar (simple columnar, transitional).
• Supplied by superior rectal artery (IMA branch - portal system).
• Venous drainage: superior rectal vein → portal system.
• Lymph drainage: internal iliac nodes.
• Nerve supply: autonomic (insensitive to pain, touch; sensitive only to stretch).
• Internal haemorrhoids are above the pectinate line.

• Epithelium: stratified squamous (non-keratinised).
• Supplied by inferior rectal artery (pudendal artery - IIA branch - systemic).
• Venous drainage: inferior rectal vein → internal pudendal → IVC.
• Lymph drainage: superficial inguinal nodes.
• Nerve supply: somatic (inferior rectal nerve - sensitive to pain, temperature, touch).
• External haemorrhoids are below the pectinate line (painful when thrombosed).

• Internal anal sphincter (IAS): Involuntary, smooth muscle; thickening of the circular muscle layer; maintains resting tone.
• External anal sphincter (EAS): Voluntary, striated muscle; three parts (deep, superficial, subcutaneous); innervated by the inferior rectal nerve (S2,S3) and perineal branch of S4.

• Primary positions: 3, 7, 11 o'clock (patient in lithotomy position) - correlate with the three superior rectal artery terminal branches.
• Internal haemorrhoids (above pectinate line): painless bleeding.
• External haemorrhoids (below pectinate line): painful, especially if thrombosed.

17. PERINEUM, UTERUS & CHILDBIRTH ANATOMY (Pages 24-25)

• Diamond-shaped area below the pelvic floor (levator ani).
• Divided by a line between the two ischial tuberosities into:
  • Urogenital triangle (anterior): contains external genitalia and urethra.
  • Anal triangle (posterior): contains anal canal, external anal sphincter, ischiorectal fossa.

• Fatty layer (fascia of Camper): continuous with fatty layer of the abdomen; in the scrotum = replaced by dartos muscle.
• Membranous layer (fascia of Colles / Scarpa's): fuses posteriorly with the perineal body and the base of the urogenital diaphragm; laterally with the ischiopubic rami. Clinically important in urethral rupture - urine extravasates within the confines of Colles' fascia (upward into anterior abdominal wall but not into the thigh or perineal triangle posterior to the UG diaphragm).

• The uterine cervix projects into the vault of the vagina, creating the vaginal fornices (anterior, posterior, lateral).
• The posterior fornix is closely related to the rectouterine pouch (Douglas) - separated only by the posterior vaginal wall and peritoneum.
• Culdocentesis: needle aspirates fluid/pus from the rectouterine pouch via the posterior fornix.

• External os: opens into the vagina.
• In nulliparous women: circular.
• In multiparous women: transverse slit (due to lacerations during delivery).

SUMMARY TABLE: Key Clinical Correlates