Surgical Anatomy of the Abdomen

Surface Anatomy of the Abdomen

Boundaries

Superior:

• Xiphoid process
• Costal cartilages of the 7th–10th ribs

Inferior:

• Pubic bone and pubic symphysis
• Inguinal ligaments

Lateral: 

• Superior: inferior aspect of the 10th rib
• Inferior: iliac crest

Landmarks

• Umbilicus
• Linea alba: fibrous junction of the right and left rectus muscles that runs down the midline of the abdomen 
• Semilunar lines: lateral borders of the rectus abdominis muscles
• Anterior superior iliac spine
• Iliac crests 
• Pubic symphysis
• Inguinal grooves

Lines and planes

The following divide the abdomen into its 9 regions:

• Right and left midclavicular lines
• Subcostal plane
• Transtubercular, or intertubercular, plane

Regions of the abdomen

• Right and left hypochondria
• Epigastrium
• Right and left lateral abdominal regions or flanks 
• Umbilical
• Right and left inguinal regions or iliac fossae 
• Hypogastrium

Dermatomes

• T7–L1
• Visceral pains are named according to their respective dermatomes. 

Abdominal wall

Layers

• Skin
• Superficial fascia (subcutaneous tissue):
  • Superficial fatty layer (Camper’s fascia) 
  • Deeper membranous layer (Scarpa’s fascia)
• Anterior fascial layer:
  • Anterior rectus sheath (medial)
  • External abdominal oblique fascia (lateral)
• Abdominal muscles:
  • Rectus abdominis
  • External abdominal oblique
  • Internal abdominal oblique
  • Transversus abdominis
• Posterior fascial layer:
  • Posterior rectus sheath (medial; ends at the arcuate line midway between umbilicus and pubic symphysis)
  • Transversalis fascia (lateral)
• Peritoneum

Relevant procedure

Ventral herniorrhaphy: surgical repair of hernias of abdominal wall

Right Hypochondrium

The surgically relevant structures of the right hypochondrium include the liver and the biliary tree.

Liver

Location: 

• ¾ in the RUQ
• Adjacent to the inferior surface of diaphragm
• Location is breath-dependent (rises during exhalation, lowers during inhalation).

Limits:

• Superior: 5th intercostal space during exhalation
• Inferior: right costal arch during inhalation 

Surfaces: 

• Diaphragmatic and visceral
• Liver is intraperitoneal except for bare area, porta hepatis, and gallbladder fossa.
• Enclosed in the Glisson capsule (external layer of fibrous connective tissue)

Biliary tree

Gallbladder:

• Bile-filled sac located in a fossa on the inferior aspect of the liver beneath the junction of hepatic segments Ⅳb and Ⅴ
• 7–10 cm in length, average capacity 30–50 mL
• Anatomic divisions:
  • Fundus (superiormost aspect)
  • Corpus (body)
  • Infundibulum (round, blind end extending below the liver margin)
  • Neck (connects with cystic duct)
• The cystic duct connects the gallbladder to the biliary tree.

Biliary tree:

• The right and left hepatic ducts join to form the common hepatic duct.
• The cystic duct joins the common hepatic duct to form the common bile duct.
• The cystic duct length is highly variable.

Relevant procedures

• Cholecystectomy (open and laparoscopic): surgical removal of the gallbladder, usually because of cholelithiasis (gallstone disease) with or without cholecystitis
• Choledochostomy: surgical incision on the common bile duct
• Choledochojejunostomy: anastomosis of a common bile duct to the jejunum (for oncologic resections or treatment of common bile duct injuries)
• Hepatic lobectomy: surgical removal of a lobe of the liver
• Hepatic segmentectomy: surgical removal of a segment of the liver
• Needle biopsy of the liver
• Hepatic abscess drainage

Epigastrium

The epigastrium contains the transverse colon, the duodenum, and the pancreas.

Transverse colon

• Part of the colon distal to the ascending colon and proximal to the descending colon that travels transversely across the upper abdomen
• Suspended by mesentery (transverse mesocolon)
• Supplied by ileocolic and middle colic branches of the superior mesenteric artery
• Venous drainage is through the superior mesenteric vein that joins the portal vein.

Duodenum

• First C-shaped segment of the small intestine
• Surrounds the head of the pancreas
• Consists of 4 segments
• The 2nd, or descending, segment contains the ampulla of Vater (opening of the common bile duct).
• 1st segment (duodenal bulb): intraperitoneal
• Descending, horizontal, and ascending parts: retroperitoneal
• Ends at duodenojejunal flexure: fixed to the posterior abdominal wall by the ligament of Treitz

Pancreas

Segments:

• Caput pancreatis (head)
• Uncinate process
• Collum pancreatis (neck)
• Corpus pancreatis (body)
• Cauda pancreatis (tail): the only intraperitoneal segment of the pancreas 

Ducts:

• Pancreatic duct (Wirsung’s duct) and common bile duct open into ampulla of Vater, which presents as major duodenal papilla.
• Major duodenal papilla contains the hepatopancreatic sphincter (sphincter of Oddi), which regulates the secretion of bile and pancreatic fluid.
• Accessory pancreatic duct (when present) opens into minor duodenal papilla.

Relevant procedures

• Transverse colostomy: an opening along the length of the transverse colon to the exterior skin surface
• Transverse hemicolectomy: surgical removal of the transverse colon
• Pancreaticojejunostomy (Puestow procedure): surgically made communication between the pancreas and the jejunum (treatment of chronic pancreatitis)
• Pancreaticoduodenectomy (Whipple procedure): surgical removal of the head of the pancreas and the duodenum
• Distal pancreatectomy: removal of the body and tail of the pancreas
• Total pancreatectomy: surgical removal of the pancreas

Left Hypochondrium

The most important structures of the left hypochondrium are the spleen and the stomach.

Spleen

Location:

• Positioned against ribs 9–11
• Intraperitoneal

Relations:

• Anterior: stomach
• Lateral: abdominal muscles
• Medial: left kidney
• Posterior: diaphragm
• Inferior: colon and left colic flexure

Ligaments:

• Gastrosplenic
• Splenorenal
• Phrenicocolic

Blood supply: splenic artery and vein

Stomach

Segments:

• Has 2 curvatures (lesser and greater) 
• Cardia: 
  • Entrance of the stomach
  • Originates from the z-line and creates the angle of His, or angle of the cardiac orifice (the angle between the fundus and abdominal esophagus)
  • Crucial landmark in the construction of the gastric pouch 
• Fundus: a dome-shaped region located at the highest point of the stomach
• Body: 
  • Main section of the stomach
  • Extends from the fundus to the pylorus
  • Bordered by the lesser and greater curvatures
• Pylorus: 
  • Connects to the duodenum
  • Contains the pyloric sphincter
  • Consists of a wide pyloric antrum and narrow pyloric canal

Arterial supply:

• Left gastric artery: main supply of the gastric pouch in a gastric bypass
• Right gastric artery
• Right and left gastroepiploic (gastro-omental) arteries
• Splenic artery
• Short gastric arteries
• Posterior gastric artery

Venous drainage:

• Homonymous veins that accompany the arteries
• Right and left gastric veins drain into the portal vein.
• Left gastroepiploic vein drains into the splenic vein.
• Right gastroepiploic vein drains into the superior mesenteric vein.

Innervation:

• Parasympathetic innervation: anterior and posterior vagal trunk
• Sympathetic innervation: greater splanchnic nerve and gastric branches from celiac plexus

Relevant procedures

• Splenectomy: surgical removal of the spleen
• Splenorrhaphy: surgical repair of the spleen, usually performed after trauma
• Bariatric surgery: group of invasive procedures that surgically reduce the size of the stomach to produce early satiety and decrease food intake (restrictive type) and/or alter digestion and artificially induce malabsorption of nutrients (malabsorptive type).
• Total and subtotal gastrectomy: surgical removal of a part of or an entire stomach (for oncologic resections and gastric ulcers)
• Truncal or selective vagotomy: transection of the vagal nerves or branches that can be combined with partial gastric resections to control acid secretion and prevent ulcer recurrence

Right and Left Flanks

Ascending and descending colon

• Ascending and descending portions of the large intestine found in the right flank and the left flank, respectively
• Arterial supply: superior and inferior mesenteric arteries
• Venous drainage: superior and inferior mesenteric veins that join portal circulation

Kidneys

Location:

• Between T12 and L3, in the paravertebral gutter
• Their superior pole rests at the level of the 11th and 12th ribs.
• The parietal peritoneum anchors them to the posterior abdominal wall. 
• Retroperitoneal

Renal capsule:

• Holds the kidneys in position
• Consists of:
  • Paranephric adipose tissue (fat)
  • Renal fascia

Relations:

• Superomedially: adrenal glands
• Posteriorly:
  • Nerves: subcostal, iliohypogastric, ilioinguinal
  • Muscles: diaphragm, quadratus lumborum

External characteristics:

• Superior pole
• Inferior pole
• Convex lateral surface
• Concave medial surface: renal hilum

Blood supply: renal arteries and veins

Relevant procedures

• Right hemicolectomy: surgical removal of the right segment of the transverse colon and ascending colon
• Left hemicolectomy: surgical removal of the left segment of the transverse colon and descending colon
• Nephrectomy: surgical removal of the kidney
• Kidney transplantation: surgical implantation of a donated kidney

Umbilical Region

Small intestine

• Average length: 6–7 m
• Segments:
  • Duodenum
  • Jejunum
  • Ileum

Blood supply: 

• Duodenum: superior and inferior pancreaticoduodenal arteries
• Jejunum and ilium: jejunal arteries and ileal arteries
  • Form anastomotic loops that run parallel to the small intestine = arcades
  • Small branches leave these arcades = vasa recta (or straight arteries)
• Venous drainage: portal system

Abdominal aorta

• Retroperitoneal
• Extending from the aortic hiatus of the diaphragm (T12) to its bifurcation into the common iliac arteries (L4)

Vascular branches: 

• Unpaired (forward branches):
  • Celiac trunk
  • Superior mesenteric 
  • Inferior mesenteric 
• Paired visceral (lateral): 
  • Renal
  • Gonadal
• Paired parietal (posterolateral): inferiormost intercostal

Relevant procedures

• Small intestine resection: surgical removal of a segment of the small intestine, usually because of adhesions, volvulus, obstruction, and regional ileitis
• Ileostomy: surgically made communication between the ileum and the skin 
• Aortic aneurysm repair using grafts

Right and Left Inguinal Regions (Iliac Fossae)

Appendix

• Also referred to as vermiform appendix
• Slender, hollow, blind-ended pouch arising from the proximal cecum
• The appendiceal orifice is always located at the confluence of the taenia coli.
• On average, the appendix is approximately 9 cm long, but it can vary from 2 to 22 cm.

McBurney’s point:

• Junction between the lateral and medial thirds of a line drawn from the anterior superior iliac spine (ASIS) to the umbilicus
• Localized tenderness at this point is a classic sign of appendicitis.
• Both McBurney’s and Rocky-Davis incisions for open appendectomy are performed through this point.

Inguinal canals

Boundaries:

• Superior: inferior edge of the internal oblique and transverse abdominal muscles
• Inferior: inguinal ligament (continuation of the external abdominal oblique aponeurosis)
• Anterior: aponeurosis of the abdominal external oblique muscle
• Posterior: transversalis fascia and interfoveolar ligament

Course:

• The inguinal canal is approximately 4 cm long, situated in the lower anterior abdominal wall, connecting its outer and inner layers above the inguinal ligament (superior anterior iliac spine to pubic tubercle).
• Runs from an upper lateral to an inferior medial direction.
• Inner orifice/deep inguinal ring: evagination of the transversalis fascia (surrounding the spermatic cord as the internal spermatic fascia)
• External orifice/superficial inguinal ring: fissure in the aponeurosis of the abdominal external oblique muscle

Contents:

• Men: 
  • Spermatic cord (cremaster muscle, internal and external spermatic fasciae surrounding the vas deferens, pampiniform plexus, lymphatic vessels, testicular neurovasculature, and tunica vaginalis)
  • Ilioinguinal nerve
  • Genital branch of the genitofemoral nerve
• Women: 
  • Round ligament and artery
  • Ilioinguinal nerve 
  • Genital branch of the genitofemoral nerve

Descending and sigmoid colon

• Suspended by mesentery (sigmoid mesocolon)
• Arterial supply: inferior mesenteric artery (sigmoid arteries)
• Venous drainage: inferior mesenteric vein → portal vein

Fallopian tubes

Segments:

• Uterine (intramural)
• Isthmus
• Ampulla
• Infundibulum (opens into the peritoneal cavity)

Broad ligament (ligamentum latum):

• Runs from the uterus to the lateral pelvic wall
• Contains the fallopian tubes
• Segments:
  • Mesometrium (uterine part of the ligament)
  • Mesosalpinx (tubal part of the ligament)
  • Mesovarium (ligament to the ovary)

Blood supply:

• Arterial: ovarian and uterine arteries
• Venous supply is from ovarian veins: 
  • The right ovarian vein drains into the inferior vena cava.
  • The left ovarian vein drains into the left renal vein.

Relevant procedures

• Appendectomy: surgical removal of the vermiform appendix, most commonly because of appendicitis
• Inguinal herniorrhaphy: surgical repair of inguinal hernias; can be done laparoscopically or via an open approach (Lichtenstein technique is the most common)
• Salpingectomy: surgical removal of the fallopian tube, commonly performed to treat ectopic pregnancy
• Salpingostomy: incising the fallopian tube open, commonly to remove an occupying lesion (ectopic pregnancy), leaving the remainder of the tube intact
• Sigmoid colectomy: surgical removal of a sigmoid colon, commonly performed for cancer or diverticulitis
• Rectosigmoidectomy: surgical removal of the sigmoid colon and rectum
• Descending colon colostomy

Hypogastrium

Urinary bladder

• In females, the urinary bladder is anterior to the uterus and anterior vaginal wall. 
• In males, it is anterior to the rectum.
• Anchored by median umbilical ligament

Prostate

Location: 

• Surrounding the neck of the urinary bladder
• Inferior to the pubic symphysis and anterior to the rectal ampulla

Lobes:

• Anterior lobe (isthmus): located anterior to the urethra 
• Posterior lobe:
  • Posterior to urethra
  • Inferior to ejaculatory ducts
• Lateral lobes: located on either side of the urethra 
• Median lobe: lies between the urethra and ejaculatory ducts

Related structures:

• The urethra enters the prostate near its anterior border and usually passes between its anterior and middle thirds.
• The ejaculatory ducts pass anteroinferiorly through its posterior region to open into the prostatic urethra.

Accessory glandular structures:

• Seminal vesicles
• Bulbourethral glands (Cowper’s glands)

Uterus

Location:

• 7–9 cm long, found within the pelvis, connected to the end of the vaginal canal via the uterine cervix 
• Dorsal to the urinary bladder, anterior to the rectum, in an anteverted and anteflexed position
• Rectovaginal space or Douglas pouch: lowermost recess of the peritoneum, located between the uterus and rectum
• Vesicouterine pouch: shallower pouch between urinary bladder and uterus

Structure:

• Fundus: comprises all the uterus superior to the fallopian tubes
• Body: region between the fundus and cervix
• Isthmus: the narrowing at the cervix–body transition
• Cervix: comprised of the internal orifice (aperture to the uterine body), cervical canal, and the external orifice (vagina–cervical canal junction)

Supporting structures:

• Broad ligament
• Round ligament (ligamentum teres) runs from the tubouterine junction through the inguinal canal to the labia majora. Corresponds to the vas deferens in men.
• Cardinal ligament (ligamentum transversum cervicis) consists of the transversalis fascia connecting the cervix with the pelvic wall. 

Blood supply: 

• Arterial:
  • Primary supply: uterine artery, a branch of the anterior division of the internal iliac artery, located in the broad ligament
  • Secondary supply: ovarian artery, which originates from the aorta at the level of L2
• Venous: Uterine veins drain into internal iliac veins.

Relevant procedures

• Cystotomy: surgical incision performed on the urinary bladder for repair (cystoplasty), bladder laceration, or rupture due to trauma or a defect in the bladder wall
• Cystectomy: surgical removal of the urinary bladder, usually indicated by malignancy
• Urostomy: surgically made communication between the bladder and skin to facilitate evacuation of bladder contents
• Abdominal hysterectomy: surgical removal of the uterus via an infraumbilical midline laparotomy
• C-section: delivery of a fetus via a horizontal incision (Pfannenstiel or Joel-Cohen)
• Suprapubic prostatectomy: surgical removal of the prostate via an infraumbilical midline laparotomy