The Nine Abdominal Regions vs the Four Quadrants: Organs and Referred Pain

Anatomists and clinicians divide the front of the abdomen in two ways, and exams expect both. The four quadrants use two planes that cross at the umbilicus: the median plane, running vertically down the midline, and the transumbilical plane, running horizontally through the umbilicus at about the level of the L3-L4 intervertebral disc. The result is the right upper, left upper, right lower and left lower quadrants. Quadrants are quick to use and are the language of the bedside. The nine regions use four planes and give a finer grid. Two vertical lines, the midclavicular lines, run from the midpoint of each clavicle down to the midinguinal point, halfway between the anterior superior iliac spine and the pubic symphysis. Two horizontal planes cross them: the subcostal plane, along the lower border of the tenth costal cartilages, and the transtubercular plane, through the tubercles of the iliac crests at about the level of the L5 vertebral body. Some texts use the transpyloric and interspinous planes as the horizontal lines instead, so check which pair your course uses. The top row of the grid is the right hypochondriac, epigastric and left hypochondriac regions. The middle row is the right lumbar (flank), umbilical and left lumbar regions. The bottom row is the right iliac (inguinal), hypogastric (pubic) and left iliac regions.

The upper row lies largely under the rib cage. The right hypochondriac region holds the right lobe of the liver and the gallbladder, along with part of the duodenum, the hepatic flexure of the colon and the upper part of the right kidney. The epigastric region holds much of the stomach, the left lobe of the liver, the pancreas and duodenum, and the abdominal aorta running down behind them. The left hypochondriac region holds the spleen, the upper stomach, the tail of the pancreas, the splenic flexure of the colon and the upper part of the left kidney. The middle row is dominated by bowel. The umbilical region is mostly coils of small intestine with the transverse colon and part of the duodenum. The two lumbar regions hold the ascending colon on the right and the descending colon on the left, with the lower parts of the kidneys behind them. The bottom row holds the end of the gut and the pelvic organs that rise out of the pelvis. The right iliac region holds the cecum, the appendix and the end of the ileum. The hypogastric region holds the urinary bladder when it is full, part of the sigmoid colon and, in females, the uterus. The left iliac region holds the sigmoid colon. Treat this as the usual arrangement, not a fixed rule. Organ positions shift with body build, breathing and posture, and a long transverse colon or a low cecum is common. The kidneys are also retroperitoneal, so they sit deep to these surface regions rather than just under the skin.

Pain from the abdomen comes in two kinds, and the difference explains most referred pain patterns. The parietal peritoneum lining the abdominal wall is supplied by the same somatic nerves as the overlying skin and muscle: the lower intercostal nerves, the subcostal nerve and the first lumbar nerve. It is sensitive to pain, and the pain is sharp and well localized, felt right over the irritated spot. The organs and their visceral peritoneum are different. Their pain fibers travel with the sympathetic nerves back to particular spinal cord segments. Visceral pain is triggered by stretch, spasm or a lack of blood supply rather than by cutting, and it is dull, cramping and poorly localized. Because the gut develops as a single midline tube, its visceral pain is usually felt in the midline, whichever side the organ ends up on. The brain cannot easily tell which structure a pain signal came from, so it maps visceral pain onto the body wall supplied by the same spinal segments. That mapping is referred pain.

The embryological divisions of the gut predict where its pain is felt. Sources draw the spinal levels slightly differently, but the commonly taught pattern is consistent. Foregut (stomach, the upper duodenum, liver, gallbladder and pancreas): pain is felt in the epigastric region, through spinal segments of roughly T5 to T9. Midgut (the rest of the duodenum, the jejunum and ileum, the appendix, cecum, ascending colon and the first two-thirds of the transverse colon): pain is felt around the umbilicus, through segments around T10. Hindgut (the last third of the transverse colon, the descending and sigmoid colon, the rectum and the upper anal canal): pain is felt in the hypogastric region, through lower thoracic and upper lumbar segments, roughly T12 to L2. This matches the blood supply as well: the celiac trunk feeds the foregut, the superior mesenteric artery the midgut and the inferior mesenteric artery the hindgut, so learning the three divisions once pays off in two topics.

Appendicitis is the standard example of pain moving from visceral to somatic. Early on, the inflamed appendix produces dull midgut pain around the umbilicus. As the inflammation reaches the parietal peritoneum, the pain becomes sharp and settles in the right iliac region, classically near McBurney's point, one-third of the way along a line from the anterior superior iliac spine to the umbilicus. Gallbladder pain starts in the epigastric or right hypochondriac region and can be referred to the right shoulder or below the right shoulder blade. Part of the shoulder pattern comes from irritation of the diaphragm. That diaphragm link explains shoulder tip pain in general. The central diaphragm is supplied by the phrenic nerve (C3-C5), so irritation under it, from blood or inflammation, is felt over the shoulder, in the C4 dermatome. Left shoulder tip pain after a splenic injury is called Kehr's sign. Pain from the kidney and ureter is felt in the flank and can travel toward the groin, following segments of roughly T11 to L2, which is why a stone moving down the ureter produces pain that seems to move from loin to groin. For each pattern, an exam answer usually needs three steps: the organ, its spinal segments, and the body wall region those segments supply.