The abdominal and pelvic cavities contain the majority of the body’s internal organs, spanning the area from the diaphragm down to the pelvis. Given this large surface area, anatomists and healthcare providers rely on standardized systems to precisely locate organs, pain, or masses. The most detailed and anatomically specific method divides this entire area into nine distinct abdominopelvic regions for clear reference.
Why Anatomical Regions are Necessary
The sheer volume of organs housed within the trunk necessitates a structured system for communication. Without a common anatomical map, describing the location of a patient’s symptoms would be vague and prone to error, making diagnosis difficult. Dividing the abdomen into smaller sections allows for precise clinical language among medical professionals. This standardization supports the accurate assessment of pain and guides the diagnosis of conditions ranging from appendicitis to gallstones. During surgical procedures or imaging, these regional divisions guide the focus to the specific internal structures suspected of being involved, narrowing down the list of potential causes.
Defining the Nine Abdominopelvic Regions
The nine regions are created by a grid system utilizing four imaginary lines drawn across the anterior surface of the trunk. This division results in a three-by-three pattern, creating nine distinct areas. The two horizontal lines define the upper, middle, and lower levels of the grid.
The superior horizontal line is the subcostal plane, which is drawn across the lowest margin of the tenth costal cartilage on each side. The inferior horizontal line is the transtubercular plane, which connects the tubercles, or slight bumps, on the upper part of the hip bones (iliac crests). Two midclavicular lines form the vertical boundaries, each drawn straight down from the midpoint of the collarbone (clavicle) to the groin on the same side.
The resulting nine regions are named based on their location and relation to the ribs and stomach. The top row includes the right hypochondriac, the epigastric, and the left hypochondriac regions. The middle row consists of the right lumbar (or flank), the umbilical, and the left lumbar regions. Finally, the bottom row contains the right iliac (or inguinal), the hypogastric (or pubic), and the left iliac regions.
Mapping Key Organs Within Each Region
The right hypochondriac region is typically home to the liver’s right lobe and the gallbladder, while the left hypochondriac region houses the spleen and the majority of the stomach’s fundus. The central epigastric region is the location for the main body of the stomach, parts of the liver, and the head of the pancreas.
The middle row, flanking the navel, contains structures involved in digestion and waste filtration. The umbilical region, centered on the navel, contains portions of the small intestine and part of the large intestine. The right lumbar region includes the ascending colon and the right kidney, while the left lumbar region contains the descending colon and the left kidney.
The bottom row focuses on structures within the pelvis and lower abdomen. The right iliac region is the common location of the appendix, where inflammation causes characteristic pain. The central hypogastric region contains the urinary bladder and, in females, the uterus. The left iliac region houses the final parts of the large intestine, including the sigmoid colon.
The Simpler Four Quadrant System
While the nine-region system offers detailed anatomical precision, a simpler division is often used for quick clinical assessment, particularly in emergency settings. This alternative method divides the abdomen into only four sections, known as quadrants.
This is achieved using two intersecting lines: a single vertical line runs down the midline of the body, and a single horizontal line passes through the navel (umbilicus). These lines divide the area into the Right Upper Quadrant (RUQ), Left Upper Quadrant (LUQ), Right Lower Quadrant (RLQ), and Left Lower Quadrant (LLQ). This less precise system allows medical staff to rapidly communicate the general location of symptoms, such as pain in the RLQ, which directs attention toward the possibility of appendicitis.