Abdominal and Pelvic Anatomy in Section

In cross-section the abdomen and pelvis present the solid and hollow viscera, the great vessels, and the peritoneal and retroperitoneal spaces in a layered, level-dependent arrangement. CT and MRI resolve the liver, spleen, pancreas, kidneys, bowel, bladder, and reproductive organs and clarify the compartments and spaces that organize their relationships.

Definition

Abdominal and pelvic sectional anatomy is the slice-by-slice arrangement of the abdominal and pelvic viscera, vessels, and the peritoneal and retroperitoneal spaces as displayed on axial, coronal, and sagittal cross-sectional images.

Scope

The topic covers normal sectional anatomy of the abdomen and pelvis: the solid organs (liver, spleen, pancreas, kidneys, adrenals), the gastrointestinal tract, the abdominal aorta and inferior vena cava, the peritoneal and retroperitoneal spaces and their boundaries, and the pelvic viscera, as displayed on standard imaging planes. It is reference and educational orientation to normal anatomy, not a guide to interpreting disease.

Core questions

• Which abdominal and pelvic organs appear at a given axial level from the diaphragm to the pelvic floor?
• How are the peritoneal and retroperitoneal compartments distinguished in section?
• How are the hepatic segments and the vascular landmarks of the abdomen identified?

Key concepts

• Solid viscera (liver, spleen, pancreas, kidneys, adrenals)
• Couinaud hepatic segments
• Gastrointestinal tract in section
• Peritoneal spaces and recesses
• Retroperitoneal compartments
• Abdominal aorta and inferior vena cava
• Pelvic viscera (bladder, rectum, reproductive organs)
• Mesenteric and ligamentous attachments

Mechanisms

On axial images the upper abdomen at the diaphragm shows the liver and spleen flanking the stomach, with the pancreas and the origins of the coeliac and superior mesenteric vessels appearing slightly lower; the kidneys and the great vessels lie in the retroperitoneum; descending further, the bowel loops occupy the central abdomen and then the pelvis, where the bladder, rectum, and reproductive organs are arranged within the bony pelvis. The peritoneal cavity and the retroperitoneum are organized into compartments bounded by fascial planes and ligamentous attachments, and recognizing these spaces explains the relationships and the routes by which fluid and processes spread. The liver is conventionally divided into segments defined by the portal and hepatic venous landmarks. CT and MRI both display these structures, with intravenous and luminal contrast helping to separate vessels, enhancing organs, and bowel from surrounding soft tissue.

Clinical relevance

Knowing normal abdominal and pelvic sectional anatomy and the compartments that organize it is prerequisite to reading the body CT and MRI that are central to abdominal and pelvic imaging. This entry describes normal anatomy for educational orientation and is not guidance for diagnosis or treatment.

Evidence & guidelines

Sectional abdominal and pelvic anatomy is documented in comprehensive anatomy texts and imaging atlases; the segmental anatomy of the liver derives from Couinaud's anatomical work, and the organization of the peritoneal and retroperitoneal spaces is detailed in reference works on abdominal radiologic anatomy.

History

Cross-sectional imaging of the abdomen and pelvis became practical with computed tomography in 1973, which for the first time directly displayed the solid organs and the spaces between them. Couinaud's segmental description of the liver and Meyers' work on the dynamic anatomy of the peritoneal and retroperitoneal spaces provided the anatomical frameworks that sectional imaging now routinely applies.

Key figures

• Claude Couinaud
• Morton Meyers
• Godfrey Hounsfield

Seminal works

• couinaud-1957
• meyers-2011
• hounsfield-1973

Frequently asked questions

What are the Couinaud segments of the liver?

They are a division of the liver into functionally independent segments defined by the branching of the portal and hepatic veins, a scheme widely used to localize structures in the liver on cross-sectional images.

Why does it matter whether a structure is intraperitoneal or retroperitoneal?

The peritoneal and retroperitoneal compartments are bounded by fascial planes, so an organ's location within them determines its relationships to neighbouring structures and the routes along which fluid and processes can spread.