A Computed Tomography (CT) scan uses a series of X-rays taken from multiple angles to generate detailed, cross-sectional images of the body’s internal structures. This non-invasive procedure combines the X-ray data with computer processing to create comprehensive views of bone, soft tissue, and blood vessels. A CT scan of the abdomen and pelvis is performed as a single, combined examination, providing a continuous, detailed picture of the anatomy spanning from the diaphragm down to the hip bones.
Visualizing the Abdominal Structures
The abdominal portion of the CT scan provides a detailed inventory of the solid organs located in the upper and middle sections of the torso. The exam clearly maps the liver and the spleen, which is situated in the upper left quadrant. Detailed images also capture the kidneys, which are assessed for size, shape, and the presence of any masses or fluid collections.
The scan visualizes the pancreas, located behind the stomach, along with the smaller adrenal glands positioned atop the kidneys. The upper gastrointestinal tract is also mapped, including the stomach, small bowel, and colon. CT imaging is effective at differentiating these soft tissue organs and the surrounding fat, which helps distinguish normal anatomy from potential abnormalities.
Beyond the organs, the scan offers high-resolution views of the major vascular structures that supply the abdomen. The abdominal aorta, the body’s largest artery, and the inferior vena cava (IVC), the largest vein, are clearly delineated. Smaller vessels, such as the portal vein, are also visible and can be assessed for blockages or structural integrity.
Visualizing the Pelvic Structures
The pelvic component extends the visualization downward, focusing on the structures contained within the bony ring of the hips. The urinary bladder is examined for wall thickening, masses, or stones. The lower portion of the bowel is also included, primarily the sigmoid colon and the rectum, which are assessed for inflammation or other changes.
In males, the prostate gland is clearly visualized, and in females, the uterus and ovaries are included in the scan coverage. The CT provides information on the size, contour, and internal texture of these reproductive organs. The scan also delivers clear images of the dense bony structures forming the pelvis, including the sacrum and the hip joints.
The muscles and soft tissues that line the pelvic wall, such as the psoas and iliacus muscles, are also defined. This comprehensive view ensures that conditions affecting structures in this lower part of the body are thoroughly evaluated.
Identifying Common Conditions and Abnormalities
The primary purpose of the combined CT scan is to identify the source of unexplained abdominal or pelvic symptoms, such as pain or abnormal bleeding. The detailed images allow for the diagnosis of acute inflammatory processes. For instance, the scan can reveal the thickened, inflamed wall of the appendix in cases of appendicitis or the characteristic pockets of infection seen in diverticulitis.
The CT is effective for detecting masses and is routinely used for cancer staging, which involves identifying the location, size, and spread of tumors. It can pinpoint cancers originating in organs like the liver, pancreas, kidneys, colon, or ovaries, and assess if the disease has spread to lymph nodes or distant sites. Findings like hypoattenuating lesions, which appear darker than surrounding tissue, may be identified, often representing benign cysts or concerning masses.
Vascular diseases are also readily assessed, including the detection of an abdominal aortic aneurysm (AAA), an abnormal enlargement of the aorta. The scan can quickly identify the presence of blood clots within major vessels (thrombosis). In trauma cases, the speed and detail of the CT make it the preferred tool for rapidly identifying internal injuries, such as lacerations to the liver or spleen, and locating internal bleeding.
The scan is sensitive for urinary tract issues, particularly the detection of kidney stones and bladder stones. It can also show hydronephrosis, the swelling of the kidney due to a blockage of urine flow, often caused by a stone or other obstruction. The CT can also reveal abscesses, which are localized collections of pus, and other fluid collections that signal infection.
The Role of Contrast Material
A CT of the abdomen and pelvis is often performed using contrast material to enhance the visibility of internal structures and pathology. Intravenous (IV) contrast, an iodine-based dye injected into a vein, is absorbed by tissues with good blood flow. This highlights blood vessels and makes it easier to differentiate between normal tissue and areas of active inflammation or tumors, which often show increased blood supply.
The process of a lesion “enhancing” or brightening after contrast injection provides information about its nature, aiding in the classification of masses. Oral contrast, a liquid ingested before the scan, works by filling the gastrointestinal tract. This helps to clearly delineate the walls of the stomach, small bowel, and colon, making it easier to distinguish bowel loops from adjacent organs or fluid collections.
The type and timing of contrast administration are tailored to the suspected diagnosis. For example, IV contrast is used for suspected vascular issues or tumors, while oral contrast is often used to investigate bowel pathology. Using contrast improves the diagnostic accuracy of the scan by providing a clearer distinction between different tissues.