ABDOMEN

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ABDOMEN




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Abdominopelvic Cavity


The abdominopelvic cavity consists of two parts: (1) a large superior portion, the abdominal cavity, and (2) a smaller inferior part, the pelvic cavity. The abdominal cavity extends from the diaphragm to the superior aspect of the bony pelvis. The abdominal cavity contains the stomach, small and large intestines, liver, gallbladder, spleen, pancreas, and kidneys. The pelvic cavity lies within the margins of the bony pelvis and contains the rectum and sigmoid of the large intestine, the urinary bladder, and the reproductive organs.


The abdominopelvic cavity is enclosed in a double-walled seromembranous sac called the peritoneum. The outer portion of this sac, termed the parietal peritoneum, is in close contact with the abdominal wall, the greater (false) pelvic wall, and most of the undersurface of the diaphragm. The inner portion of the sac, known as the visceral peritoneum, is positioned over or around the contained organs. The peritoneum forms folds called the mesentery and omenta, which serve to support the viscera in position. The space between the two layers of the peritoneum is called the peritoneal cavity and contains serous fluid (Fig. 16-1). Because there are no mesenteric attachments of the intestines in the pelvic cavity, pelvic surgery can be performed without entry into the peritoneal cavity.



The retroperitoneum is the cavity behind the peritoneum. Organs such as the kidneys and pancreas lie in the retroperitoneum (Fig. 16-2).








Abdominal Radiographic Procedures



EXPOSURE TECHNIQUE


In examinations without a contrast medium, it is imperative to obtain maximal soft tissue differentiation throughout the different regions of the abdomen. Because of the wide range in the thickness of the abdomen and the delicate differences in physical density between the contained viscera, it is necessary to use a more critical exposure technique than is required to show the difference in density between an opacified organ and the structures adjacent to it. The exposure factors should be adjusted to produce a radiograph with moderate gray tones and less black-and-white contrast. If the kilovolt peak (kVp) is too high, the possibility of not showing small or semiopaque gallstones increases (Fig. 16-3, A).



Sharply defined outlines of the psoas muscles, the lower border of the liver, the kidneys, the ribs, and the transverse processes of the lumbar vertebrae are the best criteria for judging the quality of an abdominal radiograph (Fig. 16-3, B).



IMMOBILIZATION


A prime requisite in abdominal examinations is to prevent voluntary and involuntary movement. The following steps are observed:



Voluntary motion produces a blurred outline of the structures that do not have involuntary movement, such as the liver, psoas muscles, and spine. Patient breathing during exposure results in blurring of bowel gas outlines in the upper abdomen as the diaphragm moves (Fig. 16-4). Involuntary motion caused by peristalsis may produce either a localized or a generalized haziness of the image. Involuntary contraction of the abdominal wall or the muscles around the spine may cause movement of the entire abdominal area and produce generalized radiographic haziness.




Abdomen



RADIOGRAPHIC PROJECTIONS


Radiography of the abdomen may include one or more radiographic projections. The most commonly performed projection is the supine AP projection, often called a KUB because it includes the kidneys, ureters, and bladder. Projections used to complement the supine AP include an upright AP abdomen or an AP projection in the lateral decubitus position (the left lateral decubitus is most often preferred), or both. Both radiographs are useful in assessing the abdomen in patients with free air (pneumoperitoneum) and in determining the presence and location of air-fluid levels. Other abdominal projections include a lateral projection or a lateral projection in the supine (dorsal decubitus) body position. Many institutions also obtain a PA chest radiograph to include the upper abdomen and diaphragm. The PA chest radiograph is indicated because any air escaping from the gastrointestinal tract into the peritoneal space rises to the highest level, usually just beneath the diaphragm.



POSITIONING PROTOCOLS


Radiographs obtained to evaluate the patient’s abdomen vary considerably depending on the institution and physician. Some physicians consider the preliminary evaluation radiograph to consist of only the AP (supine) projection. Others obtain two projections: a supine and an upright AP abdomen (often called a flat and an upright). A three-way or acute abdomen series may be requested to rule out free air, bowel obstruction, and infections. The three projections usually include (1) AP with the patient supine, (2) AP with the patient upright, and (3) PA chest. If the patient cannot stand for the upright AP projection, the projection is performed using the left lateral decubitus position. The PA chest projection can be used to detect free air that may accumulate under the diaphragm.

Mar 3, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on ABDOMEN
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