OUTLINE ANATOMY, RADIOGRAPHY,

Transcription

1 16 ABDOMEN R OUTLINE SUMMARY OF PROJECTIONS, 84 ANATOMY, 85 Abdominopelvic cavity, 85 SUMMARY OF ANATOMY, 86 SUMMARY OF PATHOLOGY, 86 EXPOSURE TECHNIQUE CHART, 87 ABBREVIATIONS, 87 RADIOGRAPHY, 88 Abdominal radiographic procedures, 89 Abdominal sequencing, 89, 90 R L

2 SUMMARY OF PROJECTIONS P R O J E C T I O N S, P O S I T I O N S, A N D M E T H O D S Page Essential Anatomy Projection Position Method 91 AP Supine; upright 93 PA Upright 93 AP L lateral decubitus 95 Lateral R or L 96 Lateral R or L dorsal decubitus Icons in the Essential column indicate projections frequently performed in the United States and Canada. Students should be competent in these projections. 84

3 ANATOMY nal 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 con- Liver Stomach 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 abdomitains 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). Abdominopelvic Cavity Parietal peritoneum Visceral peritoneum Parietal peritoneum Visceral peritoneum R Pancreas Kidney (top) Retroperitoneum Spleen Fig Axial CT image of abdomen showing organs of upper abdomen. Retroperitoneum is posterior and medial to dashed line. L Liver Stomach (From Kelley LL, Petersen CM: Sectional anatomy for imaging professionals, ed 2, St Louis, 2007, Mosby.) Peritoneal cavity Retroperitonenum Transverse colon Mesentery Omentum Jejunum Sigmoid colon Urinary bladder Diaphragm Liver, left lobe Falciform ligament Liver, right lobe Gallbladder Ascending colon Ileum Appendix Esophagus Stomach Spleen Pancreas Transverse colon Descending colon Small intestine Urinary bladder A B Fig A, Lateral aspect of abdomen showing peritoneal sac and its components. B, Anterior aspect of abdominal viscera in relation to surrounding structures. 85

4 SUMMARY OF ANATOMY Peritoneum Abdominopelvic cavity Abdominal cavity Pelvic cavity Peritoneum Parietal Peritoneum Visceral Peritoneum Mesentery Omenta Peritoneal cavity Retroperitoneum SUMMARY OF PATHOLOGY Condition Definition Abdominal aortic aneurysm (AAA) Bowel obstruction Ileus Metastases Pneumoperitoneum Tumor Localized dilation of abdominal aorta Blockage of bowel lumen Failure of bowel peristalsis Transfer of a cancerous lesion from one area to another Presence of air in peritoneal cavity New tissue growth where cell proliferation is uncontrolled 86

5 EXPOSURE TECHNIQUE CHART ESSENTIAL PROJECTIONS D I G E S T I V E S Y S T E M Dose Part cm kvp* tm ma mas AEC SID IR (mrad) AP s cm 185 PA s cm 185 AP (decubitus) s cm 300 Lateral s cm 916 Lateral (decubitus) s cm 1040 *kvp values are for a three-phase, 12-pulse generator or high frequency. Relative doses for comparison use. All doses are skin entrance for average adult at cm indicated. Bucky, 16:1 grid. Screen-film speed 300 or equivalent CR. s, small focal spot. Abdominopelvic Cavity ABBREVIATIONS USED IN CHAPTER 16 AAA ERCP NPO PTC RUQ Abdominal aortic aneurysm Endoscopic retrograde cholangiopancreatography nil per os (nothing by mouth) Percutaneous transhepatic cholangiography Right upper quadrant See Addendum B for a summary of all abbreviations used in Volume 2. 87

6 RADIOGRAPHY 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-andwhite 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: To prevent muscle contraction caused by tension, adjust the patient in a comfortable position so that he or she can relax. Explain the breathing procedure, and ensure the patient understands exactly what is expected. If necessary, apply a compression band across the abdomen for immobilization but not compression. Do not start the exposure for 1 to 2 seconds after the suspension of respiration to allow the patient to come to rest and involuntary movement of the viscera to subside. 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. A B Fig A, AP abdomen showing proper positioning and collimation. B, AP abdomen showing kidney shadows (dotted line), margin of liver (dashed line), and psoas muscles (dot-dash lines). 88

7 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 airfluid 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. Positioning for radiographs of the abdomen is described in the following pages. (For a description of positioning for the PA chest, see Chapter 10.) Abdominal Sequencing To show small amounts of intraperitoneal gas in acute abdominal cases, Miller 1,2 recommended that the patient be kept in the left lateral position on a stretcher for 10 to 20 minutes before abdominal radiographs are obtained. This position allows gas to rise into the area under the right hemidiaphragm, where the image would not be superimposed by the gastric gas bubble. If larger amounts of free air are present, many radiology departments suggest that the patient lie on the side for a minimum of 5 minutes before the radiograph is produced. Projections of the abdomen are taken as follows: Perform an AP or PA projection of the chest and upper abdomen with the patient in the left lateral decubitus position. Use the chest exposure technique for this radiograph (Fig. 16-5). Maintain the patient in the left lateral decubitus position while the patient is being moved onto a horizontally placed table. Tilt the table and patient to the upright position. Turn the patient to obtain AP or PA projections of the chest and abdomen (Figs and 16-7). Return the table back to the horizontal position for a supine AP or PA projection of the abdomen (Fig. 16-8). Abdominal Sequencing 1 Miller RE, Nelson SW: The roentgenologic demonstration of tiny amounts of free intraperitoneal gas: experimental and clinical studies, AJR Am J Roentgenol 112:574, Miller RE: The technical approach to the acute abdomen, Semin Roentgenol 8:267, R Fig AP abdomen showing blurred bowel gas in right upper quadrant (RUQ), caused by patient breathing during exposure. Fig Enlarged portion of AP abdomen, left lateral decubitus position in a patient injected with 1 ml of air into abdominal cavity. 89

8 Fig Enlarged portion of upright AP chest showing free air in same patient as in Fig Fig AP abdomen, upright position, showing air-fluid levels (arrows) in intestine (same patient as in Fig. 16-8). Fig AP abdomen. Supine study showing intestinal obstruction in same patient as in Fig

9 AP PROJECTION Supine; upright Image receptor: inch (35 43 cm) lengthwise Position of patient For the AP abdomen, or KUB, projection, place the patient in either the supine or the upright position. The supine position is preferred for most initial examinations of the abdomen. Position of part Center the midsagittal plane of the body to the midline of the grid device. If the patient is upright, distribute the weight of the body equally on the feet. Place the patient s arms where they do not cast shadows on the image. With the patient supine, place a support under the knees to relieve strain. For the supine position, center the IR at the level of the iliac crests, and ensure that the pubic symphysis is included (Fig. 16-9). For the upright position, center the IR 2 inches (5 cm) above the level of the iliac crests or high enough to include the diaphragm (Fig ). If the bladder is to be included on the upright radiograph, center the IR at the level of the iliac crests. If a patient is too tall to include the entire pelvic area, obtain a second radiograph to include the bladder on a inch (24 30 cm) IR if necessary. The inch (24 30 cm) IR is placed crosswise and centered 2 to 3 inches (5 to 7.6 cm) above the upper border of the pubic symphysis. If necessary, apply a compression band across the abdomen with moderate pressure for immobilization. Shield gonads: Use local gonad shielding for examinations of male patients (not shown for illustrative purposes). Respiration: Suspend at the end of expiration so that the abdominal organs are not compressed. Central ray Perpendicular to the IR at the level of the iliac crests for the supine position Horizontal and 2 inches (5 cm) above the level of the iliac crests to include the diaphragm for the upright position Fig AP abdomen, supine. Collimation Adjust to inches (35 43 cm) on the collimator. For smaller patients, collimate to within 1 inch (2.5 cm) of shadow of the abdomen. Fig AP abdomen, upright. 91

10 Structures shown AP projection of the abdomen shows the size and shape of the liver, the spleen, and the kidneys and intra-abdominal calcifications or evidence of tumor masses (Fig ). Additional examples of supine and upright abdomen projections are shown in Figs and EVALUATION CRITERIA The following should be clearly shown: n Evidence of proper collimation n Area from the pubic symphysis to the upper abdomen (two radiographs may be necessary if the patient is tall) n Proper patient alignment, as ensured by the following: Centered vertebral column Ribs, pelvis, and hips equidistant to the edge of the radiograph on both sides n No rotation of patient, as indicated by the following: Spinous processes in the center of the lumbar vertebrae Ischial spines of the pelvis symmetric, if visible Alae or wings of the ilia symmetric n Soft tissue gray tones showing the following: Lateral abdominal wall and preperitoneal fat layer (flank stripe) Psoas muscles, lower border of the liver, and kidneys Inferior ribs Transverse processes of the lumbar vertebrae Right or left marker visible but not lying over abdominal contents n Diaphragm without motion on upright abdominal examinations (crosswise IR placement is appropriate if the patient is large). n Density on upright abdominal examination, similar to supine examination; however, reduce density if pneumoperitoneum suspected n Upright abdomen identified with appropriate marker R A B Fig A, AP abdomen, supine position. B, AP abdomen, upright position. 92

11 PA PROJECTION Upright When the kidneys are not of primary interest, the upright PA projection should be considered. Compared with the AP projection, the PA projection of the abdomen greatly reduces patient gonadal dose. Image receptor: inch (35 43 cm) lengthwise Position of patient With the patient in the upright position, place the anterior abdominal surface in contact with the vertical grid device. Center the abdominal midline to the midline of the IR. Center the IR 2 inches (5 cm) above the level of the iliac crests (Fig ), as previously described for the upright AP projection. The central ray, structures shown, and evaluation criteria are the same as for the upright AP projection. AP PROJECTION L lateral decubitus position Image receptor: inch (35 43 cm) Position of patient If the patient is too ill to stand, place him or her in a lateral recumbent position lying on a radiolucent pad on a transportation cart. Use a left lateral decubitus position in most situations. If possible, have the patient lie on the side for several minutes before the exposure to allow air to rise to its highest level within the abdomen. Place the patient s arms above the level of the diaphragm so that they are not projected over any abdominal contents. Flex the patient s knees slightly to provide stabilization. Exercise care to ensure that the patient does not fall off the cart; if a cart is used, lock all wheels securely in position. Position of part Adjust the height of the vertical grid device so that the long axis of the IR is centered to the midsagittal plane. Position the patient so that the level of the iliac crests is centered to the IR. A slightly higher centering point, 2 inches (5 cm) above the iliac crests, may be necessary to ensure that the diaphragms are included in the image (Fig ). Adjust the patient to ensure that a true lateral position is attained. Shield gonads. Respiration: Suspend at the end of expiration. COMPENSATING FILTER For patients with large abdomens, a compensating filter improves image quality by preventing overexposure of the upper-side abdominal area. Central ray Directed horizontal and perpendicular to the midpoint of the IR Collimation Adjust to inches (35 43 cm) on the collimator. For smaller patients, collimate to within 1 inch (2.5 cm) of shadow of the abdomen. NOTE: A right lateral decubitus position is often requested or may be required when the patient cannot lie on the left side. Fig PA abdomen, upright position. This projection is suggested for survey examination of the abdomen when the kidneys are not of primary interest. Fig AP abdomen, left lateral decubitus position. 93

12 Structures shown In addition to showing the size and shape of the liver, spleen, and kidneys, the AP abdomen with the patient in the left decubitus position is most valuable for showing free air and air-fluid levels when an upright abdomen projection cannot be obtained (Fig ). EVALUATION CRITERIA The following should be clearly shown: n Evidence of proper collimation n Diaphragm without motion n Both sides of the abdomen. If this is not possible, do the following: Elevate and show the side down when fluid is suspected Show the side up when free air is suspected n Abdominal wall, flank structures, and diaphragm n No rotation of patient n Proper identification visible, including patient side and marking to indicate which side is up R Free air Diaphragm Intestinal gas Surgical clips Crest of ilium Patient support R Fig AP abdomen, left lateral decubitus position showing free air collection along right flank. Note correct marker placement. 94

13 LATERAL PROJECTION R or L position Image receptor: inch (35 43 cm) lengthwise Fig Right lateral abdomen. Position of patient Turn the patient to a lateral recumbent position on either the right or the left side. Position of part Flex the patient s knees to a comfortable position, and adjust the body so that the midcoronal plane is centered to the midline of the grid. Place supports between the knees and the ankles. Flex the elbows, and place the hands under the patient s head (Fig ). Center the IR at the level of the iliac crests or 2 inches (5 cm) above the crests to include the diaphragm. Place a compression band across the pelvis for stability if necessary. Shield gonads. Respiration: Suspend at the end of expiration. Prevertebral space Bowel gas Central ray Perpendicular to the IR and entering the midcoronal plane at the level of the iliac crest or 2 inches (5 cm) above the iliac crest if the diaphragm is included R Collimation Adjust to inches (35 43 cm) on the collimator. For smaller patients, collimate to within 1 inch (2.5 cm) of shadow of the abdomen. Structures shown A lateral projection of the abdomen shows the prevertebral space occupied by the abdominal aorta and any intra-abdominal calcifications or tumor masses (Fig ). Fig Right lateral abdomen. EVALUATION CRITERIA The following should be clearly shown: n Evidence of proper collimation n Abdominal contents visible with soft tissue gray tones n No rotation of patient, indicated by the following: Superimposed ilia Superimposed lumbar vertebrae pedicles and open intervertebral foramina n As much of the remaining abdomen as possible when the diaphragm is included 95

14 LATERAL PROJECTION R or L dorsal decubitus position Image receptor: inch (35 43 cm) Position of patient When the patient cannot stand or lie on the side, place the patient in the supine position on a transportation cart or other suitable support with the right or left side in contact with the vertical grid device. Place the patient s arms across the upper chest to ensure they are not projected over any abdominal contents, or place them behind the patient s head. Flex the patient s knees slightly to relieve strain on the back. Exercise care to ensure that the patient does not fall from the cart or table; if a cart is used, lock all wheels securely in position. Position of part Adjust the height of the vertical grid device so that the long axis of the IR is centered to the midcoronal plane. Position the patient so that a point approximately 2 inches (5 cm) above the level of the iliac crests is centered to the IR (Fig ). Adjust the patient to ensure no rotation from the supine position occurs. Shield gonads. Respiration: Suspend at the end of expiration. Central ray Directed horizontal and perpendicular to the center of the IR, entering the midcoronal plane 2 inches (5 cm) above the level of the iliac crests Collimation Adjust to inches (35 43 cm) on the collimator. Structures shown The lateral projection of the abdomen is valuable in showing the prevertebral space and is quite useful in determining air-fluid levels in the abdomen (Fig ). EVALUATION CRITERIA The following should be clearly shown: n Evidence of proper collimation n Diaphragm without motion n Abdominal contents visible with soft tissue gray tones n Patient elevated so that entire abdomen is shown Fig Lateral abdomen, left dorsal decubitus position. L Gas-filled colon Gas level in colon Diaphragm Posterior ribs Support elevating patient Fig Lateral abdomen, left dorsal decubitus position, showing calcified aorta (arrows). Note correct marker placement. 96