P113TOPOGRAPHIC LANDMARKSAbdominal borders and organs within the abdomen are not visible from the exterior, and because these soft tissue organs cannot be pedp,ited directly, certain bony landmarks are used for this purpose. NOTE: Palpation must be done gently because the patient may have painful or sensitive are within the abdomen and pelvis. Also, ensure that the Patient is informed of the purpose of palpation before beginning. SEVEN LANDMARKS OF THE ABDOMEN The following seven palpable landmarks are important in position-ing the abdomen or locating organs within the abdomen(Figs.k3.2 1 and 3.22). You should practice finding these bony landmars on yourself before attempting to locate them on another person or on a patient for the first time. Positioning for abdominal radiographs in AP or posteroanterior (PA) projections requires quick but accurate localization of these landmarks on all patient body types. 1 Xiphoid. process (level of T9-T10): The tip of the xiphoid process is the most inferior process of the sternum. This land-mark can best be palpated by first gently pressing on the soft abdomen below the distal sternum, then moving upward care-fully against the firm, distal margin of the xiphoid process. This landmark approximates the superior anterior portion of the diaphragm, which is also the superior margin of the abdomen. However, this is not a primary landmark for positioning the abdomen because of variation in body types and the importance of including all of the lower abdomen on most radiographs of the abdomen. 2.Inferior costal (rib) margin (level of L2-L3): This landmark is used to locate upper abdominal organs, such as the gallbladder and stomach. 3. Iliac crest (level of L4-L5 vertebral interspace): The crest of the ilium is the uppermost portion of the curved border of the i ilium. The iliac crest can be palpated easily by pressing inward and downward along the midlateral margin i of the abdomen. The uppermost or most superior portion of this crest is the most commonly used abdominal landmark and corresponds approximately to the level of the mid-abdominopelvic region, which is also at or just slightly below the level of the umbilicus on most people. NOTE: Ensuring that the entire upper abdomen, including the dia-phragm, is included on the radiographic image may require centering about 5 cm (2 inches) above the level of the crest for most patients which subsequently may cut off some of the important lower abdomen: A second projection centered lower would be required to include this lower region. 4 .Anterior superior iliac spine (ASIS): The ASIS can be found by locating the iliac crest, then palpating anteriorly and inferiorly until a prominent projection or "bump" is felt (more prominent on females). This landmark is commonly used for positioning of pelvic and vertebral structures but can also serve as a secondary landmark for generdl dbdominal positioning (Fig. 3.23). 5.Greater trochanter: This landmark is more easily palpated on thin patients, Gentle but very firm palpation generally is required to feel the movement of the trochanter with one hand, while rotating the leg internally and externally at the knee area with the other hand. This is not as precise a landmark as the other bony landmarks of the pelvis, but the prominence of the greater trochanter is at about the same level as the superior border of the symphysis. With practice, the greater trochanter can be used as a secondary landmark for abdominal positioning. 6. Symphysis pubis: The symphysis pubis is the anterior junction (joint) of the two pelvic bones. The most superior anterior portion of the pubis can be palpated when the patient is in a supine position. This landmark corresponds to the inferior margin of the abdomen. However, palpation of this area may be embarrassing to some patients and palpating the greater trochanter may be a better option. 7. Ischia tuberosity: This landmark can be used to determine the lower margin on a PA abdomen with the patient in a prone position. These two bony prominences, which can be palpated most easily on thin patients, bear most of the weight of the trunk when one is seated. The lower margins of the ischial tuberosities are about 1 to 4 cm (inches) below or distal to the symphysis pubis. This landmark may be used for positioning a PA projection of the colon when the rectal area is to be included on the IR. However, this may be uncomfortable and embarrassing for the patient, and other landmarks can and should be used when possible.