Abdominal Film

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c Chilaiditi syndrome c Chilaiditi syndrome

d Chronic pancreatitis
Stool Abdominal Film

Fig. 9.2a This is a normal abdominal film. The liver shadow occupies the right upper abdomen. Its inferior margin can only be guessed on this film. The peritoneal fat stripe along the right lateral abdominal wall is visible, however. The spleen in the left upper abdomen is completely disguised by the splenic flexure of the colon. Almost the whole colon is filled with air. Stool is seen in the cecum, the descending colon, and the sigmoid colon. The small bowel is not visible at all. The gastric bubble is barely appreciated medial to the splenic flexure. In this slim patient the retroperitoneal fat is not abundant enough to clearly outline the contours of the kidneys and the iliopsoas muscle. b The lower margin of the liver, the contour of the kidney, and the border of the iliopsoas muscle are beautifully depicted in this patient. c In this patient, air-filled large-bowel loops are projecting over the liver. This entity is called Chilaiditi syndrome and tends to be an incidental finding without symptoms. d In chronic pancreatitis typical calcifications occur in the parenchyma (arrows) and have to be differentiated from atherosclerosis of the splenic artery e This cut-out of an abdominal radiograph of a patient positioned on the left side and taken with a horizontal beam shows air-filled small-bowel loops with air-fluid interfaces—so-called "sentinel loops." They indicate disturbances of the intestinal peristalsis. The difference in fluid level in the larger loop hints at peristalsis working to overcome an obstacle: this is a sign of a mechanical (dynamic) bowel obstruction or early obstructive ileus. The colon is devoid of air: the obstruction must be somewhere in the distal small bowel.

The structures of the retroperitoneum are easily distinguished as long as they have interfaces with the retroper-itoneal fat: the contours of the kidneys and the iliopsoas muscle are regularly appreciated; the pancreas tends to be discernible only if its parenchyma contains punctate calcifications, for instance due to chronic pancreatitis (Fig. 9.2d).

The urinary bladder can be delimited in the lower pelvis if it is filled well. When fully expanded it tends to lift the intestines out of the pelvis.

Calcifications are frequently found in the following locations:

• Vascular walls: Particularly frequent in the aorta, the celiac artery and its branches, in particular the splenic artery and in the iliac arteries. Oval calcifications in the pelvis are often due to phleboliths in pelvic veins, particularly common in the veins next to the uterus and in the venous plexus around the bladder.

• Parenchymal organs: Kidneys (kidney stones), uterus (fibroids), liver and spleen (after granulomatous infec tions such as histoplasmosis), pancreas (chronic pancreatitis).

• Hollow organs: Particularly frequent in the gallbladder lumen (gallstones) or wall (porcelain gallbladder).

• Lymph nodes: Particularly frequent in the mesentery. The distribution of the intestinal air and the thickness of the intestinal walls is of special importance. Air in the small bowel is rare in the healthy adult. It is an obligatory (regular) finding in neonates and frequent in small children. The stomach and the colon routinely contain varying amounts of air. The differences in caliber and wall structure (valvulae conniventes—or Kerckring folds—in the small bowel and haustral folds in the large bowel) make it easy to differentiate small and large bowel in most cases. Any air outside the intestinal lumen is abnormal and should prompt careful correlation with the patient's history: if surgery has recently been performed, free air may be related to the procedure. Careful comparison with prior radiographs is warranted if these are available, to ensure that this finding is not new or increasing

The thickness of the bowel wall is evaluated by observing the distance between two neighboring loops. In inflammatory and ischemic processes of the bowel, the thickness of the wall increases. If intramural gas (mostly in the form of small bubbles like a "string of pearls" or as streaks in the bowel wall, particularly in dependent parts of the bowel wall) is found, further diagnostic measures need to be taken. Although there is a benign condition termed "pneumatosis intestinalis," characterized by air in the bowel wall, this finding may also be associated with life-threatening conditions such as intestinal infarction or severe inflammation of the intestinum that need to be excluded.

The amount and distribution of stool throughout the colon should also be noted. Patients with severe constipation may present with acute abdominal pain.

Why Are You Interested in the Standard Chest Radiograph in a

Patient with Abdominal Pain?

The areas under the diaphragm are of particular interest when confronted with abdominal symptoms: Air seen underneath the right hemidiaphragm (above and surrounding the liver) is intraperitoneal by definition. Free air in the peritoneum, of course, also reaches the underside of the left hemidiaphragm, but there the air in the stomach and in the splenic flexure of the colon may obscure it and can often not be distinguished from true free air, which leaves too much room for mistakes. For that reason, in patients unable to stand, the abdominal radiograph is performed with the patient turned all the way up on their left side: potential free air then rises to the right into the nondependent space between the diaphragm and the liver. Patients should remain in that position for at least 5 minutes before the radiograph is taken because it takes time for the air to rise into the right upper quadrant of the abdomen.

I See an Abnormality—What Do I Do Now?

First reflect on whether the perceived abnormality may be clinically relevant in that particular patient; put the observation into context with history and findings on clinical examination.

Most calcifications in the abdomen are of no clinical significance for the health of the patient. Exceptions are the calcifications seen in the expected location of the pancreas (chronic pancreatitis) and the ureter (renal colic). The combination of clinical findings and history in a given patient will often guide the diagnostic process toward the dominant clinical problem.

Free intraperitoneal air is very relevant finding and indicates the perforation of a hollow viscus. (Just a few milliliters of air is detectable!) But be aware: It may also be seen in patients who have undergone recent abdominal surgery, a common situation in a hospital setting. As mentioned above, careful comparison with prior postoperative radiographs is warranted, if these are available, to ensure that this finding is not new or increasing. In case of doubt, a phonecall to the clinician taking care of the patient is good practice and will often clarify the significance of the finding as well as help determine the need for further imaging or even surgical intervention. So do not ring the grand alarm bell right away.

Air in the retroperitoneum is always pathological. The contours of the kidneys, the pararenals, and the ilio-psoas muscle become very distinct. Reasons may be the perforation of a retroperitoneal bowel segment (duodenum, parts of the colon and rectum) or the transit of air from the mediastinum into the retroperitoneal space in mediastinal emphysema.

The analysis of the distribution of bowel gas can help in the diagnosis of a number of entities: An air-distended stomach is frequently found after resuscitation and may point to an earlier false intubation. It doesn't hurt to mention the distended stomach to the referring physician, because placement of a nasogastric tube can often provide relief to the patient. Wide, air-filled small-bowel loops indicate a disturbance of the bowel peristalsis and are due to either a partial or complete ileus or small-bowel obstruction.

f Differentiation between an ileus and a small-bowel obi struction is most readily afforded by auscultation: the absence of bowel sounds suggests an ileus (or extremely advanced obstruction), while high-pitched active bowel sounds suggest a mechanical bowel obstruction. Remember that even (!) radiologists may consider using the stethoscope every now and then to help make the right diagnosis.

The actual image appearance of the air- and fluid-filled small-bowel loops—also called "sentinel loops"— (Fig. 9.2e) hints at the character of the disturbance: If a mechanical obstruction is present, the intestinal peristalsis continues and tries to force the bowel content across the point of obstruction. A characteristic sentinel loop shows air-fluid interfaces at significantly different levels.

The air-filled bowel segments are naturally located proximal to the point of obstruction because the air distal to it is absorbed in time.

If the peristaltic problem is due to a paralysis or if the obstructed bowel is eventually exhausted, the air-fluid interfaces in the sentinel loops tend to remain at the same level: an adynamic ileus is present. (To observe the potential difference in fluid levels, the patient must remain motionless in the above-described positions for a few minutes.) Bowel sounds are typically absent in this situation. Extremely dilated air-filled large-bowel segments may be seen in toxic megacolon, in large-bowel obstruction due to tumor, or in volvulus (torsion of the bowel around its mesenteric root). The more chronic the problem, the larger the intestines can appear. Now let us try this out on the first patient.

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