2007-05-23 00:00 来源:丁香园 作者:丁香园集体创作
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Case 4

A 6-year-old girl had abdominal pain and vomiting with a vague mass to the left of the umbilicus. The child had had a similar attack lasting for a few hours about 10 days before this second episode. The clinical impression was intussusception. Sonography revealed 2 loops of dilated small bowel to the left of the umbilicus with the zone of transition in the midline. There was a thin membrane covering these 2 loops, which was seen because of minimal fluid in the sac and peritoneal cavity (Figure 7). No further investigation was performed. The clinical situation warranted a laparotomy, which revealed a left paraduodenal hernia containing dilated small-bowel loops due to obstruction of the efferent loop at the neck of the sac.


Figure 7. Compound transverse scan of the left side of abdomen showing the dilated loops of bowel within a sac (arrowhead) outlined by fluid on either side of it and the zone of transition at the neck of the sac (arrow).


Internal hernia involves protrusion of a viscus, usually the small bowel, through a normal or abnormal aperture within the peritoneal cavity. This hernia may be either congenital or acquired. Congenital internal hernias include paraduodenal, foramen of Winslow, mesenteric, and supravesical hernias. During fetal development, the mesentery of the duodenum, ascending colon, and descending colon becomes fixed to the posterior peritoneum. These segments of the bowel become retroperitoneal. Anomalies of mesenteric fixation may lead to abnormal openings through which internal hernias may occur. This is the likely mechanism of paraduodenal and supravesical hernias. Abnormal mesenteric fixation may lead to abnormal mobility of the small bowel and right colon, which facilitates herniation. During fetal development, abnormal openings may occur in the pericecal, small bowel, transverse colon, or sigmoid mesentery, as well as the omentum, leading to mesenteric hernias.

Paraduodenal hernias are thought to occur because of anomalies in fixation of the mesentery of the ascending or descending colon. In cases of left paraduodenal hernia, an abnormal foramen (fossa of Landzert) occurs through the mesentery close to the ligament of Treitz, leading under the distal transverse and descending colon, posterior to the superior mesenteric artery. The small bowel may protrude through this fossa. The mesentery of the colon thus forms the anterior wall of a sac enclosing a portion of the small intestine. Mesenteric hernias occur when a loop of intestine protrudes through an abnormal opening in the mesentery of the small bowel or the colon. The most common area for such an opening is in the mesentery of the small intestine, most often near the ileocolic junction. The intestine finds its way through the defects by normal peristaltic activity. Various lengths of intestine may herniate posterior to the right colon into the right paracolic gutter. Compression of the loops may lead to obstruction of the herniated intestine. Strangulation may occur by compression or by torsion of the herniated segment. Obstruction may be acute, chronic, or intermittent. The herniated bowel may also compress arteries in the margins of the mesenteric defect, causing ischemia of nonherniated intestine. Acquired internal hernias may occur as a complication of surgery or trauma if abnormal spaces or mesenteric defects are created.

Any of the various forms of internal hernias may cause symptoms of acute or chronic intermittent intestinal obstruction. The diagnosis is difficult among patients with chronic symptoms and is rarely made preoperatively among patients with acute obstruction. About half of patients with paraduodenal hernias have intestinal obstruction, which may be low grade, chronic, and recurrent or may be high 3–5 grade and acute. In acute bowel obstruction, patients have colicky abdominal pain with vomiting. Features of internal hernia on a barium meal study and CT scan are available, but reports are very scanty. Barium radiographs may show the small bowel to be bunched up or agglomerated, as if it were contained in a bag, and displaced to the left or right side of the colon. The small bowel is often absent from the pelvis. The colon may be deviated by the internal hernia sac. The bowel proximal to the hernia may be dilated.

However, barium radiographic findings may be normal if the hernia has spontaneously reduced. There are a few reports of features of internal hernia on CT. The largest series was a retrospective review of 17 patients by Blachar et al. They put forth the following CT findings in internal hernia: (1) evidence of small-bowel obstruction, (2) a cluster of small-bowel loops, (3) a saclike mass of small bowel, (4) crowding of mesenteric vessels, and (5) displacement of the mesenteric trunk. 7 Schaffler et al described a pathognomonic anterior and upward displacement of the inferior mesenteric vein in paraduodenal internal hernia. A barium meal study of the small bowel involves more time and may delay the diagnosis. The clinical condition of the patient may preclude a time-consuming investigation. A CT scan is the investigation of choice at present, but it has the disadvantage of cost and nonavailability, particularly in developing nations. In contrast, sonography is more readily available and affordable in this part of the world. Sonography is the first investigation requested for patients with abdominal symptoms. Hence, recognition of sonographic features of internal hernia will be an advantage, and it will be useful in the treatment of such patients, especially in developing countries. An acute occurrence of an internal hernia is due to obstruction of the small bowel. Sonographic features of small-bowel obstruction are well described. There are dilated small-bowel loops showing active peristalsis. The peristalsis is usually pendular, with to-and-fro movement of fluid on the lumen. This is because of reverse peristalsis occurring due to distal obstruction. Sonography is useful in differentiating mechanical obstruction from paralytic ileus. In the absence of peristalsis, passive to-and-fro movement of the fluid in the lumen with respiration, widespread distri-bution of dilated bowel loopswithout a demonstrable level, uniformity of bowel obstruction, and demonstration of the cause of ileus are the features of paralytic ileus. The sensitivity and specificity of sonography for the diagnosis of small-bowel obstruction are as high as 83% and 100%, as reported by Suri et al. The level of obstruction is correctly predicted by sonography in 70% of patients, but sonography is poor (23%) in showing the etiology of obstruction. The difficulty is caused by gas in the obstructed bowel, which makes sonography difficult. This can be partly overcome by compression of the bowel loop, displacing the air; thus, the bowel can be traced distally to identify the level and cause of obstruction. This technique may be difficult in very obese patients. So far, to my knowledge, there is only 1 report of sonographic features of internal abdominal hernia, which describes an abdominal mass with the presence of changing cystic or tubular internal components and a surrounding membrane.

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