Sonographic Features of Internal Hernia

Case Series Sonographic Features of Internal Hernia S. Boopathy Vijayaraghavan, MD, DMRD Objective. The purpose of this series is to describe the sonographic findings in 4 patients with intestinal obstruction due to internal hernia. Methods. Four patients had clinical features of intestinal obstruction. Sonography was performed with broadband convex and linear array transducers in these patients. Results. In all 4 patients, there were features of intestinal obstruction with a zone of transition between dilated and nondilated bowel. There was a cluster of crowded, compressed, and aperistaltic small-bowel loops, as if they were tightly packed within a sac, by the side of this zone in 3 patients. This appearance was due to obstruction of the afferent loop caused by compression. In the last patient, there were 2 loops of dilated bowel within a sac outlined by fluid due to obstruction of the efferent loop. All 4 patients had obstructed internal hernias at laparotomy. Conclusions. Sonographic features of internal hernia are described. Key words: internal hernia; paracecal; paraduodenal; sonography. Abbreviations CT, computed tomography Received June 6, 2005, from Sonoscan Ultrasonic Scan Centre, Coimbatore, India. Revision requested July 11, 2005. Revised manuscript accepted for publication July 20, 2005. Address correspondence to S. Boopathy Vijayaraghavan, MD, DMRD, 16 B Venkatachalam Rd, R. S. Puram, Coimbatore 641 002, India. E-mail: sonoscan@vsnl.com or sboopathy@eth.net Internal hernias are rare, with reported incidence of 0.2% to 0.9% of autopsies. 1 A substantial proportion of these remain asymptomatic. Internal hernia is an uncommon cause of small-bowel obstruction. About 4% of bowel obstructions are due to internal hernia. 2 Because of the risk of strangulation of the hernia contents, even small internal hernias are dangerous and may be lethal. This necessitates an early and confident diagnosis. The diagnostic features of this condition on barium studies, angiography, and computed tomography (CT) have been described. To my knowledge, there is only 1 report of sonographic features of internal hernia, but diagnostic criteria that would allow more confident sonographic diagnosis have not been evaluated. Four cases of internal hernia are reported here. Case Descriptions Case 1 A 25-year-old man had epigastric pain and vomiting. Because the symptoms did not resolve with conservative treatment, he was referred for sonography. There were multiple dilated small-bowel loops showing active peristalsis suggestive of small-bowel obstruction. The dilated loop was traced to determine the level of obstruction. A point of transition between the dilated and nondilated 2006 by the American Institute of Ultrasound in Medicine J Ultrasound Med 2006; 25:105 110 0278-4297/06/$3.50

Sonographic Features of Internal Hernia bowel was seen close to the midline above the umbilicus, with the dilated bowel on the right side (Figure 1). The bowel did not show any intrinsic abnormality at the site of transition. There was a cluster of collapsed small-bowel loops to the left of this zone of transition (Figure 2). These loops did not show peristalsis and had an appearance of compressed and crowded loops, as if they were tightly packed within a sac. Because of the clinical condition of the patient, no further investigation was done. The patient was subjected to laparoscopy, which revealed a left paraduodenal internal hernia that was repaired appropriately. The patient had an uneventful recovery. Case 2 An 8-year-old boy had acute right flank pain and vomiting. Sonography revealed small-bowel obstruction. The zone of transition between the dilated and nondilated small bowel was seen in the right iliac fossa (Figure 3). There was a cluster of a few loops of crowded, compressed, and aperistaltic small bowel above and to the right of this zone with the suggestion of encapsulation (Figure 4). Because of prior experience with the previous case, a diagnosis of small-bowel obstruction due to internal hernia was made. The patient was taken for surgery without any other investigation. Laparotomy revealed a small-bowel obstruction due to a paracecal internal hernia. Case 3 A 1-year-old girl had a sudden attack of persistent vomiting lasting for almost 24 hours. Sonography was performed with a clinical diagnosis of malrotation of the midgut. It revealed markedly dilated hyperperistaltic small-bowel loops suggestive of small-bowel obstruction. There was a zone of transition in the right iliac fossa (Figure 5) with a cluster of crowded and compressed loops of small bowel to the right of the zone of transition (Figure 6). The child did not undergo any other imaging investigation. Because the child did not improve with conservative treatment, laparotomy was done, which showed a small-bowel obstruction due to a paracecal internal hernia. 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 smallbowel loops due to obstruction of the efferent loop at the neck of the sac. Discussion 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 Figure 1. Oblique scan above the umbilicus showing the zone of transition (arrow) between the dilated and nondilated bowel. 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 106 J Ultrasound Med 2006; 25:105 110

Vijayaraghavan 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. 1 About half of patients with paraduodenal hernias have intestinal obstruction, which may be low grade, chronic, and recurrent or may be high grade and acute. 3 5 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. 1,3,5 However, barium Figure 2. Transverse (A) and longitudinal (B) scans to the left of the zone of transition showing the cluster of crowded and compressed loops of bowel as if they are tightly packed within a sac. A B J Ultrasound Med 2006; 25:105 110 107

Sonographic Features of Internal Hernia Figure 3. Oblique scan of the right iliac fossa showing the zone of transition (arrow) of the dilated to nondilated bowel. 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. 6 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. Schaffler et al 7 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 smallbowel obstruction are well described. 8,9 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- Figure 4. Oblique scan above and to the right of the zone of transition showing the cluster of crowded and compressed loops. Figure 5. Oblique scan in right iliac fossa showing the zone of transition (arrow). 108 J Ultrasound Med 2006; 25:105 110

Vijayaraghavan bution of dilated bowel loops without a demonstrable level, uniformity of bowel obstruction, and demonstration of the cause of ileus are the features of paralytic ileus. 10 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. 9 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. 11 Here, the sonographic appearance of internal hernia in 4 patients is reported. The features were identical in 3 of them. Of these 3 cases, 1 was paraduodenal and 2 were paracecal. The features seen were (1) small-bowel obstruction as evidenced by dilated hyperperistaltic loops, (2) a zone of transition between the dilated and nondilated bowel, and (3) a cluster of collapsed, crowded, and compressed small-bowel loops, as if enclosed in a bag. This appearance is seen away from the zone of transition, to the left in paraduodenal hernia and to the right in paracecal hernia. These are the features seen when the afferent loop entering the sac is obstructed because of crowding and compression of bowel loops in the sac. These features are similar to those described on CT. In the fourth patient, there was a sac containing dilated loops of small bowel with a zone of transition at the neck of the sac. This appearance is due to the obstruction to the efferent loop at the neck, resulting in dilatation of the loop within the hernial sac. The differential diagnosis for the sonographic appearance of internal hernia is an abdominal cocoon. The sonographic features of this condition have been described here previously, 12 and 4 additional patients with an abdominal cocoon were seen after that first report. In all those patients, there was no evidence of smallbowel obstruction or zone of transition. The loops do not appear to be compressed and show normal peristalsis. These features help differentiate between these conditions. In conclusion, there are recognizable features of internal hernia on sonography. When such features are seen, a sonographic diagnosis of internal hernia can be made. Figure 6. Transverse scan showing the cluster of crowded and compressed loops. 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). J Ultrasound Med 2006; 25:105 110 109

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