Normal Anatomy and Complications after Gastric Bypass Surgery: Helical CT Findings 1

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1 Gastrointestinal Imaging Radiology Jinxing Yu, MD Mary Ann Turner, MD Shao-Ro Cho, MD Ann S. Fulcher, MD Eric J. DeMaria, MD John M. Kellum, MD Harvey J. Sugerman, MD Normal Anatomy and Complications after Gastric Bypass Surgery: Helical CT Findings 1 Index terms: Gastrointestinal tract, CT, , Gastrointestinal tract, radiography, Gastrointestinal tract, surgery, , Gastrojejunostomy Stomach, surgery, , Published online /radiol Radiology 2004; 231: From the Departments of Radiology (J.Y., M.A.T., S.R.C., A.S.F.) and Surgery (E.J.D., J.M.K., H.J.S.), VCUHS/ MCV Hospitals and Physicians, 401 N 12th St, Main Hospital, 3rd Floor, PO Box , Richmond, VA Received April 7, 2003; revision requested June 25; revision received October 20; accepted November 25. Address correspondence to J.Y. ( jiyu@hsc.vcu.edu). PURPOSE: To determine the usefulness and potential pitfalls of helical computed tomography (CT) for depiction of normal anatomy and diagnosis of complications after gastric bypass surgery. MATERIALS AND METHODS: From March 1998 to July 2002, 100 abdominal and pelvic CT examinations were performed in 72 patients after gastric bypass surgery for treatment of morbid obesity. Two of four attending abdominal radiologists retrospectively assessed the CT images in consensus for normal postoperative gastrointestinal anatomy and complications such as leaks, staple line dehiscence, bowel obstruction, abscess, hepatic or splenic infarction, and hernia. CT findings were compared with clinical, surgical, and other imaging findings. RESULTS: The gastric pouch, excluded stomach, proximal efferent loop, oversewn jejunal loop, and distal jejunojejunal anastomosis were identified in 96 (96%) of 100 studies and 69 (96%) of 72 patients, 100 (100%) of 100 studies and 72 (100%) of 72 patients, 99 (99%) of 100 studies and 71 (99%) of 72 patients, 88 (88%) of 100 studies and 61 (85%) of 72 patients, and 67 (67%) of 100 studies and 46 (64%) of 72 patients, respectively. The fundus of the excluded stomach was filled with a combination of air, fluid, and contrast material, which mimicked a loculated fluid collection in 15 (15%) of 100 studies and 13 (18%) of 72 patients. Sixty-two abnormalities, detected in 41 patients, included leak (n 12), loculated fluid collection unrelated to leak (n 9), markedly distended excluded stomach (n 6), small-bowel obstruction (n 6), gastric staple line dehiscence (n 6), splenic infarction (n 5), hematoma (n 5), left hepatic lobe infarction (n 3), and hernia related to gastric bypass (n 10, including three internal hernias, three incisional hernias, and four nonincisional ventral hernias). Seventeen patients required a total of 21 CT-guided interventional procedures. CONCLUSION: Helical CT is useful for identifying normal postoperative anatomy and complications after gastric bypass surgery. RSNA, 2004 Author contributions: Guarantors of integrity of entire study, M.A.T., A.S.F., J.Y.; study concepts, M.A.T., A.S.F., J.Y.; study design, J.Y., M.A.T.; literature research, J.Y.; clinical studies, J.Y.; data acquisition, J.Y., M.A.T., A.S.F., S.R.C.; data analysis/ interpretation, J.Y., M.A.T., A.S.F.; statistical analysis, J.Y.; manuscript preparation, J.Y.; manuscript definition of intellectual content and editing, J.Y., M.A.T., A.S.F.; manuscript revision/review, all authors; manuscript final version approval, A.S.F., M.A.T., J.Y. RSNA, 2004 Obesity is one of the most prevalent public health problems in the United States (1 3). The prevalence of obesity (body mass index, 30 kg/m 2 ) has progressively increased for the past few decades. Severe obesity is associated with diseases such as hypertension, type 2 diabetes, and coronary heart disease, as well as early mortality (1). Results of nonsurgical treatments for obesity have been disappointing, and surgical approaches are now more widely used to treat morbid obesity (1 3). The gastric bypass operation described by Mason and Ito (4) has been successful for the surgical treatment of morbid obesity. In general, it entails transection or stapling of the stomach to create a very small gastric pouch (about cm 3 ), which empties through a Roux-en-Y gastrojejunostomy (3 7) (Fig 1). The Roux-en-Y limb ranges from 50 to 150 cm in length and is anastomosed side-to-side to the jejunum (3,7). Distention of the pouch results in early satiety, and vomiting will occur if further ingestion continues (7). The 753

2 Roux-en-Y gastric bypass surgery has been shown to yield a greater weight loss than other bariatric surgical techniques and has become the procedure of choice for bariatric surgery in North America (8,9). Computed tomography (CT) in postoperative morbidly obese patients may be difficult or impossible because of excessive weight and girth and associated medical conditions. However, over the past decade, advances in helical CT technology have resulted in shorter scanning time and improved image quality (10). These factors have contributed to the increased use of helical CT for the detection of complications of gastric bypass surgery that might not be readily identified with a conventional upper gastrointestinal series. CT also offers the added advantage of providing guidance for interventional procedures such as aspiration and drainage of fluid collections. Some studies have been published regarding the range of CT findings after gastric bypass surgery (1 3,7 9,11 17). The purpose of our study was to describe the normal anatomy, complications, and diagnostic pitfalls at helical CT after gastric bypass surgery. MATERIALS AND METHODS Patient Population Review of the computer database in the department of surgery at our institution revealed 890 patients who underwent Roux-en-Y gastric bypass surgery from March 1998 through July Seventy-two of the 890 patients had undergone 124 abdominal and pelvic CT examinations performed 2 days to 35 months after gastric bypass (mean, 95 days; median, 9 days). Twenty-four of these studies were excluded from analysis because they were performed as follow-up to initial CT and for the same clinical indications as initial CT. Only the initial 100 examinations in 72 patients were included in the analysis. These examinations were performed for a wide variety of clinical indications, including unexplained abdominal pain (n 34), signs of infection (n 26), known or suspected leak (n 15), small bowel obstruction and hernia (n 14), dilatation in the excluded stomach that might require decompression (n 7), and hematoma (n 4). Fifty-eight of the 72 patients were women, and 14 were men. Patients ranged in age from 18 to 72 years (mean, 39 years). Forty-one of the 72 patients had open Roux-en-Y gastric bypass surgery, and 31 had laparoscopic Roux-en-Y gastric bypass surgery. The patients medical records were reviewed by a single radiologist (J.Y.). The study was approved by the institutional review board of our hospital. Informed consent was waived. Abdominal and Pelvic CT Imaging At our institution, all patients undergo a routine upper gastrointestinal series within 24 to 48 hours after gastric bypass to assess for leaks or other complications prior to the initiation of oral feeding. All 100 CT examinations were performed by using one of two commercially available helical CT scanners (Somatom Plus 4 or Somatom Plus 4 Volume Zoom; Siemens Medical Systems, Erlangen, Germany) with section thickness of 5 or 8 mm. Of 100 CT studies, 86 were obtained by using single detector row helical CT scanners with a section thickness of 8 mm, and 14 were obtained by using a multi detector row CT scanner with four detector rows, 2.5-mm collimation, and reconstruction at a section thickness of 5 mm. At 88 of the CT examinations, iohexol (Omnipaque 300; Nycomed, Princeton, NJ) was administered intravenously at a dose of 150 ml with a mechanical injector at a rate of 2 3 ml/sec. Eight examinations were performed with the use of oral contrast material alone, because of impaired renal function (n 5) or lack of intravenous access (n 3). Four examinations were performed without oral or intravenous contrast material. In 96 examinations, an oral contrast material, either 900 ml of barium sulfate suspension (Fast Transit; Lafayette Pharmaceuticals, Lafayette, Ind) or 450 ml of a 2% solution of diatrizoate meglumine and sodium (Gastrografin; Bracco Diagnostics, Princeton, NJ), was administered 1 to 2 hours prior to the study and again after the patient was positioned on the CT table. Image Analysis All 100 CT studies were reviewed retrospectively in consensus by two of four abdominal imaging radiologists (J.Y., S.R.C., M.A.T., A.S.F.). The abdominal imaging experience of the four radiologists ranged from 4 to 26 years (mean, 16 years). A total of three review sessions were conducted, and in each session, CT studies were reviewed by two of the radiologists in consensus. One radiologist (J.Y.) participated in all three sessions. Conflicting opinions were resolved through discussion between the two readers and, occasionally, with the Figure 1. Diagram of gastric bypass anatomy shows a small gastric pouch (GP) created with stapling (dotted line) of the stomach; anastomosis of the pouch to a Roux-en-Y limb (straight thick black arrows); route of gastric contents to the efferent loop (white arrows); oversewn jejunal loop (curved arrow), or blind loop, of the Roux-en-Y limb; and jejunojejunal anastomosis (thin black arrows). help of a third reader. For all 100 examinations, the patients clinical indications for CT and the initial radiologic reports of both upper gastrointestinal series and CT were available to the readers at the time of review. However, the clinical outcome was not known to the readers. Sixty-four of 100 CT examinations were conducted prior to the installation of our picture archiving and communication system, and hard-copy film images were reviewed with body, liver, and lung windows provided; the remaining 36 studies were reviewed at a workstation. Structures assessed in the postoperative normal anatomy included the gastric pouch, proximal efferent loop of the small bowel and oversewn jejunal loop (blind loop), excluded stomach, and distal jejunojejunal anastomosis. Assessed complications included extraluminal contrast material, air, and/or fluid collection; dilatation of excluded stomach or of small or large bowel; defect of the abdominal wall; oral contrast material in the excluded stomach only, or in both the excluded stomach and the duodenum; and infarction of the liver or spleen. The finding of the fundus of the excluded stomach mimicking a leak was made when the excluded fundus was filled with a combi- 754 Radiology June 2004 Yu et al

3 TABLE 1 Depiction of Postoperative Gastrointestinal Anatomy at 100 CT Examinations in 72 Patients Structure No. Depicted Comments Radiology Gastric pouch 96 Four were not seen, two because of absence of oral contrast material administration and the other two because of a dilated excluded stomach. Excluded stomach 100 Proximal efferent Roux jejunal loop 99 One was obscured by a markedly dilated excluded stomach. Oversewn jejunal loop 88 Distal jejunojejunal anastomosis 67 Oral contrast material obscured anastomotic sutures in most instances of nondepiction. of abnormally low attenuation in the liver or a peripheral low-attenuation focus in the spleen. The diagnosis of hematoma was made if a fluid collection had a high attenuation (60 80 HU) and the patient had no clinical symptoms of infection. Comparisons In order to verify the results of the CT image analysis, CT findings were correlated with surgical findings in 25 patients, findings from imaging-guided interventions in 18 patients (17 CT-guided procedures and one ultrasonography [US]- guided procedure), and findings from clinical follow-up of at least 3 months in 29 patients. Chart review was conducted in all 72 patients (J.Y.). CT results were also correlated with reported results of upper gastrointestinal series in all 72 patients (J.Y., S.R.C., M.A.T., A.S.F.). Figure 2. Transverse CT images show normal postoperative anatomy in the gastrointestinal tract, including (a) a small gastric pouch (solid arrow) and gastric staple line (open arrow), (b) gastrojejunal anastomosis (solid arrow) and oversewn jejunal loop or blind loop (open arrow), (c) air (arrow) in the nondilated excluded stomach, and (d) an efferent loop (arrow) that is antecolonic in location where it passes through the transverse mesocolon. nation of air, contrast material, and fluid, and when the excluded fundus was located proximal to and was wider than the adjacent excluded gastric body. Imaging features of anastomotic leak included a collection with a combination of extravasated contrast material, fluid, and/or air adjacent to the anastomosis. Diagnosis of a fluid collection that was not related to a leak was based on the absence of a leak demonstrated on an upper gastrointestinal study. Ancillary CT findings included the absence of oral contrast material within the collection and the remote location of the collection from an anastomosis. Distention of the excluded stomach was diagnosed if the excluded stomach was dilated with a combination of air, fluid, and/or contrast material. Features of smallbowel obstruction included dilatation of the proximal small-bowel loops terminating at a transition point with collapse or nondistention of distal small bowel and colon. Features of gastric staple line dehiscence included oral contrast material in the excluded stomach, without evidence of contrast material refluxed from the afferent loop. A diagnosis of hepatic or splenic infarction was based on the presence of a segmental or subsegmental focus RESULTS Depiction of the Postoperative Gastrointestinal Tract The CT depiction of the postoperative gastrointestinal anatomy is summarized in Table 1 (Fig 2). The gastric pouch was seen in all but four (96%) of the 100 studies and in 69 (96%) of the 72 patients. In two studies, oral contrast material was not administered, and in the remaining two studies, an extremely dilated excluded stomach obscured the pouch. The excluded stomach was depicted in all 100 studies and all 72 patients. The proximal efferent Roux-en-Y jejunal loop was seen in all but one (99%) of the 100 studies and in 71 (99%) of 72 patients. In one patient, the excluded stomach was markedly dilated and obscured the proximal jejunal limb. The oversewn jejunal loop was identified in 88 (88%) of 100 studies and in 61 (85%) of 72 patients. The distal jejunojejunal anastomosis was seen in 67 (67%) of 100 studies and in 46 (64%) of 72 patients. A normal excluded stomach was de- Volume 231 Number 3 Helical CT Findings after Gastric Bypass Surgery 755

4 TABLE 2 Complications Depicted with CT in 41 of 72 Patients Radiology Complications No. of Patients Time from Surgery to CT Detection of Complications (d)* Outcome or Treatment Leaks (13) Surgery (n 3), drainage (n 5), resolution (n 4) Dilated excluded stomach (31) Percutaneous decompression (n 5), surgery (n 1) Bowel obstruction (107) Surgery (n 5), resolution (n 1) Incisional hernia (72) Surgery (n 3) Nonincisional ventral hernia (425) Surgery (n 3), conservative treatment (n 1) Internal hernia (154) Surgery (n 3) Gastric staple line dehiscence (167) Surgery (n 3) Abscess (16) Drainage (n 7), surgery (n 2) Splenic infarction (11) Resolution (n 4), drainage for infection (n 1) Hepatic infarction (7) Surgery (n 1), conservative treatment (n 2) Hematoma (8) Surgery (n 1), resolution (n 4) Note. Some patients had more than one complication. * Given as range, with mean in parentheses. Confirmed also at endoscopy (n 1) and upper gastrointestinal series (n 2). picted in 83 CT studies. Six CT studies showed gastric staple line dehiscence, six showed a distended excluded stomach, and five showed a gastrostomy tube in the excluded stomach. Of the 83 normal studies, seven showed a complete collapse of the excluded stomach. In the other 76 studies, the excluded stomach was filled with a combination of fluid, air, and/or contrast material, as follows: 18 studies showed air, fluid, and contrast material, seven showed fluid and contrast material, 22 showed air and fluid, and 29 showed fluid. Of 25 CT studies that depicted oral contrast material in the excluded stomach, 21 also showed oral contrast material in the duodenum. In 15 (15%) of the 100 CT studies and 13 (18%) of the 72 patients, the fundus of the excluded stomach was proximal to and wider than the adjacent excluded stomach and was filled with a combination of fluid, contrast material, and/or air findings similar to those in a loculated fluid collection and suggestive of a leak from the gastrojejunal anastomosis (Fig 3). Among these 15 CT studies, three showed oral contrast material in the fundus of the excluded stomach, as well as in the distal excluded stomach and the duodenum. Complications Depicted at CT after Gastric Bypass Figure 3. Excluded fundus mimics loculated fluid collection in a 20-year-old man 16 days after gastric bypass surgery. (a) Transverse CT image shows fluid in the fundus (arrow) that mimics a leak from the gastrojejunal anatomosis. (b) Transverse CT image at a level 3 cm inferior to a shows the continuity of the apparent fluid collection with the excluded stomach (arrow). Thirty-one of 72 patients had normal abdominal and pelvic CT findings, without any complications associated with gastric bypass surgery. Sixty-two abnormalities were identified at CT in the remaining 41 patients (Table 2). Gastrojejunal anastomosis and excluded stomach. Leaks were depicted in 12 patients (Fig 4) (loculated collections adjacent to the gastric pouch in nine patients, diffuse abdominal fluid in two patients, and a trace amount of oral contrast material in a drainage tract in one patient). Five of these 12 patients required CT-guided drainage, and two of the five patients underwent repeated drainage. Three patients underwent exploratory surgery at which a leak from the gastrojejunal anastomosis was confirmed. Leaks in the remaining four patients resolved after conservative treatment, without percutaneous drainage or surgery. A markedly distended excluded stomach was seen in six of the 72 patients (Fig 5). Five patients required percutaneous decompression of the excluded stomach. Among these five patients, one eventually underwent surgery to correct a smallbowel obstruction. The patient who was not treated with percutaneous decompression underwent surgery after CT; a leak from the gastrojejunal anastomosis and a small-bowel obstruction were found and surgically treated. Gastric staple line dehiscence was diagnosed at CT in six patients (Fig 6). Images obtained in five patients showed oral contrast material in the excluded stomach but not in the duodenum or the remaining afferent loop. In one patient, images showed oral contrast material in both the excluded stomach and the duodenum. Surgery was performed in three of these six patients, and the diagnosis was confirmed. The diagnosis in one patient was confirmed at endoscopy. Upper 756 Radiology June 2004 Yu et al

5 Figure 4. Leak from gastrojejunal anastomosis in a 41-year-old woman 9 days after gastric bypass surgery. (a) Transverse CT image of the upper abdomen shows a large collection of oral contrast material and air (arrows) consistent with leak. (b) Transverse CT image obtained immediately after the insertion of a percutaneous drainage catheter (arrow) into the fluid collection shows a marked decrease in the size of the collection. Figure 5. Edema at the jejunojejunal anastomosis with resultant reflux of oral contrast material into the excluded stomach in a 52-year-old woman 4 days after gastric bypass surgery. Transverse CT images show the excluded stomach (arrow) (a) while distended with oral contrast material and (b) after initial decompression performed with a percutaneous 8-F pigtail catheter. gastrointestinal studies in the remaining two patients depicted gastric staple line dehiscence. Small bowel and abdominal wall. Six of 72 patients had small-bowel obstruction (Fig 7). CT images in all six depicted dilated proximal small bowel loops with collapse of the distal small bowel and colon. Five of these six patients underwent surgery, at which stenosis of the jejunojejunal anastomosis (n 2), adhesions (n 2), or both stenosis and adhesions (n 1) were found. The bowel obstruction in the remaining patient resolved with conservative treatment. Three incisional hernias and four nonincisional ventral hernias were depicted at CT. One of three incisional hernias occurred at the laparoscopic port site, and the other two occurred at the abdominal open incision site. All three patients had a small-bowel obstruction that required surgical treatment. All four nonincisional ventral hernias occurred in the anterior abdominal wall, near the midline. The content of the ventral hernias included bowel loops (n 4), omental fat (n 2), stomach (n 1), and liver (n 1). There was no associated small-bowel obstruction. Three patients with nonincisional ventral hernias underwent surgical repair. Three of the 72 patients in our study had surgically proved internal hernias. Two of these hernias were detected at CT. Three types of internal hernias were seen in these three patients: One had herniation of the small bowel through the transverse mesocolon (Fig 8), the second had herniation of the small bowel through a surgical defect in the small bowel mesentery, and the third had a Petersen-type herniation of the small bowel behind the Roux-en-Y mesentery before it passed through a defect in the transverse mesocolon. The two patients in whom diagnosis was correct at CT had a saclike cluster of dilated small bowel loops in the left upper abdominal quadrant. The third patient, in whom a correct diagnosis was not made at CT, had an internal hernia of the Petersen type. This patient had a cluster of mildly dilated small bowel loops superior to the excluded stomach and against the left diaphragm and abdominal wall. Oral contrast material was able to pass through the internal hernias in all three patients. In none of these three patients was there clinical evidence of smallbowel obstruction. Liver and spleen. Splenic infarction was diagnosed in five patients. CT images obtained in four of these five showed typical low-attenuation foci in the spleen (solitary infarction in two and multiple infarctions in two patients). One patient had an infarction that involved the entire spleen. In this patient, 10 days after the first CT examination, a fluid collection that also contained air was identified in the spleen at CT; US-guided drainage was performed, and a diagnosis of abscess was confirmed. All patients recovered without additional treatment. Three liver infarctions were diagnosed at CT (Fig 9), all of which involved the lateral segment of the left lobe of the liver. Two patients were treated conservatively. One patient developed an abscess within the infarction and required surgical resection of the affected liver segment. Other complications. Postsurgical abscesses that were unrelated to anastomotic leak but related to the surgical procedure were diagnosed in nine patients: in the abdomen in four, in the pelvis in two, and in the abdominal wall in three. Among the four abscesses found in the abdomen, one was in the hepatorenal pouch, one was in the lesser sac, one was in the mesentery inferior and posterior to the excluded gastric antrum, and one was inferior to the spleen. Imaging-guided interventions were performed in seven patients, and surgical drainage was performed in two patients. Hematoma was diagnosed in five patients: in the abdomen in four, and in the pelvis in one. All hematomas were seen as high-attenuation (60 80-HU) foci. Volume 231 Number 3 Helical CT Findings after Gastric Bypass Surgery 757

6 Figure 6. Gastric staple line dehiscence in a 45-year-old woman years after gastric bypass surgery. (a) Transverse CT image of the upper abdomen shows a nondistended excluded stomach (solid arrow), which contains oral contrast material that has entered from the gastric pouch through staple line dehiscence, as well as the oversewn jejunal loop (blind loop) (open arrow). (b) Transverse CT image at a level inferior to a shows no oral contrast material in the distal stomach and duodenum (arrows) and, thus, supports the conclusion that oral contrast material in the excluded stomach occurred as a result of gastric staple line dehiscence. The diagnosis was confirmed at surgery. Figure 8. Transmesocolonic internal hernia in a 50-year-old woman 3 months after gastric bypass surgery. Transverse abdominal CT image shows a cluster of dilated small bowel loops (arrows) posterior to the excluded stomach (S), which contains oral contrast material that has refluxed from the afferent Roux-en-Y limb. The diagnosis was confirmed at surgery. Figure 7. Small-bowel obstruction caused by stenosis of the jejunojejunal anastomosis in a 27-year-old woman 10 days after gastric bypass surgery. (a) Transverse CT image shows a dilated proximal efferent loop of small bowel (arrow) filled with oral contrast material, medial to the excluded stomach (S). (b) Transverse CT image shows dilatation in proximal small bowel loops (solid arrows) that continues to the level of the jejunojejunal anastomosis demarcated by the surgical staple line (open arrow). One patient had a large hematoma posterior to the excluded stomach that required surgical treatment. Four patients were treated conservatively. A small amount of free fluid was found in the abdomen and/or pelvis in 10 patients. These small fluid collections represented postsurgical changes and were not related to either leak or infection. None of these patients required treatment. DISCUSSION A wide variety of complications may occur after gastric bypass surgery (1 3,7 9,11 17). The anatomy of the postoperative gastrointestinal tract is often altered by surgery in a way that makes it difficult to detect these complications. At CT, the normal excluded stomach contains a combination of fluid, air, and contrast material but is not dilated. The source of contrast material and air in the excluded stomach is reflux from the afferent limb. Postsurgical edema may occur at the jejunojejunal anastomosis and may cause a partial obstruction that results in reflux of contrast material into the duodenum and, subsequently, into the excluded stomach (5,7,18). When the excluded gastric fundus contains a combination of contrast material, fluid, and air and is disproportionately distended, as it was in Figure 9. Liver infarction in a 52-year-old woman 5 days after gastric bypass surgery. Transverse CT image shows an area of decreased attenuation (arrows) that corresponds to the entire lateral segment of the left lobe of the liver. 15% of cases in the present study, it may mimic a leak from the gastrojejunal anastomosis. Confirmation of continuity between the excluded fundus and the remainder of the excluded stomach is very helpful for distinguishing between a leak and a normal excluded fundus. A gastric leak that results in peritonitis is the most severe life-threatening complication after gastric bypass. Sepsis and death may result if the leak is not diagnosed promptly (2,3,7,18). When the stomach is mobilized for gastric bypass, some short gastric vessels and, perhaps, branches of the left gastric artery may 758 Radiology June 2004 Yu et al

7 be ligated, which may compromise the blood supply to the gastric pouch (12, 19). If an anastomotic leak occurs after the immediate postoperative period, it is likely the result of ischemia in the gastric side of the anastomosis (7). Another factor that may lead to the development of a leak may be distention of the excluded stomach in the early postoperative period, with narrowing of the jejunojejunal anastomosis from edema (12). We routinely perform an upper gastrointestinal series within 24 to 48 hours after surgery. Water-soluble contrast material is used initially; if no leak is depicted, the examination is repeated with barium sulfate suspension. The results of the upper gastrointestinal series are usually highly reliable for the diagnosis of leaks (7,15). However, helical CT also may play an important role in the diagnosis of leaks, especially when the patient has unexplained fever, tachycardia, abdominal pain, and distention despite negative results of the upper gastrointestinal series. A leak may be readily diagnosed on the basis of CT images that depict a fluid collection mixed with oral contrast material and air near the anastomotic site. CT-guided percutaneous drainage of fluid collections due to leak was performed in five of 12 patients in our series, after which all five recovered without additional surgery. Gastric staple line dehiscence is most often caused by repeated overdistention of the gastric pouch with food (5). In patients who experience suboptimal postoperative weight loss, dehiscence of the gastric staple line must be considered a possibility (12). When oral contrast material is present in the proximal excluded stomach but not in the duodenum, this condition is considered. If a diagnosis of staple line dehiscence is critically important for clinical treatment planning, an upper gastrointestinal series is recommended to confirm suspicious CT findings. One of the six studies in our series that were positive for staple line dehiscence showed oral contrast material in both the excluded stomach and the duodenum, but the amount of contrast material near the gastric staple line was disproportionate to the amount of contrast material in the duodenum. It is important to realize that a normal excluded stomach may contain oral contrast material because of reflux from the afferent loop. Normal reflux of contrast material into the distal stomach should not be misinterpreted as staple line dehiscence (5,18). It is difficult to quantify the extent of dehiscence on the basis of CT images, but the amount of contrast material seen in the excluded stomach is probably related to the severity of dehiscence. The cause of infarction of the left lateral segment of liver is unclear. This complication has not been reported previously. One possibility is that the lateral segment of the left lobe of the liver or the left hepatic artery was injured during the surgery, possibly because of retraction. It is also possible that a branch of the left hepatic artery may arise from the left gastric artery and that left lateral hepatic infarction may occur if the left gastric artery is ligated. A diagnosis of infarction of the lateral segment of the left lobe of the liver is usually straightforward when segmental or subsegmental decreased attenuation is observed. Five patients in our study had splenic infarction, most likely caused by venous compromise. Rates of thromboembolic events have proved higher in markedly obese patients after gastric bypass (2,16, 17). The majority of splenic infarctions in our study were depicted at CT as solitary (two of five patients) or multiple (two of five patients) small peripheral low-attenuation foci in the spleen. One patient had an infarction that involved the entire spleen. Internal hernias present a diagnostic challenge to radiologists in the interpretation of CT images and the upper gastrointestinal series (2,3,7,13,20 23). A negative imaging study does not necessarily exclude an internal hernia. Any patient with nonspecific symptoms of persistent periumbilical abdominal pain after gastric bypass surgery should undergo examination to exclude this complication (2). During gastric bypass surgery, defects are created in the small bowel mesentery or transverse mesocolon, and they must be closed at the time of surgery (2). One factor that may predispose patients to develop internal hernia is rapid massive weight reduction, which results in decreased intraperitoneal fat that may enlarge the defect in the mesentery or transverse mesocolon (3). The CT finding of a cluster of dilated small bowel loops in the left upper abdomen, against the abdominal wall, indicates a strong possibility of internal hernia, especially if it occurs in conjunction with similar manifestations at upper gastrointestinal examination (20,21,23). Postoperative abdominal wall hernias are common in patients who have undergone gastric bypass surgery. One of the major advantages of laparoscopic procedures for treatment of obesity is the associated decrease in occurrence of incisional hernias (2). However, in our study, one of three incisional hernias was found at the laparoscopic port site. The CT image showed a transitional point at the port site and a subtle tubular structure that protruded through the port and into the abdominal wall. With the increased popularity of laparoscopic Roux-en-Y gastric bypass surgery, it is important to be aware of the occurrence and appearance of an incisional hernia at the port site. Delayed diagnosis can lead to strangulation and obstruction of the small bowel because of the small caliber of the port. Three of four patients with nonincisional ventral hernias underwent surgical repair because of cosmetic concerns and because the clinical symptom of abdominal pain was compromising their quality of life. Massive gaseous distention of the excluded stomach may develop occasionally after gastric bypass procedure. It may occur because of edema at the enteroenterostomy, or it may be secondary to small bowel obstruction (2). The distention may be severe enough to cause a leak if the Roux-en-Y limb is overstretched by the markedly dilated excluded stomach and if tension is placed on the gastrojejunostomy or gastric staple line such that pressure necrosis occurs (2). In our experience, CT- or fluoroscopy-guided percutaneous decompression with a fine needle and/or drainage catheter is successful for treatment of marked distention of the excluded stomach. Although CT performs well in depicting the normal postoperative anatomy and complications in patients after gastric bypass, CT examinations and CTguided interventions in this patient population are technically challenging. The girth and weight of the patient may preclude entry into the CT gantry. In addition, artifacts related to a large body habitus may degrade the quality of the images. The primary limitation of our study is that it is retrospective, and our study results therefore are compromised by the factors that limit all retrospective studies. In addition, our results are affected by a population bias in that only patients with suspected or known abnormalities were referred for CT. Furthermore, because all patients underwent an upper gastrointestinal series within 48 hours after gastric bypass surgery, many immediate postoperative conditions were diagnosed at this examination, as a result of which the patient was not referred for CT. Additional information may be learned about the CT detection of com- Volume 231 Number 3 Helical CT Findings after Gastric Bypass Surgery 759

8 plications in this population by the performance of a prospective study. In conclusion, helical CT of the abdomen and pelvis is useful for delineating normal anatomy after gastric bypass surgery and for diagnosing postoperative complications such as abscess, bowel obstruction, hernia, hepatic or splenic infarction, and anastomotic leak. CT guidance may be useful also during intervention for treatment of these postsurgical complications. Surgical alterations of the anatomy in the gastrointestinal tract may mimic a number of complications at CT. Therefore, familiarity with the CT appearance of the normal postoperative gastrointestinal tract and of complications after gastric bypass surgery is necessary to avoid misdiagnosis in this patient population. References 1. Blachar A, Federle MP, Pealer KM, Ikramuddin S, Schauer PR. Gastrointestinal complications of laparoscopic Rouxen-Y gastric bypass surgery: clinical and imaging findings. Radiology 2002; 223: Byrne TK. Complications of surgery for obesity. Surg Clin North Am 2001; 81: Blachar A, Federle MP. Gastrointestinal complications of laparoscopic Roux-en-Y gastric bypass surgery in patients who are morbidly obese: findings on radiography and CT. AJR Am J Roentgenol 2002; 179: Mason EE, Ito C. Gastric bypass. Ann Surg 1969; 170: Goodman P, Halpert RD. Radiological evaluation of gastric stapling procedures for morbid obesity. Crit Rev Diagn Imaging 1991; 32: Alden JF. Gastric and jejunoileal bypass: a comparison of the treatment of morbid obesity. Arch Surg 1977; 112: Moffat RE, Peltier GI, Jewell WR. The radiological spectrum of gastric bypass complications. Radiology 1979; 132: Schauer PR, Ikramuddin S. Laparoscopic surgery for morbid obesity. Surg Clin North Am 2001; 81: Kellum JM, DeMaria EJ, Sugerman HJ. The surgical treatment of morbid obesity. Curr Probl Surg 1998; 35: Silverman PM, Cooper CJ, Weltman DI, Zeman RK. Helical CT: practical considerations and potential pitfalls. RadioGraphics 1995; 15: Fakhry SM, Herbst CA, Buckwalter JA. Complications requiring operative intervention after gastric bariatric surgery. South Med J 1985; 78: Koehler RE, Halverson JD. Radiographic abnormalities after gastric bypass. AJR Am J Roentgenol 1982; 138: Serra C, Baltasar A, Bou R, Miro J, Cipaguauta LA. Internal hernias and gastric perforation after a laparoscopic gastric bypass. Obes Surg 1999; 9: Cariani S, Nottola D, Grani S, Vittimberga G, Lucchi A, Amenta E. Complications after gastroplasty and gastric bypass as a primary operation and as a reoperation. Obes Surg 2001; 11: Smith C, Deziel D, Kubicka R. Evaluation of the postoperative stomach and duodenum. RadioGraphics 1994; 14: Zingas AP, Amin KA, Loredo RD, Kling GA. Computed tomographic evaluation of the excluded stomach in gastric bypass. J Comput Tomogr 1984; 8: Nguyen NT, Goldman C, Rosenquist CJ, et al. Laparoscopic versus open gastric bypass: a randomized study of outcomes, quality of life, and costs. Ann Surg 2001; 234: Fobi MA, Lee H, Holness R, et al. Gastric bypass operation for obesity. World J Surg 1998; 22: Maini BS, Blackburn GL, McDermott WV Jr. Technical considerations in a gastric bypass operation for morbid obesity. Surg Gynecol Obstet 1977; 145: Blachar A, Federle MP. Bowel obstruction following liver transplantation: clinical and CT findings in 48 cases with emphasis on internal hernia. Radiology 2001; 218: Blachar A, Federle MP, Brancatelli G, Peterson MS, Oliver JH 3rd, Li W. Radiologist performance in the diagnosis of internal hernia by using specific CT findings with emphasis on transmesenteric hernia. Radiology 2001; 221: Higa KD, Boone KB, Tienchin H. Complications of the laparoscopic Roux-en-Y gastric bypass: 1040 patients what have we learned? Obes Surg 2000; 10: Blachar A, Federle MP, Dodson SF. Internal hernia: clinical and imaging findings in 17 patients with emphasis on CT criteria. Radiology 2001; 218: Radiology June 2004 Yu et al