Imaging of Gastrointestinal Perforation

Transcription

1 Imaging of Gastrointestinal Perforation Poster No.: C-1527 Congress: ECR 2011 Type: Educational Exhibit Authors: M. A. A. Vieira, M. Baptista, H. Martelo, M. Matias; Beja/PT Keywords: Contrast agent-oral, CT, Gastrointestinal tract DOI: /ecr2011/C-1527 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 36

2 Learning objectives To provide an overview of the imaging findings and radiologic approach for investigating the wide variety of gastrointestinal perforations. Background Gastrointestinal (GI) tract perforation is an emergent condition that usually requires prompt surgery. It can be caused by a variety of disease entities, including inflammatory, neoplasic, traumatic, iatrogenic lesions, postoperative conditions or foreign body, and has variable clinical presentations, particularly in the early clinical course. Imaging findings OR Procedure details Diagnosis largely depends on imaging examinations, and identification of the presence, level, and cause of perforation is important. A correct and timely diagnosis for appropriate patient management and surgical planning. The rupture of any hollow viscus may produce pneumomediastinum, pneumoperitoneum or extravasation of fluid. In some cases extraluminal air is not seen as it is contained within the inflammatory tissue around the perforated site. Plain radiography remains the first imaging study and can detect small amounts of free air. If a perforation is suspected but no free air is seen, upper GI examination with luminal contrast agent or Computed tomography (CT) should be performed, looking for extravasation of contrast. CT is highly sensitive at detecting free air and can to be important to determine the level and etiology of perforation. Bedside ultrasonography potentially can be used to detect a pneumoperitoneum, but it is mostly useful to detect extraluminal fluid. Imaging modalities Table 1 presents a summary of imaging modalities for approaches to GI perforation. Page 2 of 36

3 Radiologic modalities Plain radiographs Technique: Plain film evidence of pneumoperitoneum is best seen on radiographs obtained with the patient in the standing or sitting position. In addition to upright and supine abdominal radiographic images, upright chest films and/or left lateral decubitus abdominal films should be included for the assessment of GI tract perforation. Indications: Demonstration of free gas. Findings: The extraluminal air may be free in the peritoneal cavity, retroperitoneal spaces, mesentery, or ligaments' organ. Pneumomediastinum and/or subcutaneous emphysema may also be seen. Small amounts of air are clearly demonstrated beneath the domes of the diaphragm in erect radiographs. Signs of pneumoperitoneum on supine radiographs include the following: gas on both sides of the bowel wall (Rigler sign), gas outlining the falciform ligament, gas outlining the peritoneal cavity (the football sign), and triangular or linear localized extraluminal gas in the right upper quadrant. Left lateral decubitus and cross-table lateral views may be used with very ill patients to demonstrate air outlining the liver. Limitations: The reported sensitivity in the detection of extraluminal air on plain radiography is 19% to 70%. Upright chest radiographs are the most sensitive for free air. Ultrasound Technique: The detailed assessment of the primary GI pathology usually requires evaluation by an experienced operator with a high-frequency linear probe. Many useful indicators can be found with the basic curvilinear or sector abdominal scan. Indications: Demonstration of fluid, collections and free gas. Page 3 of 36

4 May suggest the etiology in some cases. One significant advantage of ultrasound is that it is usually an 'interactive' process. In the acute setting, the simple question 'Where does it hurt?' will frequently direct the operator to the underlying pathology. Findings: Perforation of an abdominal viscus can produce small amounts of fluid. This is usually containing particulate or gas bubble echoes, and may be localized close to the perforation site. Fluid collections such as abscesses may also be demonstrated. Specific patterns of gas echoes can alert to the possibility of a pneumoperitoneum. The air usually casts a shadow that has reverberative artefacts. Limitations: The accuracy of the ultrasound scan is directly attributable to the skill and experience of the operator. Free gas is usually regarded as an obstacle to ultrasound diagnosis. Contrast examination Technique: Water-soluble iodinated contrast material is administrated orally or transrectally depending on the suspected site of perforation. Water-soluble iodinated contrast agents, contrarily of barium, do not incite an inflammatory reaction in the mediastinum or peritoneum. They also are resorbed quickly from these sites. Ionic water-soluble contrast agents are associated with a theoretical risk of inducing pulmonary edema if aspirated into the pulmonary alveoli because of their hyperosmolality. If there is a strong suspicion of aspiration, the study is initially performed with a nonionic water-soluble contrast agent and swallowing is assessed fluoroscopically. Other radiologists advocate the use of barium as the initial contrast agent if a perforation of the pharynx or esophagus is suspected and there is serious clinical concern about aspiration. Although initial use of barium in patients with a known or suspected perforation is contraindicated, it may be used when the water-soluble iodinated contrast material fails to demonstrate extraluminal leakage. Barium suspensions are superior in the diagnosis of leaks because they have greater radiographic density and adhere to extraluminal tracks. Another potential disadvantage of barium suspensions is that follow-up studies can be more difficult to interpret if barium persists in the region of the leak. Indications: Page 4 of 36

5 When a more precise assessment regarding the specific site of perforation is needed. It is complimentary of CT in detection and characterization of gastrointestinal perforation. A contrast luminal study is often superior to CT to demonstrate fistulous tracks and the site of origin of GI when a perforation of tract GI superior is suspected. May be performed to exclude perforation in immediate postoperative patients or patients with penetrating trauma in which the presence of a collection or extraluminal air does not necessarily indicate luminal perforation. Findings: Extravasation of contrast material from the lumen of the GI tract and demonstration of fistulous tracks. Should suggest the cause of perforation. Limitations: Contrast luminal studies are inferior to CT in assessing both the presence and extent of the extraluminal inflammatory process (can only indirectly imply the presence of a adjacent inflammatory process when extrinsic mass effect and spiculation of the contour of the wall are demonstrated). The sensitivity of contrast enema study is not always high, because a leak may have sealed off by the time a contrast study is performed. It should be used prudently in cases where the wall is already weak and friable due to inflammatory, ischemic, or neoplastic changes. Computed Tomography Technique: The entire abdomen from the dome of the diaphragm to the pelvic floor should be scanned by using 1 to 2.5 mm collimation when a multidetector row CT scanner is used. Contiguous axial images 5 to 7 mm thick are obtained and thinner sections or multiplanar reconstruction may be applied when necessary. Oral or rectal contrast administration before the examination may be utilized. Although extraluminal leakage of contrast has been reported to be a specific finding for perforation, is not a frequent CT finding. Several authors have raised doubts about the added benefit of oral contrast material. These reports cite safety issues (i.e., the risk of aspiration and the subsequent complications), the potential delay in the diagnosis and the lack of substantial added benefit for detecting perforation. Further, the slow progression of the oral contrast material in the GI tract of a patient suffering from paralytic ileus and the rapid sealing of the perforation site may preclude extraluminal leakage of oral contrast material in patients with GI tract perforation. Page 5 of 36

6 Accurate evaluation of the GI tract is wall continuity and wall thickening can only be performed on the distended lumen. Optimized assessment may include additional scanning following good opacification and distension of the lumen, either by a delayed repeat study that can be useful whenever there is diagnostic uncertainty on the initial scan or after rectal administration of contrast medium. Distention of the stomach can be accomplished by ingestion of large amount of oral contrast medium and colonic distention by insufflation of air through a rectal tube. The increased intraluminal pressure of the bowel loop caused by the retrograde air administration may make the impending but not yet perforated bowel become true perforation. However, the upgrading of the criteria for the colonic wall thickness (5 mm), the prominent bowel wall thickening (especially the soft tissue mass of tumor) and adjacent fat stranding at or near the perforation sites can compensate for the disadvantage of poor colonic distention and prompt the definite diagnosis. After the precontrast images have been acquired, CT scanning is initiated 70 to 80 seconds after the intravenous injection of contrast material (300 to 370 mgi/ml; 100 to 150 ml at a rate of 2 to 4 ml/s) unless contraindications exist, this will aid in the assessment of the site and cause of perforation. Assessment of lung (that distinguishes air from fat densities) and bone window settings, in addition to the standard abdominal window setting, serves as a useful complementary tool for enhancing sensitivity to detect extraluminal air and foreign bodies, respectively. Indications: CT can display extraluminal, intraperitoneal or retroperitoneal air that is too small to be demonstrated on plain radiography. In most cases a spiral or multidetector row CT scanner, GI mural pathology and adjacent inflammation are precisely assessed with thin-section images and multiplanar reformations that aid in the assessment of the site and cause of perforation and associated extraluminal complications such as phlegmon, abscess and peritonitis. Findings: Diagnosis is based on direct and indirect findings. The CT findings of GI tract perforation may be different according to the perforation site, and the various CT findings can help predict the perforation site. Direct findings of perforation: extraluminal air or luminal contrast material discontinuation of the GI wall Indirect findings of perforation: wall thickening abnormal wall enhancement peritoneal fluid Page 6 of 36

7 abscess or an inflammatory mass or phlegmon related to the lumen with or without associated an enterolith or extraluminal foreign body. The site of perforation can be assessed by : focal interruption of the GI wall the site of luminal contrast medium leakage the level of bowel obstruction a abrupt GI wall thickening with or without an associated phlegmon, inflammatory mass, or abscess. Focal wall thickening may occur in peptic ulcer disease, trauma, foreign body, iatrogenic event, ischemia, inflammation, appendicitis, diverticulitis and neoplasm. Some studies showed that free air bubbles in close proximity to the wall may indicate the location of the perforation especially when the amount of air is small. CT can suggest the presence of fistulas to the bladder and vagina by showing air (or oral contrast, if administered) in these structures with adjacent inflammation. In fact, CT is better for suggesting the possibility of fistulas, but contrast studies are better for depicting them. Limitations: CT has been established as the most valuable imaging technique for identifying the presence, site and cause of GI tract perforation. It can demonstrate free air in % of cases. The overall accuracy of CT for predicting the site of bowel perforation has been reported to range between 82% and 90%. Direct visualization of the discontinuity of the wall is usually seen in less than 50% of the patients with GI tract perforation. The relatively infrequent detection of this finding is partly due to the small size of the lesion. When CT findings are nondiagnostic and obvious clinical signs of perforation are absent, close monitoring with repeated CT examination may be indicated. Table 1.Radiologic techniques to investigating GI perforation. Findings according to Level of the GI Tract Perforation The site of perforation can also be assessed by the amount and location of extraluminal air on CT images. (table2) Page 7 of 36

8 A pneumoretroperitoneum is caused by perforation of any site where the alimentary tract is extraperitoneal. Perforation of the sigmoid diverticula also causes a pneumoretroperitoneum because three-fourths of the diverticulum extraperitoneal. Gas in the retroperitoneum dose not spread freely as in the peritoneal space. When the amount is small, it tends to remain regional with respect to the boundaries of the retroperitoneal compartment in which it arises. In general, extraperitoneal gas that originates in the pelvis commonly spreads bilaterally into the anterior and/or posterior pararenal spaces, whereas gas that originates above the pelvic brim tends to remain unilateral and does not cross the midline. Although air in the peritoneal space can reach the retroperitoneum and vice versa. Intraperitoneal and extraperitoneal air should suggest an extraperitoneal structure as the source.. Intraperitoneal air may also arise from the thorax or female genital tract. Pneumoretroperitoneum can be caused by air from pneumomediastinum or pneumothorax. It should be noted that pneumoperitoneum and pneumoretroperitoneum occur without luminal perforation in chest trauma or post operative patients for example. Perforation site Free air Location Esophageal Amount -Lining anatomic structures Variable within the mediastinal contours -In the lesser sac is less commonly from rupture of the lower esophagus Gastroduodenal Around liver and stomach Large amount - Stomach or duodenal -Free air or an bulb airfluid level crossing the midline and an accentually falciform ligament ("falciform ligament sign") and free air confined to the intrahepatic fissure for the ligamentum teres ("ligamentum teres sign -Lesser sac on posterior wall perforation Page 8 of 36

9 -Seldom air is seen in mesenteric folds in gastric perforation -Duodenum (post bulbar) -Right anterior pararenal space Small bowel Mesenteric folds, around anterior peritoneal surfaces of the liver and midabdomen Small or absent in most cases (extraluminal air is detected in only approximately 50% of cases even with CT examination) Appendix Around the appendix Small or absent Colon Pelvis, mesenteric folds, Usually small amount retroperitonal space -Ascending descending colon and -Right anterior pararenal space and left anterior Large amounts occur in pararenal space, bowel perforation which is respectively caused by obstruction or an -Right anterior pararenal endoscopic procedure space and pararenal respectively left anterior space, -Transverse colon -Lesser sac -Sigmoid (diverticula) -Left anterior pararenal -Rectum -Anterior and/or posterior pararenal spaces Table 2: Site of perforation according the amount and location of extraluminal air on CT images Etiologies of the GI Tract Perforation GI tract perforation can be caused by a variety of disease entities. These etiologies are discussed according to the perforation level. Perforations of the pharynx and esophagus Spontaneous esophageal perforation Boerhaave's syndrome is a spontaneous esophageal perforation due a sudden, rapid increase in intra-abdominal pressure, Page 9 of 36

10 most commonly caused by severe retching and vomiting. Patients with Boerhaave's syndrome are severely ill, with mediastinitis, sepsis, and shock developing after an episode of severe retching. Although Boerhaave's tears are usually on the left side of the distal esophagus (fig.1), they occasionally may be located on the right side of the distal esophagus or even in the cervical esophagus. Esophageal perforation can also result from other causes of rapidly elevated intraabdominal pressure including seizures, childbirth, blunt trauma, and severe straining to defecade. Plain radiographic signs of perforation include subcutaneous emphysema, pneumothorax, and pneumomediastinum. Foreign body perforation Large or sharp foreign bodies may be lodge in the pharynx or esophagus and cause acute dysphagia. Large foreign bodies that occlude the laryngeal aditus may cause severe dyspnea. Small fragments of glass are often trapped in the interstices of the palatine tonsils, whereas bone fragments are often trapped in the tips of the piriform sinuses, above the cricopharyngeus or in the upper cervical esophagus. A plain radiograph of the neck should be obtained with the patient in the lateral position during phonation of the sound "Eee." Radiopaque fragments of glass or bone can often be demonstrated in the palatine tonsils and hypopharynx, respectively, but some fish bones and glass fragments are not radiopaque. Iatrogenic perforations Endoscopic procedures are responsible for most nonsurgical iatrogenic Page 10 of 36

11 perforations of the pharynx and esophagus. Perforations related solely to intubation (fig.2) are usually located in the lower piriform sinus or region of the cricopharyngeal muscle. Perforations also tend to occur at sites of pharyngeal or esophageal narrowing, such as cervical esophageal webs; outpouchings, such as Zenker's diverticulum; or areas of extrinsic compression by osteophytes or the aortic arch. Endoscopic procedures, such as dilatation of the lower esophageal sphincter for achalasia, sclerotherapy, laser coagulation of tumors, or stent placement, are also associated with a substantial risk of esophageal perforation. Postoperative esophageal perforation An anastomotic or staple line leak is the most common serious complication of esophageal surgery. Anastomotic leaks may result in mediastinitis, abscess formation, and sepsis. Esophageal anastomoses are more prone to leak than other gastrointestinal anastomoses because the esophagus lacks a serosa. The esophageal mucosa also tends to retract from a cut margin because there is considerable mobility between the squamous mucosa, submucosa, and muscularis propria. Delayed esophageal perforations may also occur. If there is any clinical suspicion of a leak during the postoperative period, an upper gastrointestinal series should be performed. A postoperative chest radiograph that shows pneumomediastinum, a widened mediastinum, subcutaneous air, or an enlarging pleural effusion should also suggest the possibility of an anastomotic or staple line leak. When contrast studies are performed on patients after Page 11 of 36

12 esophagogastrectomy, the radiologist should look for laryngeal penetration, leaks or obstruction at the anastomosis, leaks along the stomach if a gastric tube has been created, obstruction where the stomach passes through the diaphragm, leaks or obstruction at the pyloroplasty or pyloromyotomy, and leaks or obstruction at the jejunostomy tube site if a jejunostomy tube has been placed. This can be a very difficult examination for both the patient and the radiologist, because postoperative patients are often immobile; unable to stand; and are connected to numerous intravenous lines, monitors, and chest tubes. The patient should be studied in a erect position, as much as possible and at least once in a recumbent position to ensure that the anastomosis and upper gastric body are bathed in contrast. Fig.: 1: 70-years-old man with Boerhaave's syndrome. (a) Radiograph obtained in frontal position shows right-sided pneumomediastinum (arrow) and levels air-fluid in left hemitorax (arrowhead). (b) CT confirms the presence of air surrounding the distal esophagus and hidropneumothorax. (c) Enema barium was performed to exclude diaphragmatic hernia, indicating that levels air-fluid not represents bowel loops, but are due to empiema. (d) Water-soluble contrast examination shows contrast flowing from the left lateral wall of the distal esophagus (arrow) into the left side of the mediastinum (large arrows). References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Page 12 of 36

13 Fig.: 2: 74-years-old man with perforation of esophagus after intubation. Plain radiograph (a) and CT on a conventional window setting (b) and on a lung window (c) shows pneumomediastinum (arrows), subcutaneous emphysema (large arrows), large left and right pleural effusion (asterisk) with lung actlectasia (arrowhead) and right mediastinum dislocation. The site of perforation was not accessed by CT. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Perforations of the stomach Peptic ulcer disease Gastroduodenal perforation associated with peptic ulcers is commonly found in the gastric antrum and duodenal bulb. A large percentage of perforated gastric and duodenal ulcers, however, seal off rapidly. As a result, free intraperitoneal gas can be detected on plain abdominal radiographs in only about two thirds of patients with perforated ulcers (fig.3). About half of the anterior wall perforations flow freely into the intraperitoneal space; the other half form walled-off collections. Less than half of the patients with penetrating posterior wall ulcers have free intraperitoneal gas on plain radiographs or extravasation of water-soluble contrast agent from the lumen of the stomach or duodenum. Ulcers on the posterior wall of the stomach and duodenum may perforate into pancreas, lesser omentum, transverse mesocolon, liver, spleen, biliary tree, or colon. Posterior wall peptic ulcers most Page 13 of 36

14 commonly perforate into the pancreas, resulting in pancreatitis or true abscess formation. Ulcers that perforate into the biliary tree or colon may also lead to fistula formation. An abscess in the left lobe of the liver or spleen may result from posterior wall penetrating ulcers. The stomach is connected to the transverse colon by the proximal portion of the greater omentum, also known as the gastrocolic ligament. Any inflammatory or neoplastic disease may spread to and from the stomach to the colon by this ligament. Currently, the most common cause of a fistula between the stomach and transverse colon is a benign gastric ulcer related to the use of nonsteroidal antiinflammatory agent. Crohn's disease of the transverse colon and adenocarcinoma of the stomach or transverse colon, however, can also result in the development of gastrocolic fistulas. Necrotic or ulcerated malignancies The differential diagnosis of malignant ulcer includes gastric adenocarcinoma, lymphoma, leiomyoma, and leiomyosarcoma. Signs of malignancy include (1) location within the lumen of the stomach; (2) eccentric location within the tumor mound; (3) width greater than depth; (4) nodular, rolled, irregular, or shouldered edges; and (5) Carmen meniscus sign (a large flatbased ulcer with heaped-up edges that fold inward to trap a lens-shaped barium collection that is convex toward the lumen). CT is useful in demonstrating the extent of the tumor mass and the degree of involvement of the gastric wall. Iatrogenic injuries Endoscopic procedures and intubation are responsible for most nonsurgical iatrogenic perforations. Page 14 of 36

15 Traumatic injuries Traumatic injuries occur mostly by blunt trauma in children and by penetrating trauma in adults. The descending and horizontal segments of the duodenum are the most common sites of perforation caused by blunt trauma because of their firm attachment, the acutely angled flexures and the compression against the vertebral column. Foreign body perforation Correct diagnosis of perforation caused by foreign body may be difficult to reach preoperatively due to nonspecificity of the clinical course and is caused by material with sharp, pointed ends such as toothpicks, fish and chicken bones (Fig.4). Postoperative perforations Anastomotic leaks and staple line dehiscences after surgery for peptic ulcer disease are not very common. Leaks may also occur at the oversewn proximal duodenal stump after Billroth II surgery or after Grahm plication of perforated duodenal ulcers. Anastomotic or staple line dehiscence also may occur after vertical banded gastroplasty or gastric bypass procedures for morbid obesity. Perforation of a gastric pouch may be caused by gastric hyperacidity, ischemia, or an indwelling tube. Transmural necrosis may develop 24 to 36 hours after surgery, resulting in a delayed postoperative perforation. Postoperative perforation or anastomotic leakage usually occurs within the first week after surgery. Because extraluminal air in this period is present in every patient, it cannot be a hallmark of the presence of perforation or leakage. Perforation or leakage should be suspected with persistent or progressively increasing free air and must be confirmed by contrast examination with water-soluble iodinated contrast material. Page 15 of 36

16 The postoperative contrast examination may show contrast material outside the expected lumen filling a collection or fistula. CT is also useful to demonstratethe size and location of an abscess cavity or guiding percutaneous drainage of an abscess collection. Fig.: 3: 78-year-old man with perforated gastric ulcer.(a) Pneumoperituneum is seen in plain radiogram. (b) CT image shows a focal defect in the posterior wall of gastric antrum (black arrow). Peritoneal fluid (white arrow) and free air (arrowhead) anterior to the liver and in the lesser sac are demonstrated. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Page 16 of 36

17 Fig.: 4: 74-years-old woman with gastric perforation caused by a fish bone. In CT image an inflammatory mass is displayed adjacent to the pyloric antrum and a fish bone (arrow) is present in the mass. The mass inflammatory is containing the extravasation of free air, so a small amount of extraluminal air is seen (arrowhead). References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Perforations of the small bowel Ischemia Small intestinal ischemia has a wide spectrum of etiologies and severity. The most serious complication of small intestinal ischemia is transmural necrosis and perforation, leading to peritonitis, with possible sepsis and death. Superior mesenteric arterial occlusion may result from embolism caused by atrial Page 17 of 36

18 fibrillation, cardiac valve disease, left ventricular thrombus related to myocardial infarction, and left atrial myxoma. Other etiologies include atherosclerosis, blunt or penetrating abdominal trauma, mesenteric vascular compression or twisting caused by adhesions, internal hernias, midgut volvulus, intussusception and tumors in the small bowel mesentery. The most common form of small intestinal ischemia in hospitalized patients is splanchnic vasoconstriction related to hypovolemia and hypotension. Mesenteric venous occlusion usually occurs secondary to thrombosis related to portal hypertension, surgery, trauma, oral contraceptives, and various hypercoagulable states. In patients with ischemia, plain radiographs may demonstrate dilated small bowel loops with air-fluid levels; thickening of valvulae conniventes and the bowel wall; pneumatosis in a linear or speckled configuration; and, rarely, portal venous gas. (fig.5) On an unenhanced CT scan, bowel wall thickening may be of increased attenuation, reflecting blood within the lamina propria and submucosa. The small bowel mesentery may also have increased attenuation caused by vascular engorgement, obstruction or leaking of intestinal contents into the interloop spaces. If closed loop obstruction is the cause of the ischemia, CT may demonstrate bowel twisting at the site of the adhesive band or internal hernia. Mesenteric vessels converge to a point near the band or entrance to the hernia. The small intestinal loops may be aligned in a U-shaped or radial configuration. Page 18 of 36

19 Inflammatory conditions (bacterial The most common inflammatory etiologies enteritis, Crohn disease, diverticulitis) are perforated diverticula and Crohn's disease. Small bowel diverticula are commonly located in the duodenum or proximal jejunum and is seen less frequently in the terminal ileum. Acute inflammation may lead to free perforations and peritonitis or sealed off perforations with abscesses. On CT imaging the distended diverticulum can be visualized, associated with adjacent inflammatory stranding and extraluminal air. Walled-off abscesses can also be seen adjacent to the small bowel in patients with jejunal diverticulitis. In Crohn's disease, abscesses may be closely related to the bowel wall or may extend well beyond the bowel wall into adjacent structure. Inflammatory stranding and changes in the small bowel mesentery adjacent to thick-walled segments of bowel are not specific to perforation in patients with Crohn's disease. Although fistulas may be detected with CT, barium studies. Rarely, perforation with abscess formation can also be seen in patients with ectopic pancreas complicated by pancreatitis. Blunt trauma Blunt abdominal trauma may result in rapid elevation of intraluminal pressure and intestinal perforation. Even a small amount of peritoneal fluid may be the only sign indicating intestinal perforation. The most common CT findings are bowel wall thickening, hemoperitoneum or ascites and extraluminal air or contrast medium. Perforating tumors Primary non-hodgkin's lymphomas and malignant stromal tumors of the small bowel may invade the adjacent small bowel mesentery. If these tumors become necrotic, a cavity forms within the mesenteric tumor. The cavity may Page 19 of 36

20 communicate with the bowel lumen. Some of these lesions also show true perforation into the intraperitoneal space. CT may reveal a cavitated mass with a wall of varying thickness. The adjacent small bowel wall may be thickened by tumor. The perforation may also result of invasion by other organ tumors (fig.6). Postoperative perforation anastomotic leakage or Small bowel anastomoses do not leak very frequently. Water-soluble contrast agents are diluted further if the postoperative small intestine is dilated. It may be very difficult to demonstrate a leak from an oenterostomy during a small bowel follow-through performed with water-soluble contrast material, especially if the leak is a considerable distance from the stomach and the intestine is dilated. The ability to demonstrate a small intestinal leak may also be compromised by overlapping loops of small intestine. Leaks from the proximal jejunum can be evaluated adequately by performing a water-soluble contrast study, either by having the patient drink contrast or by injecting a water-soluble contrast through a nasogastric tube. If a suspected leak from a mid small bowel anastomosis needs to be evaluated, a CT scan should initially be performed to ascertain if there are any CT findings to suggest a leak. If there is a low suspicion of a leak or the likelihood is that the leak is walled-off, barium study should be performed. Rarely, patients with suspected mid small intestinal leaks may be evaluated by enteroclysis with water-soluble contrast agents. Ileocolic anastomoses or distal enteroileal anastomosis are best evaluated by a retrograde approach through the rectum using a water-soluble contrast enema. Page 20 of 36

21 The duodenal stump of the afferent loop of a Billroth II procedure or Roux-en-Y procedure may be difficult to visualize by per-oral studies. If an indwelling duodenal tube or a biliary tube are present, the duodenum can be evaluated via the tube. If no tube is present, CT may be performed. Ileal pouches are frequently created as fecal reservoirs proximal to an ileoanal anastomosis in patients who have undergone total colectomy for ulcerative colitis or familial adenomatous polyposis syndrome. This is usually performed as a two-stage procedure because of a very high pouch leak rate. In the first stage, an ileoanal pouch is created and an ileostomy is performed to divert the fecal stream from the operative site. About 6 weeks later, the diverting ileostomy is taken down as a second-stage procedure. A watersoluble contrast study of the pouch before the diverting ileostomy is often necessary. A Foley catheter is placed in the anal canal. If injection of water-soluble contrast material reveals no evidence of a leak at the ileoanal anastomosis, the catheter is advanced into the ileal pouch. Watersoluble contrast is then injected into the pouch. Possible sites of leak include the ileoanal anastomosis and the staple lines of the pouch and at the stump of the pouch. CT may be helpful for showing an abscess and inflammatory stranding of the fat in the presacral space or elsewhere in the pelvis, but CT is inferior to contrast enema for showing the size and location of the leak. Page 21 of 36

22 Fig.: 5: 79-year-old man with small bowel ischemia, infartation and perforation. (a) Erect radiograph of the abdomen shows pneumatosis intestinalis as dark linear streaks of air (arrowhead) in the wall of bowel and pneumoperitoneum. (b, c) CT shows circumferential thickening of the bowel wall (white arrows), pneumatosis intestinalis (arrowheads), edema into the mesentery and air bubbles in the peritoneal cavity. Note the discontinuation of the small bowel wall (black arrows). Intravenous contrast administration was contraindicated in this patient. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Fig.: 6: 71 years-old man with abdominal carcinomatosis (advanced rectal cancer antecedents) and small bowel perforation. (a) Erect radiograph of the abdomen shows sub-diaphragmatic free air (arrow), indicating perforation. (b) CT shows a "omental cake" appearance of carcinomatosis (asterisk) and adjacent extraluminal gas bubbles to the small bowel (arrowheads). On surgery, a necrotic, perforated bowel segment was found. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Page 22 of 36

23 Perforations of the colon and recto Colon cancer Perforations from malignant neoplasm, spontaneous perforation, diverticulitis, blunt trauma, and ischemia tend to occur in the left colon, whereas those from inflammatory lesions and penetrating trauma are frequently observed in the right colon. The cecum is predisposed to perforate when the intraluminal pressure of the colon is increased, as in cases of bowel obstruction and toxic megacolon. Perforation related to colonic tumors has a reported incidence of 1.2-9%. Once a colonic carcinoma has invaded the serosal fat, the possibility of abscess or free perforation or fistula formation is present. The perforation may occur remotely, mainly at the cecum (Fig.7), secondary to marked prestenotic dilatation with a competent ileocecal valve, or at the site of the tumor, due to tumor necrosis (Fig.8). In about 10% of cases it is difficult to determine whether the perforation is caused by diverticulitis or a perforated colon cancer. If there is an abrupt transition of focal wall thickening, local lymphadenopathy, or a wall thickness greater than 1.5 cm, the possibility of a perforated colon cancer should be considered. Diverticulitis Diverticulitis with formation of a pericolic abscess is a classic example of local gastrointestinal perforation. Because diverticula extend into the pericolic fat, inflammation with subsequent microscopic perforation of a diverticulum usually leads to a pericolic inflammatory process with possible abscess formation. Only rarely does diverticulitis result in free intraperitoneal perforation. Page 23 of 36

24 CT is the modality of choice for the demonstration of an acute pericolic inflammatory process. Diverticulitis is manifested by disruption of the pericolic fat by linear streaks of soft tissue attenuation or focal fluid collections. CT may reveal bubbles of extraluminal gas or fluid tracking along the sigmoid mesentery (fig.9). Ingested foreign bodies Correct diagnosis of bowel perforation caused by foreign body may be difficult to be made preoperatively due to nonspecificity of the clinical course, frequent lack of awareness of having ingested a foreign body and nonvisualization of nonmetallic foreign bodies in plain films of abdomen. Perforation occurs in higher frequency in the ileocecal and rectosigmoid regions and is due to material with sharp, pointed ends such as toothpicks, fish and chicken bones. Trauma Colorectal trauma is primarily a result of penetrating trauma. Colon injury in blunt trauma is very rare. Ischemia Vascular impairment of the colonic wall, leading to bowel wall ischemia and infarction, may be related to direct vascular occlusion, ischemic ulceration caused by fecal impaction (stercoral perforation), various vasculitides characterized by inflammation and necrosis of small systemic blood vessels and bowel distension in mechanical obstruction, with vascular compromise involving mainly the cecum (fig.7). The most specific finding of bowel ischemia is lack or poor enhancement of its wall. Spontaneous perforation Stercoral perforation of the colon is a rare distinct clinical and pathologic entity. It occurs due to pressure necrosis of the colonic wall from a rock-hard fecaloma most often involving the sigmoid or Page 24 of 36

25 rectosigmoid. The combination of free air and fecaloma protruding through the colonic wall demonstrate a appearance of a mass with mottled radiolucence in the pelvis or lying freely in the abdominal cavity must lead to a suspicion of stercoral perforation of the colon. Risk factors include conditions leading to longstanding constipation such as druginduced constipation, scleroderma and an underlying obstructing colonic lesion such as neoplasm or stricture. Iatrogenic injury The rectum and sigmoid colon are the predominant sites of iatrogenic injuries. Perforation occur during about 1 in 10,000 barium enema examinations about 0.2% of colonoscopy. Most perforations related to barium enema occur in diseased portions of the colon or because of insufflation of an enema tip balloon. It is necessary to insufflate the enema balloon in only about 5% to 10% of patients. The enema balloon is inflated only after a normal rectum has been demonstrated by the barium column. Relative contraindications for enema balloon insufflations include suspected colitis; a history of pelvic radiation; chronic mucosal prolapse syndromes (ie, solitary rectal ulcer syndrome); suspected rectovaginal fistula; known rectal mass; or perianal inflammatory diseases, such as Crohn's disease or hidradenitis suppurativa. Teares related to the enema tip usually result in contained leakage of barium, depicted radiographically as linear streaks of barium in a submucosal location paralleling the course of the rectal wall. There is also a risk of colonic perforation if a barium enema is performed Page 25 of 36

26 immediately after polypectomy or large forceps biopsy. These procedures can create a mucosal tear or complete trans-mural perforation of the colon. A barium enema should be postponed for about 1 week after an endoscopically performed polypectomy, mucosal cautery, or large forceps biopsy through a rigid sigmoidoscope. A barium enema can be performed after a small forceps biopsy through a flexible sigmoidoscope or colonoscope. The post-polypectomy perforation, in therapeutic colonoscopy, occurs at the site of the excised polyp. A relatively rare, but potentially morbid complication of CT-colonography (CTC) is perforation of the colon. Older age, underlying concomitant colon pathology and recent colonic biopsy increase the risk of perforation. Colorectal perforation caused by a cleansing enema is a rare, potentially lethal event, most often presenting with severe abdominal pain and fever that usually appear during or following the procedure. Retroperitoneal perforations have minimal symptoms while intraperitoneal perforations present with rectal bleeding and mild abdominal complaints followed by progressive sepsis and peritonitis. Postoperative colonic perforation The radiologist may be asked to exclude a leak from a colon that has been partially resected or bypassed. Sites of possible perforation include the stump of a Hartmann's pouch, the stoma of a colostomy or mucus fistula, a colocolic or ileocolic anastomosis, or the diseased colon that was being treated. Page 26 of 36

27 In general, the radiologist should perform a retrograde contrast enema by the anus or rectum to visualize a suspected leak. If the site of suspected leak cannot be reached by a contrast enema through the rectum because of the surgical anatomy, the colon can be evaluated by a contrast enema through a stoma. Water-soluble contrast agents instilled into the peritoneal cavity are not deleterious, but the radiologist should remember that in the presence of a perfuration leaked feces are also being swept into the peritoneal space, potentially exacerbating peritonitis or a walled-off abscess. Inflammatory bowel disease Perforating complications in Inflammatory bowel disease (IBD) are rare. In ulcerative colitis free perforation, occurring in about 2%, are often associated with toxic megacolon, which denotes marked colonic dilatation during the course of a severe, fulminating disease. Free colonic perforating Crohn's disease (CD) occurs in up to 3%, often during exacerbation of toxic colitis, while sealed-off perforations are more commonly seen in CD, related to the transmural inflammatory process and inter-loop adhesions, leading to phlegmon and abscess formation with localized peritonitis. Appendiceal perforations Surgery is indicated for most with acute appendicitis, but it be avoided once perforation has because of the relatively high perioperative complications. patients tends to occurred rates of Therefore, distinguishing nonperforated from perforated appendicitis is clinically important but not always simple because Page 27 of 36

28 rupture of the appendix can be a localized process and may not show a typical clinical presentation. In addition, the amount of extraluminal air is usually small or absent, usually no more than 1 or 2 ml, in perforated appendicitis because acute appendicitis is typically initiated by luminal obstruction. A high performance of US and CT diagnosis for perforated appendicitis has recently been reported with combined findings of extraluminal air, extraluminal appendicolith, fluid collections, abscess, phlegmon, with or without wall thickening of the terminal ileum, cecum and ascending colon and a defect in enhancing the appendiceal wall (Fig.10). Fig.: 7: 49-year-old man with perforation of cecum secondary to a mechanical obstruction by a rectal malignant neoplasm. (a) Erect radiograph of the abdomen shows sub-diaphragmatic free air (arrows), indicating perforation. Dilation of the colon from the cecum to the point of obstruction is not seen due to decompression by perforation. Dilated air-filled loops of small bowel containing fluid levels (arrowheads) are seen. (b, c) US demonstrated fluid in the peritoneal cavity - hepatorenal recess in this image - (white asterisk) and pneumoperitoneum (black asterisk). References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Page 28 of 36

29 Fig.: 8: 72-year-old man with perforated colonic carcinoma. CT image shows an annular tumor in the ascending colon with adjacent fluid (arrow) in right paracolic gutter and an air bubble in close proximity to colon wall. (arrowhead) Small adjacent mesenteric lymph nodes (large arrow) are also seen. The surgery confirmed the microperfuration of the tumor. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Page 29 of 36

30 Fig.: 9: 45 Years-old man with perforated acute diverticulitis. CT shows mural thickening of the descending colon with adjacent fat stranding, small amount of adjacent fluid and an extraluminal air bubble. Surgery confirmed a perforated diverticulitis. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Fig.: 10: 17-year-old boy with acute perforated appendicitis. (a) Graded compression US demonstrates a distended appendix with a diameter (between calipers) of 9 mm. The blunt tip confirms identification of this tubular structure as the appendix with Page 30 of 36

31 an appendicolith in the lumen. Inflammation of the periappendiceal fat results in increased echogenicity. (b) A small amount of free peritoneal fluid (asterisk) is also seen indicating perforation. (c) Hipervascularization is not seen in color Doppler. Surgery confirmed an acutely inflamed and focally necrotic appendix. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Perforations of the biliary tree Penetrating or blunt trauma Perforations may result in the development of intrahepatic or extrahepatic bilomas and abscesses; bile peritonitis; or fistulas to the skin, duodenum, or colon. A biloma is depicted on CT as a fluid collection or thin-walled cyst of low attenuation (Fig.11). On US, a few septs may be seen within a nonechoic collection. Although the presence of a bile collection is best demonstrated on CT or ultrasound, the site of biliary perforation is often best demonstrated by endoscopic retrograde cholangiopancreatography, percutaneous transhepatic cholangiography, or Ttube cholangiogram. An endoscopic retrograde cholangiopancreatography has the additional advantage of allowing treatment of the bile leakage by draining the biliary tree with a stent or nasobiliary tube. Bile peritonitis is manifested on CT as ascites associated with diffuse inflammatory changes on the peritoneal surface and mesenteries. Mesenteric vascular engorgement may also be present. Cholecystitis Perforation of the gallbladder is a lifethreatening complication seen in 5% to 10% of cases. Perforation may occur adjacent to the liver, resulting in pericholecystic abscess; into the peritoneal cavity, resulting in generalized peritonitis; or into adjacent bowel, resulting Page 31 of 36

32 in a biliary-enteric fistula. Overall mortality is as high as 24%. A focal pericholecystic fluid collection suggests pericholecystic abscess. Iartrogenic Perforations of the biliary tree may be caused by various procedures, such as surgery, percutaneous transhepatic cholangiography, endoscopic retrograde cholangiopancreatography, sphincterotomy, and stent placement. Intrahepatic ductal perforations may occur during extraction of biliary calculi when the surgeon or endoscopist uses guidewires or balloon extraction devices in the biliary tree. CT or endoscopic retrograde cholangiopancreatography may demonstrate irregular collections in a peribiliary location within the liver parenchyma. Most of these biliary perforations are not important, but some of these collections may develop into abscesses (Fig12). A biloma may form in the subhepatic space or porta hepatis. Leakage of bile frequently occurs around the insertion site of the T tube, before or after the T tube has been removed. This type of leak may result in a biliarycutaneous fistula. Leakage from both the cystic duct stump and the T tube entry site may be exacerbated by distal biliary obstruction because of stones, blood clots, or T-tube obstruction. Postoperative perforations The most common site of biliary leakage following cholecystectomy is the cystic duct stump. Leakage from this site may result from slippage of sutures or clips, intraoperative laceration, ischemic necrosis caused by crush injury, or ligation of the arterial blood supply.(fig.12) The accessory cholecystohepatic ducts of Luschka drain a portion of the right lobe Page 32 of 36

33 of the liver directly into the gallbladder in 25% to 35% of patients. Leakage from these ducts after cholecystectomy may result in the development of a biloma in the gallbladder fossa. An aberrant right hepatic duct courses along the gallbladder fossa in 5% to 8% of patients. Transection of this aberrant right hepatic duct at cholecystectomy may also result in the development of a biloma in the gallbladder fossa. Perforations with formation of fistula Cholecystoduodenal fistula is most commonly caused by erosion of a gallstone through the gallbladder and into the duodenum. When the gallstone is large, it may cause small bowel obstruction (gallstone ileus) (Fig.13). The gallstone may also erode into the colon and pass spontaneously in the feces. Choledochoduodenal fistula is caused by a penetrating peptic ulcer eroding into the common bile duct. In both cases gas in the biliary tract is seen, but it is most commonly encountered in the patient with a surgically created biliary-enteric anastomosis or who has undergone a sphincterotomy to facilitate stone passage. Page 33 of 36

34 Fig.: 11: 61-years-old with a biloma detected on CT after cholecistectomy. CT through the level of the gallbladder fossa demonstrates a fluid collection. Clips of cholecystectomy are also seen. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Page 34 of 36

35 Fig.: 12: A 76-year-old man with fever after endoscopic intervention stent placement by common hepatic duct cholangiocarcinoma. CT shows a large collection with septations in the left lobe of liver and gastrohepatic ligament (arrows) probably due to infected biloma arising from a intrahepatic ductal perforation. References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Fig.: 13: 68-years-old woman with gallstone ileus. Bowel obstruction is caused by a large gallstone that eroded through the gallbladder wall and passed into the intestine. (a) Plain radiography demonstrates gas in the biliary tree, indicating the existence of a biliary-enteric fistula. (c) On US pneumobilia is characterized by highly reflective linear echoes, which follow the course of the biliary ducts (arrows). (c, d) Specific radiographic signs are present on CT image. Rigler's triad consists of the following: air in the biliary tree or gallbladder, dilated stomach small bowel loops (arrow) and calcified gallstone in an ectopic location -distal ileum-(arrowhead). References: M. A. A. Vieira; Imagiologia, Unidade Local de Saúde do Baixo Alentejo, Beja, PORTUGAL Page 35 of 36