Duodenal ulcers (DUs) affect nearly 10% of the adult population at some time,  and these lesions account for two thirds of all peptic ulcers, which are defined as mucosal breaks of 3 mm or greater; gastric ulcers account for the rest. Unlike gastric ulcers, which may be malignant in about 5% of cases,  duodenal ulcers are almost invariably benign; therefore, treatment with antisecretory drugs can be commenced after radiologic diagnosis, without endoscopy being performed beforehand. [2, 3] Images of duodenal ulcers are provided below.
Endoscopy has become the diagnostic procedure of choice for patients with suspected duodenal ulcer. However, endoscopy is more invasive and costly than double-contrast barium study. Double-contrast examinations of the upper gastrointestinal tract remain a useful alternative to endoscopy but have a lower sensitivity, especially in the detection of small duodenal ulcers. [4, 5, 6] Endoscopy with biopsy has a sensitivity of as high as 95%, but small ulcers in the base of the duodenal bulb may be missed. In the presence of gastric outlet or proximal duodenal obstruction, the endoscope may be unable to pass through the stenosis, and the full extent and cause of the obstruction may not be defined.
Single-contrast barium studies may cause as many as 40% of small ulcers to be missed, but double-contrast barium images depict as many as 95% of ulcers larger than 10 mm  ; these results are comparable to those of endoscopy. However, the sensitivity of double-contrast barium examination decreases with smaller ulcers and recurrent ulcers in a deformed duodenal bulb; therefore, this modality is not reliable in the detection of duodenitis or duodenal erosions. Barium studies have a disadvantage because biopsy specimens cannot be obtained to test for Helicobacter pylori infection or to evaluate a suspicious lesion.
The differential diagnosis includes a calculous c holecystitis, acute c holecystitis, cholelithiasis, Crohn disease, gastric ulcer, gastroesophageal reflux, upper gastrointestinal bleeding, acute and c hronic p ancreatitis, G astrointestinal tuberculosis, and Zollinger-Ellison syndrome.
Failure to diagnose duodenal ulceration and the complications of duodenal ulceration (eg, hemorrhage, gastric outlet obstruction, and perforation) are special concerns. [7, 8, 9, 10] Esophagogastroduodenoscopy, in one study, showed that complicated duodenal ulcer disease was accompanied by a significantly higher detection rate of erosive esophagitis (20%), gastritis (52%), duodenitis (25%), multiple ulcers (28%), and larger ulcer sizes. 
Transcatheter embolization may be used to treat bleeding duodenal ulcers.  Terminal muscular-branch vessel embolization is more effective than gastroduodenal artery embolization in the initial and long-term control of bleeding. Terminal vessels may be occluded with 6-cyanoacrylate, but duodenal stenosis is a late complication in one quarter of all patients.
In a study of 29 patients with massive bleeding from duodenal ulcer disease, 26 patients achieved immediate hemostasis, and technical success rate reached 90%. No hemostasis was observed in 27 patients within 30 days after emergency transcatheter arterial embolization, and clinical success rate was 93%. 
Fluoroscopically guided balloon (15 or 20 mm in diameter) dilatation may be used for benign duodenal strictures caused by peptic ulcers, Crohn disease, or postoperative adhesion.  Duodenal perforation may occur, necessitating emergency surgery.
Most duodenal ulcers are depicted as round or ovoid pools of barium; about 5% may be linear, and most are smaller than 1 cm in diameter. Giant duodenal ulcers, defined as those >2 cm in diameter, have an increased risk of perforation, obstruction, and bleeding. Multiple ulcers occur in about 15% of patients  ; Zollinger-Ellison syndrome should be considered in these patients.
About 95% of duodenal ulcers occur in the duodenal bulb,  and the rest occur in the postbulbar duodenum, which consists of the proximal 2 cm of the descending duodenum above the ampulla of Vater. As many as half of all duodenal ulcers occur in the anterior wall of the bulb.
Technique of double-contrast barium study
Biphasic examination combines the advantages of the double-contrast views of the duodenum using high-density barium with the advantages of the prone or erect compression views using low-density barium to show ulcers in the anterior wall of the bulb. Intravenous (IV) glucagon 0.1 mg and effervescent granules are administered as part of the double-contrast examination, which is followed by the acquisition of single-contrast compression views with low-density barium.
Bulbar ulcer craters are depicted as well-defined round or ovoid pools of barium that can be seen en face or in profile (see the following images); they are often surrounded by a smooth mound of edematous mucosa.
Radiating folds converge to the edge of the crater, as shown in the first image below. Ulcers in the anterior wall may be detected as a ring shadow, as seen in the second image below, with barium coating the edge of the unfilled ulcer crater. These craters are filled on prone or erect compression views.
The duodenal bulb is often deformed by edema and spasm associated with the ulcer or by scarring from a previous ulcer (see the following images). Small ulcers may not be detected in a deformed bulb.
Postbulbar ulcers are usually located in the medial wall of the proximal descending duodenum above the ampulla of Vater (see the images below) and are prone to bleeding. Detection of the ulcer niche or crater is often difficult because of the associated edema and spasm, which may also cause indentation of the lateral wall of the descending duodenum opposite the ulcer. This indentation may lead to stricture formation as a result of fibrosis and may mimic a carcinoma of the duodenum.
Healing is often rapid, with a decrease in the size of the ulcer and a change from a round to a linear configuration. Healing may lead to scarring, with radiating mucosal folds converging to the site of the previous ulcer. Bulbar deformity results from asymmetrical scarring and retraction during healing (see the following images). Pseudodiverticula result from the expansion of normal segments of the cap between areas of fibrosis. If present, the typical cloverleaf appearance of the scarred bulb is caused by multiple pseudodiverticula formation.
Complications of duodenal ulceration
Hemorrhage occurs in 20-30% of ulcers.  Endoscopy is the investigation of choice, with a sensitivity of more than 90% in the detection of the bleeding site.  Double-contrast barium studies are limited by poor mucosal coating in the presence of bleeding. Nevertheless, the bleeding site may be detected in as many as 75% of cases.  A filling defect resulting from a blood clot, food debris, or granulation tissue may be seen at the base of the barium-filled ulcer.
Gastric outlet obstruction occurs in 5% of patients with peptic ulcers.  It is most common in duodenal ulcers but also occurs in antral or pyloric channel ulcers. Peptic ulcers account for two thirds of cases of gastric outlet obstruction in adults.  The images typically show narrowing and deformity of the pylorus or duodenal cap, as shown in the image below.
Nasogastric suction of the large gastric residue (see the following image) may be required before performing the upper gastrointestinal series.
The descending duodenum may be obstructed by fibrosis caused by a postbulbar ulcer, as shown in the second image below.
Less common causes of gastric outlet (or proximal duodenal) obstruction include malignancy (see the first image below), such as carcinoma of the duodenum (see the second image below); large duodenal adenomas (see the third image below); Crohn disease; tuberculosis; mural hematoma; and extrinsic compression caused by pancreatic lesions.
Perforation occurs in as many as 10% of patients with peptic ulcer disease,  most of which arise from ulcers in the anterior aspect of the duodenal cap. In 75% of cases, free gas is present in the peritoneum  ; this is best shown on an erect chest radiograph, as demonstrated below. A water-soluble contrast upper gastrointestinal series may demonstrate the presence and site of the perforation or whether it has sealed.
Subphrenic collections are common sequelae of a perforated duodenal ulcer. Occasionally, they may be shown on an erect chest radiograph (see the first image below), but these collections are best assessed with ultrasonography or computed tomography (CT) scanning (see the second image below). 
Penetrating posterior wall duodenal ulcers result in a walled-off perforation. An abscess may form in the lesser sac, and the pancreas is involved in two thirds of cases. 
Fistulas may be also be present.  Duodenocolic fistulas are usually caused by invasion of the second part of the duodenum by a carcinoma of the hepatic flexure or ascending colon. Rarely, these lesions may be a result of a penetrating ulcer of the duodenal bulb or postbulbar region that has caused erosion into the adjacent colon. In addition, choledochoduodenal fistulas may occur.  About 95% of these are associated with complications of biliary tract calculi. Only 5% of these fistulas are a result of duodenal ulcers that cause erosion into the common bile duct. Abdominal radiographs may show gas in the biliary tree.
Degree of confidence
Single-contrast barium studies may cause as many as 40% of small ulcers to be missed, but double-contrast barium images depict as many as 95% of ulcers larger than 10 mm; these results are comparable to those of endoscopy. However, the sensitivity of double-contrast barium examination decreases with smaller ulcers and recurrent ulcers in a deformed duodenal bulb. Double-contrast barium examination is not reliable in the detection of duodenitis or duodenal erosions.
Ulcers may be obscured by edema, spasm, or scarring. False-positive results are caused by pseudodiverticula and small pools of barium in a deformed bulb resulting from previous peptic ulceration.
CT scanning has little role in the primary detection of duodenal ulcers. However, primary inflammatory processes of the duodenum, such as ulcers, duodenitis, and secondary involvement from pancreatitis, can reliably be diagnosed with CT scanning.  Careful CT scanning technique and 3-dimensional (3-D) imaging can help optimize detection of abnormalities and disease, as well as help with surgical planning. They include the use of oral contrast, preferably water, as well as IV contrast. [8, 16]
CT scanning also has a role in the detection of subphrenic and other collections that may occur after perforation of a duodenal ulcer (see the following image).
Ultrasonography may indicate the presence of a giant duodenal ulcer. Its main role is in the detection of other causes of upper abdominal pain such as that caused by gallstones and pancreatitis. This modality also depicts subphrenic and other collections resulting from a perforated duodenal ulcer.