Small bowel capsule endoscopy (SBCE) remains the gold standard for practice for the diagnosis of small bowel disorders. A rather challenging task, for those who start to use this diagnostic modality, is the recognition of the typical anatomic landmarks and the distinction of normal small bowel anatomy from abnormal findings. The reader of SBCE images may also often encounter unusual views of the normal anatomy as well as various artifacts that need to be distinguished from pathologic findings. Experience gained through standard endoscopy is invaluable to the interpretation of capsule examinations; however, formalized training and credentialing in reading competency are essential.
Key points
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Recognizing typical anatomic landmarks as well as distinguishing normal small bowel anatomy from abnormal findings on small bowel capsule endoscopy (SBCE) may be challenging, especially for novice readers.
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The reader of capsule images may often encounter unusual views of the normal anatomy and various artifacts that need to be recognized and distinguished from pathologic findings; small, innocent findings should not be overinterpreted.
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Experience gained through standard endoscopy is invaluable to the interpretation of SBCE examinations; however, formalized training and credentialing in reading competency are essential.
Introduction
Small bowel capsule endoscopy (SBCE) is fundamentally different from conventional flexible endoscopy, albeit still digestive endoscopy. Differentiating normal from abnormal in SBCE is not always as easy as it sounds; often it is hampered by the lack of control over the capsule movement and/or the direction of view. Furthermore, the inability to carry out typical maneuvers of conventional endoscopy, such as suctioning, flushing, or simply biopsying in case of uncertainty, represents one of the major limitations of current SBCE. Therefore, diagnosis or even a presumptive one is often based solely on the images captured by the video capsule. Normal variants and nonpathologic findings must also be clearly recognized. Hence, when interpreting SBCE, some special features of this diagnostic modality should be taken into account; that is, the image is more magnified than the image obtained with conventional endoscopy, and therefore, small innocent findings should not be overrated. The SBCE readers should also be familiar with technical details of different available capsules, which differ for number and location of cameras (ie, the recently introduced panoramic lateral-viewing capsule provide a tape view instead of the tubular view of frontal viewing capsules), field of view, depth of view, battery duration, and image capture rate. Experience gained through standard digestive endoscopy is certainly invaluable to the interpretation of SBCE videos; nevertheless, formalized training and credentialing in SBCE reading competency are also essential.
This article deals with the normal anatomy of the small bowel as realized by SBCE as well as some artifacts and normal variants that may be found during a capsule examination; the reader should become familiar with the latter in order to be able to distinguish them from pathologic findings.
Introduction
Small bowel capsule endoscopy (SBCE) is fundamentally different from conventional flexible endoscopy, albeit still digestive endoscopy. Differentiating normal from abnormal in SBCE is not always as easy as it sounds; often it is hampered by the lack of control over the capsule movement and/or the direction of view. Furthermore, the inability to carry out typical maneuvers of conventional endoscopy, such as suctioning, flushing, or simply biopsying in case of uncertainty, represents one of the major limitations of current SBCE. Therefore, diagnosis or even a presumptive one is often based solely on the images captured by the video capsule. Normal variants and nonpathologic findings must also be clearly recognized. Hence, when interpreting SBCE, some special features of this diagnostic modality should be taken into account; that is, the image is more magnified than the image obtained with conventional endoscopy, and therefore, small innocent findings should not be overrated. The SBCE readers should also be familiar with technical details of different available capsules, which differ for number and location of cameras (ie, the recently introduced panoramic lateral-viewing capsule provide a tape view instead of the tubular view of frontal viewing capsules), field of view, depth of view, battery duration, and image capture rate. Experience gained through standard digestive endoscopy is certainly invaluable to the interpretation of SBCE videos; nevertheless, formalized training and credentialing in SBCE reading competency are also essential.
This article deals with the normal anatomy of the small bowel as realized by SBCE as well as some artifacts and normal variants that may be found during a capsule examination; the reader should become familiar with the latter in order to be able to distinguish them from pathologic findings.
Esophageal and gastric passage
Although SBCE is an examination primarily devoted to the study of the small bowel, useful information can sometimes be extracted from the esophageal and gastric portion of the study. In addition, although SBCE has some inherent limitations in the study of the stomach and the esophagus, the SBCE readers have to inspect these organs because obvious clinically relevant findings, missed by previous gastroscopies, are discovered in the upper gastrointestinal (GI) tract in up to 15% of SBCE examinations.
The capsule records images of the mouth and oropharynx, but they are limited and not adequate for making a formal diagnosis. The upper esophageal sphincter is rarely identified, whereas the rest of the esophagus only occasionally can be reliably evaluated because of the exceptionally swift passage of the capsule. The first images of the esophagus show a dark hollow tube ( Fig. 1 ). The squamous epithelium lining appears pale white; the vessels beneath the epithelium are seen as tiny pale red curly lines ( Fig. 2 ). In the normal esophagus, the Z-line is coincident with the gastroesophageal junction, defined as the upper end of the gastric folds. The Z-line is shortly visualized during the examination in most patients ( Fig. 3 ). It can display different shapes: round, starlike, flamelike, blurry, and/or distorted. Complete visualization of the Z-line is often challenging because the individual frames obtained might include only a portion of it. Z-line visualization can be accurately achieved in most cases if the patient swallows the capsule while lying in the right supine position or when dual cameras with higher image capture rate (ie, PillCam Colon Capsule 2 [Pill Cam, Medtronic, Minneapolis, MN]) are used.
Pathologic findings are occasionally seen, most commonly at the Z-line: when they are well demarcated such as Barrett’s esophagus or esophagitis, they should be described but need clarification by additional investigations such as esophagogastroduodenoscopy.
The first gastric image is usually dark, given the wide space present in the gastric cavity. Passage into the stomach is featured by several rapid changes in the capsule direction. Typical passage times of the capsule in the stomach range from a few minutes to 1 hour. Similarly to the esophagus, the gastric mucosa is incompletely visualized at SBCE, and this examination cannot substitute for examining the upper GI tract by esophagogastroduodenoscopy, when clinically indicated. Attention to the surface structure of the gastric mucosa, that generally appears smooth and sometimes exhibits a mosaic pattern ( Fig. 4 ), can provide important clues, especially for its differentiation from the mucosa of the duodenal bulb.
Subdivision of the small bowel
The small bowel is a tubular organ up to 5 m long, which starts at the pylorus and ends at the ileocecal valve. It is subdivided into the duodenum, the jejunum, and the ileum. Although there are some differences in structure between jejunum and ileum, a precise transition cannot be defined; however, the duodenum and terminal ileum can be identified easily. The localization software of capsule endoscopy is occasionally helpful in distinguishing the distal duodenum from the jejunum and the terminal ileum from the mid ileum. Therefore, in SBCE interpretation, the subdivision of the small bowel is based mostly on pragmatic considerations. The time that elapses between the pylorus and the first cecal image is divided into 3 equal parts. The small bowel segments in SBCE may thus be enumerated in this way: duodenum, proximal third of the small bowel, middle third of the small bowel, distal third of the small bowel, and terminal ileum. The position of the capsule or any identified abnormality can also be reported by indicating the time that has elapsed between the passage of the imaging device through the pylorus and its current position, thereby estimating its position in the “proximal” or “distal” portion of the small bowel.
Pylorus and duodenal bulb
The typical aspect of the pylorus is easily recognized at capsule endoscopy ( Fig. 5 ) and, while the capsule is still in the stomach, it is occasionally possible to get a transpyloric view into the duodenal bulb ( Fig. 6 ). If the capsule is pointing in a favorable direction, the distal aspect of the pylorus may be visible from within the bulb as a circular ridge ( Fig. 7 ). In this situation, the mucosa of the pylorus appears flat, whereas the surrounding mucosa of the duodenum is covered by villi ( Fig. 8 ). Therefore, the somewhat protuberant appearance of the pylorus in this view should not be mistaken for a polyp or mass lesion ( Fig. 9 ). A back-and-forth movement across the pylorus may also occasionally be observed with retrograde passage of the capsule from the duodenal bulb into the stomach and then again into the bulb. Views of the duodenal bulb are usually brief. Unlike the gastric mucosa, the duodenal bulb typically reveals superficial breaks and fissures that correspond histologically to the presence of crypts (see Fig. 8 ). At this level, the presence of fluid, bile, and food particles may obscure luminal views and hamper the correct interpretation of the device location.
Single or multiple small nodules, representing Brunner glands, are a typical feature of the duodenum, but they can also be found in the descending duodenum. Foci of heterotopic gastric mucosa may also present as discrete nodules or multiple sessile polyps in the duodenum ( Fig. 10 ). Both conditions are typically asymptomatic and discovered incidentally; their differentiation requires histologic evaluation by biopsy specimens.
Folds are first seen past the apex of the bulb, and circular folds first appear in the descending duodenum. Bile is usually visible in the bowel lumen at this level.
Papilla of vater and minor papilla
The major papilla, also termed papilla of Vater, is difficult to identify in the nondistended duodenum; it is sometimes concealed by luminal content such as bile or may be missed due to the quick duodenal passage of the capsule. It is imaged in approximately 10% of patients during SBCE with frontal viewing capsules and up to 70% in SBCE with lateral panoramic view (CapsoCam, CapsoVision, Cupertino, California). If identified, the major papilla appears as a small nodule with a central pinpoint or slitlike opening that is sometimes marked by the drainage of bile ( Figs. 11 and 12 ). The minor papilla, which is located just proximal to the papilla of Vater, is even more rarely seen. Time after ingestion to reach the papilla of Vater is quite variable, as is the time interval between passage through the pylorus to the papilla. Usually this takes only seconds to a few minutes, but rarely, prolonged stay of the capsule in the duodenum or retroperistalsis may cause visualization of the papilla up to l or 2 hours after it passes the pylorus.
