J Korean Radiol Soc 2008;58:283-295 Evaluation of Small Bowel Obstruction Using Multidetector Computed Tomography (MDCT)1 Jee Hye Lee, M.D., Soon-Young Song, M.D., On Koo Cho, M.D., Byung Hee Koh, M.D., Yongsoo Kim, M.D.2 Small bowel obstruction is a relatively common clinical condition and its diagnosis is based on the clinical signs, the patient’s history and the radiologic findings. For a pa- tient with suspected small bowel obstruction, it is essential to determine the site, loca- tion and cause of obstruction for the appropriate management. Because of the poor ac- curacy of plain radiography, computed tomography (CT) now has an essential role to diagnose bowel obstruction. With the recent evolution of conventional CT into multi- detector computed tomography (MDCT), it is possible to obtain cross sectional images with high spatial resolution and different post-processes can be done, such as obtain- ing the volume rendering (VR), maximum intensity projection (MIP), or multiplanar reformatted (MPR) images from the volume data. In this article, we illustrate and dis- cuss the utility of the multiplanar images of MDCT for diagnosing the sites, causes and complications of small bowel obstruction. Index words : Intestine, small intestinal obstruction Tomography, spiral computed, multi-detector Multiplanar images Imaging, three-dimensional Although plane radiography is the first step for mak- sional imaging technique, it is possible to reconstruct the ing the diagnosis of small bowel obstruction, its accura- VR, MIP or MPR images from the volume data. In this cy for determining the presence of obstruction is only article, we illustrate and discuss the usefulness of the 46-80% (1-7). CT currently has an essential role in di- multiplanar MDCT images for diagnosing the site of agnosing small bowel obstruction. It has a high sensitivi- bowel obstruction and characterizing the specific causes ty of 94%-100% and an accuracy of 90%-95% (1, 3, 8). of small bowel obstruction. In addition, we also illus- In addition, the recent evolution of conventional CT into trate the findings of complicated loops due to small bow- MDCT has brought about great advances in the evalua- el obstruction. tion of the small bowel. With the use of the 3-dimen- Scan parameters of the MDCT Examination 1Department of Radiology, Hanyang University College of Medicine, Hanyang University Hospital, Korea A 16-detector row spiral CT scanner (Sensation 16; 2Department of Radiology, Hanyang University College of Medicine, Hanyang University Kuri Hospital, Korea Siemens Medical Systems, Erlangen, Germany) with a Received September 13, 2007 ; Accepted November 1, 2007 gantry rotation time of 0.5 seconds was used at our insti- Address reprint requests to : Soon-Young Song, M.D., Department of Radiology, Hanyang University College of Medicine, Hanyang University tute for the abdominal examinations. All the patients Hospital, 17 Haengdang-dong, Seongdong-gu, Seoul 133-792, Korea were placed in the supine position on the CT table. The Tel. 82-2-2290-9160 Fax. 82-2-2293-2111 E-mail: [email protected] acquisition volume included the whole abdomen from ─ 283 ─ Jee Hye Lee, et al : Evaluation of Small Bowel Obstruction Using Multidetector Comp uted Tomography (MDCT) the dome of the diaphragm to the lower margin of the CT scan for the hepatic arterial-phase images was start- symphysis pubis. An 18-gauge intravenous cannula was ed 8 seconds after the attenuation reached 150 H.U. An inserted into a vein in the antecubital fossa, forearm or additional CT scan for the portal-phase images was start- wrist. Scanning of the abdomen was performed after in- ed 60 seconds after starting the contrast injection. The travenously injecting 2 mg/kg of contrast medium (io- CT scan was done during a breath holding at the end of promide [Ultravist 370]; Schering, Berlin, Germany) inspiration. The CT examination was performed by us- with an automatic power injector at a flow rate of 2.5- ing 16×1.5-mm collimation and a table feed rate of of 3.0 mL/sec. for a total of 100-120 mL. The scan delay 24 mm per gantry rotation. The X-ray tube voltage was time was determined by the automatic bolus tracking 120 kV and amperage was 140 mAs. The volume data of method. The region of interest (R.O.I.) was positioned at both the arterial and portal-phased scans was recon- the descending aorta at the level of the diaphragm. The structed at a 2-mm thickness and with a 1-mm interval. A B C D Fig. 1. A-D. Small bowel perforation in a 50 year-old male patient with advanced Crohn’s disease. A. The axial CT scan shows marked dilatation of the small bowel loops and multifocal mural thickening. There are multiple foci of extraluminal air suggesting intestinal perforation (not seen). An abrupt change of caliber is noted (arrow). B, C. The coronal reformatted images also easily demonstrate the site of obstruction with an abrupt change of caliber (arrow). Multifocal extraluminal air bubbles are noted in the peritoneal cavity. There is a well-demonstrated site of perforation (arrow- head). D. The gross specimen shows strangulated bowel loops and the site of perforation (arrowhead). ─ 284 ─ J Korean Radiol Soc 2008;58:283-295 Image Interpretation Intrinsic Causes The volume data of the whole abdomen was acquired Inflammatory diseases during a single breath hold for all the patients who un- Crohn’s disease derwent abdominal CT for the evaluation of small bow- Crohn’s disease is an idiopathic inflammatory disease el obstruction. The axial images of both the portal and that can affect any part of the gastrointestinal tract from arterial phases and the coronal image of the arterial the mouth to the anus. The small bowel is the major site phase were reformatted for routine study. We acquired of involvement. Small bowel wall thickening and lumi- additional MPR images at various angles and the curved nal narrowing may be the common findings. The in- MPR images from the volume data with using PC-based flamed mucosa and serosa may be markedly enhanced, 3-dimensional software (Rapidia 2.8; InfinitⓇ, Seoul, and the intensity of enhancement correlates with the Korea). clinical activity of the disease. Mural stratification disap- pears during the chronic phase, so that the affected bow- Classifying the Causes of Small Bowel Obstruction el wall typically has homogeneous attenuation at CT (2, 9). In the advanced or stenotic phase of Crohn’s disease, The causes of small bowel obstruction can be classi- the patients frequently present with recurrent episodes fied in two major categories, that is, the intrinsic and ex- of partial small bowel obstruction associated with stric- trinsic causes. The intrinsic causes include inflammato- ture. Dilated small bowel loops with an abrupt change ry disease and neoplastic disease. Other conditions such in caliber can be detected on the routine axial CT images as an intraluminal bezoar or a foreign body can also (Fig. 1A) (2). The reformatted images can demonstrate cause obstruction. The extrinsic extraluminal patholo- the full-length of the obstruction site (Fig. 1B). Severe gies can result in small bowel obstruction. Adhesion and obstruction can sometimes lead to perforation of the hernia are seen frequently. Although other conditions small bowel, which requires emergency surgical inter- such as superior mesenteric artery (SMA) syndrome are vention (Fig. 1C). MDCT may be a useful tool not only infrequent, it can be a cause of duodenal obstruction. for diagnosing the level and cause of obstruction, but al- Complicated cases such as strangulation, closed loop ob- so for detecting the site of perforation (Fig. 1A to 1D). struction and afferent loop syndrome are classified in the third category of the complicated small bowel ob- Intestinal tuberculosis struction. Even though Mycobacterium tuberculosis can involve any part of the gastrointestinal tract, the ileocecal region A B C Fig. 2. A-C. Intestinal tuberculosis with focal stricture in a 65 year-old female patient. A, B. The slab VR images of CT shows a dilated jejunal loop, and note the abrupt change of caliber (arrow). C. The curved MPR image shows focal bowel wall thickening that is suggestive of inflammatory lesion (arrowhead). ─ 285 ─ Jee Hye Lee, et al : Evaluation of Small Bowel Obstruction Using Multidetector Comp uted Tomography (MDCT) is the most common site of involvement for tuberculosis bowel disease with the advantage of an overlap-free dis- of the gastrointestinal tract. Intestinal tuberculosis may play of such individual structures as the bowel, vessels cause stricture of the small bowel and subsequent ob- and solid organs. The images of the small bowel can be struction. The gross morphologic features of this patho- reconstructed in a pattern resembling enteroclysis and logic process have been well evaluated with CT (9). this makes the pathologic segment more easily de- When the inflammation is mild, CT demonstrates only tectible (Fig. 2A to 2C). slight, symmetric mural thickening and a few small re- gional nodes. When the pathologic process is severe and Parasitic infestation advanced, then the more characteristic abnormalities Parasites can be a rare intrinsic inflammatory cause of are evident. Characteristically, the CT findings include small bowel obstruction. The possible organisms that asymmetric thickening of the ileocecal valve and the can infest the bowel are Ascaris lumbricoides, hook- medial wall of the cecum, with an exophytic extension worm (Ancylostoma duodenale and Necator ameri- that engulfs the terminal ileum. Massive lym- canus), tapeworm (Diphyllobothrium latum, Taenia phadenopathy can be combined with this, and the lym- solium), Strongyloides stercoralis, Giardia lamblia and phadenopathy shows central areas of low attenuation the Anisakis species. When adult Ascaris are present in (10, 11). The cecum becomes conical, shrunken and re- large numbers, they may form an intertwined bolus, tracted out of the iliac fossa due to fibrosis within the causing intestinal obstruction (14).