Medical application of transabdominal ultrasound in gastrointestinal diseases Hsiu-Po Wang Department of Emergency Medicine National Taiwan University Hospital Real-time ultrasound has become a standard technique in evaluation of intraabdominal disorders. It is a good tool easily available and without radiation. For the first-line physicians, only anatomic explanation by ultrasound is not enough. Combining ultrasound findings with history taking and physical examination is very important, and may lead to more rapid and appropriate management of patients. That means taking ultrasound not only as an image tool but also physicians’ “secondary stethoscope”. Besides intraabdominal solid organs, ultrasound has also been applied on hollow organs, that is the gastrointestinal tract. For the solid organs, including liver, gallbladder, pancreas, kidneys, spleen etc, ultrasound has been applied widely and every field has set up its standard diagnostic picture. Its application is considered easier than the gastrointestinal tract. For survey of the gastrointestinal tract, from esophagogastric junction to rectum, ultrasound can also play its important diagnostic role. Maybe bowel gas is a main problem for ultrasound imaging, but most causes can get some clinical implication form the study. Gas is may be a friend for sonographer in evaluation of GI tract. For example, free air means hollow organ perforation; air in close space usually means abscess; air in a tract means a fistula or perforation hole. Role of ultrasound in gastrointestinal diseases The application of ultrasound in the gastrointestinal tract is as followings: 1. For screening of GI symptoms. 2. Localize and define the nature of GI lesions. 3. Evaluation of severity of GI lesions. 4. Follow-up of GI lesions after treatment. 5. As a assistant tool added to other image modalities. 6. Preventing hazardous and unnecessary procedures. 7. Promoting efficient works in ER. For screening of GI symptoms, it may be not as efficient as when applied to solid organs, especially early GI tract cancer. But for acute lesions or conditions such colitis, ileus or perforation, etc, sometimes it works. Evaluation of severity of GI lesions gives much clinical implication to physicians, because the treatments depend on the severity of GI lesions. Preventing hazardous and unnecessary procedures by ultrasound is an important issue, especially in emergency service. It includes 1. to prevent hazardous endoscopic procedures in PPU, colon perforation and diverticulitis. 2. to prevent hazardous enema for colon perforation & diverticulitis. 3. to prevent unnecessary enema for upper GI obstruction. About the promoting efficient works in ER, it is time and money-saving and makes quick diagnosis. For example, if we detect fluid-filled stomach, NG tube will be inserted for drainage to prevent aspiration & to facilitate efficient endoscopic procedures. How to apply GI ultrasound First, to familiar with ultrasound anatomy of GI tract is very important. For gross anatomy, we should realize the fixed portion and unfixed portion of GI tract. Fixed portion of GI tract includes EG junction, duodenum, ascending colon, descending colon & rectum. Unfixed portion of GI tract includes small bowels, transverse colon and sigmoid colon. Terminal ileum and appendix, which connect the fixed cecum, are considered partially fixed and not difficult to scanning by ultrasound. For the macroscopic anatomy, we should realize the layering of walls of GI tract and also the characteristic ultrasound pictures of different segments of GI tract. Five-layered structure of GI tract wall is the basic concept (fig. 1) . Loss of the stratifications always means abnormal events. Characteristic ultrasound pictures of small bowels and colon is different. Small bowels reveals with folds of Kerckring (valvulae conniventes) which present on ultrasound as small “spikes” with short distance from each other on small bowel wall. On the other side, colon shows haustration which looks like “bamboo” on ultrasound. Fig 1 Second, selection of proper MHz of ultrasound probes is essential. Usually, 5 or 7 MHz for average or thin patients is recommended. For heavy patients, 3 MHz is considered. Of course, it depends on the operators. Third is ultrasound scanning method. Scanning may be generalized but more focused over target area with symptom/sign. It may be started from fixed portions to mobile portions, A/D/R colon to T/S colon and colon to small bowel. Longitudinal and transverse scanning should be used alternatively. Recognize the abnormal GI tract lesions When scanning the GI tract, what to check is: Wall thickening Location of lesions Perienteric change degree intraluminal fat tissue distribution mural lymph node exophytic abscess Intraluminal lesion usually indicates foreign bodies such as bezoars. GIST sometimes presents with exophytic growing. Characters of abnormal GI tract lesions were as follow: Normal Abnormal Layered appearance Loss of layered appearance Compressible Lack of compressibility Intermittent peristalsis Increased thickness ( > 4 mm ) Decrease in intraluminal gas or fluid Using compression method, the diseased bowel usually does not change its morphology. Sometimes, indirect signs on echogram for diseases of GI tract are helpful. It includes free air, creeping fat, air in portal vein, whirlpool sign, etc. Application of ultrasound in GI diseases EG junction Hiatal nernia Achalasia Cancer Stomach Gastric ulcer Gastric tumor PPU Outlet obstruction AGML Varices Bezoar Duodenum Duodenal ulcer PPU Duodenal tumor SMA syndrome H-S purpura Small bowel Perforation Pneumatosis intestinalis Tumor Ileus Intussusception Bezoar, fish bone, chicken bone Ileitis Crohn disease Colon Diverticulitis Typhlitis Colon tumor Infectious colitis Ischemic colopathy Ulcerative colitis Epipolic appendagitis Appendicitis Echo signs which may help diagnosis of GI tract diseases Echo sign Diseases Aurora sign Pneumatosis intestinalis Gastric pneumatosis Corona sign Pneumatosis intestinalis Circle sign Pneumatosis intestinalis Crescent-in-donut Intussusception Dome sign Diverticulitis Hay-fork sign Intussusception Multi-centric sign Intussusception Key-Board sign Intestinal obstruction Peudokidney sign Bowel tumor Target sign Intussusception Mid-gut malrotation Whirlpool sign Volvulus US characters for individual GI diseases Appendicitis Distended & fixed ( without peristalsis ) ( diameter > 6 mm ) Appendicolith Echogenic appendiceal fat For equivocal case – US doppler may be helpful Diverticulitis Hypoechoic outpouchings from GI wall Containing echogenic materials - air, fecal material, enteroliths Indirect signs neighboring bowel wall thickening perienteric echogenic fat change local anechoic abscess with echogenic foci ( “dirty shadow” from air ) fistula Right sided diverticulitis More common in the Asian population Must be D/D with appendicitis Consevative treatment is the first choice Epiploic appendagitis Echogenic fingerlike projection arising from colon surface Echogenic & mass-like pericolonic fat Torsion or venous thrombosis of epiploic appendages Pseudomenbranous colitis prominent gyral pattern of submucosa Ischemic colitis segmental wall thickening, most R-S-D colon Crohn disease Transmural involvement Acute phase – echogenic band of SM layer Chronic phase – hypoechoic thickening Fistula :hypoechoic tract with echogenic air bubble Perienteric fat – creeping fat Adenopathy – 20 % Small bowel obstrcuction Dilated, fluid-filled bowel loops Key-board sign Edematous wall due to vascular or lymphatic obstruction To-and fro motion of bowel content Whirlpool sign for volvulus In conclusion, It is possible to figure out lesions of GI tract by ultrasound. Through the daily practice, although operator-dependent, there may be “ general rules “ in proceeding ultrasound on diseases of GI tract.
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