Medical application of transabdominal ultrasound in gastrointestinal

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					            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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posted:12/7/2011
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