Imaging of Bowel Obstruction

Discussion on the role of radiography and CT on bowel obstruction.

1. Imaging of Bowel Obstruction!
Rathachai Kaewlai, MD!
Ramathibodi Hospital, Mahidol University, Bangkok!
Emergency Radiology Minicourse 2015 !

2. What to Cover…!
Imaging techniques!
Gastric obstruction!
Small bowel obstruction!
Large bowel obstruction!

3. Bowel Obstruction!
Lack of transit of bowel contents!
Small bowel obstruction: high or low!
Large bowel obstruction!
Simple (intact blood supply) vs. strangulated!

4. Bowel Obstruction!

5. Clinical Presentation!
Depend upon site of obstruction!
High SBO – vomiting early, profuse, rapid dehydration!
Low SBO – pain with distension!
LBO – constipation !
Strangulation – shock, rigidity/rebound (localized/diffuse)!

6. Treatment!
Conservative!
Surgery: !
!Early – !
!!Strangulation!
!!Closed loop obstruction!
!!Obstructed/strangulated hernia!
!Delayed – !
!!Adhesive obstruction without pain!

7. Aims of Investigations!
Is obstruction present?!
Where is the location?!
What is the cause?!
Is emergent surgery needed?!
!Strangulation!
!Closed loop!
!Obstructed hernia!
Radiography!
CT!

8. CT Techniques!
Helical scan, thinnest collimation!
Coronal reformats!
IV contrast, single venous phase!
No need for oral contrast. May be neutral
contrast!
No rectal contrast needed!
!May be helpful if LBO, neutral contrast preferred!

9. Gastric Outlet Obstruction (GOO):"
Etiology!
Malignancy > benign (PUD)!
Extrinsic: pancreatitis with pseudocyst, hematoma!
Intrinsic: malignancy, PUD with stricture!
Intraluminal: bezoars, FB, GS!
Acute incarceration or strangulation:
obstructed paraesophageal hernia, gastric volvulus!

10. Radiography!
Markedly dilated stomach,
air or fluid filled!
Filling defect (cancer)!
Calcified gallstone
(Bouveret syndrome)!

11. CT!
Marked distension!
Etiology!
!Enhancing soft tissue mass!
!Focal thickening of gastric wall
with mucosal hyper-
enhancement and/or ulcers!
!Pancreatitis w/wo pseudocyst!
!Acute cholecystitis!
!Filling defects (polyp, gallstone,
bezoar)!
Stomach!

12. GOO: Malignant "
Etiologies!
Ampullary, duodenal,
cholangiocarcinoma,
gastric cancer!
Pancreatic cancer with
extension to duodenum/
stomach!
!15-25% with GOO!
!Usually have biliary
obstruction!
Stomach!
Mass!
Gastric cancer with GOO!

13. GOO: Benign Etiologies!
PUD (acute vs scarring/fibrosis)!
Polyps, caustic ingestion, web, GS, pancreatic
pseudocyst, bezoar!

14. Gastritis vs. Neoplasm!
Difficult differentiation on
imaging. Endoscopy necessary
to differentiate neoplasm!
Gastritis!
!Layered (halo) appearance!
!Diffuse, segmental, or annular !
Neoplasm!
!Nodal disease!
!Metastasis!
Pseudothickening of antrum!

15. Diagnostic Approach!
Dilated stomach may contain up to 5L of fluid!
Functional disturbance!
!Postoperative, severe trauma, immobilization,
inflammatory disease of abdomen, neurogenic,
diabetes!
Mechanical obstruction (stomach, duodenal, high SB)!
!Differentiate benign from malignant processes!

16. Gastric Volvulus!
Abnormal rotation around its axis!
Surgical emergency if acute!
Organo-axial, mesenteroaxial, or both!
Organoaxial!
!Stomach rotates around axis
connecting EGJ and pylorus!
Mesenteroaxial!
!Less common!
!Stomach rotates around axis bisecting
both lesser and greater curvatures!
Image:'Differen-al'diagnosis'in'conven-onal'gastrointes-nal'radiology.'Burgener'FA,'Kormano'M.'

17. Gastric Volvulus!
Diaphragmatic defect m.c.
causative factor!
Intrathoracic stomach!
!Transverse lie with single air-
fluid level = organoaxial!
!Spherical lucency with beak
in distal stomach +
differential air fluid levels =
mesenteroaxial!
Case courtesy of Radiopaedia.org!
Case courtesy of Dr Maxime St-Amant, Radiopaedia.org!
Organoaxial volvulus!
Mesenteroaxial volvulus!
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18. Gastric Volvulus!
“Organoaxial volvulus” Case courtesy of Dr David Cuete, Radiopaedia.org!
“Mesenteroaxial volvulus” Case courtesy of Dr Maxime St-Amant, Radiopaedia.org!

19. Superior Mesenteric "
Artery Syndrome!
Dilatation of 1
st
and 2
nd
part of
duodenum with abrupt
narrowing at 3
rd
portion!
Relieved by changing position!
Aorta-SMA distance <8-10
mm !
Aortomesenteric angle <22
degrees!
(compression of LRV – renal
vein thrombosis,
pneumatosis, PVG, AAA)!
Narrow aortomesenteric angle and
compression at 3
rd
portion of duodenum!

20. Small Bowel Obstruction (SBO)!
Dilated small bowel proximal to the site of obstruction
with distal decompression!

21. Radiography!
Diagnostic in 50-60% !
!Non-diagnostic or
misleading in 40%!
Poor predictor of!
!Location !
!Cause !
!Complications!
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Dilated small bowel loops with relative
absence of colonic gas!

22. Radiography!
Dilated small bowel >3 cm!
Paucity of colonic gas!
Air fluid levels!
!Multiple!
!Differential!
!Longer than 2.5 cm!
String of beads sign!
Multiple air fluid levels in dilated small
bowel loops!

23. CT!
Quick and accurate!
No need for luminal
contrast!
Bowel wall assessment!
Extraluminal abnormalities!
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Diffuse, fluid-filled, dilated loops !
of small bowel!
Free fluid!

24. CT: Indications!
Non-diagnostic radiography but clinical suspicion!
Virgin abdomen!
History of abdominal malignancy!
Suspected complications!

25. Indications for CT in SBO:"
Non-diagnostic Radiography!
SBO due to gallstone obstruction!
Normal bowel gas pattern despite SBO
shown on CT because of fluid-filled
small bowel loops!

26. Indications for CT in SBO:"
Virgin Abdomen!
Known diseases!
!Metastasis (54%)!
!Crohn disease (46%)!
No known diseases!
!Adhesions (75%)!
!Metastasis (10%)!
!Rare: sclerosing encapsulating peritonitis, Meckel
diverticulum, gallstone ileus!
Beardsley'C,'et'al.'Am'J'Surg'2014''

27. Indications for CT in SBO:"
History of Abdominal Malignancy!
Spread/extent of tumor around bowel!
Pre-operative planning for bypass/debulking procedures!

28. Transition Point!
Dilated loops change in caliber to decompressed loops!
Trace rectum ! colon ! small bowel!
Small bowel feces!
Scroll images on workstation!
(difficult on hardcopy films) !
Multiplanar reformats!

29. Transition Point!
Adhesions inferred when no cause identified !
!Abrupt tapering!
!Beak!
External hernias!
Tumors, esp. metastasis to bowel/peritoneum!
Inflammation/infection, gallstones!
CT accuracy 63-95% for identifying transition point!

30. Transition Point Tells Etiology of
Obstruction!
Cecal cancer! Femoral hernia!
Transition point!
Transition point!

31. Small Bowel Feces Sign!
Gas bubbles and particulate
matter within dilated SB!
Usually just proximal to
transition point!
Secondary to prolonged
stasis! Transition point!

32. Small Bowel Feces Sign!
Suggestive of preserved SB
function!
Negative predictor of
failure of conservative Rx!
Unlikely to be ischemic!
Longer segment, less chance
of getting surgery!
SB feces!

33. Etiology of SBO!
Adhesions !!!50-75%!
Hernias!!!!8-15%!
Malignancies!!10-15% !
Others: Crohn, intussusception, volvulus, trauma,
iatrogenic conditions!

34. Adhesions!
Most common sites = omentum to incision site!
Most problematic adhesions = involving small bowel!
Appendectomy, colorectal surgery and gynecology!
!Most common to produce adhesive obstruction!
Anytime from operation!
!20% <1m !
!20% >10y!
Dayton MT et al. 2012 Curr Probl Surg !

35. External Hernia!
2nd most common cause
of SBO!
Inguinal > femoral!
Umbilical = m/c congenital
hernia!
Incisional and parastomal
= m/c iatrogenic hernia!
Others: spigelian, lumbar,
Richter, Littre!
Umbilical hernia, !
obstructed & strangulated!

36. SBO: Internal Hernia!
Defects in mesentery or
peritoneum!
!Post surgical > cong!
Adhesive bands!
Most common around
duodenum!
Paraduodenal internal hernia, obstructed!

37. Obstructing Tumors!
Adenocarcinoma!
!Irregular, nodular mass!
Carcinoid rarely obstructive!
GIST!
Lymphoma rarely obstructive!
Peritoneal carcinomatosis!
!Ovary, colon, stomach,
pancreas, breast,
endometrium!Small bowel adenocarcinoma, obstructed!
Diagnologic.com!

38. Others!
Intussusception!
Inflammatory bowel!
!TB very common inflammatory cause of SBO,
ileocecal, local nodes with hypodense center!
!Acute Crohn!
!Chronic Crohn!
!Pancreatitis, diverticulitis and appendicitis!
Radiation enteropathy!
Stone and bezoar!

39. Is Emergent Surgery Needed?!
YES IF:!
Strangulation = SBO + Ischemia!
Closed loop obstruction!

40. Closed-loop SBO!
Obstructed at 2 adjacent locations !
Bowel between 2 points more
dilated than upstream to the
proximal obstruction!
Risk of torsion/volvulus!
Hernia and adhesion (usu. Single)!
Roux-en-Y gastric bypass!

41. Closed-loop SBO!
U-, C- or coffee bean!
Radial orientation of
dilated loops!
Beak!
Balloons on a string!
Whirl sign!
!Sensitivity 60%!
!PPV 80%!

42. Ischemia Complicating SBO!
Two mechanisms!
!Inc. pressure in bowel wall!
!Direct occlusion of
mesenteric vessels 2/2
torsion, hernia or tight
adhesion!
Mortality 25% (only 2% for
non-strangulated SBO)!
Need high suspicion!

43. Ischemia Complicating SBO!
Enhancement – hyper ! hypo ! absent!
!Reduced bowel wall enhancement 11x probability of
strangulation!
Wall thickening – nonspecific!
Wall thinning can be 2/2
transmural infarction !
Pneumatosis and
portomesenteric gas !
Millet I, et al. Eur Radiol 2014!

44. Mimics of SBO on AXR!
Ileus!
Mesenteric ischemia!
Obstruction of cecum/
ascending colon (cecum
filled with mass or fluid)!
SMA occlusion!

45. Large Bowel Obstruction (LBO):"
Etiology!
More in elderly!
Malignancy!!60%!
Volvulus!!!15%!
Diverticulitis!10%!
Others: incarcerated hernia, fecal impaction, adhesion!
15-20% of colorectal malignancy present with LBO !

46. Radiography!
Marked colonic dilatation
with disproportionate
distension of cecum
(>10 cm)!
Competent IC valve!
!Functional closed loop!
!Risk of perforation!
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Colonic dilatation to the sigmoid
colon due to distal LBO!

47. Radiography!
Incompetent IC valve!
!Dilated SB and colon!
!Cecum dilated v. non-
dilated!
Difficult Dx on AXR!
!Poor sensitivity,
specificity and
interobserver
agreement!
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Colonic and small bowel dilatation
to the splenic flexure colon due to
distal LBO!
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48. Colon Cancer!
CT sensitivity and specificity 90%!
!Imaging of choice = CT!
60% of LBO!
Mostly adenocarcinoma!
Mass, involvement of adjacent
structures, lymphadenopathy,
intraperitoneal metastasis!
Cancer of the splenic flexure colon!

49. Extrinsic Neoplasm!
Direct invasion!
Intraperitoneal seeding!
Hematogenous metastasis!
Lymphatic extension!

50. Sigmoid Volvulus!
Twist around sigmoid mesocolon!
Massive distension!
Lack of haustration!
Coffee bean shaped!
!classic- Rt dome!
Central stripe!

51. Sigmoid Volvulus!
Diagrams from surgeonsblog.blogspot.com and pmj.bmj.com!
Beak sign!

52. Cecal Volvulus!
Dilated cecum!
Dilated cecum!
Beak sign!

53. Volvulus: CT?!
Classic picture!
Colon dilatation alone!
!LBO!
!Toxic megacolon!
!Pseudo-obstruction!
Colon + SB dilatation!
!LBO!
!Ileus !
CT!
Rx!
CT!

54. Mimics of LBO!
Toxic megacolon!
!Clinical toxicity!
Colonic pseudo-obstruction!
!CT often needed to
exclude a mass!
Diffuse colonic dilatation. CT confirmed
no evidence of obstruction!

55. Summary!
Investigative questions: !
!Obstruction present? Where? Cause? Surgery?!
Radiography still has a limited role in bowel obstruction!
CT is the mainstay imaging: !
!Quick and safe!
!No luminal contrast!
!Confirm obstruction, site, etiology, surgical need!
!Extraluminal abnormalities!