This document discusses imaging techniques for evaluating bowel obstruction, including radiography and CT. It covers the clinical presentation, imaging features, and causes of gastric, small bowel, and large bowel obstruction. Key points include using CT to identify the location and cause of obstruction, assess for complications like strangulation or closed loop obstruction that may require emergent surgery. The most common causes of small bowel obstruction are adhesions, hernias, and malignancies, while large bowel obstruction is usually due to malignancy, volvulus, or diverticulitis in older patients.

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
*
*

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 1st and 2nd part of
duodenum with abrupt
narrowing at 3rd 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 3rd 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
*
*
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
*
*
*
*
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
*
*
*
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
*
*
Colonic and small bowel dilatation
to the splenic flexure colon due to
distal LBO
*

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