The document provides a comprehensive overview of intestinal obstruction, detailing its types, clinical features, and diagnostic approaches including imaging techniques like CT and ultrasound. It discusses the causes of both small bowel and large bowel obstructions, highlighting intrinsic and extrinsic factors, as well as differentiating simple from complicated obstructions. Additionally, it emphasizes the importance of identifying the transition point and includes various imaging findings associated with specific causes, like Crohn's disease, neoplasia, and adhesions.

1. Approach
to intestinal
obstruction
MODERATOR: DR UMAMAHESHWARI MAM
PRESENTER : DR VASANTH KUMAR L

2. INTESTINAL
OBSTRUCTION
A mechanical or functional obstruction of the
intestines, preventing the normal transit of the
products of digestion.

3. Clinical
feature
pain: colicky in nature & usually the first symptom.
abdominal distention: more obvious in low
intestinal obstruction &large bowel obstruction but
less in high intestinal obstruction.
absolute constipation-failure to pass feces & flatus.
vomiting: early in high obstruction but late or even
absent in low obstruction.
O/E:
-dehydrated if large amount of vomiting had
occurred.
-tachycardia.
-raise in temperature suggest strangulation.

4. Small bowel
obstruction
Aim of imaging is to find:
 Is the small bowel obstructed?
 How severe is the obstruction?
 where is it located?
 what is its cause?
 strangulation present?

6. Abdominal radiograph
Supine or prone
1. Dilated gas or fluid-filled small
bowel (>3 cm)
2. Dilated stomach
3. Small bowel dilated out of
proportion to colon
4. Stretch sign
5. Absence of rectal gas
6. Gasless abdomen
7. Pseudotumor sign
Upright or left lateral decubitus
1. Multiple air fluid levels
2. Air fluid levels longer than 2.5 cm
3. Air fluid levels in same loop of small bowel
of unequal heights
4. String of beads sign

7. supine upright

10. String of
pearls sign

11. enteroclysis

12. Sonography
Peristalsis of the dilated segment is increased, as
shown by the to-and-fro or whirling motion of the
bowel contents
Level of the obstruction is determined by means of
the location of the bowel loops and the pattern of
the valvulae conniventes.
Cause of the SBO may be determined by examining
the area of transition from the dilated to normal
bowel
The severity of the obstruction can also be assessed.
The presence of free fluid between dilated small
bowel loops, aperistalsis, and wall thickening (>3
mm) in a fluid-filled distended bowel segment
suggests bowel ischaemia/perforation.

13. USG

14. Findings at
Multidetector
CT
CT criteria for SBO are the presence of dilated small
bowel loops (diameter >2.5 cm from outer wall to
outer wall) proximally to normal-caliber or collapsed
loops distally

15. Severity of obstruction
• A low-grade partial SBO is considered present when there is
sufficient flow of contrast material through the point of
obstruction
•High-grade partial SBO is diagnosed when there is some
stasis and delay in the passage of the contrast medium.
•Can be also determined by the degree of distal collapse,
proximal bowel dilatation, and the presence of the “small bowel
feces” sign.
•In a high-grade obstruction, there is a 50% difference in caliber
between the proximal dilated bowel and the distal collapsed
bowel.

17. Small bowel
feces sign

18. Transition
Point
This approach should begin in a retrograde fashion by
starting at the rectum and proceeding proximally toward
the cecum, ileum, and jejunum. If the transition point is
located proximally (jejunum or duodenum), the position
should be confirmed by using an antegrade approach,
starting at the stomach.
The transition point is determined by identifying a
caliber change between the dilated proximal and collapsed
distal small bowel loops .

19. Cause of the Obstruction
A rule of thumb never to forget is that the answer is almost always in the transition point.
 Most intrinsic bowel lesions are seen at the transition point and manifest as localized mural
thickening.
 Most extrinsic causes are seen adjacent to the transition point and usually have associated
extraintestinal manifestations.
Most intraluminal causes manifest as endoluminal “foreign objects” with imaging characteristics
different from those of the remaining enteric content.

21. Intrinsic Causes of SBO

22. Crohn Disease
SBO in Crohn disease can be a manifestation of three clinical situations.
It can result from the acute presentation of the disease characterized by bowel luminal
narrowing secondary to the transmural acute inflammatory process.
 It can be a manifestation of long-standing disease, which usually results in cicatricial stenosis
of affected segments.
Finally, it can be secondary to adhesions, incisional hernias, exacerbation of the inflammatory
condition, or postoperative strictures in patients who have undergone previous intestinal surgery

24. Neoplasia
Small bowel involvement by metastatic cancer is more common than involvement by primary
neoplasms
Intrinsic small bowel neoplasms constitute less than 2% of gastrointestinal malignancies.
When a small bowel adenocarcinoma manifests as SBO, it is usually at an advanced state and
shows pronounced, asymmetric, and irregular mural thickening at the transition point.
Metastasis more frequent in the form of peritoneal carcinomatosis, which is suggested when
extrinsic serosal disease involving the small bowel wall is seen in association with a transition
point.

26. Intussusception
Accounting for less than 5% of SBO.
Only lead-point intussusceptions secondary to neoplasms, adhesions, or foreign
bodies are associated with SBO. Transient intussusceptions are not associated with
this condition.
At CT, the presence of a bowel-within-bowel configuration with or without
mesenteric fat and mesenteric vessels is pathognomonic for int.ussusception,
A leading mass as the cause of the intussusception can be identified.

28. Radiation Enteritis
Radiation enteritis causes obstruction in the late phase 1 year after radiation therapy,
usually to the pelvis.
SBO primarily by producing adhesive and fibrotic changes in the mesentery.
changes produced within the bowel include luminal narrowing and dysmotility
induced by radiation serositis.
CT shows narrowing of the lumen secondary to mural thickening, an angular bowel
wall due to adhesions, and retraction of the mesentery .

30. Hematomas
Intramural small bowel hematoma may occur secondary to anticoagulant therapy,
iatrogenic intervention, or trauma. usually due to luminal narrowing..
nonenhanced CT should be performed, as it will show a spontaneously
hyperattenuating clot

32. Vascular Causes
Occlusion or stenosis of the mesenteric arterial or venous vascular supply to the
bowel usually produces bowel ischemia, which subsequently causes wall thickening,
resulting in SBO.
CT shows thrombosis or occlusion of the mesenteric vessels and also thickening of
the bowel wall in the affected loops with noncircumferential or asymmetric wall
enhancement.
In advanced cases, a bowel infarct may be present, which manifests at CT as
pneumatosis and air in the portal venous system

35. Extrinsic Causes of SBO

36. Adhesions
main cause of SBO, ranging from 50%–80% of all cases.
Mainly post-operative, but can also occur secondary to peritonitis.
Diagnosis: abrupt change in the caliber of the bowel is seen without any
associated mass lesion, significant inflammation, or bowel wall thickening at the
transition point.
Combined with history of abdominal surgery and associated kinking and tethering
of the adjacent nonobstructed bowel usually suggests the diagnosis.

38. Hernias
second most common cause of SBO, responsible for 10% of cases.
s. They are broadly classified as external or internal.
 An external hernia results from a defect in the abdominal and pelvic wall at sites
of congenital weakness or previous surgery .
The less common internal hernia occurs when there is protrusion of the viscera
through the peritoneum or mesentery and into a compartment within the abdominal
cavity.

40. Endometriosis
Endometrial implants are typically located on the antimesenteric edge of the bowel,
and their appearance is variable.
The typical appearance of intestinal endometriosis is a solid nodule with positive
enhancement contiguous with or penetrating the thickened bowel wall.
When the endometriotic lesion infiltrates the submucosa, it typically appears as a
hypoattenuating layer between the muscularis and the mucosa

42. Intraluminal Causes of SBO

43. Gallstone Ileus
Gallstone ileus is a rare complication of recurrent cholecystitis, caused by migration of a large
gallstone through a biliary intestinal fistula with subsequent impaction in the small bowel.
 CT findings are pathognomonic, corresponding to the radiographic triad of pneumobilia, ectopic
gallstone, and SBO

45. Distal Intestinal Obstruction Syndrome.
occurs in older children and adults with cystic fibrosis.
The obstruction is secondary to impaction of thick stool, which is probably related to
inadequately controlled intestinal absorption secondary to pancreatic insufficiency.
At CT, the findings consist of SBO with feculent filling defects in the small bowel.

47. SBO Simple or Complicated
SBO can be divided into two types: simple obstructions and closed-loop obstructions.
Simple obstruction of the bowel is considered when the bowel is occluded at one or several
points along its course
Closed-loop obstructions are diagnosed when a bowel loop of variable length is occluded at two
adjacent points along its course.

48. closed-loop obstruction
CT: Axial scans reveal a characteristic fixed radial distribution of several dilated, usually fluid-filled
bowel loops with stretched and prominent mesenteric vessels converging toward the point of
torsion.
The configuration can be U-shaped or C-shaped, depending on the orientation of the closed loop.
 narrow pedicle can be formed, leading to torsion of the loops and producing a small bowel
volvulus.
At CT, a “beak sign” is seen at the site of the torsion as a fusiform tapering, and occasionally a
“whirl sign” can be seen, reflecting rotation of the bowel loops around the fixed point of
obstruction

50. Strangulation
Defined as a closed-loop obstruction associated with intestinal ischemia.
Specific finding: lack of wall enhancement. asymmetric enhancement or even delayed
enhancement may also be found. Localized fluid and hemorrhage in the mesentery can also be
seen.
Non specific: thickening and increased attenuation of the affected bowel wall, a halo or “target
sign,” pneumatosis intestinalis, and gas in the portal vein.

52. Large bowel obstruction
LBO is four to five times less frequent than SBO
emergency surgery or colonoscopy is usually required to relieve the obstruction
Colonic obstruction is most often seen in elderly individuals

53. Large bowel
obstruction-
CAUSES
• colorectal carcinoma (most common, 50-60%)
• pelvic tumours; direct spread or metastatic disease
Malignancy
Colonic diverticulitis
• caecal volvulus (1-3%)
• sigmoid volvulus (3-8%)
Volvulus
Ischaemic stricture
Faecal impaction (most common cause in
debilitated elderly)

54. Clinical presentation
The signs and symptoms of LBO are often insidious in contrast to the abrupt onset of symptoms
seen in most SBOs;
Presentation is typically with abdominal pain, distension and failure of passage of flatus and stool
 Eventually signs of peritonism, sepsis and shock develop, when perforation occurs.
LBO caused by obstruction in the left colon manifests earlier than that caused by obstruction in
the right colon
◦ because the lumen of the sigmoid and descending colon is smaller
◦ and the stool is more inspissated in the distal colon

55. Radiography
Normal colonic caliber ranges from 3 to 8 cm, with the largest diameter in the cecum;
colon is dilated when it is greater than 6 cm and the cecum when larger than 9 cm in
diameter.
Air-fluid levels are suggest that the cause is more acute - colonic fluid has not been present
long enough to be absorbed
In advanced cases one may see the stigmata of an ischemic colon
small bowel dilatation, depends on
◦ duration of obstruction
◦ Incompetence of IC valve

57. CT
CT is the imaging modality of choice for the diagnosis of the cause of LBO
CT can be used to diagnose intraluminal,mural, and extramural causes of LBO
detection of inflammation and bowel ischemia

58. Colorectal carcinoma
Common sites-sigmoid colon and splenic flexure.
The most common site of perforation[3%–8%] in LBO is not at the site of the tumor but
at the cecum
Barium enema
seen as filling defects
appear as exophytic or sessile masses
may be circumferential -apple core sign
CT
Asymmetric and short-segment colonic wall thickening
or an enhancing soft-tissue mass centered in the colon that narrows the colonic lumen
Pericolonic lymph nodes

60. Acute colonic volvulus
If the twist is greater than 360°, the volvulus is unlikely to
resolve without intervention.
Sigmoid volvulus is three to four times more common than
cecal volvulus
volvulus of the transverse colon and splenic flexure is very
rare

61. Sigmoid volvulus

63. Frimann dahl's sign
“northern exposure” sign

65. Caecal volvulus

66. Diverticulitis
A complication of diverticulosis with elderly patients being most at risk
Can present with LBO due to bowel wall edema and pericolonic inflammation
Obstruction occurs in the setting of multiple episodes of diverticulitis, which
causes narrowing and stricture formation

67. Imaging features
CT is the modality of choice for the diagnosis and staging of diverticulitis.
 Appearances include: pericolic stranding, often disproportionately prominent
compared to the amount of bowel wall thickening
segmental thickening of the bowel wall with hyperemia, which is typically longer
segment (>10 cm) than malignant lesions
enhancement of the colonic wall
◦ usually has inner and outer high-attenuation layers, with a thick middle layer of
low attenuation

68. diverticular perforation
◦ extravasation of air and fluid into the pelvis and peritoneal cavity
abscess formation (seen in up to 30% of cases)
◦ may contain fluid, gas or both
fistula formation
◦ gas in the bladder
◦ direct visualisation of fistulous tract

70. Colocolonic intussusception.

71. LBO due to hernia

72. LBO due to Crohn colitis

73. Adynamic obstruction
Paralytic ileus
- absence of neural activity
Pseudo obstruction
- imbalance of neural activity
-sympathetic overactivity
-parasympathetic suppression

74. Paralytic ileus
Causes
-post operative
-abdominal sepsis
-metabolic;uremia and hypokalemia
-CVA/spinal injury
characterized by diffuse small- and large bowel dilatation without a transition
point

76. Acute colonic pseudo obstruction (ACPO /Ogilvie
syndrome)
secondary to interruption of sympathetic innervation of the colon
ACPO is most common in male patients over 60 years of age, and most are already
hospitalized with a severe illness
Is a disorder of bowel which symptomatically, clinically and radiologically may mimic
intestinal obstruction.

77. Pseudo-obstruction can present with a sudden painless enlargement of
the proximal colon accompanied by distension.
Bowel sounds are normal or high-pitched, but should not be absent.
Despite the absence of mechanical obstruction, patients can nonetheless
go on to bowel necrosis and perforation (especially if dilatation is severe)
which in turn can go on to become generalized peritonitis.

78. It may be acute and self-limiting and associated with inflammatory, infectious,
traumatic, metabolic conditions or certain drugs
A large proportion of patients - idiopathic intestinal pseudo-obstruction
Large quantity of bowel gas is usually present and there may be gastric, small-
or large-bowel distension with associated fluid levels just as great as in true
obstruction.
Imaging can be performed to exclude true organic obstruction - without
evidence of an abrupt transition point or mechanically obstructing
lesion.
It is important to note, however, that a gradual transition point is
frequently present, usually at or near the splenic flexure

79. Summary

80. REFERENCES
Review of Small-Bowel Obstruction: The Diagnosis and When to
Worry-338 radiology.rsna.org, Radiology: Volume 275: Number 2—May
2015
Small bowel obstruction:what to look for-
pubs.rsna.org/doi/full/10.1148/rg.292085514
Large-Bowel Obstruction in the Adult:Classic Radiographic and CT
Findings, Etiology, and Mimics-RSNA,Radiology: Volume 275:
Number3—june 2015
Textbook of gastrointestinal radiology – by GORE and LEVINE