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Learning Radiology > Ch.14 - Recognizing Bowel Obstruction and Ileus > Flashcards

Ch.14 - Recognizing Bowel Obstruction and Ileus Flashcards

1
Q

2 Varieties of functional ileus:

A
  1. Localized ileus (sentinel loops).

2. Generalized adynamic ileus.

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2
Q

2 Varieties of mechanical obstruction:

A
  1. SBO.

2. LBO.

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3
Q

Key findings in a localized ileus (sentinel loops):

A

2-3 dilated loops of small bowel with air in the rectosigmoid and an underlying irritative process that frequently is adjacent to the dilated loops.

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4
Q

Some causes of sentinel loops include:

A
  1. RUQ –> Cholecystitis.
  2. LUQ –> Pancreatitis.
  3. RLQ –> Appendicitis.
    All can be readily identified using US or CT.
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5
Q

Key findings in a generalized adynamic ileus are:

A
  1. Dilated loops of large and small bowel with gas in the rectosigmoid.
  2. Long air-fluid levels.
  3. Post-op patients develop generalized adynamic ileus.
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6
Q

Key imaging findings in a MECHANICAL small bowel obstruction:

A
  1. Disproportionately dilated and fluid-filled loops of small bowel with little or no gas in the recto-sigmoid.
  2. CT is best at identifying the cause and site of obstruction or its complications.
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7
Q

MCC of SBO:

A

Adhesions.

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8
Q

A closed-loop obstruction is one in which:

A

2 points of the bowel are obstructed in the same location producing the closed-loop.
If small bowel –> High risk of strangulation.
If large bowel –> It is called VOLVULUS.

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9
Q

Key imaging findings in mechanical LBO include:

A
  1. Dilatation of the colon to the point of the obstruction.
  2. Absence of gas in the rectum.
  3. No dilation of the small bowel as long as the ileocecal valve remains COMPETENT.
    CT will often demonstrate the cause of the obstruction.
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10
Q

Ogilvie syndrome:

A

Loss of peristalsis resulting in sometimes massive dilatation of the entire colon resembling a large bowel obstruction but without a demonstrable point of obstruction.
–> Can be confused for a generalized adynamic ileus.

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11
Q

Abnormal gas patterns - Air in Rectosigmoid:

A 
Normal --> Yes.
Localized ileus --> Yes.
Generalized ileus --> Yes.
SBO --> No.
LBO --> No.
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12
Q

Abnormal gas patterns - Air in small bowel:

A

Normal –> Yes - 1-2 loops.
Localized ileus –> Yes - 2-3 distended loops.
Generalized ileus –> Yes - Multiple distended loops.
SBO –> Yes - Multiple dilated loops.
LBO –> No - UNLESS incompetent ileocecal valve.

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13
Q

Abnormal gas patterns - Air in large bowel:

A 
Normal --> Yes - Rectosigmoid.
Localized ileus --> Yes - Rectosigmoid.
Generalized ileus --> Yes - Distended.
SBO --> No.
LBO --> Yes - Dilated.
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14
Q

Causes of localized ileus:

A 
RUQ - Cholecystitis.
LUQ --> Pancreatitis.
RLQ --> Appendicitis.
LLQ --> Diverticulitis.
Midabdomen --> Ulecer or kidney/ureteral calculus.
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15
Q

Etiology of generalized adynamic ileus:

A
  1. Post-op –> Usually abdominal surgery.

2. Electrolyte imbalance –> Esp. diabetics in DKA.

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16
Q

Etiology of SBO:

A
  1. Adhesions (MCC).
  2. Malignancy.
  3. Hernia.
  4. Gallstone ileus.
  5. Intussusception.
  6. IBD.
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17
Q

Etiology of LBO:

A
  1. Tumor (MCC).
  2. Hernia.
  3. Volvulus.
  4. Diverticulitis.
  5. Intussusception.
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18
Q

3 key questions in assessing the bowel gas pattern on imaging studies:

A
  1. Is air present in the rectum or sigmoid?
  2. Are there dilated loops of small bowel?
  3. Are there dilated loops of large bowel?
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19
Q

Abnormal gas patterns - 2 Main categories:

A
  1. Functional ileus.

2. Mechanical obstruction.

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20
Q

Functional ileus - 2 subcategories:

A
  1. Localized ileus (sentinel loops).

2. Generalized adynamic ileus.

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21
Q

Mechanical obstruction - 2 subcategories:

A
  1. Small bowel obstruction.

2. Large bowel obstruction.

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22
Q

Localized ileus is also called?

A

Sentinel loops affects only one or two loops - Usually small bowel.

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23
Q

Generalized adynamic ileus affects?

A

All loops of large and small bowel + frequently the stomach.

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24
Q

Prolonged obstruction with persistently elevated intraluminal pressures can lead to …?

A

Vascular compromise + Necrosis + Perforation in the affected loop of bowel.

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25
Q

Causes of a localized ileus - Dilated loops in RUQ:

A

Cholecystitis.

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26
Q

Causes of localized ileus - Dilated loops in LUQ:

A

Pancreatitis.

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27
Q

Causes of localized ileus - Dilated loops in RLQ:

A

Appendicitis.

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28
Q

Causes of localized ileus - Dilated loops in LLQ:

A

Diverticulitis.

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29
Q

Causes of localized ileus - Dilated loops in midabdomen?

A

Ulcer or kidney/ureteral calculus.

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30
Q

Key imaging features of localized ileus - Conventional radiographs?

A

One or two PERSISTENTLY DILATED loops of small bowel.

31
Q

What does PERSISTENTLY dilated loops mean?

A

Same loops remain dilated on multiple views of the abdomen –> Supine, prone, upright abdomen OR on serial studies done over the course of time.

32
Q

What does persistently DILATED loops mean?

A

Dilated means the small bowel loops are >2.5cm.
Small bowel loops involved in a functional ileus usually do NOT dilate as greatly as those which are mechanically obstructed.

33
Q

Localized ileus - The sentinel loop may be …?

A

LARGE BOWEL rather than small bowel –> In the CECUM, with diseases such as appendicitis.

34
Q

There are frequently … seen in sentinel loops.

A

air-fluid levels.

35
Q

There is usually … in the rectosigmoid in a localized ileus.

A

GAS

36
Q

Pitfall of a localized ileus:

A

Differentiating a localized ileus from an early SBO –> A localized ileus may resemble an EARLY mechanical SBO - There may be a few dilated loops of small bowel with air in the COLON seen in both.

37
Q

What does EARLY mean?

A

The patient has had symptoms for a day or two.

38
Q

Localized ileus pitfall - Solution:

A

A combination of clinical and lab findings + CT scan of the abdomen that demonstrates the underlying pathology should differentiate localized ileus from SBO.

39
Q

A generalized dynamic ileus is almost always the result of …?

A

Abdominal + Pelvic surgery.

40
Q

Causes of a generalized adynamic ileus:

A
  1. Post-op –> Usually abdominal surgery.

2. Electrolyte imbalance –> Especially diabetics in DKA.

41
Q

Key imaging features of a generalized adynamic ileus:

A
  1. Entire bowel is usually air-containing and dilated, both large and small bowel.
  2. The stomach may be dilated as well.
  3. Production of many air-fluid levels in the bowel.
  4. There should be gas seen in the rectum or sigmoid.
  5. Bowel sounds are frequently absent or hypoactive.
42
Q

Pitfall of generalized adynamic ileus:

A

Many patients who have EITHER INTESTINAL PSEUDO-obstruction OR aerophagia can be mistakenly identified as having a generalized ileus on abdominal radiographs.

43
Q

Causes of mechanical SBO:

A
  1. Adhesions.
  2. Malignancy.
  3. Hernia.
  4. Gallstone ileus.
  5. Intussusception.
  6. IBD.
44
Q

Key imaging features of mechanical small bowel obstruction:

A
  1. Multiple dilated loops of small bowel demonstrated proximal to the point of the obstruction >2.5cm.
  2. As they begin to dilate, loops STACK UP ON one another forming a step-ladder appearance.
  3. Upright or decubitus –> Numerous air-fluid levels present in the small bowel proximal to the obstruction.
  4. If enough time has elapsed to decompress –> Little or no gas found in the colon, especially the rectum.
45
Q

Generally speaking, the more proximal the small bowel obstruction (proximal jejunum) …?

A

The more FEWER the dilated loops.

46
Q

Pitfall of partial SBO:

A

DDx from a functional localized adynamic ileus.

47
Q

What is the most sensitive study for diagnosing the site + cause of a mechanical SBO?

A

CT.

48
Q

CT scan for mechanical SBO can be utilized with or without contrast?

A

With contrast, utilizing the fluid already present in the bowel as contrast.

49
Q

Orally administrated contrast may help in identifying …?

A
  1. Dilated loops of bowel.
  2. Finding the transposition point between the proximal dilated bowel and the distal collapsed bowel.
  3. Oral contrast may also obscure important findings displayed by the use of IV contrast.
50
Q

IV contrast in CT for mechanical SBO is used for?

A

Detecting complications of bowel obstruction such as ischemia + strangulation.

51
Q

6 CT findings of a SBO:

A
  1. Fluid-filled + dilated loops of small bowel (>2.5cm in diameter) proximal to the point of obstruction.
  2. Identification of the transition point.
  3. Collapsed small bowel or colon distal to the point of obstruction.
  4. Small bowel feces sign.
  5. Closed-loop obstruction.
  6. Strangulation.
52
Q

In the absence of a transition point …?

A

Adhesions = Cause.

53
Q

Small-bowel feces sign?

A

Proximal to the transition point of a small bowel obstruction, INTESTINAL DEBRIS and fluid may accumulate producing the appearance of fecal material in the small bowel.

54
Q

Closed-loop obstruction?

A

Occurs when 2 points of the same loop of bowel are obstructed at a single location.
–> Dilated U or C shaped loop.

55
Q

Most closed-loop obstructions are caused by?

A

Adhesions.

56
Q

In the small bowel, a closed-loop obstruction carries a higher risk of …?

A

Strangulation.

57
Q

In the colon, a closed-loop obstruction is called …?

A

VOLVULUS.

58
Q

Strangulation of small bowel?

A
  1. Circumferential thickening of the wall of the bowel often with absence of normal wall enhancement following IV contrast.
  2. Associated edema of the mesentery.
  3. Ascites.
59
Q

Air-fluid levels in LBO?

A

The large bowel normally reabsorbs water, so there are usually FEW or NO air-fluid levels seen in the obstructed colon.

60
Q

In mechanical LBO - Air in the rectum?

A

Usually little or no air.

61
Q

Causes of mechanical LBO:

A
  1. Tumor.
  2. Hernia.
  3. Volvulus.
  4. Diverticulitis.
  5. Intussusception.
62
Q

A hernia may be visible on conventional radiographs if …?

A

Air is seen over the obturator foramen.

63
Q

Colonic intussusception usually occurs …?

A

Because of a tumor acting as a lead point.

64
Q

Why is it sometimes possible to identify the site of obstruction as the last air-containing segment of the colon in LBO?

A

Because there are a limited number of large bowel loops, they tend not to overlap each other (as do the loops of small bowel).

65
Q

In LBO - Regardless of the point of obstruction?

A

The cecum is often the most dilated segment of the colon.

When the cecum reaches a diameter above 12-15cm, there is danger of cecal rupture.

66
Q

In LBO, the small bowel is NOT dilated unless …?

A

The ileocecal valve is INCOMPETENT.

67
Q

LBO pitfall?

A

LBO can mimic a SBO –> Incompetent ileocecal valve –> Gas from the dilated large bowel decompresses backward into the small bowel.

68
Q

LBO pitfall - Solution:

A

Ask for a CT scan of the abdomen –> Show site of obstruction in the colon rather than the small bowel.

69
Q

Barium is NOT administered by mouth in a patient with suspected LBO, because …?

A

Water will be absorbed from the barium when it reaches the obstructed colon –> Increasing viscosity of the barium and possibly leading to IMPACTION.

70
Q

Recognizing a LBO on CT - Why is CT obtained?

A
  1. Identify the cause of obstruction.
  2. Assess for free intraperitoneal air.
  3. Identify associated lesions –> Metastases to liver or lymph nodes.
71
Q

Sigmoid volvulus tends to occur in …?

A

Older men.

72
Q

The appearance of the dilated sigmoid in sigmoid volvulus has been likened to a …?

A

Coffee bean.

73
Q

Sigmoid volvulus - Diagnosis + Treatment:

A

A contrast enema –> Beak sign –> Hydrostatic pressure of the enema can sometimes decompress the volvulus.

74
Q

Abnormal bowel gas patterns can be divided into two main groups:

A
  1. Functional ileus.

2. Mechanical obstruction.

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