CT Findings in Small Bowel Obstruction

1
CT Findings in Small Bowel Obstruction

• Faisal Budhani
• Diagnostic Radiology
• PGY-3 Resident

2
What is Important On-Call ?

• Must answer the following questions
• Bowel obstruction Y or N
• Complete vs Partial Obstruction
• Location of Transition Point
• Closed Loop or Internal Hernia
• Complications perforation, strangulation and
  ischemia

3
Outline

• Introduction
• Role of CT in SBO
• Diagnosis of SBO
• Level of Obstruction
• Degree of Obstruction
• Causes of SBO
• Intrinsic
• Extrinsic
• Intussusception
• Intraluminal
• Closed-loop
• Strangulation following SBO
• Management of SBO
• What is Important On-Call ?

4
Introduction

• Relatively common accounting for 20 of all acute
  surgical admissions
• Diagnosis based on history, physical signs and
  radiographic findings
• Site and cause of SBO and presence of
  strangulation must be determined to ensure
  appropriate treatment
• Conventional radiology is first imaging modality
  with an accuracy of diagnosing presence of SBO
  46-80

5
Role of CT in SBO

• CT able to determine presence, level, degree and
  cause of SBO and identify associated
  strangulation
• CT able to depict pathology in bowel wall,
  mesentery, mesenteric vessels and peritoneal
  cavity
• Sensitivity of CT in detecting high grade SBO is
  78-100

6
Diagnosis of SBO

• Dilated proximal bowel with collapsed distal
  bowel separated by a transition zone is
  diagnostic
• Small bowel caliber gt 2.5 - 3 cm is considered
  dilated

7
Diagnosis of SBO

• Small bowel feces sign gas bubbles mixed with
  particulate matter in small bowel loops proximal
  to site of obstruction

8
Level of Obstruction

• Cannot be determined by intra-abdominal location
  of transition zone
• Dilated bowel loops migrate from their expected
  anatomic positions
• Relative length of dilated versus collapsed bowel
  must be considered

9
(No Transcript)
10
Degree of Obstruction

• Complete vs. Partial SBO based on degree of
  collapse and amount of residual contents distal
  to obstruction
• Passage of oral contrast distal to the transition
  zone always indicates partial obstruction

11
(No Transcript)
12
(No Transcript)
13
Adhesions

• Responsible for more than half of all SBO
• Etiology
• Surgery ? 80
• Peritonitis ? 15
• Other (congenital, idiopathic) ? 5
• Adhesions may be single, multiple or extensive
• Not seen on CT? other causes of bowel obstruction
  must be ruled out

14
(No Transcript)
15
Hernia

• 2nd most common cause of SBO (10)
• External Hernia
• Prolapsed of viscera through defect in
  abdominal/pelvic wall
• CT useful in detecting hernias in unsuspecting
  sites and obese patients
• Internal Hernia
• herniation of bowel loops through developmentally
  or surgically created defect in peritoneum,
  omentum or mesentery
• Less common than external hernias

16
(No Transcript)
17
(No Transcript)
18
Other Extrinsic Causes

• Variety of neoplastic, inflammatory or vascular
  lesions can cause SBO through direct compression
  or desmoplastic reaction
• Most common extrinsic is peritoneal
  carcinomatosis
• Multiple transitions zones of nodular wall
  thickening
• Mycobacterial infections, carcinoid and desmoid
  tumors have similar imaging findings

19
(No Transcript)
20
Intrinsic Lesions

• Neoplasms, hematomas, inflammatory and vascular
  lesions may cause bowel wall thickening leading
  to SBO
• Intrinsic lesions are located at the transition
  zone
• Most common causes include adenocarcinoma,
  crohns disease and radiation enteropathy
• Rare causes include intramural hematoma and
  eosinophilic gastroenteritis

21
(No Transcript)
22
Intussusception

• Relatively rare cause of adult SBO (5)
• Unlike infants, 80 of cases caused by underlying
  neoplasm, adhesion, inverted Meckels, foreign
  body or previous surgery ? serves as lead point
• Collapsed proximal segment (intussusceptum) with
  its mesenteric fat and vessels within the wall of
  the distal bowel (intussuscipiens) ?
  characteristic target sign on axial images

23
(No Transcript)
24
Intraluminal Lesions

• Gallstones, foreign bodies and bezoars may cause
  SBO
• Gallstone ileus
• Triad of ectopic stone, pneumobillia and SBO
• Seen in elderly patients, particularly in women
• If foreign body detected, underlying obstructive
  lesion must be excluded

25
(No Transcript)
26
(No Transcript)
27
Closed Loop Obstruction

• 2 points of bowel obstructed at a single site
• Most often caused by adhesive bands external and
  internal hernias less common
• Tends to involve the mesentery ? prone to
  volvulus
• C-shaped/U-shaped loop of bowel with vessels
  converging towards site of torsion
• 2 adjacent collapsed loops with interposed
  dilated fluid filled bowel

28
(No Transcript)
29
Strangulation

• Mechanical obstruction associated with bowel
  ischemia
• Majority of cases associated with closed-loop
  obstruction
• Wall thickening (halo sign), mesenteric
  hazziness, pneumatosis and portal venous gas
• With IV contrast lack of enhancement, asymmetric
  enhancement or delayed enhancement of bowel wall
• CT detection rate of strangulation is 63-100

30
(No Transcript)
31
Management

• Acute complete SBO ? surgical
• Partial SBO ? conservative
• Follow up imaging recommended (CT or small bowel
  enteroclysis) in indeterminate cases
• Closed loop obstruction in absence of ischemia is
  a surgical emergency as it can progress to
  strangulation
• Risk of strangulation in compete SBO increases
  with time
• Surgery within 36 hrs ? mortality rate 8
• Surgery after 36 hrs ? mortality rate 25
• Exploratory laparotomy recommended in all
  patients with closed loop or signs of ischemia
• If CT findings not in keep with clinical
  presentation, patients must undergo laparotomy

32
What is Important On-Call ?

• Must answer the following questions
• Bowel obstruction Y or N
• Complete vs Partial Obstruction
• Location of Transition Point
• Closed Loop or Internal Hernia
• Complications perforation, strangulation and
  ischemia