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 %

6. Diagnosis of SBO
Dilated proximal bowel with collapsed distal bowel separated by a transition zone is diagnostic
Small bowel caliber > 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

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

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

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

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

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, crohn’s disease and radiation enteropathy
Rare causes include intramural hematoma and eosinophilic gastroenteritis

22. Intussusception Relatively rare cause of adult SBO (5%)
Unlike infants, 80% of cases caused by underlying neoplasm, adhesion, inverted Meckel’s, 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

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

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

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 %

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