RecognizingSBO, LBO and Ileus
Underlined words hyperlink to other slides
© William Herring, MD, FACR
What to ExamineWhen Looking at Plain Films of the Abdomen
Gas pattern
Extraluminal air
Soft tissue masses
Calcifications
What This Module Reviews
This module reviews abnormalities in thegas pattern
Normal Gas Pattern
Stomach
Always
Small Bowel
Two or three loops of non-distended bowel
Normal diameter = 2.5 cm = 1 US quarter
Large Bowel
In rectum or sigmoid – almost always
Gas instomach
Gas in a fewloops ofsmall bowel
Gas inrectum orsigmoid
Normal Gas Pattern
Normal Fluid Levels
Stomach
Always (except supine film)
Small Bowel
Two or three levels possible
Large Bowel
None normally
Erect Abdomen
Alwaysair/fluid levelin stomach
A fewair/fluidlevels insmall bowel
Large vs. Small Bowel
Large Bowel
Peripheral
Haustral markings don't extendfrom wall to wall
Small Bowel
Central
Valvulae extend across lumen
Maximum diameter of 2"
Complete AbdomenObstruction Series
Supine
Prone or lateral rectum
Erect or left decubitus
Chest - erect or supine
Complete AbdomenSupine
Looking for
Scout film for gaspattern
Calcifications
Soft tissue masses
Substitute – none
Complete AbdomenProne
Looking for
Gas in rectum/sigmoid
Gas in ascending anddescending colon
Substitute – lateralrectum
Complete AbdomenErect
Looking for
Free air
Air-fluid levels
Substitute – leftlateral decubitus
Complete AbdomenErect Chest
Looking for
Free air
Pneumonia at bases
Pleural effusions
Substitute – supinechest
Abnormal Gas Patterns
Functional Ileus
Localized (Sentinel Loops)
Generalized adynamic ileus
Mechanical Obstruction
SBO
LBO
Summary of Abnormal Bowel Gas Patterns
One or two persistently dilated loops oflarge or small bowel
Gas in rectum or sigmoid
Localized IleusKey Features
Supine
Prone
Sentinel Loops
Localized Ileus = Sentinel Loops
PancreatitisUlcer
Diverticulitis
Cholecystitis
Appendicitis
UlcerUreteral calculus
Sentinel Loops
Many times the locationof the sentinel loopsindicate the nature ofthe underlying irritativeprocess
Localized IleusPitfalls
May resemble earlymechanical SBO
How to differentiate
Clinical course
Get follow-up
Gas in dilated small bowel and largebowel to rectum
Long air-fluid levels
Only post-op patients get generalizedileus
Generalized IleusKey Features
Generalized Adynamic Ileus
Erect
Supine
Is It An Ileus?
Is the patient immediately post-op?
Are the bowel sounds absent orhypoactive?
If “no,” then it isn’t an ileus
Patients don’t present to the ER with ageneralized adynamic ileus!
Mechanical SBOKey Features
Dilated small bowel
Fighting loops
Little gas in colon, especially rectum
Key: disproportionate dilatation of SB
SBO
Mechanical SBOCauses
Adhesions
Hernia*
Volvulus
Gallstone ileus*
Intussusception
*Cause may be visible on plain film
Mechanical SBOPitfalls
Early SBO mayresemblelocalized ileus -get F/O
Mechanical LBOKey Features
Dilated colon to point of obstruction
Little or no air in rectum/sigmoid
Little or no gas in small bowel, if…
Ileocecal valve remains competent
LBO
Supine
Prone
Mechanical LBOCauses
Tumor
Volvulus
Hernia
Diverticulitis
Intussusception
Mechanical LBOPitfalls
Incompetent ileocecal valve
Large bowel decompresses into smallbowel
May look like SBO
Get BE or follow-up
Carcinoma of Sigmoid – LBO –Decompressed into SB
Supine
Prone
Summary of Findings in Abnormal BowelGas Patterns
Special Cases
What is this?
Answer follows on next slide
Air inbiliarytree
SBO
Gallstone
Gallstone Ileus
Post-op C-sectionAdynamic Ileus
What is this?
The patient hasmidline incision.There is a soft-tissue density inthe pelvis whichrepresents thenon-involuteduterus. All of thedilated large andsmall bowel isdisplaced intothe upperabdomen.
Sigmoid Volvulus
What is this?
There aremarkedly dilatedloops of largebowel. There is aline between 2adjacent loopsof bowel that isoriented like thered line. Thesigmoid colonhas twisted(volvulated) onitself and hascome to lie in theRUQ.
Mesenteric Occlusion
What is this?
The bowelwall ismarkedlythickenedbecausethere ishemorrhageand edema inthe wall frommestericvascularocclusion.
To RecapWhat to Examine
Gas pattern
Extraluminal air
Soft tissue masses
Calcifications
Take Home Points
The best film for the overall gas pattern is thesupine film
The four major abnormal bowel gas patterns are
Localized ileus
Generalized ileus
Mechanical SBO
Mechanical LBO
Identify the Types ofAbnormal Gas Patterns
Answer follows on slide after question
Quiz
What abnormality is represented here?
Focal Ileus
Generalized Ileus
SBO
LBO
Answer follows on next slide
SBO
There are multiple air-containing and dilated loopsof small bowel with little orno gas in the colon. Thefindings are those of amechanical small bowelobstruction. The patient hadundergone prior surgeryand the cause of thisobstruction was adhesionsform the prior surgery.
What abnormality is represented here?
Focal Ileus
Generalized Ileus
SBO
LBO
Answer follows on next slide
LBO
There is a dilated colonto the splenic flexure/Little or no gas is seenin the rectum or in thesmall bowel. Thefindings are those of amechanical large bowelobstruction. The causewas an annularconstricting carcinomaat the splenic flexure.
What abnormality is represented here?
Focal Ileus
Generalized Ileus
SBO
LBO
Answer follows on next slide
Focal Ileus
There are several air-containingand slightly dilated loops ofsmall bowel in the LLQ. Thesewere persistent. The findingsare those of a localized ileus(sentinel loops) and theirlocation would suggestdiverticulitis. The patient hadappendicitis. The sentinel loopsdo not always correspond to thearea of inflammation.
What abnormality is represented here?
Focal Ileus
Generalized Ileus
SBO
LBO
Answer follows on next slide
Generalized Ileus
All of the bowel is dilated.There is air in the rectum.The patient was post-opabdominal surgery and thebowel sounds were absent.This is a generalizedadynamic ileus as is seensometimes after abdominalsurgery.
Congratulations, You Graduate
You knowyourbowel gas