IMAGINGIMAGINGBOWEL BOWEL

OBSTRUCTIONOBSTRUCTIONRichard M. Gore, MDRichard M. Gore, MD

SCBT/MR Summer PracticumSCBT/MR Summer PracticumWilliamsburg, VirginiaWilliamsburg, Virginia

August 9, 2009August 9, 20097:30 7:30 –– 8:008:00

CT CRITERIA FORCT CRITERIA FORBOWEL OBSTRUCTIONBOWEL OBSTRUCTION

•• Change in bowel caliberChange in bowel caliber•• Dilated SB (>2.5 cm)Dilated SB (>2.5 cm)-- colon (> 6 cm) colon (> 6 cm)

proximal to transition pointproximal to transition point•• Normal or diminished caliber distal to Normal or diminished caliber distal to

transition pointtransition point•• Identification of transition pointIdentification of transition point•• Small bowel feces signSmall bowel feces sign

SBO: CLINICAL FEATURESSBO: CLINICAL FEATURES

•• 6060--80% OF INTESTINAL 80% OF INTESTINAL OBSTRUCTIONSOBSTRUCTIONS

•• 20% OF EMERGENT SURG 20% OF EMERGENT SURG ADMISSIONSADMISSIONS

•• 55--6% MORTALITY IN ALL BO6% MORTALITY IN ALL BO•• 1010--15% MORTALITY IN CLOSED LOOP15% MORTALITY IN CLOSED LOOP•• 9,000 DEATHS IN US9,000 DEATHS IN US•• PREOP DX STRANGULATION IN 48%PREOP DX STRANGULATION IN 48%

•• 6060--80% OF INTESTINAL OBST80% OF INTESTINAL OBST•• 20% OF ER SURG ADMISSIONS20% OF ER SURG ADMISSIONS•• 55--6% MORTALITY IN ALL BO6% MORTALITY IN ALL BO•• 1010--15% MORTALITY IN CLOSED LOOP15% MORTALITY IN CLOSED LOOP•• 9,000 DEATHS IN US9,000 DEATHS IN US•• PREOP DX STRANGULATION IN 48%PREOP DX STRANGULATION IN 48%

CAUSES OF SMALLCAUSES OF SMALLBOWEL OBSTRUCTION BOWEL OBSTRUCTION

•• ADHESIONS 49%ADHESIONS 49%•• HERNIAS 30%HERNIAS 30%•• NEOPLASMS 15%NEOPLASMS 15%•• OTHER 6%OTHER 6%

CAUSES OF SBOCAUSES OF SBO

•• ABSCESSABSCESS•• APPENDICITISAPPENDICITIS•• DIVERTICULITISDIVERTICULITIS•• ISCHEMIAISCHEMIA•• HEMATOMAHEMATOMA

•• ANEURYSMANEURYSM•• HEMATOMAHEMATOMA•• ENDOMETRIOSISENDOMETRIOSIS•• INTUSSUSCEPTIONINTUSSUSCEPTION•• FOREIGN BODYFOREIGN BODY

ETIOLOGY OF LBOETIOLOGY OF LBO

•• CARCINOMA 55%CARCINOMA 55%•• VOLVULUS 11%VOLVULUS 11%•• DIVERTICULTIS 9%DIVERTICULTIS 9%•• EXTRINSIC CA 8%EXTRINSIC CA 8%•• ADHESIONS 4%ADHESIONS 4%•• IMPACTION 3%IMPACTION 3%•• HERNIA 2%HERNIA 2%•• INTRINSIC 4%INTRINSIC 4%

6 CLINICAL QUESTIONS 6 CLINICAL QUESTIONS IN BOWEL OBSTRUCTIONIN BOWEL OBSTRUCTION

•• IS THE BOWEL OBSTRUCTED?IS THE BOWEL OBSTRUCTED?•• WHAT IS THE SEVERITY OF THE BO?WHAT IS THE SEVERITY OF THE BO?•• WHAT IS THE LEVEL OF THE BO?WHAT IS THE LEVEL OF THE BO?•• WHAT IS THE CAUSE OF THE BO?WHAT IS THE CAUSE OF THE BO?•• CLOSED LOOP? STRANGULATION? CLOSED LOOP? STRANGULATION? •• IS IMMEDIATE SURGERY NEEDED?IS IMMEDIATE SURGERY NEEDED?

KUB IN SBOKUB IN SBO

•• NONDIAGNOSITIC OR MISLEADING IN NONDIAGNOSITIC OR MISLEADING IN 40% OF PATIENTS40% OF PATIENTS

•• POOR AT PREDICTING LOCATION OR POOR AT PREDICTING LOCATION OR CAUSE OF OBSTRUCTIONCAUSE OF OBSTRUCTION

•• FAILS TO DEMONSTRATE FINDINGS OF FAILS TO DEMONSTRATE FINDINGS OF ISCHEMIA OR INFARCTIONISCHEMIA OR INFARCTION

EVALUATING BOWEL EVALUATING BOWEL OBSTRUCTIONOBSTRUCTION

•• Transition pointTransition point•• Small bowel feces signSmall bowel feces sign•• Character of lumen Character of lumen

contents and calibercontents and caliber•• Mural thickeningMural thickening•• Mural edemaMural edema•• ↑↑oror↓↓ mural enhancementmural enhancement•• Mesenteric fluidMesenteric fluid

•• Mesenteric vascular Mesenteric vascular engorgementengorgement

•• Patency of mesenteric Patency of mesenteric vesselsvessels

•• AscitesAscites•• VolvulusVolvulus•• Closed loop obstructionClosed loop obstruction

SIMPLE VS CLOSED LOOPSIMPLE VS CLOSED LOOPOBSTRUCTIONOBSTRUCTION

OUR MOST IMPORTANT JOBOUR MOST IMPORTANT JOB

SIMPLE BOWEL SIMPLE BOWEL OBSTRUCTIONOBSTRUCTION

•• A segment of bowel occluded at a single A segment of bowel occluded at a single point , no significant vascular compromisepoint , no significant vascular compromise

•• Most common type of obstructionMost common type of obstruction•• Fewest complications, usually managed Fewest complications, usually managed

conservativelyconservatively

CLOSED LOOP CLOSED LOOP OBSTRUCTIONOBSTRUCTION

•• A segment of bowel occluded at 2 pointsA segment of bowel occluded at 2 points•• Often caused by incarcerated hernias or Often caused by incarcerated hernias or

adhesionsadhesions•• Precursor to ischemia and infarctionPrecursor to ischemia and infarction•• Predisposes to Predisposes to volvulusvolvulus•• Treated as a surgical emergency because Treated as a surgical emergency because

of high complication rateof high complication rate

COMPLETE OBSTRUCTIONCOMPLETE OBSTRUCTION

•• Lack of Lack of antegradeantegrade passage of luminal passage of luminal contents beyond the obstructioncontents beyond the obstruction

•• Severely dilated proximal bowel and Severely dilated proximal bowel and stomachstomach

INCOMPLETE OBSTRUCTIONINCOMPLETE OBSTRUCTION

•• Some Some antegradeantegrade passage of luminal passage of luminal contents beyond the obstructioncontents beyond the obstruction

•• Mildly narrowed or normal caliber distal Mildly narrowed or normal caliber distal bowelbowel

•• Mildly dilated proximal bowelMildly dilated proximal bowel

BOWEL STRANGULATIONBOWEL STRANGULATION

•• Obstruction complicated by ischemia or Obstruction complicated by ischemia or infarctioninfarction

•• Occurs more rapidly and more frequently in Occurs more rapidly and more frequently in closed loop obstructionclosed loop obstruction

SIMPLESIMPLE

CLOSEDCLOSEDLOOPLOOP

CLOSED LOOP CLOSED LOOP OBSTRUCTIONOBSTRUCTION

•• Two points along the course of the gut are Two points along the course of the gut are obstructed at a single site. obstructed at a single site.

•• Most often found with an adhesive band and Most often found with an adhesive band and occasionally by an internal or external hernia.occasionally by an internal or external hernia.

•• CC--shaped, Ushaped, U--shaped, or coffee bean configuration shaped, or coffee bean configuration of the bowel loop with converging toward the of the bowel loop with converging toward the torsion.torsion.

•• Beak or whirl sign at the site of obstruction.Beak or whirl sign at the site of obstruction.

CLOSED LOOP OBSTRUCTIONCLOSED LOOP OBSTRUCTION

•• Radial configuration of bowel loopsRadial configuration of bowel loops-- when when vertically orientedvertically oriented

•• Convergence of mesenteric vessels to a Convergence of mesenteric vessels to a single pointssingle points

•• Close proximity of afferent and efferent Close proximity of afferent and efferent limbs, often at the site of mesenteric limbs, often at the site of mesenteric convergenceconvergence

CT FINDINGS OF STRANGULATION: CT FINDINGS OF STRANGULATION: MURAL FEATURESMURAL FEATURES

•• Circumferential mural thickening > 3mmCircumferential mural thickening > 3mm•• Target or halo sign (Target or halo sign (submucosalsubmucosal edema)edema)•• Focal loss of mural enhancement (impaired Focal loss of mural enhancement (impaired

arterial flow)arterial flow)•• Persistent mural enhancement (impaired Persistent mural enhancement (impaired

venous outflow)venous outflow)•• Mural hemorrhage or haziness on NCCTMural hemorrhage or haziness on NCCT•• PneumatosisPneumatosis

STRANGULATIONSTRANGULATION

•• Mechanical obstruction associated with Mechanical obstruction associated with bowel ischemia.bowel ischemia.

•• Occurs in 10% [5%Occurs in 10% [5%--42%]42%]•• Most associated with closed loop obstructMost associated with closed loop obstruct•• Mortality of 20Mortality of 20--37% compared to 537% compared to 5--8% for 8% for

simple obstructionsimple obstruction

STRANGULATIONSTRANGULATION

•• Risk of strangulation increases over time in Risk of strangulation increases over time in patients with acute and complete or high patients with acute and complete or high grade obstruction.grade obstruction.

•• Mortality rate of 8% within 36 hoursMortality rate of 8% within 36 hours•• Mortality rate of 25% after 36 hoursMortality rate of 25% after 36 hours

CT FINDINGS OF STRANGULATION: CT FINDINGS OF STRANGULATION: EXTRAMURAL FEATURESEXTRAMURAL FEATURES

•• Engorged mesenteric veinsEngorged mesenteric veins•• Mesenteric stranding or hemorrhageMesenteric stranding or hemorrhage•• AscitesAscites ((espesp within the mesentery)within the mesentery)•• PortomesentericPortomesenteric venous gasvenous gas•• PerforationPerforation

SB FECES SIGNSB FECES SIGN

PRESENCE OF GAS PRESENCE OF GAS AND PARTICULATE AND PARTICULATE MATERIAL MATERIAL RESEMBLING RESEMBLING FECES IN A FECES IN A DILATED SEGMENT DILATED SEGMENT OF SMALL BOWEL OF SMALL BOWEL IS ABNORMAL. 82% IS ABNORMAL. 82% WILL HAVE SBO.WILL HAVE SBO.

INTRALUMINAL CONTENTSINTRALUMINAL CONTENTS

•• + CONTRAST BECOMES MORE DILUTE + CONTRAST BECOMES MORE DILUTE CLOSER TO OBSTRUCTIONCLOSER TO OBSTRUCTION

•• DILATION WORSE AS APPROACH DILATION WORSE AS APPROACH OBSTRUCTIONOBSTRUCTION

•• SB FECES SIGN CLOSE TO LEVEL OF SB FECES SIGN CLOSE TO LEVEL OF OBSTRUCTIONOBSTRUCTION

FINDING THE FINDING THE TRANSITION POINTTRANSITION POINT

•• Diminishing bowel contrastDiminishing bowel contrast--contrast most contrast most dilute nearest transition pointdilute nearest transition point

•• Small bowel feces signSmall bowel feces sign--usually at transition usually at transition pointpoint

•• Search for prior surgical incisionsSearch for prior surgical incisions•• Bowel trackingBowel tracking

INTUSSUSCEPTIONINTUSSUSCEPTION

•• TARGET SIGN: FAT/STTARGET SIGN: FAT/ST•• SAUSAGE SHAPED MASSSAUSAGE SHAPED MASS•• WALL THICKENING FROM EDEMAWALL THICKENING FROM EDEMA

TRANSIENT TRANSIENT INTUSSUSCEPTIONINTUSSUSCEPTION

•• 37 adult SB intussusceptions37 adult SB intussusceptions•• 20 were < 3.5 cm long: self20 were < 3.5 cm long: self--limited, did not limited, did not

require surgery and no SB abnormality with require surgery and no SB abnormality with further work upfurther work up

•• 17 were > 3.5 cm long: 11 were self17 were > 3.5 cm long: 11 were self--limited, limited, 6 patients needed surgery which showed a 6 patients needed surgery which showed a neoplasticneoplastic lead point in alllead point in all

LvoffLvoff Radiology 227: 68Radiology 227: 68--72, 200372, 2003

INTUSSUSCEPTIONSINTUSSUSCEPTIONS

NO LEAD POINTNO LEAD POINT LEAD POINTLEAD POINT

DURATIONDURATION TRANSIENTTRANSIENT PERSISTENTPERSISTENT--RECURRENTRECURRENT

PREVALENCEPREVALENCE COMMONCOMMON RARERARE

BOWELBOWELOBSTRUCTIONOBSTRUCTION

NOT PRESENTNOT PRESENT OFTEN OFTEN PRESENTPRESENT

TREATMENTTREATMENT NONENONE SURGERYSURGERY

INTUSSUSCEPTIONINTUSSUSCEPTION

SMALL BOWELSMALL BOWEL COLONCOLON

BENIGNBENIGN LipomaLipoma, polyp, , polyp, MeckelMeckel diverticdivertic

LipomaLipoma, polyp, polyp

MALIGNANTMALIGNANT Mets, lymphoma, Mets, lymphoma, adenocarcinomaadenocarcinoma

AdenocarcinomaAdenocarcinoma, , lymphoma, lymphoma, metsmets

IDIOPATHICIDIOPATHIC PostopPostop adhesion adhesion motility disordermotility disorder

PostopPostop adhesion adhesion motility disordermotility disorder

HIGH GRADE HIGH GRADE vsvs LOW GRADE LOW GRADE OBSTRUCTION: CT FEATURESOBSTRUCTION: CT FEATURES

•• LOW GRADE: Mildly dilated bowel proximal LOW GRADE: Mildly dilated bowel proximal to obstructionto obstruction------normal caliber bowel distal normal caliber bowel distal to obstructionto obstruction

•• HIGH GRADE: Grossly dilated bowelHIGH GRADE: Grossly dilated bowel------collapsed, decompressed distal bowelcollapsed, decompressed distal bowel

HIGH GRADE HIGH GRADE vsvs LOW GRADE LOW GRADE OBSTRUCTION: CT FEATURESOBSTRUCTION: CT FEATURES

•• LOW GRADE: Non LOW GRADE: Non dilated stomachdilated stomach

•• HIGH GRADE: HIGH GRADE: DilatedDilated

HIGH GRADE HIGH GRADE vsvs LOW GRADE LOW GRADE OBSTRUCTION: CT FEATURESOBSTRUCTION: CT FEATURES

•• LOW GRADE: No LOW GRADE: No mesenteric fluidmesenteric fluid

•• HIGH GRADE: HIGH GRADE: Triangular Triangular collections of collections of mesenteric fluidmesenteric fluid

HIGH GRADE HIGH GRADE vsvs LOW GRADE LOW GRADE OBSTRUCTION: CT FEATURESOBSTRUCTION: CT FEATURES

•• LOW GRADE: Passage of enteric contrast LOW GRADE: Passage of enteric contrast through obstructionthrough obstruction

•• HIGH GRADE: No passage of contrastHIGH GRADE: No passage of contrast

HIGH GRADE HIGH GRADE vsvs LOW GRADE LOW GRADE OBSTRUCTION: CT FEATURESOBSTRUCTION: CT FEATURES

•• LOW GRADE: No evidence of closed loop LOW GRADE: No evidence of closed loop obstructionobstruction

•• HIGH GRADE: HIGH GRADE: ±± Closed loop obstructionClosed loop obstruction

HIGH GRADE HIGH GRADE vsvs LOW GRADE LOW GRADE OBSTRUCTION: CT FEATURESOBSTRUCTION: CT FEATURES

•• LOW GRADE: No evidence of strangulationLOW GRADE: No evidence of strangulation•• HIGH GRADE: HIGH GRADE: ±± StrangulationStrangulation

WHAT MAKES ME NERVOUSWHAT MAKES ME NERVOUS

•• AscitesAscites•• Unhappy bowelUnhappy bowel•• C and U shaped gutC and U shaped gut•• Double discordance of lumen dilationDouble discordance of lumen dilation•• Tense nonTense non--meandering (Rodney meandering (Rodney

Dangerfield) loopsDangerfield) loops