Imaging of Bowel Obstruction

Rathachai Kaewlai, MD Ramathibodi Hospital, Mahidol University, Bangkok

Emergency Radiology Minicourse 2015

What to Cover…

Imaging techniques

Gastric obstruction Small bowel obstruction Large bowel obstruction

Bowel Obstruction

Lack of transit of bowel contents

Small bowel obstruction: high or low Large bowel obstruction Simple (intact blood supply) vs. strangulated

Bowel Obstruction

Clinical Presentation

Depend upon site of obstruction

High SBO – vomiting early, profuse, rapid dehydration Low SBO – pain with distension LBO – constipation Strangulation – shock, rigidity/rebound (localized/diffuse)

Treatment

Conservative

Surgery: Early – Strangulation

Closed loop obstruction Obstructed/strangulated hernia Delayed –

Adhesive obstruction without pain

Aims of Investigations

Is obstruction present?

Where is the location? What is the cause? Is emergent surgery needed?

Strangulation Closed loop Obstructed hernia

Radiography

CT

CT Techniques

Helical scan, thinnest collimation

Coronal reformats IV contrast, single venous phase No need for oral contrast. May be neutral

contrast No rectal contrast needed May be helpful if LBO, neutral contrast preferred

Gastric Outlet Obstruction (GOO):���Etiology Malignancy > benign (PUD)

Extrinsic: pancreatitis with pseudocyst, hematoma Intrinsic: malignancy, PUD with stricture

Intraluminal: bezoars, FB, GS Acute incarceration or strangulation:

obstructed paraesophageal hernia, gastric volvulus

Radiography

Markedly dilated stomach, air or fluid filled

Filling defect (cancer)

Calcified gallstone (Bouveret syndrome)

CT

Marked distension

Etiology Enhancing soft tissue mass

Focal thickening of gastric wall with mucosal hyper-enhancement and/or ulcers Pancreatitis w/wo pseudocyst Acute cholecystitis

Filling defects (polyp, gallstone, bezoar)

Stomach

GOO: Malignant ���Etiologies

Ampullary, duodenal, cholangiocarcinoma, gastric cancer

Pancreatic cancer with extension to duodenum/stomach 15-25% with GOO

Usually have biliary obstruction

Stomach

Mass

Gastric cancer with GOO

GOO: Benign Etiologies

PUD (acute vs scarring/fibrosis)

Polyps, caustic ingestion, web, GS, pancreatic pseudocyst, bezoar

Gastritis vs. Neoplasm

Difficult differentiation on imaging. Endoscopy necessary to differentiate neoplasm

Gastritis Layered (halo) appearance Diffuse, segmental, or annular

Neoplasm Nodal disease

Metastasis Pseudothickening of antrum

Diagnostic Approach

Dilated stomach may contain up to 5L of fluid

Functional disturbance Postoperative, severe trauma, immobilization, inflammatory disease of abdomen, neurogenic, diabetes

Mechanical obstruction (stomach, duodenal, high SB)

Differentiate benign from malignant processes

Gastric Volvulus

Abnormal rotation around its axis

Surgical emergency if acute Organo-axial, mesenteroaxial, or both

Organoaxial Stomach rotates around axis connecting EGJ and pylorus

Mesenteroaxial Less common

Stomach rotates around axis bisecting both lesser and greater curvatures

Image:  Differen-al  diagnosis  in  conven-onal  gastrointes-nal  radiology.  Burgener  FA,  Kormano  M.  

Gastric Volvulus

Diaphragmatic defect m.c. causative factor

Intrathoracic stomach Transverse lie with single air-fluid level = organoaxial Spherical lucency with beak in distal stomach + differential air fluid levels = mesenteroaxial

Case courtesy of Radiopaedia.org

Case courtesy of Dr Maxime St-Amant, Radiopaedia.org

Organoaxial volvulus

Mesenteroaxial volvulus

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Gastric Volvulus

“Organoaxial volvulus” Case courtesy of Dr David Cuete, Radiopaedia.org

“Mesenteroaxial volvulus” Case courtesy of Dr Maxime St-Amant, Radiopaedia.org

Superior Mesenteric ���Artery Syndrome

Dilatation of 1st and 2nd part of duodenum with abrupt narrowing at 3rd portion

Relieved by changing position

Aorta-SMA distance <8-10 mm

Aortomesenteric angle <22 degrees

(compression of LRV – renal vein thrombosis, pneumatosis, PVG, AAA)

Narrow aortomesenteric angle and compression at 3rd portion of duodenum

Small Bowel Obstruction (SBO)

Dilated small bowel proximal to the site of obstruction with distal decompression

Radiography

Diagnostic in 50-60% Non-diagnostic or misleading in 40%

Poor predictor of Location Cause Complications

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Dilated small bowel loops with relative absence of colonic gas

Radiography

Dilated small bowel >3 cm

Paucity of colonic gas Air fluid levels Multiple

Differential Longer than 2.5 cm

String of beads sign

Multiple air fluid levels in dilated small bowel loops

CT

Quick and accurate

No need for luminal contrast

Bowel wall assessment Extraluminal abnormalities

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Diffuse, fluid-filled, dilated loops of small bowel

Free fluid

CT: Indications

Non-diagnostic radiography but clinical suspicion

Virgin abdomen History of abdominal malignancy Suspected complications

Indications for CT in SBO:���Non-diagnostic Radiography

SBO due to gallstone obstruction

Normal bowel gas pattern despite SBO shown on CT because of fluid-filled

small bowel loops

Indications for CT in SBO:���Virgin Abdomen Known diseases

Metastasis (54%) Crohn disease (46%)

No known diseases

Adhesions (75%) Metastasis (10%) Rare: sclerosing encapsulating peritonitis, Meckel diverticulum, gallstone ileus

Beardsley  C,  et  al.  Am  J  Surg  2014    

Indications for CT in SBO:���History of Abdominal Malignancy Spread/extent of tumor around bowel

Pre-operative planning for bypass/debulking procedures

Transition Point

Dilated loops change in caliber to decompressed loops

Trace rectum ! colon ! small bowel Small bowel feces Scroll images on workstation

(difficult on hardcopy films) Multiplanar reformats

Transition Point

Adhesions inferred when no cause identified

Abrupt tapering Beak

External hernias

Tumors, esp. metastasis to bowel/peritoneum Inflammation/infection, gallstones CT accuracy 63-95% for identifying transition point

Transition Point Tells Etiology of Obstruction

Cecal cancer Femoral hernia

Transition point

Transition point

Small Bowel Feces Sign

Gas bubbles and particulate matter within dilated SB

Usually just proximal to transition point

Secondary to prolonged stasis Transition point

Small Bowel Feces Sign

Suggestive of preserved SB function

Negative predictor of failure of conservative Rx

Unlikely to be ischemic Longer segment, less chance

of getting surgery

SB feces

Etiology of SBO

Adhesions 50-75%

Hernias 8-15% Malignancies 10-15% Others: Crohn, intussusception, volvulus, trauma,

iatrogenic conditions

Adhesions

Most common sites = omentum to incision site

Most problematic adhesions = involving small bowel Appendectomy, colorectal surgery and gynecology Most common to produce adhesive obstruction

Anytime from operation 20% <1m 20% >10y

Dayton MT et al. 2012 Curr Probl Surg

External Hernia

2nd most common cause of SBO

Inguinal > femoral

Umbilical = m/c congenital hernia

Incisional and parastomal = m/c iatrogenic hernia

Others: spigelian, lumbar, Richter, Littre Umbilical hernia,

obstructed & strangulated

SBO: Internal Hernia

Defects in mesentery or peritoneum Post surgical > cong

Adhesive bands Most common around

duodenum

Paraduodenal internal hernia, obstructed

Obstructing Tumors

Adenocarcinoma

Irregular, nodular mass Carcinoid rarely obstructive GIST

Lymphoma rarely obstructive Peritoneal carcinomatosis Ovary, colon, stomach, pancreas, breast, endometrium Small bowel adenocarcinoma, obstructed

Diagnologic.com

Others

Intussusception

Inflammatory bowel TB very common inflammatory cause of SBO, ileocecal, local nodes with hypodense center

Acute Crohn Chronic Crohn Pancreatitis, diverticulitis and appendicitis

Radiation enteropathy Stone and bezoar

Is Emergent Surgery Needed?

YES IF:

Strangulation = SBO + Ischemia Closed loop obstruction

Closed-loop SBO

Obstructed at 2 adjacent locations

Bowel between 2 points more dilated than upstream to the proximal obstruction

Risk of torsion/volvulus Hernia and adhesion (usu. Single)

Roux-en-Y gastric bypass

Closed-loop SBO

U-, C- or coffee bean

Radial orientation of dilated loops

Beak Balloons on a string Whirl sign Sensitivity 60%

PPV 80%

Ischemia Complicating SBO

Two mechanisms

Inc. pressure in bowel wall Direct occlusion of mesenteric vessels 2/2 torsion, hernia or tight adhesion

Mortality 25% (only 2% for non-strangulated SBO)

Need high suspicion

Ischemia Complicating SBO

Enhancement – hyper ! hypo ! absent Reduced bowel wall enhancement 11x probability of strangulation

Wall thickening – nonspecific Wall thinning can be 2/2

transmural infarction Pneumatosis and

portomesenteric gas

Millet I, et al. Eur Radiol 2014

Mimics of SBO on AXR

Ileus

Mesenteric ischemia Obstruction of cecum/

ascending colon (cecum filled with mass or fluid)

SMA occlusion

Large Bowel Obstruction (LBO):���Etiology More in elderly

Malignancy 60% Volvulus 15% Diverticulitis 10%

Others: incarcerated hernia, fecal impaction, adhesion

15-20% of colorectal malignancy present with LBO

Radiography

Marked colonic dilatation with disproportionate distension of cecum (>10 cm)

Competent IC valve

Functional closed loop Risk of perforation

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Colonic dilatation to the sigmoid colon due to distal LBO

Radiography

Incompetent IC valve

Dilated SB and colon Cecum dilated v. non-dilated

Difficult Dx on AXR Poor sensitivity, specificity and interobserver agreement

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Colonic and small bowel dilatation to the splenic flexure colon due to

distal LBO

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Colon Cancer

CT sensitivity and specificity 90%

Imaging of choice = CT 60% of LBO Mostly adenocarcinoma

Mass, involvement of adjacent structures, lymphadenopathy, intraperitoneal metastasis

Cancer of the splenic flexure colon

Extrinsic Neoplasm

Direct invasion

Intraperitoneal seeding Hematogenous metastasis Lymphatic extension

Sigmoid Volvulus

Twist around sigmoid mesocolon

Massive distension Lack of haustration Coffee bean shaped

classic- Rt dome Central stripe

Sigmoid Volvulus

Diagrams from surgeonsblog.blogspot.com and pmj.bmj.com

Beak sign

Cecal Volvulus

Dilated cecum

Dilated cecum

Beak sign

Volvulus: CT?

Classic picture

Colon dilatation alone LBO Toxic megacolon

Pseudo-obstruction Colon + SB dilatation LBO

Ileus

CT

Rx

CT

Mimics of LBO

Toxic megacolon

Clinical toxicity Colonic pseudo-obstruction CT often needed to exclude a mass

Diffuse colonic dilatation. CT confirmed no evidence of obstruction

Summary

Investigative questions:

Obstruction present? Where? Cause? Surgery? Radiography still has a limited role in bowel obstruction CT is the mainstay imaging:

Quick and safe No luminal contrast Confirm obstruction, site, etiology, surgical need

Extraluminal abnormalities