U Lecture Objectives. U Nordic Forum Trauma & Emergency Radiology. Bowel obstruction. U Bowel Obstruction: Etiologies

Transcription

1 Nordic Forum Trauma & Emergency Radiology Lecture Objectives Bowel Obstruction To illustrate the spectrum of acute obstruction of the small and the large bowel To explain how these bowel obstructions may present radiologically, with an emphasis on MDCT To discuss complications of acute bowel obstruction Borut Marincek Institute of Diagnostic Radiology niversity Hospital Zurich, Switzerland Bowel Obstruction: Etiologies = 20% of surgical hospital admissions for acute abdomen Small bowel obstruction (SBO) (80%) Postoperative adhesions (50-75%) Primary & metastatic neoplasia (10-15%) External/internal hernia (8-15%) Other: Crohn disease, intussusception, hematoma, gallstone, bezoar Large bowel obstruction (LBO) (20%) Carcinoma (60%, most frequently sigmoid) Volvulus (10-15%, sigmoid > cecum) Diverticulitis (10%) Other: intussusception, fecal impaction, ischemia, foreign object, extrinsic compression Bowel Obstruction: Four Relevant Questions 1. Is mechanical obstruction present? DDx: adynamic ileus (laparotomy, pancreatitis, peritonitis, mesenteric ischemia, neuroleptics, opiates) 2. What is the site (small bowel / large bowel)? 3. What is the cause? 4. Any complications? Simple (wall viability not compromised) or strangulation obstruction (compromised vascular supply intestinal ischemia)? rgent surgery or conservative management? Bowel Obstruction: Traditional Role of Imaging Abdominal Plain Film (APF) vs CT Sensitivity (%) Bowel obstruction rolithiasis Pancreatitis Appendicitis Pyelonephritis Diverticulitis Intraabdominal foreign body APF (N=871) CT (N=188) (Ahn, Radiology 2002)

2 Bowel Obstruction: Imaging Modalities APF: Problems Nondiagnostic or misleading in approx. 50% Poor predictor of site or cause of obstruction Frequently fails to demonstrate findings of ischemia or infarction Antegrade contrast studies: Problems Slow transit, prolonged retention of barium Water-soluble contrast usually diluted by SB fluid CT: Advantages Demonstrates site & cause of obstruction, extraluminal abnormalities Provides information about state of bowel wall (i.e. strangulation) Bowel Obstruction: Imaging Modalities APF: Problems Nondiagnostic or misleading in approx. 50% Poor predictor of site or cause of obstruction Frequently fails to demonstrate findings of ischemia or infarction Antegrade contrast studies: Problems Slow transit, prolonged retention of barium Water-soluble contrast usually diluted by SB fluid CT: Advantages Demonstrates site & cause of obstruction, extraluminal abnormalities Provides information about state of bowel wall (i.e. strangulation CT instead of AFP or antegrade contrast studies Large Bowel Obstruction Less common than SBO Different in other ways: - etiology: cancer most common - symptoms: insidious - right-sided mimics SBO APF: - dilated colon >5-6 cm, cecum largest - rectal gas? CT interpretation: - look at scout views - start in pelvis - find cecum and terminal ileum - find transition zone, look for etiology - masses, etc LBO: Annular Sigmoid Carcinoma CT confusing? Rectal contrast = key for LBO diagnosis LBO: Metastasis Breast Carcinoma Fecal Impaction (Coprostasis)? (61 yo, m) Retroperitoneal infiltration

3 Decompensated LBO (61 yo, m) LBO: Fecal Impaction (Coprostasis) Colon distended >6 cm, cecum largest Adenocarcinoma transverse colon Ischemic distention colitis of cecum LBO: Fecal Impaction (Coprostasis) High Grade LBO: Diverticulitis or Carcinoma? Most commonly in laxative abusers, psychiatric patients, severe generalized atherosclerosis / cerebral sclerosis Findings typical of diverticulitis: Long segment involved (>5 cm) Pericolic inflammation Symmetric wall thickening (75%) Findings typical of carcinoma: Short segment involved Pericolic lymph nodes Sigmoid diverticulitis LBO: Sigmoid Volvulus (= Closed Loop Obstruction) LBO: Cecal Volvulus (= Closed Loop Obstruction) Northern exposure sign (Javors, AJR 1999) Coffee bean sign (inverted -configuration) CT whirl sign indicative of volvulus

4 LBO: Cecal Volvulus with Ischemic Complication 58 yo, f: ischemic necrosis cecum LBO: Ischemic Radiation Colitis Torsion of involved colon around mesocolon = whirl sign on CT: stretching and engorgement of ileocecal artery & vein in cecal volvulus (in sigmoid volvulus IMA & IMV) Ovarian carcinoma, surgery & radiotherapy 23 yrs ago: ischemic radiation colitis of rectosigmoid LBO: Ischemic Radiation Colitis LBO: Sigmo-Sigmoid Intussusception Cervical carcinoma, surgery & radiotherapy 10 yrs ago: ischemic radiation colitis of rectum and sigmoid Bowel within bowel mesenteric fat, enhancing mesenteric vessels Lead point = polyp (adenocarcinoma T2N0) LBO: Colo-Colic Intussusception LBO: Endometriosis 40 yo, f: rectosigmoid & cecum Submucosal lipoma of ileocecal valve Cecal perforation

5 Small Bowel Obstruction More common than LBO APF: - multiple gas-fluid levels unequal heights CT technique: - oral contrast not necessary - iv contrast critical CT diagnosis: - dilated SB >2.5 cm - transition zone, maybe hard to find - small bowel feces sign - coronal & sagittal MPRs can help SBO: Multiple Postoperative Adhesions Kidney-TPL 1 month ago SB: distended (>2.5 cm) & collapsed loops No mass at transition zone adhesive SBO: adhesive bands unidentified on CT (diagnosis of exclusion) SBO: Multiple Postoperative Adhesions Ventral incisional hernia; SB faeces sign (phytobezoar) = indicator of SBO when associated with SB dilatation SBO: Neoplasia Circumferential adenocarcinoma distal ileum curved MPR Hernias: External & Internal SBO: Incarcerated Femoral Hernia External: herniation of viscera through defect (congenital weakness or previous surgery) in abdominal or pelvic wall (inguinal, femoral, ventral, lumbar, obturator, incisional) in most cases visible or palpable, CT for detection of unsuspected sites, in obese patients Internal: less common, herniation of viscera through developmental or surgically created defect of peritoneum or mesentery into a compartment within peritoneal cavity diagnosis always based on radiology Incarceration irreducible hernia (irreducible sac of jejunal loop) Incacerated hernia may strangulate, clinical diagnosis difficult in obese patients

6 SBO: Incarcerated Obturator Hernia SBO: Incarcerated Ventral (Paraumbilical) Hernia Obturator hernia f:m = 5:1 7th-8th decade of life Paraumbilical hernia: Related to diastasis of rectus abdominis muscle Risk factors: multiple pregnancies, obesity High prevalence for incarceration & strangulation SBO: Incarcerated Ventral Incisional Hernia 10 days after abdominal hysterectomy SBO: Ventral Incisional Hernia Multiple laparotomies after resection of sigmoid colon Incarceration? SBO: Ventral Incisional Hernia SBO: Internal Hernias A paraduodenal B foramen of Winslow C intersigmoid D pericecal E transmesenteric F retroanastomotic (Martin, AJR 2006) No incarceration (reducible hernia) Classic older literature: paraduodenal most common, pericecal second most common Increasing incidence of transmesenteric, transmesocolic & retroanastomotic new surgical procedures (Roux-en-Y loop in liver TPL & gastric bypass)

7 SBO: Pericecal Hernia SBO: Retroanastomotic Hernia After Gastric Bypass Mesenteric swirl best single predictor (Lockhart, AJR 2007) SBO: Crohn Disease SBO: Intussusception Crohn disease: typically partial obstruction Mesenteric fat & vessels in bowel lumen ( bowel-within-bowel appearance ) Lead point: jejunal melanoma metastasis Terminal ileum: wall thickening & layering enhancement active disease Subdiaphragmatic melanoma metastasis, left renal cyst SBO: Diagnosis? SBO: Impacted Gallstone Rigler Triad: SBO, pneumobilia, ectopic gallstone

8 SB Strangulation Obstruction SB Strangulation Obstruction Our most important job in SBO is answer to the question: Simple or strangulation obstruction? Is ischemia present? Strangulation obstruction (10% of SBO): - most are closed loop (= bowel loop occluded at two adjacent points along its course) - vascular compromise venous mesenteric blood flow compromised first, causing increasing vascular pressure and vessel engorgement with continuing arterial influx; hemorrhage into bowel wall and lumen can occur; finally arterial supply ceases, due to arterial spasm following increasing vascular resistance CT findings: Bowel wall thickening >3 mm (non-specific) Abnormal bowel wall enhancement ( or ) Target sign : alternating hypo- / hyperdense layers submucosal edema / hemorrhage Pneumatosis intestini & portomesenteric gas Mesenteric edema Ascites SBO: Strangulation Ischemia SBO: Strangulation Ischemia Appendectomy & cholecystectomy 54 yrs ago Segmental ischemia & infarction of jejunum secondary to adhesive band Appendectomy 1 yr ago Venous ischemia of ileum secondary to adhesive band SBO: Strangulation Ischemia Appendectomy & cholecystectomy several yrs ago Bowel Obstruction: Summary Remember 4 questions MDCT instead of APF for accurate diagnosis MDCT: MPRs improve visualization of transition zone prestenotic / poststenotic bowel better determination of site and cause of obstruction MDCT: improved visualization of ischemia in suspected small bowel strangulation obstruction CT whirl sign : strangulating SB volvulus ischemia & infarction of jejunum secondary to adhesive band