Imaging of the Abdomen and Pelvis

Anne Goldschmidt, MD

Radiological Associates of Duluth

Purpose

• Basic introduction to abdominal imaging modalities

• Introduction to common abdominal pathologies and how imaging can help in differential diagnosis

• Correlation with gross anatomy

Imaging Modalities

• Plain film (X-ray, KUB)

• Ultrasound (US)

• Computed Tomography (CT)

• Magnetic Resonance Imaging (MRI)– Problem solving, not primary

• Barium Studies

• Nuclear Medicine

Plain Films

• Electromagnetic energy passed through the body results in an image on the film

• Based on the density of the structures it passes through

Ultrasound

• Medical imaging technique uses high frequency sound waves

• Sound waves leave probe, travel into body and are reflected back to the machine to be analyzed

Ultrasound

• Location of structures is based on the time required for sound waves to return to the probe

• Intensity of the echoes on the image is dependent on composition of structures

Computed Tomography

• Electromagnetic energy (ionizing radiation)

• Gantry moves around patient, scanning from many angles

• Computer generates a 3D image

Magnetic Resonance Imaging

• No ionizing radiation

• Utilizes high field strength magnet to align hydrogen ions

• Radio frequency pulse specific to hydrogen ions causes them to precess

• With time hydrogen returns to alignment with magnetic field—different tissues, different time

Abdomen MRI

Nuclear Medicine

• Radiotracers are injected into body

• More functional than many tests

• Less detailed anatomic information

• GB disease

Barium Studies

• Utilizes x-rays• Contrast material

placed into GI tract• Antegrade for upper

GI tract• Retrograde for colon

Plain Films

• Dense=white– Bone or metal

• Lucent=black– Stomach bubble– Lung bases– Air in bowel

Two Views

• For CXR get PA and Lateral

• For abdominal imaging typically get supine and upright views– Lateral decubitus view if unable to stand

Abdominal Films

Approach to Interpretation

• Free air

• Bowel gas pattern

• Calcifications

• Soft tissues

• Bones

• Lines and tubes: NG tubes, drains, stents, surgical clips or hardware

Pneumoperitoneum(Free Air)

• Extraluminal air

• Post op finding

• Perforation of a hollow viscus

• Supine film—difficult to diagnose unless large volume

• Upright—look for air between liver and diaphragm

Free Air

Bowel Gas Pattern

• It is normal to see gas and stool within the colon

• Normal colon caliber less than 6cm

• Worry about cecum larger than 10cm

Plain film vs BE

Small Bowel Air

• Normal caliber less than 3cm

• Small bowel is located centrally in abdomen, compared with more peripheral colon

Dilated Small Bowel

• Primary question is whether or not there is a mechanical obstruction or if there is abnormal motility of the bowel

• Is there a SBO or ileus?

Signs and Symptoms of Bowel Obstruction

• Depends on level—higher, less bowel distention and earlier symptoms

• Vomiting—leads to loss of electrolyte rich fluid which can lead to shock

• Crampy pain

• Constipation

• Can be partial—symptoms less severe– May have diarrhea

Small Bowel Obstruction vs. Ileus

• SBO• Mechanical blockage

– Fibrous band or adhesion

– Hernia– Neoplasm– Stricture– Volvulus

• Abnormal peristalsis or motility– Post op, due to

manipulation– Intraabdominal or

retroperitoneal infection

– Ischemia

SBO

• Obstruction leads to distention proximal to level of block with collapse distally

• See differential caliber, with air/fluid levels on upright view

Complications

• Accumulation of ingested fluid and food, plus digestive secretions and gas leads to distention

• Strangulation—Abnormal blood flow– Initially see venous occlusion, then arterial

occlusion and finally ischemia and infarction– Usually seen with hernia, Volvulus, or

intussusception

Calcifications

• GB

• Kidneys

• Pancreas

• Vascular

• Pelvic—fibroids, ovary

Nephrolithiasis

• Pathogenesis related to dehydration (decreased urine volume) or increased excretion of stone constituents

• 90% calcium, 65% oxylate

• S/S:– May be silent– Renal colic—excruciating pain in flank—

genitalia, thigh

Urinary Tract Obstruction

• Excretory Urogram (IVP)– Inject x-ray dye and take serial films as it is

excreted by kidneys– Stone blocks the flow of contrast, leading to

delayed excretion and dilatation of the collecting system and ureter

– Depending on degree of obstruction can take a long time to complete

Obstruction on IVP

CT for Urinary Tract Obstruction

• CT has replaced IVP for most patients

• Requires no IV contrast material

• Very quick

• Can show other causes of pain if there is no stone

CT of Urinary Tract Obstruction

Calcifications

Calcifications

Calcifications

Calcifications

Calcifications

Common Abdominal Problems

• Appendicitis

• Cholelithiasis and Cholecystitis

• Pancreatitis

• Diverticulitis

• Abscess

Appendicitis

• Bacterial infection of appendix

• Adolescents and young adults– Peak age 15-24

• Inflammation – edema and ischemia—gangrene and perforation

Signs/Symptoms

• Midepigastrium pain—RLQ

• N/V

• +/- mild fever, elevated WBC

• Tenderness/guarding at McBurney’s point

• Rebound implies peritoneal inflammation

• Atypical location—atypical S/S

Diagnosis

• Physical exam• US—especially

women and children• CT

Ultrasound

• Normal appendix less than 6mm

• Normal appendix is compressible with transducer pressure

• DX—Tubular, dilated, non compressible structure in RLQ

CT of Appendicitis

• Normal appendix thin walled, non dilated

• Normal fat is black• DX—Dilated appendix

with thickening of the wall and dirty fat

Gall Bladder Disease

• Cholelithiasis—stones in the GB– 10% in US– 20% of patients over 40

Formation related to cholesterol biosynthesis

Often mixed—cholesterol, calcium, bilirubin

Medication may dissolve

Gall Stones

Acute Cholecystitis

• Inflammation of GB, usually due to obstruction by stone

• S/S: RUQ pain, NV, Flatulence

• Murphey’s sign—localized tenderness

Cholecystitis

• Diagnosis– Plain films– US– CT– HIDA Scan—a more functional test

Cholecystitis

• Ultrasound finding• Stones with

shadowing• Thickening of wall• Pericholecystic fluid• + Sonographic

Murphey’s

Cholecystitis

• CT diagnosis• Stones• Thick wall• Dirty fat• Abscess

HIDA Scan

• Functional study of liver uptake and excretion into biliary tree.

• Normal to see excretion into GB and then into SB

Pancreatitis

• Inflammation of pancreas

• Etiologies: Biliary disease, alcoholism, surgery, trauma, drugs—1/3 unknown

• Gross path: edema, hemorrhage, necrosis

• Complications related to enzymes: pseudocysts, abscess, fat necrosis

Signs/Symptoms

• Severe abdominal pain, radiating to back

• N/V

• Fever

• Shock: Elevated HR, Decreased BP

• Lab: Elevated serum amylase

Pancreatitis Diagnosis

• Plain Films– Calcification in chronic– GS

• CT– May be normal– Use CT to look for complications

Pancreatitis

Diverticular Disease

• Diverticula—small, sacular mucosal herniation through muscular wall of colon– Most common in sigmoid– 30-40% over age 50– Increased incidence with age– Related to refined, low fiber diet

Diverticula

Diverticulitis

• Inflammation of the Diverticula, leads to perforation with inflammation of pericolonic tissues

• Complications:– Abscess– Wall thickening with obstruction– Perforation

Diverticulitis

• S/S

• Pain with localized tenderness, esp. LLQ

• Crampy pain if obstruction

• Diagnosis– BE– CT

Diverticulitis

• Barium enema• Diverticula• Thickening of wall

with stricture• Extraluminal contrast• Mass effect from

adjacent inflammation or abscess

• CT• Diverticula• Thick wall with

stricture• Dirty fat• Abscess, Phlegmon• CAN MIMIC CANCER

BE of Diverticulitis

CT of Diverticulitis

ABCESS

• Inflammation—walled off collection

• Appendicitis, diverticulitis, IBD, PID, etc

• S/S: fever, pain with local tenderness, elevated WBC

• Diagnosis: CT– Need oral contrast material– IV helpful

Abscess

Summary

• Because of overlap in S/S of various abdominal processes, imaging is critical in evaluating patients presenting with acute abdominal complaints

• Plain films are helpful to assess bowel gas patterns

• US is primary modality for evaluating the GB

• CT is primary modality for most other DDx