Diagnostic Ultrasound - Abdomen and Pelvis

Appendicitis
TERMINOLOGY
Definitions
• Acute inflammation of appendix, which may be
precipitated by obstruction of lumen
IMAGING
General Features
• Best diagnostic clue
○ US
– Thick-walled noncompressible appendix (outer
diameter ≥ 7 mm)
□ Lumen may or may not be distended
– Periappendiceal edema seen as echogenic fat
– Increased vascularity on power Doppler
○ CT
– Distension &/or wall thickening; single wall thickness >
3 mm
□ Wall thickening more reliable than maximum outer
diameter
– Hyperenhancement of wall
– Periappendiceal inflammation seen as fat stranding
○ Additional findings include appendicolith,
periappendiceal fluid
○ Increased caliber alone is not reliable indicator: Must be
considered alongside history and other imaging findings
• Location
○ Base between ileocecal valve and cecal apex
– Position of tip variable, depending upon length and
direction
• Size
○ Length ranges between 2-20 cm
○ Wall thickening when inflamed
• Morphology
○ Blind-ending, worm-like extension of cecum
Ultrasonographic Findings
• Grayscale ultrasound
○ Thickened noncompressible appendix
– Outer diameter > 7 mm, single wall thickness > 3 mm
– May or may not be distended
– Echogenic periappendiceal fat
– Mural stratification seen in early stages
○ Sonographic McBurney sign over inflamed appendix
○ Gangrenous appendicitis: Loss of mural stratification
○ "Tip appendicitis": Changes involving only tip
○ Appendicolith may be present: Echogenic focus, with
distal acoustic shadowing
– Seen in obstructive type
– When present, increased risk of perforation
○ Perforated appendicitis
– Identifying appendix can be difficult
– Marked periappendiceal inflammatory change
– Fluid collection/abscess (thick echogenic fluid ± gas)
– Loose appendicolith may be seen in collection
○ Additional findings: Dilated adynamic small bowel loops
in right lower quadrant (RLQ), associated thickening of
adjacent bowel
○ False-negative US: Aberrant location of appendix,
appendiceal perforation, early inflammation limited to
appendix tip
○ False-positive US: Distended noninflamed appendix from
gas, fluid, and feces; thickened appendix from lymphoid
hyperplasia
• Doppler
○ Increased flow on power Doppler within wall of
appendix and periappendiceal inflamed fat
• Transvaginal US: For visualization of pelvic appendix
Radiographic Findings
• Radiography
○ Infrequently diagnostic
○ Appendicolith may be visible in 5-10% of patients
CT Findings
• CECT
○ Wall thickening
– May or may not be distended
○ Hyperenhancement of appendiceal wall
– Mural stratification seen in early stages
○ Periappendiceal fat stranding and fluid
○ Appendicolith
– Can be seen as incidental finding
□ In isolation not diagnostic of appendicitis
○ Arrowhead sign
– Focal symmetric thickening of medial cecal wall at
base of appendix
• Entire appendix should be scrutinized
○ "Tip appendicitis" may be early manifestation
• Excellent for identifying complications
MR Findings
• Overlap with CT findings
Imaging Recommendations
• Best imaging tool
○ US method 1st choice in children, thin young adults, and
pregnant patients
○ CT performed for patients with inconclusive US, if
complications suspected, or in obese patients
○ MR helpful during pregnancy; alternative to CT in
children/young adults
• Protocol advice
○ US: Transabdominal scan with graded compression
○ CT: Optimal CT technique controversial
○ MR: Adding DWI improves reader sensitivity
DIFFERENTIAL DIAGNOSIS
Mesenteric Adenitis
• Enlarged and clustered lymph nodes in mesentery and RLQ
• Normal appendix
• May have ileal/cecal wall thickening due to GI involvement
• Diagnosis of exclusion, as other inflammatory conditions
may show enlarged reactive mesenteric nodes
Cecal Diverticulitis
• Focal pericecal inflammatory changes
• Mild cecal wall thickening
• Visualization of thickened cecal diverticulum
Diagnoses: Bowel
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