Diagnostic Ultrasound - Abdomen and Pelvis

Acute Acalculous Cholecystitis
TERMINOLOGY
Definitions
• Acute necroinflammatory disease of gallbladder (GB) not
related to gallstone
○ Usually secondary to stasis of bile and ischemia
IMAGING
General Features
• Best diagnostic clue
○ Gallbladder wall thickening without impacted gallstone
○ Positive sonographic Murphy sign
○ Critical illness with sepsis, shock, recent surgery, trauma,
or burns
Ultrasonographic Findings
• Grayscale ultrasound
○ US features of acute acalculous cholecystitis are similar
to acute calculous cholecystitis except for absence of
impacted gallstone
○ GB wall thickening (> 4 mm)
– Hypoechoic, layered/striated appearance
○ GB distension
– Commonly filled with sludge
– Hydrops; GB measuring > 8 cm longitudinally and > 5
cm transversely withanechoic bile
○ Pericholecystic fluid collection
○ Positive sonographic Murphy sign
– Sonographic Murphy sign may not be elicited in
patient who is obtunded, unconscious, or sedated
○ Complication
– Gangrenous cholecystitis
□ Irregular/asymmetric GB wall thickening
□ Look for discontinuity of the wall and loss of
echogenicity
□ Intraluminal membranes and echogenic material
due to sloughed mucosa
– GB perforation
□ Collapsed GB; wall defect with adjacent
heterogeneous hypoechoic fluid collection
□ Most common at fundus
• Color Doppler
○ Hyperemia within thickened/inflamed GB wall
– Absent in gangrenous cholecystitis
CT Findings
• NECT
○ Distended GB with pericholecystic inflammation ± highdensity
sludge or hemorrhage
• CECT
○ Distended GB with hyperemic wall thickening and
pericholecystic fat stranding
– Wall may be discontinuous and poorly enhancing in
setting of gangrene
○ Complications
– Pericholecystic collection/abscess
– Gas in gallbladder wall or lumen
MR Findings
• T1WI
○ High signal intensity luminal sludge
• T2WI
○ Distended GB
○ Intraluminal lower signal from sludge or pus
○ Thick wall with increased T2 signal
○ Complications
– Pericholecystic collection/abscess
– Irregular or asymmetric wall thickening
• T2WI FS
○ Increased signal in pericholecystic fat
○ Pericholecystic and perihepatic fluid
• T1WI C+
○ "Rim" sign of increased hepatic enhancement
○ Inhomogeneous or absent wall enhancement when
gangrenous
Nonvascular Interventions
• Percutaneous cholecystostomy with bile aspiration and
culture to confirm diagnosis in patients with no source for
sepsis
• Bridge to cholecystectomy
• Catheter left in place for at least 3 weeks
Nuclear Medicine Findings
• Tc-99m iminodiacetic acid derivatives (HIDA) scan detects
functional cystic duct obstruction
• Sensitivity 30-100%, specificity 89-100%
• Nonvisualized gallbladder at 4 hours or nonvisualized
gallbladder at 90 minutes using morphine augmentation
• Less sensitive than in acute calculous cholecystitis, however
useful adjunct to indeterminate ultrasound
• False-negatives: Infected nonobstructed gallbladder
• False-positives: Poor hepatic function, fasting, total
parenteral nutrition
Imaging Recommendations
• Best imaging tool
○ US is first-line
○ HIDA for indeterminate ultrasound
○ CT for complications
DIFFERENTIAL DIAGNOSIS
Acute Calculous Cholecystitis
• US features similar to acalculous cholecystitis
• Presence of impacted gallstone
Sympathetic GB Wall Thickening
• Smooth wall thickening± sludge
• Negative Murphy sign
• Clinically not septic
○ Multiple underlying causes such as hypoalbuminemia,
cirrhosis, congestive heart failure, acute hepatitis or
pancreatitis
Hyperplastic Cholecystosis
• Focal (fundal/mid body) or diffuse GB wall thickening
• "Comet tail" artifacts
• Intramural cystic spaces
Gallbladder Mucocele
• Distended gallbladder secondary to chronic obstructing
stone
• Noninflammatory condition with minimal pain/tenderness
Diagnoses: Biliary System
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