Diagnostic Ultrasound - Abdomen and Pelvis

Amebic Hepatic Abscess
TERMINOLOGY
Definitions
• Localized collection of pus in liver due to Entamoeba
histolytica with destruction of hepatic parenchyma and
stroma
IMAGING
General Features
• Best diagnostic clue
○ Well-defined hypo- or isoechoic mass, most often solitary
and peripherally located
• Location
○ Right lobe (72%) > left lobe (13%)
○ Usually peripheral, near or abutting liver capsule
• Size
○ Varies from few millimeters to several centimeters
• Morphology
○ Most often solitary (85%)
• Other general features
○ Most common extraintestinal manifestation of amebic
infestation
Ultrasonographic Findings
• Grayscale ultrasound
○ Peripheral location
– Abuts liver capsule, often under diaphragm
○ Round or oval shape, sharply demarcated
– Amebic abscess is more likely to have round or oval
shape than pyogenic abscess
○ Hypoechoic with low-level internal echoes due to debris
○ Internal septa or wall nodularity may be present
○ May see hypoechoic halo
○ May see mild posterior acoustic enhancement
○ Often associated right pleural effusion
Radiographic Findings
• Radiography
○ Elevation of right hemidiaphragm
○ Right lower lobe atelectasis or infiltrate
○ Right pleural effusion
○ Ruptured amebic abscess into chest may cause
– Lung abscess, cavity, hydropneumothorax
– Pericardial effusion
○ Barium enema often shows changes of amebic colitis
CT Findings
• NECT
○ Peripheral, round or oval hypodense mass (10-20 HU)
• CECT
○ May appear unilocular (more common) or multilocular
○ Rim or capsule enhancement, wall nodularity
○ May demonstrate hypodense halo due to edema
○ Extrahepatic abnormalities
– Right lower lobe atelectasis
– Right pleural effusion
– Usually colonic and rarely gastric changes
MR Findings
• T1WI
○ Hypointense
• T2WI
○ Hyperintense
○ Perilesional edema: High signal intensity
• T1WI C+
○ Abscess contents: No enhancement
○ Rim or capsule: Shows enhancement
Nuclear Medicine Findings
• Hepatobiliary scan (HIDA)
○ Cold lesion with hot periphery
• Technetium sulfur colloid
○ Cold defects
• WBC scan
○ Cold center and hot rim
Imaging Recommendations
• Best imaging tool
○ Ultrasound is ideal for detecting lesion and guiding
biopsy
• Protocol advice
○ Abdominal scan to include lung bases through to pelvis
DIFFERENTIAL DIAGNOSIS
Hepatic Metastases
• More commonly multiple and smaller lesions, random
distribution
• Post-treatment metastasis
○ Cystic or necrotic nature
○ May be indistinguishable from amebic abscess
• May have internal vascularity
• Usually no elevation of diaphragm or atelectasis
• No signs of infection
Hepatic Pyogenic Abscess
• Simple pyogenic abscess
○ Well-defined lobulated and irregular, hypo- or isoechoic
mass, centrally located in liver
○ "Cluster" sign:Aggregation of small abscesses,
sometimes coalesce into single septated cavity
• May contain gas within abscess
○ Seen as air bubbles or air-fluid level
Hepatic Hydatid Cyst
• Large well-defined cystic liver mass
• Numerous peripheral daughter cysts
• May show curvilinear or ring-like pericyst calcification
• Intrahepatic duct dilatation may be seen
Biliary Cystadenoma/Cystadenocarcinoma
• Multiseptated cystic mass
• Internal solid enhancing component may be present
• No surrounding inflammatory changes
Infarcted Liver After Transplantation
• Biliary and hepatic necrosis caused by hepatic artery
thrombosis
• Less demarcated than abscess and follows vascular territory
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Diagnoses: Liver
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