Diagnostic Ultrasound - Abdomen and Pelvis

Hepatic Echinococcus Cyst
TERMINOLOGY
Synonyms
• Echinococcal or hydatid disease; echinococcosis
Definitions
• Infection of humans caused by larval stage of Echinococcus
granulosus or Echinococcus multilocularis
IMAGING
General Features
• Best diagnostic clue
○ Membranes ± daughter cysts in complex heterogeneous
mass
• Location: Right lobe > left lobe of liver
• Size: Variable, average 5 cm (max to 50 cm)
○ May contain up to 15 liters of fluid
• Key concepts
○ E. granulosus: Most common form of hydatid disease,
unilocular form
– Up to 60% of cysts are multiple
○ E. multilocularis (alveolaris): Less common but aggressive
form
○ Most common sites: Liver and lungs
Ultrasonographic Findings
• Grayscale ultrasound
○ Variable manifestations based on stage of evolution and
maturity
○ Lewall classification of hydatid lesions
– Cyst with hydatid sand and no internal architecture
– Ruptured cyst with detached endocyst
– Cyst with matrix ± daughter cysts
– Calcified mass
○ E. granulosus
– Anechoic cyst with double echogenic lines separated
by hypoechoic layer
– Honeycombed cyst, multiple septations between
daughter cysts in mother cyst
– Detachment of endocyst from pericyst (partial or
complete) results in varied appearances
– Undulating floating membrane within cyst
– "Water lily" sign: Complete detachment of membrane
– "Snowstorm pattern": Anechoic cyst with internal
debris, hydatid sand
– Dilated IHDs due to compression by cysts
○ E. multilocularis
– Single/multiple echogenic lesions
– Irregular necrotic regions and microcalcifications
– Ill-defined infiltrative solid masses
– Tend to spread to liver hilum
– Invasion of inferior vena cava and diaphragm
– Evaluate lung, heart, and brain for deposits
○ US used to monitor efficacy of antihydatid therapy
– Positive response findings include
□ Reduction in cyst size
□ Endocyst detachment
□ Progressive increase in cyst echogenicity
□ Mural calcification
Radiographic Findings
• Radiography
○ E. granulosus: Curvilinear or ring-like pericyst calcification
– Seen in 20-30% of abdominal plain films
○ E. multilocularis: Microcalcifications in 50% of cases
• Endoscopic retrograde cholangiopancreatography (ERCP)
○ Hydatid cyst may communicate with biliary tree
– Right hepatic duct 55%; left hepatic duct 29%,
common hepatic duct 9%, gallbladder 6%, common
bile duct 1%
CT Findings
• NECT
○ E. granulosus
– Large unilocular/multilocular well-defined hypodense
cysts
– Contains multiple peripheral daughter cysts of less
density than mother cyst
– Curvilinear ring-like calcification
– Calcified wall: Usually indicates no active infection if
completely circumferential
– Dilated intrahepatic bile duct: Due to
compression/rupture of cyst into bile ducts
○ E. multilocularis
– Extensive, infiltrative cystic and solid masses of low
density (14-40 HU)
– Margins are irregular/ill defined
– Amorphous type of calcification
– Can simulate primary or secondary tumor
• CECT
○ Enhancement of cyst wall and septations
MR Findings
• T1WI
○ Rim (pericyst): Hypointense (fibrous component)
○ Mother cyst (hydatid matrix)
– Usually intermediate signal intensity
– Rarely hyperintense: Due to reduction in water
content
○ Daughter cysts: Less signal intensity than mother cyst
(matrix)
○ Floating membrane: Low signal intensity
○ Calcifications: Difficult to identify on MR images
– Display low signal on both T1- and T2WI
• T2WI
○ Rim (pericyst): Hypointense (fibrous component)
○ 1st echo T2WI: Increased signal intensity
– Mother cysts more than daughter cysts
○ Strong T2WI: Hyperintense
– Mother and daughter cysts have same intensity
○ Floating membrane
– Low to intermediate signal intensity
• T1WI C+
○ Enhancement of cyst wall and septations
• MRCP
○ ± demonstrate communication with biliary tree
Imaging Recommendations
• Best imaging tool
○ US for diagnosis and follow-up
http://radiologyebook.com/
Diagnoses: Liver
223