Diagnostic imaging and interventional procedures in a growing problem: Hepatic alveolar echinococcosis

Table 1 PNM classification of alveolar echinococcosis

P	Primary lesion localized to the liver
PX	Primary lesion cannot be assessed
P0	No detectable hepatic lesion
P1	Peripheral hepatic lesion with no proximal hepatic vascular or biliary involvement
P2	Central hepatic lesion with proximal involvement of vessels or biliary ducts in one lobe1
P3	Central hepatic lesion with involvement of hilar vessels or biliary ducts in both lobes or with involvement of two hepatic veins
P4	Hepatic lesion with extension along the vessels2 and biliary tree
N	Extrahepatic involvement of neighboring organs or tissues [diaphragm, lung, pleura, pericardium, heart, gastric or duodenal wall, adrenal gland, peritoneum, retroperitoneum, parietal wall (muscles, skin, bone), pancreas, regional lymph nodes, hepatic ligaments, kidney]
NX	Cannot be evaluated
N0	No regional involvement
N1	Regional involvement of contiguous organs or tissues
M	Absence or presence of distant metastasis (in lung, distant lymph nodes, spleen, central nervous system, orbits, bone, skin, muscle, kidney, distant peritoneum, and retroperitoneum)
MX	Not completely evaluated
M0	No metastasis3
M1	Metastasis

¹For purposes of PNM classification, the liver is considered to be divided into two lobes by a plane projecting between the gallbladder bed and the inferior vena cava;

²Vessels include the inferior vena cava, portal vein and arteries;

³Absence of metastases is considered to be indicated by negative findings at chest radiography and computed tomography of the brain.

Table 2 Morphological characteristics of hepatic alveolar echinococcosis lesions

Modality	Hepatic AE lesions
US	Mass with irregular margins, scattered foci of calcification, central necrosis, and vascular and biliary involvement
CT
Unenhanced	Mass with irregular margins, hyperattenuating foci of calcification, and hypoattenuating regions of necrosis and parasitic tissue
Contrast- enhanced	Mass with no substantial enhancement and peripheral fibroinflammatory components with slight but long-lasting enhancement
CT perfusion	Lower BF, BV, ALP and PVP values in AE lesions compared with normal liver parenchyma
MRI
T1-weighted	Heterogeneous mass with irregular margins and a necrotic center that exhibits low to intermediate signal intensity
T2-weighted	Heterogeneous mass with irregular margins, a necrotic center that exhibits high signal intensity, and low-signal-intensity fibrotic and collagenous components
Contrast-enhanced	Mass with no substantial enhancement and peripheral fibroinflammatory components with slight but long-lasting enhancement
Diffusion-weighted	Mass with hypointense signal and high ADC on images obtained with high b values

AE: Alveolar echinococcosis; CT: Computed tomography; US: Ultrasonography; BF: Blood flow; BV: Blood volume; ALP: Arterial liver perfusion; PVP: Portal-venous perfusion; ADC: Apparent diffusion coefficient.