Compression-type hepatic pseudolesions occur typically when an extrinsic structure, during the patient's deep inspiration breath-hold at the time of CT acquisition, causes transient focal compression of a subcapsular region of the liver and subsequent decreased portal perfusion and minimal change in hepatic arterial perfusion. The hemodynamic alterations are temporary in accordance with the transient compression; therefore, metabolic changes such as focal fatty sparing or focal fatty steatosis will not occur. However, persistence of the compression leads to permanent hemodynamic alterations which may result in a benign malformation, known as Corset liver 4.
Extrinsic structures responsible for this type of pseudolesions include
- ribs: the right seventh to eleventh ribs can cause pseudolesions in segments 5 and 6
- diaphragm: irregular contractions of the diaphragm can cause pseudolesions in segments 7 and 8, particularly in elderly patients
Radiographic features
CT
Compression-type hepatic pseudolesions appear exclusively on portal venous phase CT as an ill-defined, low-attenuated area just beneath an extrahepatic compressing structure. Portal vein branches may be seen within.
On unenhanced, arterial phase, and delayed phase CT, no abnormal attenuation should be observed.
The disappearance of these pseudolesions when CT is repeated with a different inspiration level helps in differentiating pseudolesions from true lesions.
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