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Focal fatty sparing of the liver

Focal fatty sparing of the liver, is simply localised absence of fatty change which otherwise affects the whole liver (diffuse hepatic steatosis). 

Demographics and clinical presentation

To be added

Radiographic features

Focal fatty sparing typically has a geographic appearance and occurs in characteristic locations 1,3:

Important features, along with location and echogenicity/density/intensity are 2:

  • absence of mass effect
  • absence of distortion of vessels that run through the region.

When it occurs outside of these areas, or has a nodular appearance, it becomes problematic to distinguish from focal liver lesions, especially as regions of focal sparing are also seen around focal liver lesions 2,3. The cause of this is incompletely understood but is thought to result again from alterations in perfusion, either due to compression or invasions of portal venules by the tumour 3.

Ultrasound

Liver with fatty change demonstrates increased echogenicity and attenuation 2. The echogenic walls of the portal veins and hepatic veins are lost, due to the liver attenuation having increased.

CT

Affected regions demonstrate reduced liver attenuation on both pre-contrast and portal venous phase imaging. It is important to remember that the spleen enhances earlier than the liver (due to systemic arterial supply rather than predominantly portal) and thus arterial phase or very early portal venous phase scans should not be used.

MRI

Requires both in- and out-of-phase imaging and contrast to adequately asses 1.

Pseudolesion (focal sparing) better seen on out-of-phase imaging, but otherwise appears normal and similar to the rest of the liver on T2 and contrast enhanced sequences 1

The rest of the liver demonstrates:

  • T1: hyperintense
  • T2: mildly hyperintense
  • out-of-phase imaging: signal drop out in fatty liver

Treatment and prognosis

When focal sparing is idiopathic, and not related to a hepaic focal mass, then the prognosis is that of a patient with diffuse hepatic steatosis.

Differential diagnosis

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