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Focal hepatic steatosis

Focal hepatic steatosis (focal fat infiltration of the liver) is common and seen in a number of clinical settings, essentially the same as those that contribute to diffuse hepatic steatosis:

  • diabetes mellitus
  • obesity
  • alcohol abuse
  • exogenous steroids
  • drugs (amiodarone, methotrexate, chemotherapy)
  • IV hyperalimentation

In general treatment of the underlying condition will reverse the findings.

Location

A characteristic location for focal fatty change is the medial segment of the left lobe of the liver (segment IV) either anterior to the porta hepatis or adjacent to the falciform ligament. This distribution is the same as that seen in focal fatty sparing and is thought to relate to variations in vascular supply. This also would account for focal fatty change/sparing sometimes seen related to vascular lesions.

Radiographic features

Ultrasound

Ultrasound features only become apparent when the amount of fat reaches 15-20%. Features include:

  • increased hepatic echogenicity
  • hyper-attenuation of the beam
  • mild or absent positive mass effect
  • geographic borders
  • no distortion of vessels
  • inability to visualise the portal vein walls (as the parenchyma is as bright as the wall)
CT
  • decreased attenuation (non contrast CT)
    • normal liver 50-57 HU
    • decreases by 1.6 HU per mg of fat in each gram of liver
  • decreased attenuation (post contrast CT)
    • liver and spleen should normally be similar on delayed (70 second) scans
    • earlier scans are unreliable as the spleen enhances earlier than the liver (systemic supply rather than portal)
MRI

MRI is the imaging modality of choice in any case where the diagnosis is felt to be less than certain

  • increased T1 signal
  • signal drop-out in out of phase imaging
  • ability to quantify fat fraction

Differential diagnosis

When located in characteristic locations then there is usually little difficulty in making the correct diagnosis. If unusual in location or appearance then differential to be considered includes:

See also

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