Focal fatty sparing of the liver, is a localised absence of fatty change in a liver otherwise affects with fatty change (diffuse hepatic steatosis). Recognition of this finding is useful to prevent falsely thinking the region is a mass.
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Similar to its inverse, focal fatty infiltration, regions of focal fatty sparing are thought to have different perfusion characteristics than the rest of the liver. 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.
Focal fatty sparing typically has a geographic appearance and occurs in characteristic locations 1,3:
- adjacent to the porta hepatis (segment IV)
- gallbladder fossa
- adjacent to the falciform ligament
- subcapsular parenchyma
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 may becomes problematic distinguishing it from a focal liver lesion, especially as regions of focal sparing may be seen around focal liver lesions 2,3.
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 increased liver attenuation.
Affected regions demonstrate reduced liver attenuation on both precontrast 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.
Requires both in- and out-of-phase imaging and contrast to adequately assess 1.
Pseudolesions (focal sparing) are better seen on out-of-phase imaging, but otherwise appear 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
- IP/OP: signal drop out in out-of-phase
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.
- 1. Tom WW, Yeh BM, Cheng JC et-al. Hepatic pseudotumor due to nodular fatty sparing: the diagnostic role of opposed-phase MRI. AJR Am J Roentgenol. 2004;183 (3): 721-4. AJR Am J Roentgenol (full text) - Pubmed citation
- 2. Jamal MH, Rayment JH, Meguerditchian A et-al. Impact of the Sentinel Node Frozen Section Result on the Probability of Additional Nodal Metastases as Predicted by the MSKCC Nomogram in Breast Cancer. 2010;doi:10.1093/jjco/hyq225 - Pubmed citation
- 3. Chung JJ, Kim MJ, Kim JH et-al. Fat sparing of surrounding liver from metastasis in patients with fatty liver: MR imaging with histopathologic correlation. AJR Am J Roentgenol. 2003;180 (5): 1347-50. AJR Am J Roentgenol (full text) - Pubmed citation