Histological Scoring System for Nonalcoholic Fatty Liver Disease (NAFLD)

Components of NAFLD Activity Score (NAS) and Fibrosis Staging

NAS Components (see scoring interpretation)

Item

Score

Extent

Definition and Comment

Steatosis

0

<5%

Refers to amount of surface area involved by steatosis as evaluated on low to medium power examination; minimal steatosis (<5%) receives a score of 0 to avoid giving excess weight to biopsies with very little fatty change

1

5-33%

2

>33-66%

3

>66%

Lobular Inflammation

0

No foci

Acidophil bodies are not included in this assessment, nor is portal inflammation

1

<2 foci/200x

2

2-4 foci/200x

3

>4 foci/200x

Hepatocyte Ballooning

0

None

1

Few balloon cells

The term “few” means rare but definite ballooned hepatocytes as well as cases that are diagnostically borderline

2

Many cells/prominent ballooning

Most cases with prominent ballooning also had Mallory’s hyalin, but Mallory’s hyaline is not scored separately for the NAS

Fibrosis Stage (Evaluated separately from NAS)

Fibrosis

0

None

1

Perisinusoidal or periportal

1A

Mild, zone 3, perisinusoidal

“delicate” fibrosis

1B

Moderate, zone 3, perisinusoidal

“dense” fibrosis

1C

Portal/periportal

This category is included to accommodate cases with portal and/or peri portal fibrosis without accompanying pericellular/perisinusoidal fibrosis

2

Perisinusoidal and portal/periportal

3

Bridging fibrosis

4

Cirrhosis

Total NAS score represents the sum of scores for steatosis, lobular inflammation, and ballooning, and ranges from 0-8. Diagnosis of NASH (or, alternatively, fatty liver not diagnostic of NASH) should be made first, then NAS is used to grade activity. In the reference study, NAS scores of 0-2 occurred in cases largely considered not diagnostic of NASH, scores of 3-4 were evenly divided among those considered not diagnostic, borderline, or positive for NASH. Scores of 5-8 occurred in cases that were largely considered diagnostic of NASH.

 

 

References:

  1. Kleiner DE, Brunt EM, Van Natta M, Behling C, Contos MJ, Cummings OW, Ferrell LD, Liu YC, Torbenson MS, Unalp-Arida A, Yeh M, McCullough AJ, Sanyal AJ; Nonalcoholic Steatohepatitis Clinical Research Network. Design and validation of a histological scoring system for nonalcoholic fatty liver disease. Hepatology. 2005 Jun;41(6):1313-21. [Medline]

Created: May 11, 2007
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