Liver Pathology: Steatohepatitis

Brief Case Presentation

A 40-year-old female with a past medical history significant for obesity (BMI 36), hypertension, hyperlipidemia, and type II diabetes mellitus, presents for evaluation due to elevated AST and ALT. The patient denies drug and alcohol use. The most recent liver enzymes and antibody results are seen below.

Lab Test Results

Liver Biopsy Findings

The patient is sent for a liver biopsy, which is shown below. The hepatic architecture is distorted by nodules of hepatocytes with steatosis surrounded by fibrosis (Figure 1). Reticulin (Figure 2) and trichrome (Figure 3) stains highlight the nodularity and increased fibrosis. These findings are consistent with cirrhosis.

Approximately 90% of the lobular parenchyma shows macrovesicular steatosis (Figure 4) with prominent ballooning degeneration (Figure 5) and Mallory Hyaline (Figure 6).

These findings, in conjunction with the clinical history, are consistent with non-alcoholic steatohepatitis (NASH).

What are the characteristic histologic features of NASH?

The diagnosis of NASH requires the presence of steatosis (fat), ballooning degeneration of hepatocytes, and inflammation. Steatotic hepatocytes contain large lipid vacuoles that displace the nuclei to the periphery of the cells.  Ballooning degeneration is characterized by enlarged and swollen hepatocytes with granular material in the cytoplasm, which represents collapsed cytoskeleton.  Mallory Hyaline (i.e. Mallory-Denk bodies) refers to clumps of ropy eosinophilic material in the cytoplasm. They represent misfolded and aggregated keratin filaments.  Inflammatory cell aggregates can be found scattered throughout liver lobules. Portal inflammation can be seen occasionally but it is usually mild.

The main histologic differential diagnosis for NASH is alcoholic steatohepatitis (ASH). Features that are more often seen in ASH include prominent ballooning degeneration (often ringed by neutrophils), frequent Mallory-Denk bodies, and centrilobular sclerosing hyaline necrosis. However, NASH and ASH still overlap greatly in histologic appearance; thus the diagnosis ultimately relies upon the clinical impression.

What are the pathologic scoring systems used to evaluate non-alcoholic fatty liver disease (NAFLD) / NASH in a liver biopsy?

Scoring systems to evaluate NAFLD/NASH include the Brunt system, the NASH Clinical Research Network (NASH CRN) system, and the SAF scoring system. Each system provides a grade based upon the degree of steatosis, lobular/portal inflammation, and ballooning degeneration, as well as a stage based upon the degree of fibrosis.

The Brunt scoring system is seen in Tables 1-3 ^[3,4] and is the most commonly used system in most clinical practices. It was proposed as a method for scoring the severity of NASH and was not designed to distinguish NASH versus NAFLD.  It is categorized by steatosis, ballooning, and lobular(L)/portal (P) inflammation, as well as fibrosis. The grades of steatosis are as follows: grade 1 (≤33%), grade 2 (33-66%), and grade 3 (≥66%). The degree of lobular inflammation is scored from 0-3 based upon the number of foci that show lobular inflammation per 20x fields (Table 2). The degree of portal inflammation (Table 2) is assigned as follows: 0 (none), 1 (mild), 2 (moderate), and 3 (marked). Lastly, the fibrosis is staged as follows: 0 (no fibrosis), 1 (perisinusoidal fibrosis), 2 (periportal and perisinusoidal fibrosis), 3 (bridging fibrosis), and 4 (cirrhosis) (Table 3).

The final report includes the activity grade reported as mild (grade 1), moderate (grade 2), or severe (grade 3) and the stage of fibrosis (1-4).

The NASH CRN scoring system is seen in Table 4 ^[4], which provides a NAFLD activity score based upon steatosis grade, degree of lobular inflammation and hepatocellular ballooning, and fibrosis score. The NASH CRN system was developed to monitor disease progression in clinical trials and similar to Brunt system, it also can't be used to establish the diagnosis of NASH.  As you can see, the system is similar to that of Brunt, but the main difference is that the fibrosis score is broken down into 1a (mild/delicate zone 3 perisinusoidal fibrosis), 1b (moderate/dense zone 3 perisinusoidal fibrosis), and 1c (portal/periportal fibrosis only. The total NAFLD activity score is based upon the summation of scores for steatosis, lobular inflammation, and hepatocellular ballooning from 0-8.

In contrast to the Brunt and NASH-CRN scoring systems, the Steatosis + Activity + Fibrosis (SAF)/Fatty Liver Inhibition of Progression (FLIP) scoring system (SAF)^[5], a newer and not widely used system, was designed to establish a diagnosis of NASH directly based on the total score. SAF system also grades steatosis, inflammation and hepatocellular ballooning.  But the activity score is based on inflammation and ballooning degeneration only. A biopsy demonstrates both inflammation and ballooning degeneration with an activity score equal or higher than 2 is diagnostic for NASH. The presence of steatosis is necessary but the extent of steatosis does not contribute to the final activity score. Omitting severity of steatosis (extent of triglycerides deposition in hepatocytes) in the final score does reflect the biological essence of the disease in which injury is not caused by triglycerides, but by fatty acids and their metabolites, but it does cause problems in scoring cases of burnt-out NASH.

References

1. R. Saxena, Practical Hepatic Pathology: A Diagnostic Approach: Second Edition. 2017.
2. Torbenson, Atlas of Liver Pathology: A Pattern-Based Approach. 2020.
3. Elizabeth M. Brunt. Int J Mol Sci. Vol 17, 2016. PMID: 26771611
4. Tinakos et al. Annu Rev Pathol Mech Dis. Vol 5, 2010. PMID: 20078219
5. Bedossa et al. Hepatology. Vol 56, 2012. PMID: 22707395