NAFLD (MASLD)/NASH (MASH): Does It Bother to Label at All? A Comprehensive Narrative Review

Abstract

Nonalcoholic fatty liver disease (NAFLD), or metabolic dysfunction-associated steatotic liver disease (MASLD), is a liver condition that is linked to overweight, obesity, diabetes mellitus, and metabolic syndrome. Nonalcoholic steatohepatitis (NASH), or metabolic dysfunction-associated steatohepatitis (MASH), is a form of NAFLD/MASLD that progresses over time. While steatosis is a prominent histological characteristic and recognizable grossly and microscopically, liver biopsies of individuals with NASH/MASH may exhibit several other abnormalities, such as mononuclear inflammation in the portal and lobular regions, hepatocellular damage characterized by ballooning and programmed cell death (apoptosis), misfolded hepatocytic protein inclusions (Mallory-Denk bodies, MDBs), megamitochondria as hyaline inclusions, and fibrosis. Ballooning hepatocellular damage remains the defining feature of NASH/MASH. The fibrosis pattern is characterized by the initial expression of perisinusoidal fibrosis ("chicken wire") and fibrosis surrounding the central veins. Children may have an alternative form of progressive NAFLD/MASLD characterized by steatosis, inflammation, and fibrosis, mainly in Rappaport zone 1 of the liver acinus. To identify, synthesize, and analyze the scientific knowledge produced regarding the implications of using a score for evaluating NAFLD/MASLD in a comprehensive narrative review. The search for articles was conducted between 1 January 2000 and 31 December 2023, on the PubMed/MEDLINE, Scopus, Web of Science, and Cochrane databases. This search was complemented by a gray search, including internet browsers (e.g., Google) and textbooks. The following research question guided the study: "What are the basic data on using a score for evaluating NAFLD/MASLD?" All stages of the selection process were carried out by the single author. Of the 1783 articles found, 75 were included in the sample for analysis, which was implemented with an additional 25 articles from references and gray literature. The studies analyzed indicated the beneficial effects of scoring liver biopsies. Although similarity between alcoholic steatohepatitis (ASH) and NASH/MASH occurs, some patterns of hepatocellular damage seen in alcoholic disease of the liver do not happen in NASH/MASH, including cholestatic featuring steatohepatitis, alcoholic foamy degeneration, and sclerosing predominant hyaline necrosis. Generally, neutrophilic-rich cellular infiltrates, prominent hyaline inclusions and MDBs, cholestasis, and obvious pericellular sinusoidal fibrosis should favor the diagnosis of alcohol-induced hepatocellular injury over NASH/MASH. Multiple grading and staging methods are available for implementation in investigations and clinical trials, each possessing merits and drawbacks. The systems primarily used are the Brunt, the NASH CRN (NASH Clinical Research Network), and the SAF (steatosis, activity, and fibrosis) systems. Clinical investigations have utilized several approaches to link laboratory and demographic observations with histology findings with optimal platforms for clinical trials of rapidly commercialized drugs. It is promising that machine learning procedures (artificial intelligence) may be critical for developing new platforms to evaluate the benefits of current and future drug formulations.

Keywords: MASH; MASLD; NAFLD; NASH; classification; liver; nomenclature; scores; taxonomy.

Figure 1

Diagnostic criteria for MASLD. If hepatic steatosis is present, the identification of any CMRF (*) would lead to a diagnosis of MASLD, provided that there are no other causes of hepatic steatosis. If other causes of steatosis are discovered, then this is in line with a mix of factors contributing to the condition. When it comes to alcohol, this is referred to as MetALD. If there are no obvious cardiometabolic criteria present, other potential causes must be ruled out. If no other cause is found, this is referred to as cryptogenic SLD (**). However, based on clinical opinion, it might also be seen as probable MASLD and would, therefore, require periodic examination on an individual basis. In cases of severe fibrosis/cirrhosis, the presence of steatosis may not be evident. Therefore, clinical judgment should be used, taking into consideration the patient’s clinical, metabolic, and risk factors, as well as ruling out other possible causes. Abbreviations: ALD, alcohol-associated/related liver disease; BMI, body mass index; BP, blood pressure; CMRF, cardiometabolic risk factors; DILI, drug-induced liver disease; MetALD, metabolic dysfunction and alcohol-associated steatotic liver disease; SLD, steatotic liver disease; WC, waist circumference.

Figure 2

CHEO (Children’s Hospital of Eastern Ontario) Protocol for Pediatric Liver Biopsy. Schematic approach to a liver biopsy core with a sample reserved for FFPE, a sample dedicated to ORO staining (special stain) for cryostat cutting and staining for fat cell quantification, and one or two samples for ultrastructural examination (EM, electron microscopy). In case more cores are provided, the additional cores are channeled for formalin fixation and paraffin embedding (FFPE). Notes: TEM, transmission electron microscopy; FFPE, formalin fixation paraffin embedding; ORO, Oil red O.

Figure 3

(a) Liver fibrosis. Extensive pericentral and periportal fibrosis with collagen deposition (blue) forming bridges and nearly pseudo-nodules (arrows). Masson’s trichromic stain, 100× original magnification, scale bar: 100 μm. (b) Liver steatosis. Fatty accumulation in the hepatocytes can be highlighted (orange) using the Oil red O staining (arrows; ORO stain, 100× original magnification, scale bar: 100 μm). (c) Hepatocytic ballooning. ‘Hepatocytic ballooning’ is an often-employed combined term in liver histology that denotes the degeneration of hepatocytes, characterized by their expansion, swelling, rounding, and the presence of reticulated cytoplasm (arrows; Hematoxylin–Eosin staining, 400× original magnification, scale bar: 10 μm). (d) Councilman bodies at portal and periportal areas. Councilman bodies (black arrows) are evidence of single-cell necrosis. A Councilman body, often referred to as a Councilman hyaline body or apoptotic body, is a pink-stained globule composed of pieces of dying liver cells. In the end, the fragments are engulfed by macrophages or nearby parenchymal cells. This pediatric patient was affected by Overlap syndrome, characterized by MASLD/MASH and autoimmune hepatitis, which is characterized by plasma cells (green arrow) infiltrating the portal tracts and evidence of interface hepatitis (Hematoxylin–Eosin staining, 400× original magnification, scale bar: 10 μm).

Figure 3

(a) Liver fibrosis. Extensive pericentral and periportal fibrosis with collagen deposition (blue) forming bridges and nearly pseudo-nodules (arrows). Masson’s trichromic stain, 100× original magnification, scale bar: 100 μm. (b) Liver steatosis. Fatty accumulation in the hepatocytes can be highlighted (orange) using the Oil red O staining (arrows; ORO stain, 100× original magnification, scale bar: 100 μm). (c) Hepatocytic ballooning. ‘Hepatocytic ballooning’ is an often-employed combined term in liver histology that denotes the degeneration of hepatocytes, characterized by their expansion, swelling, rounding, and the presence of reticulated cytoplasm (arrows; Hematoxylin–Eosin staining, 400× original magnification, scale bar: 10 μm). (d) Councilman bodies at portal and periportal areas. Councilman bodies (black arrows) are evidence of single-cell necrosis. A Councilman body, often referred to as a Councilman hyaline body or apoptotic body, is a pink-stained globule composed of pieces of dying liver cells. In the end, the fragments are engulfed by macrophages or nearby parenchymal cells. This pediatric patient was affected by Overlap syndrome, characterized by MASLD/MASH and autoimmune hepatitis, which is characterized by plasma cells (green arrow) infiltrating the portal tracts and evidence of interface hepatitis (Hematoxylin–Eosin staining, 400× original magnification, scale bar: 10 μm).

Figure 4

Single and multiple aspects of hepatocellular injury and portal tract damage. Upper microphotographs (A,B) show a low-power view (A) of two teenager patients with nonalcoholic fatty liver disease (NAFLD/MASLD) ((A), the arrow exquisitely exhibits the Oil-red-O stained vacuoles of the hepatocytes) and a high-power view (B) with Periodic acid Schiff (PAS)-stained nuclei in a pediatric patient with type 1 diabetes mellitus (T1DM) and Mauriac syndrome. Mauriac syndrome is a rare complication of T1DM. It is related to low-insulin concentrations and characterized by hepatomegaly, growth and puberty delay, as well as elevated transaminases and serum lipids. The middle microphotographs highlight lobulitis (black arrow) and ballooning (red arrow) in a child with nonalcoholic steatohepatitis (NASH) (C) as well as ballooning with a hepatocyte exhibiting a Mallory–Denk body (black arrow) (D). The lower microphotographs show heavy vacuolar degeneration and prominent bridging fibrosis and perisinusoidal fibrosis (“chicken wire”; black arrow) using a Masson’s trichromic stain (E) and prominent fibrosis and Malloy–Denk bodies (red arrow) using a slightly modified Masson’s trichromic to highlight perisinusoidal fibrosis (F). Masson’s trichrome is a three-color-staining procedure used in histology and different specific applications, but all are suited for distinguishing cells from surrounding connective tissue. Overall, the stain produces red keratin and muscle fibers, blue or green collagen and bone, light red or pink cytoplasm, and dark brown to black cell nuclei. The “slightly modified” Masson’s trichromic stain was achieved by increasing the time of exposure of the tissue with the solution C, also called fiber stain, which contains Light Green SF yellowish, or alternatively Fast Green FCF. ((A), Oil-red O stain, 100× original magnification; (B), PAS stain, 630× original magnification; (C), Hematoxylin and Eosin stain, 400× original magnification; (D), Hematoxylin and Eosin stain, 630× original magnification; (E), Masson’s trichromic stain, 100× original magnification; (F), “slightly modified” Masson’s trichromic stain, 200× original magnification). All microphotographs are from patients who presented at our clinics and were younger than 18 years of age at the time of the liver biopsy.

Figure 5

Comparison of the three most used nonalcoholic fatty liver disease/nonalcoholic steatohepatitis (NAFLD (MASLD)/NASH (MASH)) scoring systems. The three most commonly used scoring systems include the Brunt’s score, the NASH Clinical Research Network (NASH CRN), and the SAF (steatosis, activity, and fibrosis) score. The SAF score separates steatosis from parenchymal necroinflammation, which are two characteristics that may have distinct prognostic potential. Five features are scored in the Brunt’s and NASH CRN scores, while only four features are scored in the SAF score. The features are explained on the left side of the figure and cartoons are depicted at the base of the photograph.