Characteristics and Outcomes of Patients With Imaging-Defined MASLD and Histological Steatosis Grade S0

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INTRODUCTION: Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent chronic liver disease, and liver biopsy remains the gold standard for diagnosis. However, a subset of patients diagnosed with MASLD by imaging paradoxically exhibit steatosis grade S0 on liver biopsy, posing a diagnostic challenge. This study investigated the outcomes and causes of steatosis 0. METHODS: Steatosis 0 was defined as imaging-detected MASLD with a biopsy-defined steatosis grade S0. We used global cohorts to evaluate outcomes, histologic progression by paired biopsies, and possible causes. The cause analysis included MRI-proton density fat fraction (MRI-PDFF) for fat distribution, pathologist consistency testing, and comparison of serial biopsy sections. RESULTS: In a follow-up cohort of 3,273 biopsy individuals from 16 centers, 123 (3.8%) exhibited steatosis 0. Of these, 29.3% of them had advanced fibrosis (burnt-out MASLD) and demonstrated a risk of liver-related events, whereas those without advanced fibrosis had no such events. In the paired-biopsy cohort of 1,865 patients, 74 (4.0%) individuals initially showed steatosis grade S0; among them, 93.2% retained no or mild steatosis on follow-up biopsy. MRI-PDFF assessments in 42 MASLD patients revealed heterogeneous hepatic fat distribution, with some segments showing steatosis grade S0 despite elevated average liver fat. Interpathologist variability and discrepancies across consecutive biopsy sections contributed to misclassification of steatosis grade. DISCUSSION: Steatosis 0 represents a potential diagnostic gray zone in MASLD. It may be caused by burnt-out MASLD, uneven liver fat distribution, or variability in pathological assessment. Understanding the causes and implications of steatosis 0 is critical for diagnosis and management.

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