ACR Appropriateness Criteria® Diffuse Lung Disease: 2026 Update.

Diffuse lung diseases (DLD) also referred to as diffuse parenchymal lung diseases or interstitial lung diseases encompass diverse disorders affecting the lung parenchyma with possible multicompartment involvement in the chest. DLD include several hundred established clinical syndromes and pathologies, with a variety of possible etiologies. Imaging plays a central role during multidisciplinary discussion, which constitutes the current standard for diagnosis and monitoring of DLD. This document aims to establish guidelines for evaluation of diffuse lung diseases for 1) initial imaging of suspected diffuse lung disease, 2) initial imaging of suspected acute exacerbation or acute deterioration in cases of confirmed diffuse lung disease, and 3) surveillance of confirmed diffuse lung disease without acute deterioration. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.