Straight-edge sign is an HRCT finding usually seen in the setting of usual interstitial pneumonia. It represents fibrosis isolated to the lung bases characterized by a clear demarcation in the craniocaudal plane on coronal images without significant extension along the lateral margins of the lungs 1-3.
The term "straight-edge" signifies the distinct boundary between fibrotic areas inferiorly and relatively unaffected lung parenchyma superiorly 1-3.
In the context of usual interstitial pneumonia, the presence of the straight-edge sign, along with the exuberant honeycombing sign and the anterior upper lobe sign, has a fairly high specificity but moderate sensitivity for being the result of connective tissue disease-associated interstitial lung disease (CTD-ILD) rather than idiopathic pulmonary fibrosis (IPF) 1,3.
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