The Pathomorphological Substrate of Sonographic Signs in Gallbladder Disease: A Sign-Based Narrative Review

Abstract

Ultrasonography is the first-line and, in most settings, the only imaging modality applied to the gallbladder, yet its findings are habitually taught disease-first: a diagnosis is named and its sonographic appearance described. At the machine the operator faces the inverse problem — an echo pattern is present and its tissue meaning must be inferred. This review reorganises the evidence accordingly. We first set out the histological architecture of the gallbladder wall, emphasising two features that govern everything downstream: the absence of a submucosa and of a muscularis mucosae, and a total mural thickness of 1–3 mm that lies at or below the axial resolution of conventional transabdominal probes. We then work through the principal sonographic signs — diffuse and focal wall thickening, the striated or layered wall, loss of layering, comet-tail reverberation, intramural anechoic spaces, polypoid lesions, intraluminal membranes, intramural gas and mural calcification — and for each specify the tissue substrate, the differential range of substrates that can generate the same appearance, and the resulting diagnostic ceiling. Three systematic reasons why sono-pathological correlation fails are identified and discussed: substrate non-specificity, the mismatch between acoustic and histological scale, and verification bias arising from the fact that histology is available almost exclusively for gallbladders selected for resection. We consider what high-resolution ultrasound, contrast-enhanced ultrasound, elastography and radiomic analysis add to each of these three problems, and we trace the persistent disagreement between international guidelines on gallbladder polyps back to a histological fact: the great majority of small polypoid lesions are cholesterol polyps, and size is a weak surrogate for neoplasia. A structured reporting template derived from the sign-substrate analysis is proposed.