radiolucencies

Radiolucencies are areas on radiographs that appear darker than surrounding tissues because they transmit more X-ray photons, reflecting lower density or greater proportion of air, gas, fat, or fluid. They are the opposite of radiopaque regions, which appear white or light due to higher mineral content or tissue density. Radiolucency is relative and depends on imaging technique, projection, and anatomic context.

Normal radiolucencies include air-filled spaces such as the maxillary and frontal sinuses, nasal cavity, and the periodontal ligament space around teeth. In dental imaging, the pulp chamber and root canal spaces also appear radiolucent, as do the spaces between teeth in a healthy periodontium.

Pathologic radiolucencies arise when a region within bone or soft tissue becomes less dense or contains air. Common examples in dentistry include dental caries (loss of mineral density within enamel or dentin), periapical radiolucencies indicating inflammatory or granulomatous processes at a tooth apex, and radiolucent cysts or tumors within the jaws. In the chest, lucencies correspond to air-filled lungs and can reflect normal aeration or pathologies such as pneumothorax or emphysema. In bone, radiolucent lesions may indicate osteolysis, cysts, tumors, or metabolic bone disease, and their appearance ranges from well-defined, corticated holes to ill-defined, destructive areas.

Interpretation relies on margins, location, effect on adjacent structures, and comparison with prior images. Imaging modality choice (plain radiographs, CT, CBCT, MRI) influences detection and characterization. When radiolucencies are unclear or clinically concerning, further evaluation or biopsy may be warranted.