When reviewing medical imaging reports, such as a lung computed tomography (CT) scan, you might encounter the term “mosaic attenuation.” This pattern, seen on lung CT scans, is an observation that guides medical professionals toward potential underlying lung conditions, rather than a diagnosis itself.
What Mosaic Attenuation Looks Like
Mosaic attenuation describes a visual pattern on a lung CT scan, resembling a patchwork or tiled floor. It consists of distinct areas within the lung tissue that show varying degrees of density, appearing as lighter and darker regions. These regions are sharply defined, creating a geographic pattern. This pattern is best observed on images taken during a full breath in (inspiratory CT images). It signifies heterogeneous lung attenuation, meaning the lung tissue is not uniformly dense throughout.
Reasons for Mosaic Attenuation
The mosaic attenuation pattern arises from different physiological mechanisms affecting the lungs, leading to variations in tissue density. These mechanisms primarily involve how air moves through the airways, how blood flows through the lung’s vessels, or changes within the lung tissue itself.
One common cause is air trapping, where certain areas of the lung do not fully exhale, retaining more air. These trapped air regions appear darker on a CT scan due to their lower density, contrasting with adjacent lung tissue. This phenomenon often occurs in small airway diseases, such as asthma, chronic obstructive pulmonary disease (COPD), or bronchiolitis.
Another mechanism is abnormal blood flow, or perfusion, within the lungs. Areas with reduced blood flow appear less dense on the scan because there is less blood volume to absorb the X-rays. Conditions like pulmonary embolism or pulmonary hypertension can lead to such perfusion differences. In these cases, the lighter areas on the CT represent the less-perfused, abnormal lung tissue.
Interstitial lung diseases can also contribute to a mosaic pattern. These conditions involve inflammation or scarring of the lung’s interstitial tissue, which can make affected areas appear denser. This increased density creates a contrast with normal lung tissue, contributing to the patchy appearance. Hypersensitivity pneumonitis, for example, can present with a combination of air trapping, ground-glass opacities, and normal lung tissue.
What Mosaic Attenuation Indicates
Mosaic attenuation serves as an important clue for medical professionals, helping them narrow down potential underlying lung conditions. It is a sign that prompts further investigation, rather than being a standalone diagnosis itself. The pattern indicates a non-uniform distribution of disease within the lungs.
To understand the cause, doctors analyze whether the darker or lighter areas represent the abnormal lung tissue. For instance, if the darker areas are abnormal due to air trapping, it points towards small airway diseases. If the lighter areas are abnormal due to reduced blood flow, vascular issues are more likely.
The patient’s overall symptoms, medical history, and other clinical findings are combined with the imaging pattern to reach an accurate diagnosis. This comprehensive approach guides the selection of additional diagnostic tests and helps determine the most appropriate treatment plan.