A chest computed tomography (CT) scan is a sophisticated imaging tool that generates detailed cross-sectional pictures of the chest cavity. The simple answer to whether a CT scan can show inflammation is yes. The scan provides visual evidence of the physical changes that occur in the lungs and surrounding structures when an inflammatory process is active. By identifying changes like fluid accumulation and tissue thickening, a CT scan aids in diagnosing and assessing the extent of various chest conditions.
How a CT Scan Works
A computed tomography scanner utilizes a rotating X-ray tube and detectors to measure the attenuation, or weakening, of the X-ray beam as it passes through the body. This data is processed by a computer to reconstruct detailed, cross-sectional images, often referred to as “slices.” The fundamental principle is density mapping, which assigns a numerical value to the tissue density called the Hounsfield unit (HU).
The Hounsfield scale is standardized: distilled water is zero HU, air is negative 1,000 HU, and dense bone has high positive values. Air-filled lungs naturally have a very low density, appearing dark on the scan. When inflammation occurs, the tissue structure changes, and CT captures this shift in density, making the pathology visible.
Recognizing Inflammatory Patterns
Inflammation involves the infiltration of fluid, immune cells, and proteins into the affected tissue, which increases its overall density. For the air-filled lungs, this density increase is easily detectable because it shifts the tissue’s Hounsfield unit value toward that of water or soft tissue. Radiologists look for specific visual patterns that correspond to these density changes, suggesting a different stage or type of inflammation.
One common pattern is consolidation, which appears as a solid white or very bright area on the scan. Consolidation signifies that the air in the lung’s alveoli has been completely replaced by fluid and inflammatory cells, making the tissue appear solid. Another distinct pattern is ground-glass opacity (GGO), a hazy gray area showing increased lung density without completely obscuring underlying blood vessels. GGO indicates that air spaces are only partially filled with fluid or that the alveolar walls are thickened, suggesting less severe inflammation than consolidation.
Inflammation can also affect the protective membranes surrounding the lungs, known as the pleura, leading to pleural effusion. This is seen as a collection of fluid in the space between the lung and the chest wall. Other signs, such as thickening of the septa (the connective tissue walls separating the lung lobules) or enlarged lymph nodes, further contribute to the overall picture of an inflammatory process.
Specific Inflammatory Conditions Identified
The visual patterns identified on a chest CT scan are linked to a variety of clinical conditions, providing context for diagnosis. Pneumonia, a frequent cause of chest inflammation, commonly manifests as consolidation or ground-glass opacities in the lung tissue (parenchyma). The CT scan helps determine the extent and distribution of this infection, regardless of whether it is bacterial, viral, or fungal.
Conditions affecting the airways, such as bronchitis or bronchiolitis, may show thickening of the bronchial walls and a “tree-in-bud” pattern, indicating inflammation and fluid in the small airways. If inflammation affects the pleura, the CT can confirm pleurisy and detect associated pleural effusion.
The scan is also effective for diagnosing and monitoring interstitial lung diseases (ILDs), chronic conditions that cause inflammation and scarring in the lung’s supporting structure. Conditions like sarcoidosis or pulmonary fibrosis are characterized by specific patterns of septal thickening or fine scarring. These patterns are often too subtle to be seen on a standard chest X-ray, and CT imaging allows physicians to track the progression of these chronic inflammatory states.
Limitations and Complementary Testing
While the chest CT scan is excellent at detecting the presence and location of inflammation, it often lacks the specificity to determine the exact cause. For example, ground-glass opacity can be a sign of many different issues, including infection, pulmonary edema, or some types of cancer. The image shows the physical effect of the inflammation, but not the underlying pathology driving it.
Therefore, a CT scan must be complemented by other tests to confirm a specific diagnosis and guide treatment. Physicians often rely on laboratory tests, such as blood work to check inflammatory markers or a sputum culture to identify a specific pathogen. In some complex cases, a biopsy of the affected lung tissue may be necessary to microscopically examine the cells. This helps definitively differentiate between infectious, autoimmune, or malignant causes of inflammation.