From the Guidelines
Yes, perilymphatic, random, and centrilobular patterns can be differentiated on a regular CT scan based on their distinct distribution characteristics. Perilymphatic nodules follow bronchovascular bundles, interlobular septa, and subpleural regions, appearing along these structures in an organized manner. Random nodules show no specific distribution pattern and are scattered throughout the lung parenchyma without relationship to anatomical structures. Centrilobular nodules are centered around the terminal bronchioles in the center of secondary pulmonary lobules, typically sparing the pleural surfaces and interlobular septa.
Key Distribution Characteristics
- Perilymphatic patterns: suggest sarcoidosis, lymphangitic carcinomatosis, or silicosis
- Random patterns: indicate hematogenous spread like metastases or miliary TB
- Centrilobular patterns: point to bronchiolitis, hypersensitivity pneumonitis, or respiratory bronchiolitis These patterns help narrow differential diagnoses. When evaluating these patterns, it's essential to assess the nodule size, margins, and density alongside their distribution, as noted in studies such as 1. High-resolution CT provides better detail but regular CT scans are usually sufficient for initial pattern recognition in most clinical scenarios. The most recent and highest quality study, 1, supports the differentiation of these patterns on CT scans, emphasizing the importance of distribution characteristics and associated findings like air trapping and mosaic attenuation in diagnosing conditions such as hypersensitivity pneumonitis.
From the Research
Differentiation of Perilymphatic, Random, and Centrilobular Patterns on CT Scan
- The differentiation of perilymphatic, random, and centrilobular patterns on a regular Computed Tomography (CT) scan is possible based on the distribution of nodules in relation to the secondary lobule 2.
- High-resolution CT (HRCT) findings can divide miliary patterns into three groups: centrilobular, perilymphatic, and random presentation 2.
- The position of bronchial, vascular, and lymphatic structures can be determined down to the secondary pulmonary lobule, allowing for the distinction of findings by their typical predominance in certain anatomical compartments of the lung 3.
- A centrilobular predominance of nodules is a frequent sign of bronchiolitis, while perilymphatic predominance in the periphery of the lobules is associated with sarcoidosis or lymphangitic spread of cancer 3.
- Random distribution of nodules is interpreted as a sign of hematogenic spread of disease 3.
Anatomic Localization of Nodules
- An algorithm for anatomic localization of small nodules evident on thin-section CT images of the lungs can be used to place nodules into four possible anatomic locations or categories: perilymphatic, random, associated with small airways disease, or centrilobular 4.
- The algorithm is reproducible and accurate in the majority of cases and facilitates nodule localization at thin-section CT 4.
- The most noteworthy source of error and of disagreement between observers is the confusion of perilymphatic and small airways disease-associated nodules in a small number of cases 4.
CT Signs and Patterns of Lung Disease
- A nodular pattern on HRCT can be narrowed by noting whether the nodules are random, centrilobular, or perilymphatic in distribution 5.
- The differential diagnosis of a nodular pattern is very long, but can be narrowed by considering the distribution of the nodules and other imaging findings 5.
- CT signs, such as the tree-in-bud pattern, can be useful indicators of a specific disease process, such as bronchiolitis or infection 5.