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5. HRCT shows patchy, small nodules consistent with a perilymphatic distribution
The diagnostic value of HRCT for the assessment of pulmonary nodular diseases relies heavily on the distribution of the nodules relative to structures within the secondary pulmonary lobule, a diagnostic approach that was first recognized by pathologists as valuable for interpretation of biopsy and surgical histopathological specimens. HRCT technique allows imagers to extrapolate these pathological findings to imaging findings. Histopathologically, at least 4 nodule distributions within the secondary pulmonary lobule are recognized: bronchiolocentric, angiocentric, lymphatic, and, random. Nodules that are bronchiolocentric in distribution are related to the centrilobular and lobular bronchi, and angiocentric nodules are related to the pulmonary arteries within the secondary pulmonary lobule. Because the artery and bronchus are in very close proximity to one another within the secondary pulmonary lobule, both nodule types are located in or very near the center of the secondary pulmonary lobule, and these two distributions are not readily distinguished from one another on HRCT. So, bronchiolocentric and angiocentric nodule histopathological distributions are grouped together as centrilobular nodules. Thus, three distributions of nodules within the secondary pulmonary lobule are recognized on HRCT: centrilobular, perilymphatic, and random (Figure 5).
Figure 5. Small nodule distributions on HRCT: Centrilobular= nodules (arrowhead) approach, but typically space, costal and fissural pleural surfaces; Perilymphatic: nodules (arrowheads) contact costal and fissural pleural surfaces and are located along interlobular septae as well. The nodule distribution is typically patchy- normal lung regions are juxtaposed against abnormally infiltrated lung regions, and; Random: nodules (arrowheads) are seen along fissural surfaces but also appear centrilobular as well, and are diffusely distributed through the lungs bilaterally.
In this case, the nodules are noticeably distributed along pleural surfaces, particularly the right major fissure, and the distribution of the nodules is patchy- this latter terms indicates abnormally infiltrated regions of lung are juxtaposed to relatively normal appearing lung, in contrast with a diffuse distribution, in which abnormally infiltrated lung is fairly widespread. The HRCT in this patient shows that the nodules are distributed along pleural surfaces and have a patchy distribution, which is most consistent overall with a perilymphatic nodule distribution. No consolidation with air bronchograms is evident and no bronchiectasis is seen.
Which of the following conditions are associated with perilymphatic nodule formation at HRCT? (Click on the correct answer to procced to the sixth of seven panels)