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Findings: Images from a high resolution CT scan (HRCT) of the chest demonstrates multiple areas of consolidation and small nodular opacities. These opacities are predominantly limited to the bronchovascular interstitium. There is evidence of traction bronchiectasis and sub pleural cystic changes in areas of more confluent parenchymal involvement.
Diagnosis: Sarcoidosis
Discussion: In the evaluation of disease patterns on HRCT of the chest, it is important to begin the evaluation by anatomic localization of the disease process. Specific diseases will often affect specific interstitial spaces. In this patient, close evaluation of the HRCT shows that the most severe disease is centered specifically along the bronchovascular bundle. This pattern of involvement is strongly suggestive of a limited number of processes. Pathologic evaluation of patients with sarcoidosis show that the distribution of the granulomas are along the lymphatics in the peribronchovascular interstitium. This distribution is often not appreciated on plain chest radiographs, and emphasizes the important role of HRCT in the diagnosis of this disease.
The HRCT evaluation of sarcoidosis has been well described. In addition to the peribronchovascular interstitium, the major fissures, subpleural regions, interlobular and centrilobular spaces are often involved. Confluence of many small sarcoid granulomas can result in larger nodules that can be >1cm in size and may rarely cavitate. It was hoped that the presence of ground glass opacities on HRCT in patients with sarcoidosis would aid in determining those patients with reversible parenchymal disease. Unlike patients with UIP, ground glass opacities have not been a good predictor of disease activity in patients with sarcoidosis. However, the predominantly peribronchovascular distribution has enabled a high percentage of diagnostic transbronchial biopsies in patients with sarcoidosis.
The differential diagnosis of the HRCT appearance of sarcoidosis includes lymphangitic carcinomatosis, silicosis,and berylliosis. In the HIV population, two important diseases that mimic sarcoidosis include Kaposi's sarcoma and lymphoma. Each can have a predominantly peribronchovascular distribution, and clinical history is important in establishing the proper diagnosis.
References:
Webb,WR, Muller NL and Naidich DP. High Resolution CT of the Lung,
Lippincott-Raven, Philadelphia.
Lynch DA, Webb WR, et al. Computed Tomography in Pulmonary Sarcoidosis.
JCAT 1989;13:405-410.
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