Diffuse cystic lung diseases: correlation between radiologic and functional status.

Background: High-resolution CT (HRCT) scanning plays an important role in the diagnosis of diffuse cystic lung diseases (DCLDs). However, its role in the clinical evaluation of patients affected by DCLD has not yet been well-clarified. At present, pulmonary function tests are the only methods available for the evaluation of lung impairment due to these diseases, but their sensitivity and reliability are still limited.

Purpose: The aim of this study was to correlate the quantitative score of cystic-aerial lesions obtained by a HRCT density mask (DM) software with pulmonary function data in DCLDs.

Methods: Spirometry, lung volumes, diffusion capacity, arterial blood gas (ABG) analysis, 6-min walking test (6-MWT), and HRCT with DM quantitative evaluation were performed in a cohort of 25 patients (lymphangioleiomyomatosis [LAM], 13 patients; Langerhans cells histiocytosis [LCH], 12 patients). Linear regression was used for the statistical analysis. The sum and mean of the air-trapping percentages at three different levels of DM study (ie, aortic arch, left lower lobe bronchus origin, and 2 cm from the diaphragmatic muscle), and various functional parameters and exercise performance values were matched for the analysis.

Results: An obstructive pattern was present in 13 patients (52%; LCH group, 8 patients; LAM group, 5 patients). A predominant restrictive pattern was detected only in three patients (12%; LCH group, two patients; LAM group, one patient). Nine patients (36%) walked < 350 m, and 14 of 23 patients (61%) had a significant decrease in arterial oxygen saturation during exercise (> 4 U). The results of DM quantitative study (sum and mean) significantly correlated with FVC (r = - 0.56; p < 0.001), FEV(1)/vital capacity (r = - 0.94; p < 0.002), midexpiratory phase of forced expiratory flow (r = - 0.84; p < 0.05), FEV(1) (r = - 0.82; p < 0.05), and diffusing capacity of the lung for carbon monoxide (r = - 0.82; p < 0.05), bronchial airway resistance (r = 0.79; p < 0.05), and distance walked on the 6-MWT (r = - 0.53; p < 0.05). No significant correlation was found with the results of ABG analysis.

Conclusions: In DCLDs, HRCT scans with quantitative assessment performed by a DM software showed a very good correlation with functional parameters. Therefore, DM could be considered, in combination with a complete functional assessment, in the initial evaluation of patients affected by DCLDs. However, further studies are needed to assess its usefulness in the follow-up of these patients.