Is high-resolution computed tomography a reliable tool to predict the histopathologic activity of pulmonary Langerhans cell histiocytosis?

High-resolution computed tomography (HRCT) has proved to be very useful in the diagnosis and follow-up of pulmonary Langerhans cell histiocytosis (PLC H), but the precise relationships between nodules and thin-wall cysts obser ved by HRCT, and granulomatous or cystic lesions present in lung tissue, re main to be established. The aim of this study was to compare quantitative d ata obtained by HRCT and those obtained by histopathological examination of corresponding lung tissue specimens in patients with biopsy-proven PLCH. T he results demonstrated that the extent of nodular abnormalities was strong ly correlated with the density of florid granulomatous lesions in lung tiss ue. A strong correlation was also found between the extent of cystic abnorm alities and the density of cavitary lesions, but the latter included both s till inflammatory cavitary granulomas and cicatricial fibrous cysts. Intere stingly, small isolated florid granulomas were found in lung tissue from mo st patients with a predominant cystic CT scan pattern. Taken together, thes e results demonstrate that HRCT has to be considered with caution to evalua te the histopathological activity of PLCH. Patients presenting with predomi nant HRCT cystic abnormalities should benefit from a long-term follow-up. b ecause these patients are susceptible to developing severe respiratory insu fficiency, they should also be considered for treatment as soon as an effec tive therapy for LCH is available.