Histologic features--Langerhans' cell histiocytosis, also known as histiocytosis X or eosinophilic granuloma of the lung (EG), is an idiopathic disease of the lung characterized in its early stages by granulomatous nodules containing Langerhans' histiocytes and eosinophils, which are primarily peribronchial in distribution. In its later stages, the cellular granulomas are replaced by fibrosis and the formation of cysts.2, 81, 82
Clinical findings--EG is an uncommon condition. The majority of patients with EG are young or middle-aged adults (average age of presentation is 32 years). Affected patients present with nonspecific symptoms such as cough, dyspnea, chest pain, weight loss, and fever.82 The physical examination is usually normal, and routine laboratory measurements are usually not helpful.2 Up to 20% of patients present with pneumothorax. There is a slight male predominance, and more than 90% of patients are smokers.83 A causal relationship with smoking is likely.81 A diminished DLCO is common,2 with varying degrees of restriction and airflow obstruction also possible.
Radiographic findings--Chest radiographs: The radiographic findings consist of reticular, nodular, reticulonodular, and cystic disease, often in combination. Abnormalities are usually bilateral, involving predominately the middle and upper lung zones with relative sparing of the costophrenic angles (figure 20 -- 40KB). Lung volumes are characteristically normal or increased.
HRCT: Cystic air spaces, which are usually <10 mm in diameter, are typically seen on HRCT. The lung cysts have walls up to several millimeters thick. The presence of distinct walls allows differentiation of these cysts from areas of emphysema, which can also be seen in some patients. Although many cysts appear round, they can also have bizarre shapes, appearing bilobed, clover-leaf shaped, or branching (figure 21 -- 49KB). An upper-lobe predominance of cysts is common; the lung bases and the costophrenic sulci are relatively spared. In some patients, cysts are the only abnormality visible on HRCT, but in the majority of cases, small nodules (usually <5 mm in diameter) are also present (figure 21 -- 49KB). The nodules are usually solid in appearance, but larger nodules (approximately 1 cm in diameter) sometimes show lucent centers, presumably corresponding to small "cavities" (figure 21 -- 49KB).84 These cavitating nodules may eventually evolve into cysts.49, 85 In many patients with cysts or nodules, the intervening lung parenchyma appears normal on HRCT, without evidence of fibrosis or septal thickening.3, 50, 82, 84, 86 Mediastinal adenopathy in EG has been reported.87 The findings of EG may stabilize or even regress with smoking cessation,85, 88 although recrudescence has also been observed.89
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