A 65-year-old female, a smoker, was admitted for evaluation of persistent dyspnea and cough for 2 months despite outpatient treatment with antibiotics. History revealed recurrent pneumonia for several months. Chest CT showed widespread irregular cysts of varying size and wall thickness in combination with centrilobular non-cavitating nodules.

The differential diagnosis includes advanced emphysema (no definable wall), bronchiectasis (communicating branching pattern), lymphangiomyomatosis (almost exclusively in women, diffuse involvement of entire lung). However, the clinical and radiological feature which favor the diagnosis of pulmonary Langerhans cell histiocytosis:

• The patient is a smoker. 
• Lung volumes, even in advanced disease, are well preserved. 
• The combination of nodules and cysts in correlation with demographic and clinical factors are considered diagnostic for pulmonary Langerhans cell histiocytosis and obviate a lung biopsy.