In a patient with a history of papillary thyroid carcinoma, new pulmonary nodules are suspicious for metastatic disease. However, ground glass is uncharacteristic of metastatic PTC, and wedge biopsies were performed to establish the diagnosis.

Pathology shows large groups of macrophages centered in the small airways, fibrotic change forming stellate nodules, and early cyst formation. Confirmation was achieved with CD1a immunohistochemistry, a stain specific for Langerhans cells. CD1a immunohistochemistry was diffusely positive. Cultures were negative.

The rapid evaluation prompted by suspicion for metastatic thyroid cancer has yielded interesting radiologic and pathologic images of the early stage of Langerhans cell histiocytosis.

Thanks to Dr Cristina Fuss and Dr David Sauer for their contributions to this case.