The Bird's Nest Sign as an Initial Presentation of Primary Pulmonary B-Cell Non-Hodgkin Lymphoma With Plasmacytic Differentiation.

The bird's nest sign (BNS) has been described as a sign on chest computed tomography (CT) in various pulmonary diseases. We report a rare case of primary pulmonary B-cell non-Hodgkin lymphoma with plasmacytic differentiation presenting with BNS, mimicking an invasive fungal disease at first. A 61-year-old Vietnamese man with a history of idiopathic thrombocytopenia and splenectomy 3 years prior to admission presented with prolonged dry cough, mild dyspnoea on exertion and chest discomfort for 3 weeks. His laboratory tests were unremarkable, but his chest CT showed bilateral consolidation with the BNS. After an unfavourable response to anti-fungal therapy, the second transthoracic lung biopsy confirmed the diagnosis of primary pulmonary B-cell non-Hodgkin lymphoma with plasmacytic differentiation. This case highlights the importance of considering lymphoma in the differential diagnosis of BNS when infection is excluded and concurrently seeking a confirmatory diagnosis with repeated diagnostic procedures when necessary.