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

ABSTRACT 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.