| Summary: | Pulmonary nodular lymphoid hyperplasia is a rare, nonneoplastic lymphoproliferative disorder mostly manifesting as one or more nodules or localized lung infiltrates. The lesion comprises reactive germinal centers with well-preserved mantle zones and sheets of interfollicular mature plasma cells, lymphocytes, histiocytes, and neutrophils. The radiological finding is not specific, and the diagnosis of pulmonary nodular lymphoid hyperplasia relies generally on pathohistological and immunohistochemical analyses. The most important differential diagnoses are extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue and immunoglobulin G4–related sclerosing disease. Nonetheless, we present a case of pulmonary nodular lymphoid hyperplasia in a 69-year-old woman with the diagnostic challenge of cytological atypia in alveolar spaces inside the lymphoid tissue, coexisting with the diagnosis of adenocarcinoma of the lepidic pattern. Therefore, this case highlights the importance of identifying these rare benign and reactive lymphoproliferative diseases given the risk of developing not only lymphoma but also carcinoma.
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