A Case of Autopsy‐Proven Exogenous Lipoid Pneumonia in a 100‐Year‐Old Woman: An Unexpected Complication of Sputum Suction

invasiveness and possible fatality. FNAC was performed again to evaluate for a pathological subtype of primary thyroid lymphoma. Immunostaining analysis on thyroid FNAC specimens was positive for CD20, CD79a, BCL2, and BCL6 and negative for CD3, CD5, and CD10; MIB-1 index was 80%. A diffuse and monotonous population of large atypical lymphocytes was consistent with involvement of an aggressive B-cell lymphoma. According to the Ann Arbor staging classification, this case was assigned to Stage IIE, so multimodal treatment incorporating a monoclonal antibody, chemotherapy, and localized radiotherapy was considered. Radiation therapy was postponed because of spread to the posterior mediastinal lymph node. A combination of the monoclonal antibody and chemotherapy (rituximab with cyclophosphamide, vincristine, and prednisone [R-CVP]) was administered without doxorubicin, which is well known to cause cardiotoxicity. After the fourth cycle of R-CVP, complete response was confirmed on computed tomography; a total of six cycles was administered. Even in elderly adults with severe complications, FNAC findings enabled the diagnosis of aggressive B-cell lymphoma, and rapid treatment was successfully applied. Primary thyroid lymphomas are mainly classified as diffuse large B-cell lymphoma (DLBCL) and marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT), and DLBCL comprises up to 70% of all thyroid lymphomas. In the case of DLBCL, it is possible to make a diagnosis using FNAC alone because of the monotonous proliferation of large abnormal lymphocytes. The prognosis with a primary thyroid lymphoma is relatively good because a rapidly enlarging goiter facilitates early detection of the disease, and the 5-year overall survival rate is 85%. In individuals with Hashimoto thyroiditis, the risk of primary thyroid lymphoma is 60 times as high as in the general population. Thus, primary thyroid lymphoma should be included in the differential diagnosis when the thyroid gland of an elderly adult with Hashimoto thyroiditis enlarges rapidly. Even in elderly adults who have difficulty undergoing invasive biopsies, FNAC can be a useful diagnostic method for the early treatment of aggressive primary thyroid lymphoma.