Malignant pleural effusion is characterized by fluid buildup between the lung and the chest wall due to cancer cells in the pleura. Most cases are caused by lung cancer, breast cancer, ovarian cancer, or malignant lymphoma. Urothelial carcinoma is a rare cause of malignant pleural effusions and is difficult to diagnose by cytological examination. We report a case of malignant pleural effusion due to urothelial carcinoma. An 80-year-old man presented with right back pain. After close examination, he was diagnosed with ureteral cancer. During the course of treatment, a unilateral pleural effusion was found, and cytological and histological examinations were performed on suspicion of malignant pleural effusion. Cytological examination revealed numerous round-to-ovoid cells with irregularly enlarged nuclei. Immunohistological studies were performed on cell block specimens, and urothelial carcinoma was diagnosed. Cytological examination of malignant pleural effusions may require estimation of the primary site. It is important to take a multifaceted approach that considers not only the cytological findings but also the clinical findings and medical history.

Background: Cell blocks (CBs) from pleural fluid are frequently used in the practice of respiratory medicine, but there have been few reports on the use of CBs from forceps and brush washing fluid in bronchoscopy for pathological diagnosis. We retrospectively analyzed the usefulness of CBs from forceps and brush washing fluid. 　Patients and Methods: Patients who underwent bronchoscopy and had CBs made from forceps and brush washing fluid in bronchoscopy at our institution between June 2016 and May 2021 were included. Cases in which additional information was obtained from CBs were reviewed in detail. 　Results: In total, 138 patients had CBs made from forceps and brush washing fluid in bronchoscopy during the study period. EBUS-GS (endobronchial ultrasound-guide sheath) was used for 102 of these patients. The final diagnosis was lung cancer in 114 cases, infection disease in 10 cases, metastatic lung tumor in 8 cases, lymphoproliferative disease in 2 cases, sarcoidosis in 1 case, and organizing pneumonia in 1 case. There were 13 cases with additional information obtained from CBs, all of which were cases of malignant tumors. 　Conclusions: CBs from forceps and brush washing fluid in bronchoscopy were useful for pathological diagnosis in some cases.