Journal of Cytology & Histology

Introduction: Bronchiolar adenoma (BA) of the lung is a recently recognized rare benign neoplasm of bronchiolar origin. Because of a lepidic growth pattern in routine histopathologic examination, pathologists often erroneously recognize this lesion as pulmonary adenocarcinoma, atypical adenomatous hyperplasia, peribronchiolar metaplasia, or basal cell hyperplasia in intraoperative frozen section diagnosis. Differential diagnosis from malignancy is especially important.

Case Presentation: We report herein a case of BA which was accurately diagnosed with both intraoperative cytology and frozen histology preparations. A 70-yearold man nonsmoker underwent computed tomography scan, revealing a 7.2 × 6.8 mm-sized solid nodule in the peripheral field of the right lower lobe. Video-assisted thoracoscopic wedge resection of the nodule followed. A localized anterior mediastinal mass was also simultaneously excised, and the diagnosis of B1 thymoma was made. The 7 × 7 × 4 mm-sized, solitary, jelly-like, and well-circumscribed and subpleural located lung mass microscopically revealed a lepidic growing lesion, consisting of non-atypical ciliated cells, mucous cells and basal cells, surrounded by mucin pools. The diagnosis of distal-type BA was made intraoperatively with both cytologic and histologic examinations. Immunohistochemically, the ciliated columnar, mucous, and basal cells were positive for cytokeratin 7 and p16INK4a. TTF-1 and napsin A were positive in the ciliated columnar and mucous cells. Mucous cells were focally immunoreactive for MUC 5AC. MUC 6 was negative. Basal cells were clearly recognized by immunostaining for CK 5/6, p40, p63 and podoplanin. Genetic analysis demonstrated mutation of BRAFV600E. The postoperative course was uneventful for four months.

Discussion/Conclusion: Previous studies have described difficulty in making a diagnosis of BA, particularly during intraoperative consultations. Appropriate recognition of a two-celled pattern with consistent association of basal cells is critically important for the intraoperative diagnosis of BA. Ultrarapid immunostaining for p40, p63 or CK5/6 using frozen sections may be of diagnostic value.