Alveolar Adenoma: A Rare Benign Tumour of the Lung with A Challenging Diagnosis

Alveolar adenoma is a rare lung benign tumour originating from type II pneumocytes. It presents as a well-defined nodule. In some cases, it is difficult to differentiate from lung cancer. Few cases of this tumour have been reported. We describe here a case of alveolar adenoma in a 63-year-old man discovered incidentally on chest X-ray. The lesion was reported as lepidic adenocarcinoma in bronchoscopic biopsy. The patient underwent a thoracoscopic left lower lobectomy. The histopathological and immunohistochemical examinations resulted in a diagnosis of alveolar adenoma. We report this case to describe its morphological and immunohistochemical characteristics and to emphasize its diagnostic difficulties.