Alveolar adenoma was described for the first time by Yousem and
Hochholzer in 1986 and is sometimes referred to as "Yousem's tumour".
It is a rare benign tumour of the lung showing proliferation of
epithelium and septal mesenchyme.
(3) Patients with alveolar adenoma are usually asymptomatic and are
diagnosed through the accidental discovery of a well-delineated nodule on a routine chest X-ray.
authors have suggested that they may represent the benign counterpart
of bronchioloalveolar carcinoma.
(5) Macroscopically, it is a well
circumscribed and hemorrhagic lesion with cystic areas (usually measure
less than 3 cm in maximal dimension).
The most important histologic feature of the tumour are the multiple
cystically dilated structures filled with proteinaceous material, with
the larger cysts usually concentrated in the middle of the tumour.
The dilated structures are lined by
alveolar pneumocytes with hobnail
cystic spaces are separated by delicate myxoid stroma containing
collagen fibrils, prominent spindle or oval shaped cells and mild to
moderate numbers of interstitial lymphocytes, plasma cells, and
studies have consistently shown that the epithelial cells are positive
for thyroid transcription factor 1 and almost all are cytokeratin
(10) Alveolar adenoma has unique histologic features, which should be
distinguished from those of sclerosing hemangioma, lymphangioma, and