Rare Adenomas

Pulmonary adenomas include alveolar adenomas, papillary adenomas, and mucinous cystadenomas. All are extremely rare neoplasms.

Part 1 Alveolar Adenoma

Alvaro C. Laga

Timothy C. Allen

Philip T. Cagle

Alveolar adenomas are extremely rare benign multicystic neoplasms that histologically resemble alveolar type 2 pneumocytes and mesenchyme. Alveolar adenomas typically present in older women as a solitary peripheral nodule.

Histologic Features

Variably sized cystic spaces lined by hobnail or cuboidal to flattened cells (type 2 pneumocytes) that are generally immunopositive for keratin and TTF-1 and focally immunopositive for CEA.
Cystic spaces tend to be larger in the center of the lesion, and squamous metaplasia may be seen.
Spaces contain eosinophilic material and occasionally scattered macrophages.
The interstitium underlying the lining of type 2 pneumocytes contains a myxoid spindle-cell matrix; the spindle cells are typically immunopositive for smooth-muscle actin and muscle-specific actin.