Pathology Network

 

 

This was my evening frozen section on Monday night.  A middle-aged woman had a 2 cm. sharply demarcated peripheral pulmonary nodule that was mildly PET positive.  She had a long-term smoking history.  The gross specimen showed a sharply circumscribed yellow-gold nodule just beneath the pleural surface.  The microscopic appearance was somewhat variable and included distinctly papillary areas with the papillae lined by bland cuboidal cells, as well as somewhat more solid areas as shown here with small sclerotic nodules surrounded by bland epithelioid cells with uniform vesicular nuclei.  This is an example of so-called sclerosing hemangioma.  This entity, like many in pulmonary pathology was first described by Averill Leibow in the 1970's.  The name derived from the fact that the epithelioid cells were though by Leibow to be endothelial.  Subsequently, they were shown to be epithelial and considered to be derived from mesothelium.  More recent and more reliable studies support that the epithelioid cells resemble type II pneumocytes and the alternate name of pneumocytoma has been suggested for this entity, but has yet to be widely accepted.  The epithelial cells will label for cytokeratin and EMA, and show strong nuclear staining for TTF-1.  They also show frequent intranuclear pseudoinclusions typical of type II pneumocytes.  It is important to distinguish this lesion from a bronchioloalveolar adenocarcinoma as it is virtually always a benign process.  The sharp demarcation, peripheral location, yellow-gold color, and occurrence in a middle-aged woman are typical features and were very helpful for suggesting the correct diagnosis at the time of frozen section.