title: Benign pulmonary epithelial inclusions within the pleura: a case report.
abstract: BACKGROUND
  The normal visceral and parietal pleura are composed of a mesothelium-lined layer of fibrous connective tissue, consisting predominantly of collagen and elastin fibers, with interspersed nerves, lymphatics, and blood vessels. There is no normal epithelial component to the pleura, and the histologic finding of epithelial cells within pleural tissue typically indicates the presence of a malignant process. The one documented exception to this rule is the occasional occurrence of endometriotic implants, which can result in cyclic thoracic symptomatology and occasionally even hemothorax.
  
  
  METHODS
  We present a case of seemingly benign epithelial inclusions within the pleura of a sixty year-old male patient who underwent exploratory thoracotomy and subsequent resection of bullous emphysematous blebs. Examination of the surgical specimen revealed well-defined nests of benign-appearing epithelial cells in glandular configurations at multiple sites within the pleura. These cells were immunopositive for TTF-1 and CK7 and immunonegative for calretenin, CK20, and CEA, indicating pulmonary epithelial derivation. Six months after resection, the patient is in stable health, with no clinical or radiologic evidence of bronchogenic carcinoma.
  
  
  CONCLUSIONS
  To our knowledge, this is the first report of benign pulmonary epithelial inclusions within pleural tissue. It is important to be aware that benign pleural inclusions occur, so as to avoid confusion with more serious processes in a population of patients who may have oncologic risk factors.
authors.affiliation: Department of Pathology, Yale University School of Medicine, 20 York St. EP-2, New Haven, CT 06510, USA. barton.kenney@yale.edu
authors.forename: Barton
authors.initials: B
authors.lastname: Kenney
authors.forename: Marguerite
authors.initials: M
authors.lastname: Pinto
authors.forename: Robert
authors.initials: R
authors.lastname: Homer