[Placentoid malformation of the lung].

The differential diagnosis of bullous and cystiform lung alterations comprises a relatively calculable number of various diseases, in which the most important are rare cystic tumors and congenial malformations, such as adenomatoid cystic malformation. We report on a rare clinical picture. In this case, the clinical diagnosis of localized unilateral emphysema caused by local displacement and with subsequent complications had led to "bullectomies" and pneumonectomy. Macroscopically, spongiform solid areas in association with areas of physaliform transformation were seen, corresponding histomorphologically to villous, placentalike formations. The "villous stroma" revealed focally regressive alterations, fatty islets and leiomyomatous areas. So far, the pathogenesis of this lesion, described as "placentoid malformation" due to its pathognomonic histological appearance, remains unclear. In contradiction to the much discussed hypothesis that this lesion may develop from pre-existing lung emphysema, our results suggest that this may be an independent lesion, possibly congenital hamartous malformation with self-developing progression. The clinically predominant emphysematic alterations are considered to be caused by a valve mechanism due to unphysiological traction forces, the lymphatic pathways regularly found in the border areas towards the original lung tissue, possibly playing an important etiological part.