Congenital peribronchial myofibroblastic tumor (so-called "congenital leiomyosarcoma"). A distinct neonatal lung lesion associated with nonimmune hydrops fetalis.

An unusual solid tumor composed of myofibroblasts in an infant with nonimmune hydrops fetalis is presented together with a review of previous cases reported under a variety of different names, most notably congenital leiomyosarcoma. Immunocytochemical, ultrastructural, and flow cytometric data plus an analysis of fetal lung specimens from various times during lung development suggest that this tumor arises from the condensed mesenchyme that surrounds those respiratory ducts that go on to form large bronchi. Because of its age of onset, cellular composition, and benign biological behavior we believe that this tumor is analogous to two other congenital myofibroblastic tumors, congenital mesoblastic nephroma, and spindle cell tumor of the intestinal tract. Although the term myofibroblastoma has gained popularity in recent reports describing localized proliferations of myofibroblasts in adults, we would like to emphasize the unique developmental origin of this lesion and suggest the term congenital peribronchial myofibroblastic tumor.