Embryogenesis of tracheal atresia.

A spectrum of tracheo-esophageal anomalies has been described in an adriamycin-treated model with common features to the human pattern. Tracheal agenesis was part of this spectrum. It is a rare congenital anomaly that has not been described in embryos. Virgin timed-pregnant Sprague-Dawley rats were injected with adriamycin i.p. at a dose of 2 mg/Kg on days 6-9 of gestation (plug day = day 0). Fetuses were recovered at term and histologic assessment of tracheo-esophageal anomalies was made. Also, embryos were removed on different gestational days and the embryology of these defects was analysed. Two out of sixty-two fetuses and nine out of 180 embryos were identified with tracheal atresia. Type III tracheal atresia was seen in the full-term fetuses with a tracheo-esophageal fistula arising from the origin of the left main bronchus. Day 13 embryos did not show normal tracheal development; instead, the lung buds developed from the ventral aspect of the foregut which continued to the stomach as a lower esophageal segment. A blind ending pouch was seen on the ventral aspect of the upper part of the foregut. The embryogenesis of tracheal atresia was similar to that of esophageal atresia except that the blind upper foregut pouch developed ventrally rather than dorsally.