Post-fusion cleft of the fetal rat palate.

Several hypotheses of post-fusion rupture of the previously intact palate as a cause of cleft palate have been advanced but with minimal supportive experimental evidence. In this investigation an animal model was evolved in which the intact palates of 19 1/2 day Sprague Dawley rat fetuses were surgically ruptured. Fetuses were grossly and histologically examined at 0.24, 48, and 72 hours after surgery. The operation resulted in a range of clefts including complete cleft of the hard and soft palate, isolated cleft of the hard palate and submucous cleft palate. There were no associated defects, and the fetal mortality was low. The various hypotheses of post-fusion rupture were reviewed, and it was concluded that this model supports the hypothesis that isolated clefts of the hard palate may result from post-fusion rupture and submucous cleft from late disturbances in palatal mesenchyme.