Complex sentence: The contact between these remnants and pharyngeal ectoderm causes in growth of respiratory epithelium and forms tornwaldt's bursa which drains into the nasopharyngeal cavity and forms cyst only when the orifice partially or completely obstructed by infection.
Split into simpler sentences: The contact between these remnants and pharyngeal ectoderm leads to the growth of respiratory epithelium. This only forms cyst when the orifice partially or completely obstructed by infection.