Complex sentence: Abnormal connections (fistulas) can develop between the esophagus and the trachea (windpipe), also increasing the risk of pneumonia, which is usually heralded by cough, fever, or aspiration.
Split into simpler sentences: Abnormal connections (fistulas) occasionally develop between the esophagus and the trachea (windpipe). Fistulas often lead to pneumonia, which is usually heralded by cough, fever, or aspiration.