Low Anterior Resection vs Sigmoidectomy vs Hemicolectomy ??

I am having trouble finding the codes for these surgeries...

1. Laparoscopic anterior resection

2. Laparoscopic abdominoperineal resection, with colostomy and lower anterior resection of the rectum

3. Lap. left hemicolectomy
VS.
4. Lap. rectosigmoid resection with ileostomy


I am having lots of trouble differentiating these.... help!

Thanks