Hello and welcome to HCM, I am Dr Nilajkumar a consultant gynecologist and I will be helping you in your queries. A 7 mm thick endometrium is normal and there is no worry about it. Chocolate cysts are caused due to a condition called endometriosis where there a uterine lining like tissue grows inside the abdomen and is shed there during each period. This leads to severe pain. A laproscopy and excision of any ovarian cyst are better options than a biopsy alone. This is because another reason for a complex cyst may be cancer [ chance very low]. But still biopsy is not advised as it may result in spread. So discuss this with your doctor as even if it is a chocolate cyst ultimately it will need removal. Also ask if they are planning an excisional biopsy meaning that the cyst will be removed and then studied for microscopy. If yes then it is fine as this is the standard of therapy. Hope this was helpful. Feel free to ask any further queries and I will be happy to help. Thanks for using HCM. Have a good day. Dr Nilajkumar Bagde Consultant Obstetrics and Gynecology