The term 'bladderlike sac' can be summarized as a CYST, which is a four-letter word. A CYST is a closed sac or capsule that is filled with fluid, gas, or other material. It can be found in any part of the body and can vary in size. Cysts are usually benign, but some can be cancerous. They can cause pain, swelling, and other symptoms depending on their location. Treatment for cysts may include draining, removal, or medication.