I code for general surgeons that do a lot of excisions of lipomas and sebaceous cysts. They never document the size of incision. They only give me size of cyst or Lipoma. It was my understanding that the incision size needs to be documented. And I would code off the size of incision not size of cyst or lipoma. My understanding is the cyst or lipoma incision could be smaller than the actual cyst or lipoma.
Also, make sure you look at the often overlooked soft tissue excision codes which are coded by site, size as well as depth (subcutaneous, subfascial, etc.). These are usually appropriate for deeper cysts like lipomas.
For example...
Site: Trunk/Back
21930 Excision, tumor, soft tissue of back or flank, subcutaneous; less than 3 cm
21931 Excision, tumor, soft tissue of back or flank, subcutaneous; 3 cm or greater
21932 Excision, tumor, soft tissue of back or flank, subfascial (e.g., intramuscular); less than 5 cm
21933 Excision, tumor, soft tissue of back or flank, subfascial (e.g., intramuscular); 5 cm or greater