Sigmoidoscopy of the neovagina-looking for coding guideline resource

[jhill@lockton.com]

I review high dollar claims for employer groups that self-fund their health plan and was asked if 340K was an acceptable case rate for two physicians to perform a sigmoidoscopy w/biopsies on patient who is trans female. If the colon is still in its original anatomical location at the time of service, would it be more appropriate for the surgeons to bill 45331 with a modifier? The surgeons are wanting to bill using 58999. Is anyone aware of coding guideline resources for gender affirming surgeries? The providers submitted several CPT codes that are not supported by their operative report, so I need to get up to speed on what the appropriate billing practices are for this type of medical care. Thank you in advance.