Billing for novel or rare imaging services using unlisted codes like 76499 is a significant challenge because they lack a standard reimbursement rate. Payers often deny these claims automatically, requiring extensive documentation to justify the procedure’s medical necessity and its comparable value to a listed code, making it a complex and often contentious issue that goes beyond standard modifier applications.
Hey! 
Something I rarely see discussed is leveraging the prior authorization approval letter in your appeal. 
That document usually has the medical reviewer’s own rationale for approving the service. If they approved it pre-service, use their own words against them in the post-service appeal to prove medical necessity. It shifts the argument from clinical to contractual. Also, always attach a copy of that approved PA to your appeal. It makes the payer’s denial look inconsistent and weakens their position right from the start. 