Question: Is it appropriate to report 61558 more than once per session, perhaps by applying modifier 59 to the second unit? Missouri Subscriber Answer: Code 61558 (Extensive craniectomy for multiple cranial suture craniosynostosis [e.g., cloverleaf skull]; not requiring bone grafts) describes release of multiple, typically bilateral, prematurely fused sutures. Because the code descriptor specifies both "extensive" and "multiple," this is a "once per session code." You would not report multiple units of 61558 per session, either with or without modifier 59 (Distinct procedural service).