Symptomatic calcified perineural cyst after use of bone morphogenetic protein in transforaminal lumbar interbody fusion: a case report

Background contextHuman recombinant bone morphogenetic protein-2 (BMP-2) is commonly used in spinal surgery to augment arthrodesis, and a number of potential complications have been documented.PurposeTo present the case of a delayed radiculopathy that occurred because of a calcified perineural cyst that formed after an L4–L5 transforaminal lumbar interbody fusion (TLIF) in which BMP-2 was used.Study design/settingCase report of a 70-year-old man presented with back and right lower extremity pain.MethodsA 70-year-old man who had previously undergone a right L4–L5 TLIF presented 20 months after surgery with progressively radiating right leg pain. Imaging revealed a right-sided L4–L5 cystic lesion posterior to the interbody cage. The patient underwent reexploration, and a calcified mass was discovered.ResultsHistopathology revealed fragments of organized collagenous connective tissue, new collagen, and partially calcified fragments of fibrocartilage, bone, and ligament.ConclusionsThis is the first reported case of a symptomatic calcified perineural cyst developing after a fusion procedure in which BMP-2 was used. The presence of connective tissue with metaplastic bone formation and maturation within the lesion suggests that formation of the cyst was secondary to application of BMP-2, as it possesses both osteogenic and chondrogenic capabilities.