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

Background context Human 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. Purpose To 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/setting Case report of a 70-year-old man presented with back and right lower extremity pain. Methods A 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. Results Histopathology revealed fragments of organized collagenous connective tissue, new collagen, and partially calcified fragments of fibrocartilage, bone, and ligament. Conclusions This 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.