OBJECTIVE: Calcifying fibrous tumor is a rare, benign soft-tissue tumor of unknown etiology, characterized by hyalinized collagenous fibrous tissue with psammomatous or dystrophic calcification and focal lymphoplasmacytic infiltrate known to involve different organ systems. Involvement of the spine and the presence of metaplastic ossification previously have not been reported. INTERVENTION: We report a 44-year-old female with progressive nontraumatic flank pain. Imaging revealed a left-sided retroperitoneal calcified mass attached to L5 body with no evidence of extension into the neural foramina, nearby vascular structures, or psoas muscle. The patient had an en bloc resection of the tumor via the transabdominal approach. A pathologic diagnosis of calcifying fibrosis with metaplastic ossification of the spine was reported. Postoperative recovery was uneventful and there is no recurrence after 18 months of follow-up. CONCLUSION: Calcifying fibrous tumor, a rare benign soft tissue tumor must be considered in the differential diagnosis of a retroperitoneal calcified mass closely associated with the spinal column. Spine surgeons should be aware of this rare pathologic disease entity and although its natural history is not clear, marginal excision is usually adequate.
OBJECTIVE: Calcifying fibrous tumor is a rare, benign soft-tissue tumor of unknown etiology, characterized by hyalinized collagenous fibrous tissue with psammomatous or dystrophic calcification and focal lymphoplasmacytic infiltrate known to involve different organ systems. Involvement of the spine and the presence of metaplastic ossification previously have not been reported. INTERVENTION: We report a 44-year-old female with progressive nontraumatic flank pain. Imaging revealed a left-sided retroperitoneal calcified mass attached to L5 body with no evidence of extension into the neural foramina, nearby vascular structures, or psoas muscle. The patient had an en bloc resection of the tumor via the transabdominal approach. A pathologic diagnosis of calcifying fibrosis with metaplastic ossification of the spine was reported. Postoperative recovery was uneventful and there is no recurrence after 18 months of follow-up. CONCLUSION: Calcifying fibrous tumor, a rare benign soft tissue tumor must be considered in the differential diagnosis of a retroperitoneal calcified mass closely associated with the spinal column. Spine surgeons should be aware of this rare pathologic disease entity and although its natural history is not clear, marginal excision is usually adequate.