Gadolinium chelates are often useful in sorting out different causes of lower back pain and lumbar radiculopathy. Gadolinium is particularly useful, for example, in distinguishing recurrent disc herniation from epidural scarring in the postoperative spine. Enhancement can demonstrate nerve roots in viral or inflammatory conditions (e.g., cytomegalovirus or Guillain-Barré syndrome), and define compression resulting from herniated discs or spiral stenoses. Gadolinium enhancement also is useful in diagnosing tumors in the intramedullary space (e.g., conus ependymoma), in the extramedullary space (e.g., drop metastases, meningioma, schwannoma), and extradural space (e.g., extraosseus extension of osseus metastases or infections).