A positron emission tomography (PET)/computer tomography (CT) scan used with the newly approved F-18 sodium fluoride (18F-NaF) PET/CT imaging agent was able to precisely pinpoint the source of chronic back pain after surgery. One of these scans has been named the 2011 Image of the Year at the Society for Nuclear Medicine (SNM) 2011 Annual Meeting.
The image was presented as part of a study in which 18F-NaF PET/CT was used to detect abnormal bone reaction in 20 patients after spinal arthrodesis or spinal fixation surgery.
In all patients, previous physical exams and magnetic resonance imaging (MRI) had failed to identify a specific source of pain. With 18F-NaF PET/CT, however, clinicians were able to discover a total of 24 bone and tissue abnormalities among 17 of the study's 20 patients.
The agent is an injected radiotracer that targets "hot spots," or areas of high bone turnover and inflammation during imaging.
"18F-NaF PET/CT has significantly greater accuracy than we have available using other methodologies. The image shows the detail and the exact site where problems are arising," said Michael M. Graham, MD, PhD, professor of radiology and radiation oncology and director of nuclear medicine at the University of Iowa College of Medicine in Iowa City. He was also president of SNM in 2009/10.
"The increased uptake of fluoride indicates there is increased osteoblastic activity in that area and that there is injury to bone that osteoblasts are trying to repair," Dr. Graham explained.
The image illustrates "accurately that there is nonunion at those locations — a complication of cervical spine fixation that needs to be addressed fairly early or follow-up fracture can occur that, in the cervical spine, can be very serious."
For the prospective study, patients underwent 18F-NaF PET/CT imaging a minimum of 8 months after the most recent surgery. On the basis of the imaging findings, 12 of the 20 patients underwent exploratory surgery of areas with abnormal scans, 4 of the 20 had a local anesthetic nerve blockade directed at the abnormal areas, and 4 were followed conservatively without intervention.
The surgical exploration confirmed that as many as 16 of 24 abnormalities resulted from hardware failure, such as a screw, rod, or cage loosening, or the failure of a bone graft.
In 4 of the cases, the local anesthetic nerve block successfully alleviated symptoms. One case was found, with surgery, to be a false positive, and 3 were determined to be false positives when clinical symptoms were alleviated without aggressive intervention.
The positive predictive value of identifying the precise site of pain was 83%, according to the study.
More than 35,000 spinal fusion surgeries are performed in the United States annually. When pain persists after the surgery, conventional imaging methods such as CT or MRI have often fallen short in identifying the source of pain, explained the study's lead author, Andrew Quon, MD, assistant professor of radiology and chief of clinical PET/CT for the molecular imaging program at Stanford University, Palo Alto, California.
"When these exams appear normal or equivocal, despite persistent pain, the source of symptoms is difficult to ascertain and is often frustrating for both the treating physician and the patient," he said.
"More information is needed to help decide on dichotomous treatment options, which include surgical intervention (such as revision of preexisting orthopedic hardware and bone grafts) and conservative management (such as local anesthesia, physical therapy, analgesics, and bed rest)."
Dr. Quon noted that, despite the promising profile, 18F-NaF PET/CT is not widely accepted by insurance companies for reimbursement; however, the cost is low and, judging by the study's results, worthwhile.
"In patients with difficult-to-diagnose recurrent back pain after spinal fusion surgery, 18F-NaF PET/CT imaging has excellent potential for diagnosing a precise source of pain and stratifying patients into surgical and nonsurgical management groups," he said.
Dr. Quon and Dr. Graham have disclosed no relevant financial relationships.
Society for Nuclear Medicine (SNM) 2011 Annual Meeting: Abstract 457.
Nancy A. Melville • Medscape Medical News © 2011