SPECT-CT assessment of pseudarthrosis after spinal fusion: Characteristic findings Gaël Amzalag (1),Osman Ratib (1), Olivier Rager (1) Service de médecine nucléaire (1) Objectif: Spinal fusion is a frequent treatment for the vertebrae’s segmental instability. It can be associated with several complications including pseudarthrosis. CT scan has become the most used modality to detect pseudarthrosis even if it is falsely positive in 8% of cases. Some recent studies have shown that new hybrid imaging using SPECT-CT (Tc-99m HDP) or PET-CT (F-18 NaF) improves diagnostic accuracy. SPECT-CT information can be useful to surgeons in order to carefully select patients who might benefit from re-operation, and to plan surgical procedures accordingly. Assessment of the posterior segment of the spine including screws and rods is necessary to identify pathological structures, as well as the anterior segment with bone graft tissue often associated with an interbody device. Persistence of focal uptake in these sites is a characteristic of pseudarthrosis.A pitfall finding is when a screw is broken outside the bone, thus no uptake is observed around the screw as the instability is focused on the interbody area. Conclusion: Understanding of the different surgical procedures and techniques of arthrodesis is key to interpret spine imaging. The analysis of SPECT-CT findings requires knowledge of these characteristics, while concurrently considering the diagnostic pitfalls. PATIENT 1: PSEUDARTHROSIS PATIENT 2: SCREW LOOSENING PATIENT 3: FACET JOINT ARTHROSIS Cage: Mismatch Cage : Match Cage: Mismatch Non-union between L2 and interbody device no uptake no uptake Non-union L4/L5 Non-union L3/L4 uptake Age 45 Corporectomy L3 + cage + posterior fixation L2/L4 for aneurysmal bone cyst Acute onset severe lumbar pain 3 years post op SPECT-CT 4 years post op No uptake around the cage. Degenerative uptake pattern Conservative treatment (local steroid infiltration) Screw: Match Clear zone around L4 right screw uptake Arthrosis: Mismatch Age 73 PLIF L4/L5 for degenerative spondylolisthesis associated with spinal canal stenosis. Lumbar pain 4y post-surgery SPECT-CT 6y post-surgery Uptake of left L4 screw shows probable mechanical instability. Full recovery after screw replacement. L5 Integrity of post. art. process uptake ++ Age 38 PLIF L5/S1 (lytic spondylolisthesis) Early post-op and chronic lumbar pain SPECT-CT 3 years post-surgery Uptake around the cage: probable instability Leads to ALIF L5/S1: Reduced Pain at 7 months follow-up PATIENT 4: DIAGNOSTIC PITFALL DUE TO A BROKEN SCREW A 43 years old drug addict female was referred for a chronic invalidating back pain and left side L5 sciatica, refractory to conservative treatment. A lumbar MRI (A) showed a L5/S1 severe discopathy with Meyerding grade I listesis and Modic type III sign. Surgery was limited to a L5-S1 postero-lateral in situ fixation with autologous graft (cf post surgery radiography B). The patient was symptom-free for 3 months. After cracking without traumatism, low back pain came back. A SPECT-CT (C,D,E) was performed 7 months after surgery (Symbia T6, Siemens healthcare, Germany) 3 hours after injection of 800 MBq of 99mTc-MDP. It revealed an intense uptake of the L5-S1 endplates (C) and a fracture of the right S1 screw without uptake and without bone resorption around the screw (E; arrow). The left S1 screw and both the L5 screws showed no abnormalities (D,E), such as the rods did. SPECT-CT hybrid imaging: increases specificity in the diagnosis of pseudarthrosis around interbody devices. increases sensitivity of detection of posterior articular process arthrosis . allows to select patients who would benefit from surgery procedure allows surgeon to make early plannng of his procedure accordingly Références: 1. Katz JN. Lumbar spinal fusion. Surgical rates, costs, and complications. Spine (Phila Pa 1976). Dec 15 1995;20(24 Suppl):78S-83S.   2. Damgaard M, Nimb L, Madsen JL. The role of bone SPECT/CT in the evaluation of lumbar spinal fusion with metallic fixation devices. Clin Nucl Med. Apr 2010;35(4):234-236. 3. Rager O, Schaller K, Payer M, Tchernin D, Ratib O, Tessitore E. SPECT/CT in differentiation of pseudarthrosis from other causes of back pain in lumbar spinal fusion: report on 10 consecutive cases. Clin Nucl Med. Apr 2012;37(4):339-343. 4. Quon A, Dodd R, Iagaru A, et al. Initial investigation of (18)F-NaF PET/CT for identification of vertebral sites amenable to surgical revision after spinal fusion surgery. Eur J Nucl Med Mol Imaging. Nov 2012;39(11):1737-1744. 5. Brans B, Weijers R, Halders S, et al. Assessment of bone graft incorporation by 18 F-fluoride positron-emission tomography/computed tomography in patients with persisting symptoms after posterior lumbar interbody fusion. EJNMMI Res. 2012;2(1):42.