1. 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
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