Percutaneous Spinal Ablation in a Sheep Model: Protective Capacity of an Intact Cortex, Correlation of Ablation Parameters with Ablation Zone Size, and Correlation of Postablation MRI and Pathologic Findings

• Published in: American journal of neuroradiology : AJNR 2017-08, Vol.38 (8), p.1653-1659
• Main Authors: Wallace, A N, Hillen, T J, Friedman, M V, Zohny, Z S, Stephens, B H, Greco, S C, Talcott, M R, Jennings, J W
• Format: Article
• Language: English
• Subjects: Ablation; Ablation Techniques - methods; Animals; Bone Marrow - diagnostic imaging; Bone Marrow - injuries; Cardiac arrhythmia; Catheters; Correlation; Female; Fluoroscopy; Hemorrhage; Injuries; Lumbar Vertebrae - diagnostic imaging; Lumbar Vertebrae - surgery; Magnetic Resonance Imaging; Medical treatment; Metastases; Microwaves; Neuroimaging; Neurosurgical Procedures - methods; Ovis aries; Postoperative Complications - diagnostic imaging; Postoperative Complications - pathology; Radio frequency; Radio Waves; Sheep; Spinal cord injuries; Spinal Injuries - diagnostic imaging; Spinal Injuries - etiology; Spinal Injuries - pathology; Spine; Spine - diagnostic imaging; Spine - surgery; Surgery, Computer-Assisted - methods; Thoracic Vertebrae - diagnostic imaging; Thoracic Vertebrae - surgery; Vertebrae
• ISSN: 0195-6108; 1936-959X
• DOI: 10.3174/ajnr.A5228

Despite the growing use of percutaneous ablation therapy for the treatment of metastatic spine disease, several issues have yet to be fully addressed. Our aims were to determine whether the vertebral body cortex protects against ablation-induced spinal cord injury; correlate radiofrequency, cryo-, and microwave ablation parameters with resulting spinal ablation zone dimensions and describe normal spinal marrow postablation changes on MR imaging. Ten thoracolumbar vertebrae in 3 sheep were treated with radiofrequency ablation, cryoablation, or microwave ablation under fluoroscopic guidance. Technique parameters were chosen to produce ablation zones that exceeded the volume of the vertebral bodies in sheep 1 and were confined to the vertebrae in sheep 2 and 3. Expected ablation zone dimensions were based on data provided by the device manufacturers. Postablation MR imaging was performed at 48 hours (sheep 1) or 7 days (sheep 2 and 3). In sheep 1, cryoablation and microwave ablations extended into the spinal canal and caused histologically confirmed neurologic injury, but radiofrequency ablation did not. The mean difference between the lengths of the radiofrequency ablation zone dimensions measured on gross pathology compared with those expected was 9.6 ± 4.1 mm. The gross pathologic cryo- and microwave ablation zone dimensions were within 1 mm of those expected. All modalities produced a nonenhancing ablation zone with a rim of enhancement, corresponding histologically to marrow necrosis and hemorrhagic congestion. An intact cortex appears to protect against radiofrequency ablation-induced spinal cord injury, but not against non-impedance-based modalities. Ablation dimensions produced by microwave and cryoablation are similar to those expected, while radiofrequency ablation dimensions are smaller. Ablation of normal marrow produces a rim of enhancement at the margin of the ablation zone on MR imaging.