Impact of Magnetic Resonance Imaging (MRI) Findings on Management of Symptomatic Patients Following Radiofrequency Ablation (RFA) of Osteoid Osteoma (OO)

Abstract

Object: To assess the impact of MRI findings on management of symptomatic patients following RFA of OO.

Materials & methods: Retrospective review of 43 patients with RFA for OO between June 2010 and June 2017 was performed. Patient, nidus and ablation data were reviewed. Pre- and 6-8 weeks post-procedural MRI (n=32) were compared for coverage of nidus by ablation zone, bone marrow edema, nidus hyperintensity and other findings. Baseline pain levels and analgesic use were compared with post-procedural follow-up visit at 6-8 weeks. Three groups of clinical and MRI outcomes of complete (CR), partial (PR) and no response (NR) were defined. A weighted-kappa statistic was used to assess for agreement.

Results: Clinical responses were CR in 34/43 (79.1%, 95%CI: 64.0-90.0%), PR in 8/43 (18.6%) and NR in 1/43 (2.3%) patients. All 19/32 patients with MRI CR experienced clinical CR. One patient with MRI NR had clinical NR. All 7/32 patients with clinical PR had MRI PR. All 4/43 complications were in MRI PR or NR groups. Substantial agreement was observed between MRI and clinical outcomes (kappa:0.69, 95%CI:0.45-0.95). MRI helped determine etiologies in all symptomatic patients and their management (n=8).

Conclusions: MRI is recommended for symptomatic patients after ablation.

Keywords: Clinical Outcomes; MRI; Osteoid Osteoma; Radiofrequency Ablation.

Figure 1.

A 15-year-old female with osteoid osteoma of the right talus. a) axial and b) sagittal T1-weighted MR images show the nidus (asterisk) and bone marrow edema (arrowheads). C and d) Follow up MRI at 6 weeks clearly show the ablation zone (arrows) completely covering the nidus (asterisk). The bone marrow edema is completely resolved. This patient had clinical CR and imaging CR.

Figure 2.

A 19 years old male with typical biologic pain of osteoid osteoma: pain with no relationship to physical activity that woke him up from sleep, got worse in supine position and resolved with nonsteroidal anti-inflammatory pain medications. a) Axial proton density MR image shows a right proximal femoral nidus (arrow) and adjacent bone marrow edema (asterisk). Contrast enhanced sequence was not obtained in this study at an outside institution. b) Contrast-enhanced fat saturated T1-weighted axial MR image 6 weeks after ablation shows improvement of bone marrow edema (asterisk) and new soft tissue inflammation from ablation zone in vastus intermedius muscle (circle). Biological pain resolved 2 days after ablation, but patient has mechanical pain that occurs with walking and resolves with resting. c) Same sequence MR image 7 months after ablation show further improvement of bone marrow edema (asterisk) and soft tissue inflammation in vastus intermedius muscle (circle). Patient now has pain only with long distance walking. d) Same sequence MR image 12 months after ablation shows resolution of bone marrow edema and soft tissue inflammation. Patient is asymptomatic.

Figure 3.

Algorithm for response assessment after image guided ablation of osteoid osteoma. Only patients with partial or no clinical response need MRI for evaluation. MRI: magnetic resonance imaging. CR: complete response. PR: partial response. NR: no response.