Impact of reactive sclerosis on outcome of MR-HIFU for osteoid osteomas.

Objectives: To evaluate the influence of clinical and procedural factors, particularly the thickness of reactive sclerosis, on clinical outcome of MR-guided high-intensity focused ultrasound (MR-HIFU) for the treatment of symptomatic osteoid osteomas (OO) of the extremities.

Materials And Methods: 18 consecutive patients (median age 19.5y) with symptomatic OO of the extremities eligible for MR-HIFU were enrolled in this ongoing prospective study (German Clinical Trials Register; nr. DRKS00015448). The Functional Assessment of Cancer Therapy - Bone Pain (FACT-BP) score was used for evaluation of symptoms and quality of life parameters at 1-week, 2-week, 1-month, 6-month and 12-month follow-up (FU) after intervention. MRI was performed prior as well as, 6 and 12 months after intervention. Assessment included procedural and imaging parameters, with a specific focus on the thickness of the reactive sclerosis surrounding the nidus.

Results: Symptoms and quality of life parameters significantly improved between baseline and all FUs on the FACT-BP (mean score at baseline: 29.7; at 6-month-FU: 5.5; at 12-month-FU: 3.4, all p < 0.01). A strong correlation was found between scores of FACT-BP and the thickness of reactive sclerosis surrounding the nidus (r = 0.62 at 6-month-FU; p = 0.006) with an optimal cutoff of 0.6 cm identified for predicting a good clinical outcome.

Conclusion: MR-HIFU is an effective method for the treatment of symptomatic osteoid osteomas of the extremities in pediatric and adult patients, with the thickness of reactive sclerosis surrounding the nidus being a relevant factor influencing patient outcomes and emphasizing its importance in MR-HIFU assessment and planning.