Minimally invasive techniques for pain palliation in extraspinal bone metastases: a review of embolization, laser photocoagulation, percutaneous ethanol ablation, and microwave ablation

Abstract

Minimally invasive techniques are an effective primary and/or alternative modality for pain palliation in extraspinal bone metastases, particularly when conventional therapies such as localized radiation therapy leave a subset of patients with refractory pain. Previous issues in this series have reviewed outcome literature demonstrating the efficacy of cryoablation, cementoplasty, and radiofrequency ablation. Historically, selective embolization therapy has more often been described as being utilized in bone metastases within 48 hr prior to planned surgery for hypervascular tumors. Over the last decade, several series have demonstrated its success as a primary treatment modality in not only achieving immediate and sustainable pain relief but also tumor reduction, while maintaining a limited complication profile. Laser photocoagulation produces necrosis in tumor through direct heating. Though more known for its role in the treatment of liver metastases, it has been reported in spine metastases and osteoid osteomas, with no reports in extraspinal bone metastases. Percutaneous ethanol ablation, though rarely used for treatment of bone metastases, is a simple method of ablation whereby ethanol is directly injected into the tumor, inducing necrosis through cell dehydration. Given the unpredictable diffusivity of ethanol, injury to local tissues remains a risk. Microwave ablation causes heat-based tissue ablation through the local administration of microwaves. In addition to pain reduction, recent evidence demonstrates that microwave ablation can achieve substantial and sustained tumor necrosis at 1 yr. For all, reported series are retrospective and small, and future prospective, randomized trials are much needed to compare the efficacy of these treatments.