HIFU for Bone Metastases and other Musculoskeletal Applications

Abstract

High-intensity focused ultrasound (HIFU) is a totally noninvasive procedure that has shown promising results in the management of numerous malignant and nonmalignant conditions. Under magnetic resonance or ultrasound guidance, high-intensity ultrasound waves are focused on a small, well-defined target region, inducing biologic tissue heating and coagulative necrosis, thus resulting in a precise and localized ablation. This treatment has shown both great safety and efficacy profiles, and may offer a multimodal approach to different diseases, providing pain palliation, potential local tumor control, and, in some cases, remineralization of trabecular bone. In musculoskeletal field, HIFU received FDA approval for treating bone metastasis, but its application has also been extended to other conditions, such as osteoid osteoma, desmoid tumor, low-flow vascular malformation, and facet joint osteoarthritis. This article illustrates the basic principles of HIFU and its main effects on biologic tissues with particular attention on bone, provides a step-by-step description of the HIFU procedure, and discusses the commonly treated conditions, in particular bone metastases.

Keywords: High-intensity focused ultrasound; bone metastases; interventional radiology; osteoid osteoma; pain palliation.

Fig. 1

( a ) Preintervention CT scan of a 58-year-old woman with metastases on the right ischiopubic ramus ( arrow ), from a primitive tumor on the left kidney; the lesion shows a predominant osteolytic pattern and determines a complete alteration of bony structure. This patient suffered from severe pain condition (VAS score = 9). ( b ) Preliminary MRI scan showing patient positioning at the beginning of HIFU session; target lesion is placed directly over the transducer ( asterisk ), which is housed within the MRI table, achieving the optimal acoustic window and the shorter length of beam path, with the lowest number of obstacles (planned beam path is illustrated in dashed lines ). ( c ) Three-month follow-up CT scan shows the persistence of bone metastases, which starts developing a sclerotic appearance ( arrow ); this patient referred a conspicuous pain relief (VAS score = 1).

Fig. 2

( a ) Preprocedural dynamic contrast-enhanced MRI showing highly vascularized bone metastasis on left ischiopubic ramus and left femoral neck of a 57-year-old man with colon carcinoma; the colorimetric map obtained from perfusion sequences clearly shows the lesions in yellow and red. ( b ) Immediately after treatment, MRI control shows a significant reduction in lesion vascularity, demonstrating an effective local tumor control. This patient reported a significant reduction of symptoms as well (from a baseline VAS score of 8 to a postoperative value of 2, starting from the following day). ( c ) However, at 6 months, MRI follow-up shows an increase in vascularization intensity and extent (particularly on the femur), which indicates disease progression; despite this condition, this patient continued to benefit from pain relief (VAS score of 2).

Fig. 3

( a ) Preprocedural dynamic contrast-enhanced MRI showing an osteoid osteoma on the calcaneus of a 21-year-old woman suffering from considerable pain (VAS = 8) and limitations to walking and other daily activities; the nidus is clearly identified as a highly vascularized focus ( red ) in the color map. ( b ) Dynamic contrast-enhanced MRI scan obtained immediately after treatment shows a complete suppression of nidus vascularity as expression of local tumor control; only a mild and vague local increase of vascularity can be seen in the surrounding region, as a normal result of postprocedural inflammation, which spontaneously resolved within days. This patient reported an immediate clinical benefit as well (VAS = 2 on the very first day after treatment, which turned to 0 at 1 week and remained stable during our 3-year follow-up period).