The most common indication for treatment is pain that is not responsive to NSAIDs. However, many families wish to undergo treatment to definitively treat a lesion and/or stop dependence on medication.

Contraindications include the inability to create a tract that maintains an adequate distance from vital structures such as nerves, arteries, and skin. A distance of >1 cm is desirable [13, 29, 30].

The patient’s imaging should be reviewed and further studies ordered if indicated. Blood work is not necessary in otherwise healthy patients.

A clinic visit is arranged to review the patient’s clinical history, discuss the treatment options (including conservative treatment), and obtain consent.

A combined approach with orthopedic surgery may be beneficial in patients with extremely thick, sclerotic overlying bone. An orthopedic bone drill can provide a large access route through the bone with minimal effort. Some access sets (Laurane, Bonopty) come with a manual drill that may also be helpful in this situation.

Treatment of OO causes significant pain so thermal ablation is performed under general anesthesia (even in adults). It is common to see an increase in heart rate and blood pressure in fully anesthetized patients when the nidus is accessed [29, 31]. Several procedural failures have been reported when ablation was attempted with sedation alone.

Antibiotic prophylaxis is used by some groups [12] but is not routinely administered.

Grounding pads are placed when necessary. The patient is positioned to allow access to the lesion keeping gantry size, instrumentation, and access during CT fluoroscopy in mind. CT is used to localize the lesion, mark the entry site, and plan the procedure.

It is essential to assure an approach that will minimize any potential risk of thermal injury to vital structures such as nerves, arteries, and skin; a distance of >1 cm should be sought [13, 29, 30]. When performing vertebral ablations, the perivenous plexus and cerebrospinal fluid can act as a heat sink. Thermal ablation in lesions with intact cortex is thought to be safe [32, 33] (Fig. 23.3) although risk of neural injury increases when using an RFA device with a 2 cm active zone [34]. When performing ablations in risky areas, the thermal protocol can be modified (less time, lower temperature, lower energy deposition) to improve safety.

In areas where heat spread could result in damage to surrounding structures, direct temperature monitoring with a thermocouple or injection of fluid or gas to act as a thermal barrier or heat sink should be considered. Fluid can be injected to protect joints, overlying subcutaneous tissues, or nearby vital structures (Fig. 23.4). Saline is not recommended when using RFA due to the potential to facilitate the RF signal due to the electrolyte content. In the spine, injection of saline, dextrose, contrast, or CO₂ is used to provide protection in high-risk areas [35].

The area is prepped and draped. Fluoroscopy, CT, and/or CT fluoroscopy is used to guide insertion of the coaxial needle. A biopsy is performed when necessary. The RFA probe is then inserted and heating is commenced. If the coaxial needle is not insulated, it is pulled back over the RFA probe to decrease the chance of a tract/skin burn. The lesion is treated in accordance with the manufacturer’s instructions. Reported protocols vary with most in the range of 85–95 C × 4–8 min [12, 29].

There are a few differences when performing laser ablation. Prior to insertion of the coaxial bone access needle, the laser fiber is inserted and marked to show when 5 mm projects beyond the end of the coaxial needle (Fig. 23.5). Some operators use a second, smaller (18 gauge) needle to protect the laser fiber during insertion [24]. The laser fiber tip is charred in a small sample of the patient’s blood. In distinction to RFA, charring helps propagate laser energy. A biopsy sample is obtained to provide a path into the center of the lesion (so that the fragile glass fiber does not break during insertion). The generator is set to provide a power of 2 W in continuous mode and is activated for a specific time based on the total energy deposition desired to treat the lesion. Higher energy deposition results in a larger area (up to 1.6 cm) of ablation up to a maximum of approximately 1,000–1,200 J. When performing laser ablation in an area where there is the potential to damage surrounding structures, the desired power administered can be determined by the formula: (nidus size in mm × 100 J) + 200 J [24]. As the heat originates only from the tip, the fiber is placed centrally in the lesion. An ice pack is placed on the skin to protect against burns of the skin and tract from potential heat conduction through the uninsulated needle. For large lesions, the use of a beam splitter allows for simultaneous treatment of up to four sites.

Depending on the heat distribution characteristics of the modality used, complete treatment of larger lesions (>1 cm in any dimension) may require ablation in multiple locations. A report by Vanderschueren demonstrated that performing more than 1 burn cycle was the best predictor of successful RFA treatment, independent of lesion size [36].

Immediately following the procedure, supportive care and analgesia is provided. An NSAID such as ketorolac will help decrease immediate postprocedure pain.

Following thermal ablation, some patients notice a change in the nature and/or intensity of pain immediately. In others, it can take 10–12 days.

Weight bearing is determined by the location of the intervention and the size and depth of the needle hole. For most patients with a low fracture risk, weight bearing as tolerated with no high-intensity exercise or contact sports for 4–6 weeks is an acceptable approach. In comparison, a patient who underwent an intervention in the intertrochanteric area with a long intraosseous pathway may require crutches with no weight bearing allowed for 6 weeks.

Informed discharge is performed. Signs and symptoms that would necessitate emergency treatment and a list of emergency contact numbers are discussed with the patient and their family. Ideally, a patient information sheet is given to the family.

Thermal, infectious, or lesion-related complications can occur.

Nearby structures such as arteries and nerves can be damaged during the heating process. Tracking of heat along the probe or guide needle could result in a burn to the needle tract or the skin [37]. Formation of a draining fistula has been reported following treatment of a tibial lesion [29].

Infectious complications include osteomyelitis, septic arthritis, and cellulitis.

Fracture can subsequently occur at the access site. The needle hole creates a riser concentrating stress in the area of the defect increasing the potential for fracture.

Incomplete or partial treatment can occur in approximately 10 % of patients necessitating a second treatment. Late recurrence of OO has been reported.

The patient is reassessed in the interventional radiology clinic 2 weeks following the procedure. If the patient has residual pain, a second procedure is booked.

There are no specific recommendations for imaging follow-up. While regular imaging can be performed to monitor the change in appearance of the OO, a change in the patient’s clinical status will provide an indication that repeat imaging should be undertaken.

ABCs are benign multiloculated, cystic, expansile bone neoplasms that are locally aggressive [38–42]. Histologically, ABCs contain a fibroproliferative mesenchymal stroma with giant cell-like osteoclasts and vascular spaces [42]. The vascular spaces do not have an epithelial lining. The lytic lesions demonstrate a “soap bubble” appearance on plain films and commonly demonstrate fluid-fluid levels on CT and MRI. A rare solid variant exists. ABCs can occur in any bone but are most commonly seen in the femur, tibia, spine, and pelvis [43].

Telangiectatic osteosarcoma has a similar appearance to ABC creating a controversy surrounding the need for biopsy prior to treatment. Some authors feel that biopsy is absolutely essential to exclude telangiectatic osteosarcoma and will postpone treatment for several months [44–46]. Others perform biopsy at the time of treatment as long as no atypical or aggressive imaging or clinical findings are present [42, 47–50]. Both surgical and percutaneous biopsies have been advocated [45, 47, 49].

The pathogenesis of ABC has been controversial. Recently it was recognized as a clonal neoplasm driven by upregulation of the USP6 oncogene [38–41]. Historical hypotheses for formation include posttraumatic reaction, intraosseous vascular anomaly, and chromosomal abnormalities [45].

Several methods of categorization exist. If the ABC is an isolated finding, it is classified as primary. Secondary ABCs are associated with other osseous abnormalities (such as a giant cell tumor, chondroblastoma, fibrous dysplasia, osteoblastoma, and osteosarcoma).

A recent paper suggests classifying ABCs as lymphatic or venous anomalies based on the appearance of aspirated fluid contents. This differentiation predicts the likelihood of venous drainage (and consequent risk of sclerotherapy). Lambot-Juhan et al. demonstrated that venous drainage correlated with the appearance of fluid aspirated from ABCs. Cysts with sanguinous fluid all demonstrated venous drainage where only 1/7 did when the fluid was clear. Fluid that was intermediate in appearance showed venous drainage in 3 of 7 cases [46].

In addition to venous and lymphatic components, ABCs demonstrate variable arterial perfusion. Treatment-related deaths have been reported secondary to intraoperative bleeding in one patient [51] and retrograde arterial embolization of Ethibloc following treatment of a cervical ABC in another [52].

The lack of consensus in the literature makes specific treatment recommendations difficult. Surgical methods such as curettage or resection are associated with a recurrence rate as high as 71 % [42, 53]. Cryotherapy and radionuclide treatment have also been described [54, 55]. Interventional radiologists are involved when embolization or percutaneous sclerotherapy is undertaken.