Bone tumor ablation: methods, indications, complications

Q: What are the main complications that can occur after spinal cementoplasty?

The main and most dangerous complication following spinal cementoplasty is cement leakage. - Cement leak — can occur into the epidural space, neural foramina, intradiscal space (intradiscal leak), perivertebral venous plexus, paravertebral soft tissues, and the arterial system. - Spinal cord compression — occurs when cement enters the spinal canal, requiring emergency neurosurgical decompression. - Pulmonary cement embolism — a potentially fatal condition when the material enters the perivertebral venous plexus. - Thermal injury — trauma to nerve roots and the spinal cord due to the exothermic reaction during extensive extravasation. - Progressive collapse — further subsidence of the affected vertebra.

Q: Which thermal method is better to use near large blood vessels?

Microwave thermocoagulation is preferred as it generates higher temperatures and is less affected by the heat-sink phenomenon compared to RFA.

Radiofrequency and microwave thermal ablation

These methods are based on heating pathological tissues to critical values that cause irreversible coagulative necrosis.

Radiofrequency ablation (RFA / RFA): Utilizes high-frequency alternating current (460–500 kHz). The current causes ion oscillation in tissues, which generates frictional heat. The destruction zone must encompass 0.5–1 cm of healthy tissue. The efficacy of RFA may drop due to the "heat-sink phenomenon" (heat-sink phenomenon), where adjacent large vessels cool the treatment zone, as well as due to tissue charring, which increases its electrical resistance. Grounding pads on the patient's body are required for the procedure.
Microwave thermal coagulation: Affects tissues with electromagnetic waves (about 900 MHz), causing water molecules to oscillate at ultra-high frequency. The method works faster than RFA, forms larger zones of necrosis, does not require grounding pads, and suffers significantly less from blood flow heat sink.

Cryoablation and chemical destruction

Alternative methods use extreme cold or toxic chemical substances to destroy cells.

Cryoablation: Relies on the Joule-Thomson effect. High-pressure argon gas expands in the probe, instantly lowering the temperature to −100°C. The protocol includes freezing cycles (argon) and thawing cycles (helium). Necrosis occurs at temperatures below −20°C due to ice crystallization and osmotic shock. The main advantage is the ability to visualize the ice ball (iceball) on CT or MRI in real time, as well as reduced pain syndrome. The disadvantage is that the procedure is long and expensive, and prone to the "cool-sink phenomenon" (cool-sink phenomenon).
Percutaneous ethanol injection (PEI): The most accessible method. 96% alcohol is injected into the tumor, causing direct cellular dehydration and vascular thrombosis. Before the procedure, a test injection of contrast with lidocaine is mandatory to evaluate diffusion. The method is rarely used due to the risk of unpredictable alcohol leakage into neural structures.

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Cementoplasty and protection of neural structures

When working on weight-bearing bones (weight-bearing bones) or in cases of a high risk of pathological fracture (cortical destruction >50%, lytic lesion >3 cm), ablation is combined with the administration of polymethyl methacrylate cement (PMMA). Cement not only mechanically stabilizes the bone but also possesses intrinsic antitumor activity.

Features of working with PMMA:

Heated tissues (after RFA) accelerate cement hardening.
Cooled tissues (after cryotherapy) significantly slow down polymerization, increasing the risk of leakage. Therefore, after freezing, the cement is injected the following day.

Protection methods: To prevent thermal injury to the spinal cord and nerve roots, carbon dioxide ($CO_2$) insufflation is used, which serves as an excellent thermal insulator and carries no risk of gas embolism. Passive thermocouples (thin sensor needles) are also used in sensitive areas. In case of cement leakage into the epidural space, cold saline with steroids is injected to prevent neuritis.

Arterial embolization of bone tumors

Transcatheter embolization is used prior to extensive resections to reduce intraoperative blood loss (by 30–50%) or as an independent palliative treatment for hypervascular metastases and primary tumors (e.g., hemangiomas, chordomas, renal cell carcinoma).

The procedure requires high-resolution subtraction angiography. PVA particles or microspheres (100–500 µm), penetrating deep into the capillary bed, are injected into the feeding vessels via a microcatheter. Metallic coils are used exclusively to occlude normal vascular anastomoses to prevent non-target embolization.

Critical anatomy: During embolization in the spine region, it is vital to visualize the radiculomedullary arteries (radiculomedullary arteries) and the largest of them, the artery of Adamkiewicz. Their accidental occlusion leads to catastrophic spinal cord infarction.

Briefly: answers to topical questions

What are the main complications that can occur after spinal cementoplasty?

The main and most dangerous complication after spinal cementoplasty is cement leakage.

Cement leakage (cement leak) can occur into the epidural space, neural foramina (neural foramina), intervertebral disc (intradiscal leak), perivertebral venous plexus, paravertebral soft tissues, and the arterial system.
Spinal cord compression — occurs when cement enters the spinal canal, requiring emergency neurosurgical decompression.
Pulmonary cement embolism — a potentially fatal condition when material enters the perivertebral venous plexus.
Thermal injury — trauma to nerve roots and the spinal cord due to an exothermic reaction during extensive extravasation.
Progressive collapse — further settling of the affected vertebra.

How to memorize

To memorize gases in cryoablation: Argon — Arctic (used for freezing), Helium — Heats (used for thawing).

Class and exam questions

Which thermal method is better to use near large blood vessels?

Microwave thermal coagulation is preferred because it generates higher temperatures and suffers less from the heat-sink phenomenon (heat-sink phenomenon) compared to RFA.

Why is general or spinal anesthesia required for the treatment of osteoid osteoma?

Osteoid osteoma is a sclerotic island with a nidus. The insertion of the trocar into the nidus and its subsequent thermal destruction are accompanied by extremely intense pain.

How to prevent inadvertent nerve damage during thermal ablation of vertebrae?

Passive thermocouples are placed in the neural foramina for temperature monitoring, alongside carbon dioxide ($CO_2$) insufflation to displace structures and create a thermal insulation cushion.

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Bone tumor ablation