PERCUTANEOUS ULTRASOUND-ASSISTED THYROID LASER ABLATION. PERCUTANEOUS LASER ABLATION
LASER is an acronym of Light Amplified Stimulated Emission of Radiation. Optical fibers deliver high energy laser radiation to the target lesion. The penetration of laser light is only a few millimeters as a result of scattering and absorption. Scattering results in a relatively uniform distribution of absorbed energy, and heat is produced by conversion of absorbed light. Temperatures greater than 60° C result in rapid coagulation necrosis. Irreversible cell death, without preceding coagulation, also occurs at lower temperatures (40–45° C), but requires duration of treatment that inversely correlates with temperature.
In Reggio Emilia, we started to use PLA in patients with benign thyroid cold nodules in 2002. Since then, several studies have been published confirming effectiveness and safety of this technique.
PLA is an office-based intervention. We established careful precautions for patient safety. A sterile operative setting is arranged. The operator stands on the left side of the patient, while US equipment is used by the ultrasonography assistant who sits on the right side. An auxiliary monitor permits direct US vision by the operator while the assistant looks in the US machine monitor. A cardiac monitor is connected to the patient showing continuous ECG. A venous catheter is inserted in a peripheral forearm vein before starting the procedure to ensure continuous venous access. Emergency care facilities and materials are on hand in the operating room. An anesthesiologist is present during PLA.
The patient is placed in the supine position with hyperextended neck with a pillow under her/his shoulders. Eyes are protected by special glasses. The laser machine is placed behind the patient’s head. There is room for the operator to move around the patient’s head between the bed and laser appliance. Delimitation of the nodule by palpation with a marker pen helps to find the point of needle insertion and plan optimal needle trajectory (Figure 1). Light conscious sedation is obtained by IV diazepam (2–3 mg, repeatable during procedure if necessary). Local anesthesia with ropivacaine subcapsular and subcutaneous infiltration is performed under US assistance. US visualization of needle used for local anesthesia allows correct tissue lidocaine infiltration. In addition, multiplanar scans of this non-traumatic, thin needle (G 29–30) help in planning subsequent 21 G Chiba PLA needle point of insertion and trajectory. Guidance attachment may be used for 21 G Chiba needles insertion. We prefer manual needle placement as it permits to fit needles according to variable anatomy of the nodule. Sedation and local analgesia reduce patient anxiety, swallowing, cough or other untoward movements that could impede precise needle insertion.
After needle placement, fibers are inserted through the needle sheath into the nodule and laser firing is started US images through continuous axial, longitudinal and multiplanar scans are performed by the assistant throughout laser illumination duration (10–30 minutes), allowing real time visual control of each fiber (Figure 2). A highly echogenic area due to tissue heating and vaporization slowly enlarges over time. The hyperechoic image gradually increases until coalescence between fibers is observed. Peripheral capsular vascularization is preserved, while no blood flow is observed inside the nodule (Figure 3). The nonvascular, hypoechoic necrotic tissue will be reabsorbed over several weeks following PLA with consequent nodule shrinkage.
Fig. 1 Con un pennarello chirurgico si demarca il nodulo tiroideo da ablare con laser
Fig. 2 Laser fibers are inserted into the thyroid nodule
Fig. 3 Left: ultrasound image of a laser fiber during firing inside a thyroid nodule; Right: ultrasound image of the nodule after thyroid laser ablation
Video. Laser ablation of a benign thyroid nodule