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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3863_Библиотеки_им_академика_М_И_Перельмана.pdf
Macroscopic features
18 Interventional Treatment ofThyroid Nodules
Fig. 18.19 Macroscopic
phenomena during thyroid
RFA. (With permissions
from Park [20])
279
>60°C 50°C 43°C
Friction heat
Conduction heat
tip), 20W (7mm active tip), or 35W (10mm active tip) of RF power under the
impedance control mode. If a transient hyperechoic zone at the electrode tip does
not appear within 5–10 s, RF power is increased in 5–10 W increments up to
15–80W [24] (Fig.18.22). For thyroid RFA, a short shaft length (7cm) is used, as
it allows for more precise control in treating the gland, which is located close to the
surface of the neck. An internally cooled electrode is used to prevent or minimize
charring (Fig.18.23).
Pump: Chilled saline (>0°C) is circulated by a peristaltic pump. The pump
continuously reduces the temperature around the electrode tip to prevent or minimize charring (Fig.18.24). The temperature on the panel of the generator indicates the temperature inside the electrode tip. It is not the actual temperature of
the tissue.
280
A. W. Park et al.
>100°C Vaporization/carbonization/charring
Temperature
> 45°C
> 42°C
< 40°C
Irreversible
cellular
damage
Susceptibility to chemotherapy or radiation
ablation
temperature
> 50°C
Homeostasis
Ideal
Instantaneous
> 60°C
Fig. 18.20 Tissue reaction to heat. (Modied from Hong and Georgiades [28])
Fig. 18.21 Echogenic
effects by microbubble
protein
coagulation
18 Interventional Treatment ofThyroid Nodules
281
Fig. 18.22 Various sizes
for radiofrequency
electrode needle tips. (With
permissions from
STARmed Co., Ltd.
Goyang-si, South Korea)
10 mm
7 mm
5 mm
3.8 mm
7 cm
Chilled saline
Fig. 18.23 Internal cooling of an electrode tip. (With permissions from Park [20])
Grounding Pads: The grounding pad, which is adhered to the patient’s skin away
from the ablation site, is intended to safely return the electrical current from the
patient back to the generator through a cable (Fig.18.25). Because the conductive
surface area of the grounding pad is much larger than the active electrode, the current is dispersed over a wide area, minimizing the heating of the tissue under the
grounding pad. A patient burn risk is increased when contact quality is poor between
the grounding pad and the patient because the current is concentrated at the contact
points rather than dispersed over the entire grounding pad [29, 31].
Planning the Access Route
Careful observation of the vessels along the approach route is required to prevent an
electrode from causing serious hemorrhage. Three approach methods can be used
(Fig.18.26).
The Transisthmic Approach Method Is Recommended: The electrode approach is
made from the medial (isthmus) to the lateral (nodule) aspect along the transverse
axis of the targeted nodule. The entire length of the electrode and the tip can be easily visualized on the transverse US view. This view allows visualization of the
282
A. W. Park et al.
With internal cooling
Without internal cooling
No carbonization/charring Carbonization/charring
Fig. 18.24 Ex vivo ablation in cow’s liver with and without internal cooling; carbonization/charring without internal cooling resulting in a limited ablation
High current densityLow current density
Fig. 18.25 Equipment: generator, pump, monopolar electrode, and grounding pad. (With permissions from STARmed Co., Ltd. Goyang-si, South Korea)
18 Interventional Treatment ofThyroid Nodules
Fig. 18.26 Three approach
methods for thyroid RFA;
a, transisthmic; b,
craniocaudal; c, lateral.
(With permissions from
Park [20])
283
relationship among the electrode tip, the thyroid nodule, the trachea, and the great
vessels and may also be used to locate the RLN.Clear visualization of the relationship between the electrode tip and these structures may prevent complications.
Passing the electrode through a sufcient amount of thyroid parenchyma (in the
isthmus) may prevent the electrode tip’s position from moving during swallowing
or talking and may also prevent leakage of hot ablated uid outside the thyroid
gland [25, 32].
The Craniocaudal (Longitudinal) Approach Method: The electrode approach is
made from the superior to the inferior aspect of a targeted nodule along the long axis
of the nodule. It is difcult to determine the relationship between the electrode tip
and adjacent structures in the neck. Frequently, movement of the electrode is limited
by the mandible or clavicle.
The Lateral Approach Method: If enlarged vessels are present in the isthmus, the
lateral approach may prevent serious hemorrhage.
The Moving-Shot Technique
The moving-shot technique for thyroid RFA was designed to avoid thermal injury
to surrounding structures [23, 24]. The ablation technique for thyroid nodules
should differ from those used to treat tumors in other organs such as the liver or
kidneys. For instance, the basic ablation technique for liver tumors requires that the
electrode be xed during ablation. However, the thyroid gland is smaller than other
organs, and thyroid nodules are usually ellipsoid rather than round. Therefore, prolonged xation of the electrode during the ablation of thyroid nodules can cause
thermal damage to adjacent structures.
The thyroid nodule is divided into several “conceptual ablating units” of vari-
ous sizes. These units are smaller at the periphery of the nodule or in areas bordering the adjacent structures around the thyroid gland. The conceptual ablating units
are larger in the safer, central portion of the nodule. RFA should be performed unit
by unit by moving the electrode, hence the name “moving-shot technique” [25,
32]. Initially, the electrode tip is positioned in the deepest, most remote portion of
the nodule, which enables easy monitoring of the electrode tip without disturbances caused by microbubbles. When a transient echogenic area appears in the
284
Fig. 18.27 Moving-shot
technique; T trachea, E
esophagus; red circle,
common carotid artery;
blue oval, internal jugular
vein; yellow solid circle,
vagus nerve; yellow dotted
circle, recurrent laryngeal
nerve; yellow heptagon,
middle sympathetic
ganglion; numbers 1–7,
ablation units. (With
permissions from Park
[20])
A. W. Park et al.
targeted ablating unit, the electrode is continuously moved backward and in the
supercial direction to enter untreated ablating units. In predominantly cystic thyroid nodules, the cystic uid should be aspirated before ablation of the solid portion (Fig.18.27).
Postprocedural Care andFollow-Up
Immediate Postprocedural Care
Thyroid RFA is an outpatient procedure. The patient will stay in the postprocedural care unit for at least 1h with monitoring vital signs. After 1–2h of observation, patients can be discharged. Before the discharge, patients should be
evaluated for pain, discomfort, and minor or major complications through physical examination of the thyroid/neck with or without US.The dressing should be
changed with a Band-Aid®. Instructions with a follow-up schedule or appointment should be given. Postprocedural medication is not usually required.
However, patients who complain of pain or discomfort may benet from treatment with oral analgesics such as oral acetaminophen or ibuprofen. Admission
might be needed when a further observation or clinical care is required in cases
of major complications.
For patients experiencing the symptom of difcult breathing by extrinsic com-
pression of the trachea, admission and careful monitoring in an intensive care unit
bed might be needed. In severe trachea stenosis, intubation or tracheal stent should
also be considered and discussed at a planning stage with ENT surgeons.
During the rst day of ablation, neck bulging could be aggravated, and the vol-
ume of the ablated nodule may increase. These ndings are caused by edema and
swelling of the ablated nodule and surrounding soft tissue. Volume reduction usually starts 3–7days after ablation. The maximal reduction in volume will be observed
() ()
()
18 Interventional Treatment ofThyroid Nodules
285
at the 1-month follow-up, with further gradual reduction anticipated after
3–6months. Changes in clinical status should be evaluated serially on follow-up
visits using symptom and cosmetic scores.
If TSH and thyroid hormones remain abnormal after RFA, they should be re-
assayed closely with monthly follow-up interval.
Nonfunctioning Thyroid Nodules
Patients are usually followed up at 1, 3, 6, and 12months after the procedure and
every 6–12months during the second year after ablation. The physician should
check the following items during follow-up visits. For guidelines for monitoring
patients after RFA, see [14].
• Any discomfort or complications
• Ablation status of the nodule: volume analysis
• Status of clinical problems: symptom and cosmetic scores, respectively
• Labs: TFT including TSH, freeT4, and T3
US scan is the primary examination tool, with CT or MRI serving ancillary roles.
Patients with the intrathoracic extension of the thyroid nodule may require a repeat
CT or MRI examination for comparison with CT or MRI data obtained before the
procedure.
US ndings of successful ablation are as follows:
• Loss of intranodular vascular signal in Doppler US examination
• Decreased nodule volume: >50%
• Decreased echogenicity of the ablated nodule (which looks like a malignancy)
Changes in size, echogenicity, and intranodular vascularity of the nodule should
be evaluated on follow-up US examinations. Volume reduction (VR) is calculated
using the following equation:
VR %= initial volumemLfinal volumemL 100 /initial
é
ë
-
ù
´ vvolume
û
Autonomously Functioning Thyroid Nodules
99m
Tc pertechnetate scintigraphy, blood, and US examinations are essential to evaluate the ablation status of AFTN. US examination and laboratory tests for TSH and
thyroid hormone should be performed 1, 3, 6, and 12months after RFA.Measurements
of thyroid autoantibodies and
99m
Tc pertechnetate scintigraphy should be performed
6–12months after RFA.
Results
The results of RFA of benign nodules are evaluated by changes in volume (cytoreduction) and clinical problems (pressure symptoms and cosmetic issues). For
patients who undergo ablation of AFTNs, the serum concentration of TSH and
286
A. W. Park et al.
thyroid hormones in addition to nuclear scan is needed to see the conversion to
euthyroidism.
Nonfunctioning Thyroid Nodules
A prospective multicenter study revealed that the mean volume reduction was 80%,
84%, 89%, 92%, and 95% at the 12-, 24-, 36-, 48-, and 60-month follow-ups,
respectively [33]. After RFA, symptoms and cosmetic problems improved or disappeared in the majority of patients.
In a retrospective longitudinal observational study, 215 patients were followed
up after a single RFA session for >3years [33]. At 6months after the procedure,
median nodule volume was signicantly lower than at baseline, with further progressive volume reduction at 1- and 2-year follow-up. There was no signicant
change in nodule volume at 3 and 4years, but at 5years, there was an additional
slight volume reduction. The best response was observed in small nodules with a
volume below 10mL (early reduction of 82%). Large nodules showed a smaller
reduction in volume (75% reduction of nodules with a volume of 10 to 20mL and
65% reduction in those with a volume of ≥20mL). This shows the difculty in
complete ablation of large nodules with a single-session ablation. Large nodules
may require additional treatment of untreated peripheral portions of nodules which
can regrow on long-term follow-up.
Autonomously Functioning Thyroid Nodules
In a systemic review and meta-analysis, radiofrequency ablation has proven to
be effective in treatment of AFTN.The volume reduction rate was 79% at the
1-year follow-up. TSH normalization or scintigraphically proven efcacy of
RFA was about 60% [35]. AFTNs are more likely to respond when their baseline
volume is <12 mL and when the volume is reduced by at least 80% after
12months from the treatment [35, 36]. The result is in line with the concept that
the greater the baseline volume, the higher the likelihood to undertreat hyperfunctioning areas, leading to hyperthyroidism or symptom relapse. A tailored
patient selection with complete ablation seems the key to successful conversion
to euthyroidism in AFTN.
Marginal Regrowth
Even with excellent volume reduction and improved symptomatic and/or cosmetic
problems, nodule recurrence has been reported after RFA, which varies from 5% to
35% [37–44]. Regrowth is dened as >50% increase of nodule volume compared to
the smallest volume recorded previously during the postprocedural follow-up evaluations [45]. Most cases of regrowth occur as a result of marginal regrowth [46].
() () ()
() ()
()
18 Interventional Treatment ofThyroid Nodules
Marginal regrowth, also known as regrowth phenomenon, occurs from the undertreated peripheral portion of the tumor. When follow-up US results suggest regrowth
of an untreated peripheral portion of the nodule, an additional RFA should be
scheduled.
According to Dr. Sim etal., a volume increase of the viable portion was an early
indicator of regrowth in treated nodules, which occurred about 1year earlier than
the increase of the total volume [37]. The volume of the viable portion in a treated
nodule can be calculated by the following formula (Fig.18.28).
287
reduction and preventing regrowth of the nodule, which requires repeat sessions.
Because of recurrence induced by marginal regrowth, complete ablation of the nodule margin was emphasized [46].
47–51]. It is reported that single-session ablation is effective in most thyroid nod-
ules [33, 52]; however, for nodules larger than 20mL, additional ablation may be
required to achieve sufcient volume reduction [34, 52]. Tumor vascularity was
another inuencing factor. The tendency to regrow is relatively high for nodules
with abundant peripheral vascularity, which can be attributed to incomplete ablation
by the heat-sink effect [53]. To prevent this, vascular ablation technique was suggested by Park etal. [26].
Total volumeVt=Viable volumeVv+Ablated volumeVa
Viable volumeVv=Total volumeVtAblated volumeVa
Ablation of the peripheral portion is the key to achieving a satisfactory volume
Several factors were described to inuence the nodule regrowth or efcacy [42,
-
Fig. 18.28 The viable portion (blue outer shell) vs. the ablated portion (yellow inner core) of an
ablated tumor. (With permissions from Park [20])
288
A. W. Park et al.
Moreover, possible other inuencing factors of the regrowth or efcacy are the
tissue characteristics of the thyroid nodule, nodular margin, proximity of the nodule
to the critical structures, the total energy deposition during the initial session, and
the type of energy source by treatment modalities [23, 47, 52–55].
Complications
Although the complication rate of RFA is low, various complications may still
occur. No deaths related to RFA have been reported. The rst and largest study of
complications in the treatment of benign nodules with US-guided RFA was reported
in 2012 by KSThR.From June 2002 to September 2009, 1459 patients underwent
RFA of 1543 thyroid nodules with an RF system with internally cooled electrodes
at 13 thyroid centers. Twenty (1.4%) major complications were reported, including
voice changes in 15 patients, nodule rupture in 3 patients (including 1 patient with
abscess formation), hypothyroidism in 1 patient, and brachial plexus injury in
Table18.11 [50].
Pain
Pain is the most common symptom associated with the procedure. Most patients
complain of various degrees of pain at the ablated site or pain radiating to the head,
ears, shoulders, chest, back, or teeth.
Table 18.11 Complications resulting from thyroid radiofrequency ablation
Complication or side effect
Major 20 (1.4%) 1–180 1–90
Voice change 15 (1.02%) 1–2 1–90
Nodule rupture 2 (0.14%) 22–30 <30
Nodule rupture with abscess
formation
Hypothyroidism 1 (0.07%) 180 None
Brachial plexus injury 1 (0.07%) 1 60
Minor 28 (1.92%) 1–2 1–30
Hematoma 15 (1.02%) 1 <30
Vomiting 9 (0.62%) 1–2 1–2
Skin burn 4 (0.27%) 1 <7
Side effect 46 (3.15%) 1 1–2
Pain 38 (2.6%) 1 1–2
Vasovagal reaction 5 (0.34%) 1 1
Coughing 3 (0.21%) 1 1
Note: As reported by Baek etal. [50]
Number of
complications
1 (0.07%) 50 None
Time of detection
(days)
Time to recovery
(days)