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Part II
Clinical Applications
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53
T. Clark, T. Sabharwal (eds.), Interventional Radiology Techniques in Ablation,
Techniques in Interventional Radiology,
DOI 10.1007/978-0-85729-094-6_7, © Springer-Verlag London 2013
Clinical Features
Thyroid nodules are very common in adults, found in 4–8% by palpation, in •
10–41% by ultrasonography (US), and in 50% by pathologic examination at
autopsy.
Most thyroid nodules are benign. Whereas the majority of nodules do not require •
treatment, some may need it, for various reasons including pressure symptoms
and cosmetic problems.
Patients with autonomously functioning thyroid nodules (AFTNs) may have •
subclinical hyperthyroidism, with approximately 4% per year progressing to
obvious hyperthyroidism or thyrotoxicosis. These conditions may have detri-
mental effects on the skeletal (osteoporosis) and cardiovascular (atrial fi brillation)
systems. Large AFTNs may result in clinical problems similar to those of benign
cold nodules, such as cosmetic problems and pressure symptoms.
Repeat surgery in the central or lateral compartments of the neck may be dif fi cult •
in patients with recurrent thyroid cancer because previous neck dissection may
be associated with high rates of morbidity.
Hyperparathyroidism is a major problem in patients with parathyroid nodules. •
Secondary hyperparathyroidism is caused by chronic dialysis in patients with
chronic renal failure. Long-standing hyperparathyroidism causes cardiovascular
disease, hypertension, renal stones, osteoporosis, and bone pain. Large parathy-
roid nodules may cause neck discomfort and cosmetic problems.
J. H. Baek , M.D.
Department of Radiology and Research Institute of Radiology ,
University of Ulsan College of Medicine, Asan Medical Center ,
86 Asanbyeongwon-Gil, Songpa-gu , Seoul 138-736 , Korea
e-mail: radbaek@naver.com , www.gap.kr
Chapter 7
Radiofrequency Ablation of Thyroid
and Parathyroid Nodules
Jung Hwan Baek
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J.H. Baek
Diagnostic Evaluation
Clinical
Have patients rate their symptoms using a 10-cm visual analog scale [ • 1– 4 ] .
Have physicians sort patients into those with four categories of cosmetic prob-•
lems [ 1– 4 ] :
1. No palpable mass
2. No cosmetic problem but palpable mass
3. Cosmetic problem on swallowing only
4. Readily detected cosmetic problem
Assess clinical symptoms related to thyroid function abnormality (e.g., tachycar-•
dia, atrial fi brillation, fatigue, asthenia, emotional lability, and dyspnea).
Evaluate clinical symptoms related to hyperparathyroidism (e.g., easy fatigue, •
bone pain, depression, acid re fl ux, high blood pressure, renal stones, thinning
hair, palpitations, and osteoporosis).
Laboratory
The following parameters should be assessed before radiofrequency (RF) ablation
is considered:
CBC •
Blood coagulation test •
Thyrotropin (TSH), thyroid hormone, and thyroid autoantibody levels •
Calcitonin level •
Thyroglobulin level in patients with recurrent thyroid cancer after total •
thyroidectomy
Parathyroid hormone, calcium, and phosphate levels, to diagnose •
hyperparathyroidism
Imaging
Preprocedural US examination should be performed to evaluate thyroid nodules •
and to plan RF ablation:
Size – calculated by measuring three orthogonal diameters of each nodule –
Volume – calculated using the equation: – V = p abc /6 ( V volume, a the largest
diameter, b and c the other two perpendicular diameters)
Characteristics of the nodules (shape, margin, internal content, echogenicity, –
and calci fi cations)
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7 Radiofrequency Ablation of Thyroid and Parathyroid Nodules
Composition – classi fi ed as solid (having a solid portion >90%), predomi- –
nantly solid (having a solid portion >50%), predominantly cystic (having a
cystic portion >50%), or cystic (having a cystic portion >90%)
Vascularity – classi fi ed as vascular status in <25%, 25–50%, 50–75%, or –
>75% of the nodule
Presence of abnormal lymph nodes in the neck –
Relationship between the target nodule (or recurrent cancer) and critical neck –
structures (vessels, trachea, recurrent laryngeal nerve, esophagus, vagus
nerve, phrenic nerve, and sympathetic chain)
[ •
99m
Tc] pertechnetate scintigraphy may be helpful in differentiating cold nodules
from AFTNs in some patients with elevated serum TSH.
A neck CT scan may be useful to evaluate the intrathoracic extent of benign •
thyroid nodules and the degree of recurrent thyroid cancer.
A parathyroid scan and US examination are essential to localize targeted para-•
thyroid nodules. CT or an MRI scan may also be required to evaluate ectopic
mediastinal parathyroid nodules.
Indications
Benign nodules diagnosed by fi ne-needle aspiration cytology (FNAC) at two •
separate times and showing no malignant US features [ 5, 6 ] .
Subjective symptoms (pain, discomfort, swallowing dif fi culty, and pressure –
symptoms)
Cosmetic problems –
AFTN –
Recurrent thyroid cancer: patients who are poor candidates for surgery or who •
refuse to undergo surgery.
Parathyroid adenoma: patients who are poor candidates for surgery or who refuse •
to undergo surgery.
Contraindications
Absolute
There are no absolute contraindications. •
However, RF ablation is not recommended for patients with thyroid cancer •
(primary or recurrent) who are good candidates for surgery.
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J.H. Baek
Relative Contraindications
Bleeding tendency •
Contralateral vocal cord palsy •
Follicular neoplasm •
Patient Preparation
Patients are allowed to drink clear fl uids up to the time of the procedure, but •
should have no solid food for at least 6 h before a procedure.
Patients should be given an information lea fl et, so that they can learn about the •
technique, the surgical aims, and potential complications.
Patients should be aware that the therapeutic response to RF ablation is gradual. •
A venous line should be established in the antecubital vein of the arm, which is •
the preferred route of drug delivery (e.g., for control of pain or hypertension).
Thermal ablation has been classi fi ed as a procedure carrying a high risk of bleed-•
ing [ 7 ] . Patients taking aspirin or antiplatelet drugs should be told to discontinue
such medication 7–10 days before RF ablation, and patients taking warfarin
should be told to cease taking the drug 3–5 days before ablation. However, physi-
cians should weigh the bene fi ts of RF ablation against potential complications
related to interruption of aspirin, warfarin, or antiplatelet drugs, and, if needed,
should consider hospitalization or use of parenteral anticoagulation therapy [ 7 ] .
Relevant Anatomy
Normal Anatomy
The thyroid gland lies anterior and lateral to the trachea in the visceral space of •
infrahyoid neck.
The common carotid artery and the internal jugular vein are located posterolater-•
ally to the thyroid gland.
The infrahyoid strap muscles are located anteriorly to the thyroid gland. •
The sternocleidomastoid muscles are located anterolaterally to the thyroid gland. •
The parathyroid glands, usually four in number, lie close to the deep surface of •
the thyroid gland. Normal parathyroid glands are ovoid in shape and approxi-
mately 4–6 mm in length, with the inferior glands being larger than the superior
glands. The location of the superior parathyroid glands, relative to the thyroid
gland, is more constant than is that of the inferior parathyroid glands.
The superior thyroidal artery runs super fi cially on the anterior border of the thy-•
roid gland. This artery is closely associated with and anterolateral to the external
branch of the superior laryngeal nerve.
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7 Radiofrequency Ablation of Thyroid and Parathyroid Nodules
The interior thyroidal artery enters the tracheo-esophageal groove in a plane pos-•
terior to the carotid space and branches thereof penetrate the posterior aspect of
the lateral thyroid lobe.
Many delicate structures are located around the thyroid gland and in the neck.•
The recurrent laryngeal nerve is located on the right posteromedial aspect of –
the trachea and the left tracheo-esophageal groove.
The esophagus is usually located on the left posteromedial aspect of the trachea. –
Trachea. –
The common carotid artery and internal jugular vein are located in the poste- –
rolateral aspect of the thyroid gland.
The vagus nerve, located posterolateral to the common carotid artery and pos- –
teromedial to the internal jugular vein, is easily detected on US using a linear
probe.
The anterior jugular vein begins near the hyoid bone at the con fl uence of sev- –
eral super fi cial veins arising from the submaxillary region. The vein descends
along the anterior border of the sternocleidomastoid muscle and passes
beneath that muscle to open into the external jugular vein in the lower part of
the neck. This vein is located along the approach route (in front of the isth-
mus) of the electrode.
The brachial plexus runs from the spine and is formed by the ventral rami of –
the lower four cervical and fi rst thoracic nerve roots (C5-T1). The roots of the
brachial plexus are posterior to the thyroid gland. Therefore, a posteriorly
bulging thyroid mass may be very close to the brachial plexus.
The phrenic nerve descends obliquely with the internal jugular vein across the –
anterior scalene muscle. On the left, the phrenic nerve crosses anterior to
the fi rst part of the subclavian artery. On the right, the phrenic nerve lies on the
anterior scalene muscle and crosses anterior to the second part of the subcla-
vian artery. On both sides, the phrenic nerve runs posterior to the subclavian
vein and anterior to the internal thoracic artery as the nerve enters the thorax.
The cervical sympathetic trunk, which is ventral to the transverse process of the –
cervical vertebra and close to the carotid artery, is located in the carotid sheath or
in the connective tissue between the sheath and the longus colli/capitis muscle.
Aberrant Anatomy
Anterior and medial variations of the vagus nerve may be located very close or •
attached to the thyroid gland and/or the targeted thyroid nodule [ 8– 10 ] .
Right-sided esophagus: Although the esophagus is usually located on the left, it •
can be located on the right.
An aberrant recurrent laryngeal nerve is usually detected on the right side, asso-•
ciated with an aberrant right subclavian artery. If the latter is suspected, the phy-
sician should remember that the aberrant recurrent laryngeal nerve can also be
located on the right.
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J.H. Baek
The far-lateral portion of the normal thyroid gland may extend to the area between •
the common carotid artery and the internal jugular vein. Thyroid nodules arising
from this portion may be very close to the vagus nerve.
Inferior parathyroid glands are more commonly in aberrant locations than are •
superior parathyroid glands. The aberrant locations of the former include the
mediastinum, the carotid artery bifurcation, within the carotid sheath, and the
intrathyroid, retroesophageal, and retropharyngeal areas.
Equipment
Generator
An RF generator supplies RF power to the tissue through an electrode. •
Electrode
Internally cooled electrode [ • 1– 4, 11– 13 ] .
Conventional straight type (17-gauge; 15 cm in length; 1-cm active tip). –
Modi fi ed straight type (18-gauge; 7 cm in length; 0.5-, 0.7-, 1-, or 1.5-cm –
sized active tips). Modi fi ed electrodes are short (7 cm), to permit easy control,
and thin (18-gauge), to minimize injury to the normal thyroid gland [ 2 ] .
Small-sized (0.5- and 0.7-cm) active tips have been used to treat small recur-
rent thyroid cancers [ 14 ] .
Multitined expandable electrodes (14-gauge; 10 cm in length; bearing 4–9 hooks •
expandable to 3.5–4 cm) have been used in Italy [ 15, 16 ] .
Grounding Pads
Grounding pads act to disperse electricity in an RF circuit. •
Pump
A peristaltic pump is used to perfuse cool water through the perfusion port of the •
electrode, preventing vaporization and carbonization.
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7 Radiofrequency Ablation of Thyroid and Parathyroid Nodules
Preprocedure Medications
Premedication is generally not required. •
For patients on warfarin, see the section on “patient preparation.” •
Procedure
Patient
Patients are placed in the supine position with mild neck extension. •
Two grounding pads are attached fi rmly to both thighs. •
Lidocaine (2%, w/v) is used for local anesthesia of the puncture site and around •
the thyroid gland and/or thyroid nodule.
The skin is not incised, thus preventing unnecessary scar formation. •
Planning an Access Route
Careful observation of the vessels along the approach route is required to prevent •
the electrode from causing serious hemorrhage.
Three approach methods have been developed: •
• Trans - isthmic approach method [ 1, 3, 4, 12, 17 ] :
The electrode approach is made from the medial (isthmus) to the lateral (nod- –
ule) aspect along the transverse axis of the targeted nodule (Fig. 7.1 ).
The entire length of the electrode and the tip can be easily visualized on the –
transverse US view (Fig. 7.2a ). This allows visualization of the relationship
Fig. 7.1 Diagram of the
trans-isthmic approach
method. The electrode
approaches from the medial
(the isthmus) region in the
direction of the lateral aspect
(the nodule). The electrode
passes through an amount of
normal thyroid parenchyma
(in the isthmus) suf fi cient to
steady the needle. The thyroid
nodule is very close to the
recurrent laryngeal nerve
( arrows ), trachea, and vessels
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J.H. Baek
a
b
c
d
ef
Fig. 7.2 Sequential ultrasonographic images of the moving shot technique. ( a ) On a transverse
ultrasonographic view, and using the trans-isthmic approach, the entire length of the electrode and
the tip thereof can be easily visualized ( arrows ). Initially, the tip is positioned in the deepest, most
remote portion of the tumor, enabling the tip to be easily monitored without disturbances caused
by microbubbles. ( b – e ) When a transient echogenic area appears in the targeted ablating unit, the
electrode is continuously moved backward and in the super fi cial direction to treat other ablation
units. ( f ) When all conceptual ablation units of the targeted nodule have changed to transient
hyperechoic zones, RF ablation is terminated
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7 Radiofrequency Ablation of Thyroid and Parathyroid Nodules
among the electrode tip, the thyroid nodule, the trachea, and the great vessels,
and may also be used to locate the recurrent laryngeal nerve. Clear visualiza-
tion of the relationship between the electrode tip and these structures may
prevent complications.
Passing the electrode through a suf fi cient amount of thyroid parenchyma (in –
the isthmus) may prevent the position of the electrode tip from moving during
swallowing or talking, and may also prevent leakage of hot ablated fl uid out-
side the thyroid gland.
• Cranio - caudal ( longitudinal ) approach method [
15, 16 ] :
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 dif fi cult to determine
the relationship between the electrode tip and delicate structures in the neck.
Frequently, movement of the electrode is limited by the mandible or
clavicle.
• Lateral approach method :
If many enlarged vessels are present in the isthmus, the lateral approach –
method may prevent serious hemorrhage.
Ablation Technique: Moving Shot Approach
The moving shot technique for thyroid RF ablation was designed to avoid ther-•
mal injury to surrounding structures [ 1– 4, 11, 12 ] (Fig. 7.2 ).
The basic ablation technique for liver tumors requires that the electrode be fi xed •
during ablation. The ablation technique for thyroid nodules should differ from
that used to treat the liver tumors.
The thyroid gland is smaller than the liver, and thyroid nodules are usually ellip-•
soid in shape rather than round (liver tumors). Therefore, prolonged fi xation of
the electrode during ablation of thyroid nodules may damage surrounding deli-
cate structures.
Conceptual ablating units: The thyroid nodule is divided into several conceptual •
ablating units of various sizes.
These conceptual ablating units are smaller at the periphery of the nodule or –
in areas adjacent to the delicate structures of the neck.
The conceptual ablating units are larger in the central safer portion of the –
nodule.
RF ablation should be performed unit-by-unit by moving the electrode –
(Fig.
7.2 ) .
The moving shot technique should be used, together with an internally cooled •
electrode, because this type of electrode minimizes charring and is easy to move
continuously.
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