MANAGMENT OF THYROID NODULE
A thyroid nodule is a discrete lesion within the thyroid gland. Thyroid nodules are four
times more common in women than in men, and the incidence increases with age, radiation
exposure, and reduced iodine intake. The prevalence of nodular thyroid disease has been
reported to be 15% in areas of iodine deficiency.
The majority of thyroid nodules are benign. Colloid nodules, cysts, and thyroiditis account
for approximately 80%, and benign follicular and Hurthle cell adenomas account for 10% to
15% of all thyroid nodules. Only 5% of thyroid nodules are malignant.
The challenge for a clinician is to distinguish patients with malignancy, who are treated
surgically, from patients with benign disease, who are followed clinically. This is
accomplished by a diagnostic approach that consists of routine fine needle aspiration biopsy
(FNAB), a routine screening third-generation thyrotropin (thyroid-stimulating hormone
[TSH]) level, and selective use of high-resolution ultrasound (US) and iodine-123 (I-123)
thyroid scintigraphy.
Laboratory Evaluation
The only laboratory test that must be performed routinely in the evaluation of a patient with
a thyroid nodule is a third-generation TSH level. In the majority of patients, the TSH level
will be normal, indicating that the patient is euthyroid.
1) If TSH low : Approximately 10% of patients with a solitary nodule have a suppressed (
low) TSH level, which suggests a benign hyperfunctioning nodule. In these patients, a free
thyroxine and a free triiodothyronine level should be measured. An I-123 thyroid scan is
obtained to distinguish a hyperfunctioning (“hot”) nodule from a hypofunctioning (“cold”)
nodule. If the thyroid scan confirms a functioning nodule in the setting of a low TSH, no
further diagnostic evaluation is necessary. The incidence of malignancy in patients with a
hyperfunctioning nodule is less than 1%. The patient can be treated with a thyroid lobectomy
or with radioiodine ablation. Patients with thyrotoxicosis and a hypofunctioning nodule
should undergo FNAB.
2) If TSH high : In patients with a dominant thyroid nodule and an elevated serum TSH level,
a free T4 and serum antithyroperoxidase antibody level should be obtained. An elevated
serum antithyroperoxidase antibody level is indicative of Hashimoto's thyroiditis. In these
patients, an FNAB is indicated to rule out malignancy, including lymphoma, which accounts
for a minority of thyroid cancers but is known to be associated with Hashimoto's thyroiditis.
In patients with a family history of MTC or MEN 2, a basal serum calcitonin level should be
obtained. Baseline levels of calcitonin greater than 100 pg/ml are highly suggestive of MTC.
In patients without a history of familial MTC, routine calcitonin testing is not recommended
because large studies of nodular thyroid disease have reported a prevalence of MTC of less
than 1.5%.
Fine Needle Aspiration Biopsy
FNAB is the diagnostic procedure of choice in the evaluation of thyroid nodules, the routine
use of FNAB has resulted in a reduction of unnecessary testing, and fewer operations.
FNAB can be performed as either a palpation-guided or US-guided procedure. If the patient
has a palpable nodule, an FNAB is performed at the initial clinic visit before any other
diagnostic study.
To perform an FNAB, the patient is positioned supine with the neck extended. The nodule is
then identified and stabilized between the clinician's two fingers. Biopsy is then performed
using a 22-gauge, 1.5-inch needle attached to a 10-ml disposable syringe. The needle is
moved vigorously up and down while continuous suction is applied to the plunger of the
syringe to disrupt the follicular epithelium. Aspirated material in the hub of the needle is then
smeared on a slide and either fixed with alcohol or allowed to air dry. It is then submitted for
staining and cytologic evaluation. It should be emphasized that this technique provides a
cytologic rather than histopathologic diagnosis because it cannot provide any information
about capsular or vascular invasion. Patients tolerate this procedure well, and it has a low rate
of complications.
The results of cytologic analysis of FNAB specimens are divided into four main categories:
1)nondiagnostic, 2) benign,3) suspicious for neoplasm, and 4) malignant (Table 1).
In the absence of cytologic findings consistent with malignancy, a biopsy is considered
adequate only if it contains at least 6 groups of 10 or more well-preserved follicular epithelial
cells on one or more slides. Specimens not fulfilling these criteria are categorized as
nondiagnostic. Nondiagnostic aspirates account for 10% to 20% of all FNAB results.
Aspirates are more likely to be nondiagnostic if the nodule has a predominant cystic
component or if the nodule is small or difficult to palpate. The reported incidence of
malignancy is 5% to 10% in patients with a thyroid nodule and a nondiagnostic FNAB, and
therefore a repeat FNAB should always be obtained.
For patients with a nondiagnostic palpation-guided FNAB, a repeat FNAB can be obtained
under ultrasound guidance. Using US guidance. In the majority of these patients, repeat
FNAB confirmed a benign lesion and helped to avoid an unnecessary operation. If FNAB is
persistently nondiagnostic, thyroid lobectomy is recommended with frozen section exam of
the nodule.
Table 1 -- Fine Needle Aspiration Biopsy Cytologic Diagnoses
I.
Nondiagnostic
II. Benign
a. Colloid nodule
b. Adenomatous hyperplasia
c. Thyroiditis
III. Indeterminate or suspicious
a. Consistent with a follicular neoplasm
b. Consistent with a Hurthle cell neoplasm
c. Suspicious for papillary carcinoma
IV. Malignant
a. Papillary carcinoma
b. Medullary carcinoma
c. Anaplastic carcinoma
d.
Lymphoma
e. Metastatic carcinoma
Repeat FNAB in a patient with an initial benign cytologic diagnosis may be of value when
1. the cytologic specimen contains abundant red blood cells that obscure the evaluation
of the follicular cell nuclei,
2. a nodule is greater than 4 cm because of an increased risk of a sampling error,
3. a nodule is difficult to palpate raising concern for sampling error,
4. or a nodule undergoes progressive enlargement.
Patients with a benign FNAB are asked to return in 6 months, at which time they are
evaluated for an increase in nodule size or development of compressive symptoms. If the
patient is asymptomatic and there is no change in the nodule size, follow-up with history,
physical examination, and a screening serum TSH level is recommended at yearly intervals.
Yearly US evaluation can provide objective measure of nodule size when necessary.
Thyroidectomy is recommended for a progressive increase in nodule size and development of
compressive symptoms.
The false-negative rate for FNAB is 2% to 5%. Sampling errors tend to occur with
particularly small or large nodules, hemorrhagic nodules, or multinodular glands.
Cytologic analysis of FNAB specimens cannot differentiate benign and malignant follicular
or Hurthle cell lesions. The risk of malignancy is approximately 20% in nodules with an
FNAB interpreted as a follicular or Hurthle cell neoplasm. At present, there are no clinical,
imaging, or cytologic features accurate enough to determine which patients have a
malignancy; therefore patients require thyroid lobectomy to make a definitive diagnosis. If the
final pathology reveals a clinically significant carcinoma, completion thyroidectomy is
performed. Alternatively, patients are counseled regarding the 20% risk of their lesion being
malignant and may be offered total thyroidectomy as their initial surgical procedure. Such an
approach eliminates the need for reoperative surgery should the final pathology reveal
malignancy; however, it guarantees that thepatient will require thyroid hormone replacement
therapy.
FNAB is malignant in approximately 5% of patients with a dominant thyroid nodule.
Because the false-positive rate for patients with a malignant FNAB is 1% to 2%, definitive
therapy is recommended on the basis of the cytologic result alone. The malignancies that
FNAB can reliably identify include papillary, medullary, and anaplastic thyroid cancer.
FNAB may also be helpful in diagnosing metastatic cancer and lymphoma.
Diagnostic Imaging
High-Resolution Ultrasound
US is indicated for
1. evaluation of patients with nondiagnostic palpation-guided FNAB. In 50% of these
patients, US facilitates obtaining a diagnostic aspirate. 2)
2. US is also useful in the evaluation of patients with nodules that are difficult to palpate.
3. a US examination is obtained preoperatively in patients with a thyroid nodule and a
malignant FNAB to evaluate for abnormal lymph nodes in the central and lateral neck.
Preoperative, high-quality US in these patients has been shown to detect lymph node
or soft-tissue metastases in neck compartments believed to be uninvolved by PE in
almost 40% of patients. Finding metastatic disease preoperatively alters the surgical
procedure in these patients, facilitating complete resection of disease and helping to
minimize local and regional recurrence.
Although certain sonographic features should raise suspicion for malignancy, the presence
or absence of these sonographic findings cannot reliably distinguish benign from malignant
lesions. As a result, all patients with a nodule 1 cm or larger in size should be evaluated with
FNAB. For lesions less than 1 cm in size however, such sonographic findings may help to
determine which nodules warrant FNAB versus observation. Additional findings suggesting
local invasion or the presence of lymph node metastases are worrisome for malignancy and
warrant immediate FNAB, regardless of the nodule size. Sonographic findings suggestive of
invasion include the extension of irregular hypoechoic lesions beyond the thyroid capsule or
invasion of adjacent musculature.
Additional Imaging Modalities
Iodine-123 thyroid scintigraphy also has utility in selected patients with a thyroid nodule.
On the basis of the pattern of radionuclide uptake, nodules are classified as hyperfunctioning
(“hot”), isofunctioning, or nonfunctioning (“cold”).
Hyperfunctioning nodules almost never represent malignant lesions. Isofunctioning and
hypofunctioning nodules have a reported 5% to 10% risk of malignancy. Because more than
80% of nodules are hypofunctioning and only 5% to 10% are malignant, the predictive value
of thyroid scintigraphy for the presence of malignancy is low. Because of the low specificity
of I-123 thyroid scintigraphy, its routine use in the evaluation of patients with nodular thyroid
disease is not recommended.
Table -- Selected Indications for Iodine-123 Thyroid Scintigraphy in Patients with a
Dominant Thyroid Nodule
1) Low TSH before performing FNAB .
2 FNAB consistent with a follicular neoplasm and a low serum TSH level .
3 Persistently nondiagnostic FNAB and a low serum TSH level
source
Current Surgical Therapy , J. L. Cameron, 9 th eddition, 2008
DR. S. ALDAQAL