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Archived Issues of Radiology Rounds
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Management of Thyroid Nodules
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- Palpable thyroid nodules are found in 4-7% of the population
Non-palpable thyroid nodules are found in approximately 50% of persons over 60 yrs
The vast majority of thyroid nodules are benign (malignancy rate 2-5%)
Ultrasound can help determine which nodules are suspicious but a biopsy is needed for a definitive
diagnosis
A low TSH followed by a 123I scan may define a nodule as "hot" or functioning, and virtually
always benign in which case an ultrasound may be unnecessary
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The
detection rate of thyroid nodules has increased dramatically because
they are common incidental findings during carotid ultrasonography as
well as. MRI and CT images of the neck and thorax, ordered for a
variety of diagnostic purposes. These nodules are typically
non-palpable, asymptomatic, and medically insignificant. Nevertheless,
there is a concern that they may be cancerous even though thyroid
cancer is rare. Approximately 5% of solitary thyroid nodules are
malignant; multinodular thyroid glands can harbor cancer, but the risk
of malignancy per nodule is lower in this situation.
Although the discovery of thyroid nodules warrants attention and
follow-up, there is considerable concern that the increase in the
number of incidental findings may lead to unnecessary testing and
treatment, adding to the cost-burden of health care and some risk for
the patient. It should be noted that the prevalence of non-palpable
thyroid nodules has been estimated to be in the range of 19-67% of the
population, and about 50% in those over the age of 60. In comparison,
only 4-7% of the populations are discovered to have thyroid nodules by
palpation. Furthermore, autopsy studies indicate that the prevalence of
occult (microscopic) papillary thyroid carcinoma, which rarely has any
clinical significance, may exceed 10%. Unfortunately, there is no
perfect answer to the need for the detection of all clinically
significant cancers while avoiding unnecessary biopsy procedures and
surgery.
Evaluation of Thyroid Nodules
Risk factors for thyroid cancer include age less than 20 or over 60, a
history of head or neck irradiation, and a family history of thyroid
cancer or familial multiple endocrine neoplasias. Thyroid function
tests may be helpful. If the serum TSH is below normal, an 123I
scan should be performed to exclude a “hot” nodule, which are benign
over 99% of the time. In this situation, a biopsy is not necessary.
Because only 5% of nodules are hot, a thyroid scan should only be
performed if the TSH is low. Due to the limitations in the resolution
of a radionuclide scan only nodules greater than 1 cm can generally be
imaged with this modality.
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Grey
scale ultrasound image of a pathologically proven thyroid cancer
demonstrates an isoechoic nodule (within calipers) with a well-defined
margins and microcalicifications. This case illustrates the point
that many nodules that harbor malignancy will only demonstrate one of
the several features (hypoechoic, microcalcifications, poorly defined
margins, etc.) associated with malignancy.
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As a general rule, most endocrinologists recommend a FNA (Fine Needle
Aspiration Biopsy) for palpable nodules larger than 1 to 1.5 cm.
There is currently intense debate about whether all identified nodules
over 1 (or 1.5 cm) require FNA. Some feel that only the smaller
non-palpable nodules (e.g. < 1.5 cm) with suspicious characteristics
(see below) need to be biopsied.
Ultrasound Imaging
Ultrasound imaging can detect nodules as small as 2 mm and it is useful
for determining the number of thyroid nodules and measuring their size.
It can also differentiate simple cysts, which are unlikely to be
malignant. Radiologists have defined ultrasound characteristics that
make a nodule more likely to be malignant. These have been particularly
useful in deciding which non-palpable nodules between 0.8 and 1.5 cm
might require biopsy. These characteristics include a hypoechoic nodule
with one of the following: microcalcifications, central blood flow, or
irregular border. Although one or more of these features in a nodule
increase the chance for malignancy, small nodules that have these
characteristics still only prove to be malignant 22% of the time.
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Thyroid Ultrasonography
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Useful Applications
- To supplement physical examination of patients with thyroid nodular disease
- To screen patients with a history of head or neck irradiation
- To differentiate solid and cystic nodules
- To follow up patients with benign nodules
- To look for recurrence of cancer in patients who have had surgery
- To guide fine needle aspiration biopsy of small solid, partially cystic, or non-palpable nodules
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Limitations
- Cannot unequivocally rule out cancer (sensitivity 87-94%)
- Attenuation of sound waves in deeper tissues makes evaluation of large goiters difficult
- Passage of sound waves blocked by calcific deposits in thyroid and bone – Substernal portions of thyroid not visualized
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Sensitivity, Specificity and Predictive Value of Ultrasound Imaging of Non-Palpable Thyroid Nodules
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Hypoechoic |
Hypoechoic and Blurred Margins |
Hypoechoic and Intranodular Vascularization |
Hypoechoic and Microcalcifications |
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Sensitivity
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87% |
74% |
61% |
26% |
| Specificity |
48% |
88% |
86% |
96% |
| Predictive Value |
11% |
39% |
26% |
36% |
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Data from Papini et al., 2002
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Fine Needle Aspiration Biopsy
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Scheduling
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Fine
needle aspiration (FNA) biopsy provides the most direct and specific
information about a thyroid nodule. If the nodule is palpable, image
guidance is unnecessary. However, FNA biopsy is more successful if
guided by ultrasound when nodules are small, partly cystic, or
non-palpable. FNA biopsy is performed on an outpatient basis and is a
low risk procedure, usually requiring no sedation and only local
anesthesia. It is not precluded by anti-coagulant or aspirin therapy.
The most likely complication is local discomfort.
FNA results can be classified as a) non-diagnostic, in which case the biopsy should be repeated; b) benign, usually a macrofollicular pattern in which case the nodule can be followed; c)
malignant; most commonly a papillary thyroid carcinoma and occasionally
a medullary thyroid carcinoma, in which case surgery is necessary; or d)
suspicious, often called a follicular neoplasm, which usually has a
microfollicular pattern or abundant oxyphil (Hurthle) cells, in which
case surgery is necessary to decide if a nodule is benign or malignant.
The suspicious category is a reflection of our inability to diagnose
follicular carcinomas by FNA. The distinction between a benign
microfollicular adenoma and a follicular carcinoma (or a benign oxyphil
cell tumor or a malignant one) requires surgery. A suspicious biopsy
(follicular neoplasm) will be found in 10 to 20% of biopsies. Ten to
twenty percent of these (higher in men and in larger nodules) will
ultimately prove to be malignant.
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Ultrasound
examination of patients with thyroid nodules may be performed at Mass
General West Imaging in Waltham, Mass General Imaging in Chelsea, or at
the main MGH campus. Appointments can be scheduled by calling 4-XRAY
(617-724-9729) or through the web-based Radiology Order Entry system, http://mghroe
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Ultrasound-guided FNA biopsy is performed on the main campus only and
can be scheduled by calling Interventional Radiology (617-726-8386).
FNA biopsies are also performed in the Thyroid Unit and by the Cytology
FNA service.
Further Information
For further questions on thyroid ultrasound, please call Joseph Simeone, M.D., Radiologist, Abdominal Imaging and Intervention Division, at 617-726-3091.
We would like to thank Gilbert H. Daniels, M.D.,
endocrinologist in the Thyroid Unit at MGH for his advice on the
management of thyroid nodules in the preparation of this article.
This article provided useful information about the appropriate use of imaging studies:
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References
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Blum, M. (2004) Use of ultrasonography in thyroid disease Up-to-Date Online http://uptodateonline.com/application/topic.asp?file=thyroid/22414
Hegedus, L. (2004) The Thyroid Nodule. N Engl J Med 351: 1764-1771
Kane, RA. (2003) Ultrasound of the thyroid and parathyroid glands: Controversies in the diagnosis of thyroid cancer. Ultrasound Q. 19:177-178
Mandel, SJ (2004) A 64-year-old woman with a thyroid nodule. JAMA 292: 2632-2642
Papini, E, Guglielmi, R, Bianchini, A, Crescenzi, A, et al. (2002) Risk of malignancy in nonpalpable thyroid nodules: predictive value of ultrasound and color-Doppler features. J Clin Endocrinol Metab 87: 1941-1946
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