Ecase:  1/16/2002

Tom Heller, MD

Woman with a thyroid nodule

A 50 year old healthy woman presents for a yearly physical exam.  She is without complaints, has no chronic health problems, takes no medications, has had no significant past health problems, exercises regularly, works as a loan officer in a bank, does not smoke or drink alcohol to excess.  Review of symptoms is negative.  Specifically, she has yet to begin menopause, has regular periods, has no symptoms to suggest hyper- or hypothyroidism.  She denies hoarseness or dysphagia.  On physical examination you discover a 2cm nodule on the left side of her thyroid gland, which had not been mentioned in the report from an  exam done 15 months earlier by a colleague.  The nodule moves with the thyroid.  Exam is otherwise entirely normal including absence of any cervical lymph nodes.  You point out the finding to the patient.  She had not previously noticed it.  You order a TSH, which comes back normal.

Is there any further history you wish to ask the patient?

What do you tell the patient she most likely has?

What is the next step you take?

• order other blood tests?  What tests?

• order an ultrasound of the thyroid?

• get a thyroid scan?

• send directly to endocrinologist for fine needle aspiration of the nodule?

• reassure patient that she has an isolated nodule that is of no consequence?

Discussion

The frequency of palpable thyroid nodules, half of which are single on physical exam, increases throughout life, afflicting about 1% of an asymptomatic population around age 20 and increasing to about 5% in those 50 and older.  A solitary thyroid nodule is defined as a palpably discrete swelling within an otherwise apparently normal gland, whereas a multinodular goiter is an enlarged thyroid gland with one or more palpable nodules.  However, when apparently solitary thyroid nodules are studied by ultrasonography, about half the glands contain multiple nodules. 

Most thyroid nodules (80%) occur in women.  The frequency of thyroid cancer in thyroid nodules is about 4% of those subjected to fine needle aspiration, and the incidence is the same whether the gland has a palpably single nodule or contains multiple nodules.  The incidence is higher in persons exposed to radiation of head, neck, and chest.  A 50 year old woman should be asked whether she was treated in childhood with radiation for recurrent tonsillitis, which was a common practice until the late 1950's, or whether she grew up near a nuclear reactor or dump site.

The differential diagnosis of a thyroid nodule includes the following:  thyroid adenoma, thyroid cancer, thyroid cyst, thyroiditis, and other inflammatory disorders.  Papillary thyroid cancer is the most common thyroid malignancy.  Fifteen to 25% of all thyroid nodules are cystic; a few are simple cysts, but the majority are hemorrhagic colloid cysts or necrotic papillary cancers.  Of the 75 to 85% of cysts that are solid, there are no ultrasound features that distinguish a malignant from a non-malignant nodule.  Hence, ultrasound does not help in the work-up of this patient.

Features that increase the likelihood of a thyroid nodule being cancerous are the following:  age less than 20 or greater than 60;

• hx of head or neck radiation;

• male sex;

• nodule greater than 4cm in diameter;

• rapid tumor growth;

• very firm nodule;

• fixation to adjacent structures--doesn't rise in the neck with swallowing;

• vocal cord paralysis

• enlarged regional lymph nodes.

However, absence of these features does not rule out malignancy.  In one study, 5 of 44  patients (11%) with a palpable nodule but none of the above symptoms or signs had malignancy identified by fine needle aspiration or by open biopsy.

Once a thyroid nodule is found on exam, the only laboratory test usually necessary are a serum TSH level and a thyroid fine needle aspiration.  About 5 to 10% of thyroid nodules yield insufficient cytology for diagnosis.  When this occurs, open biopsy often is needed to determine diagnosis.  When the cytology specimen is adequate,  4% are found to be malignant, 70%  are benign colloid nodules, and 20% are highly cellular specimens showing sheets of normal or atypical follicular cells without colloid, that are not clearly diagnostic of cancer (an indeterminate diagnosis).  A thyroid scan should be done only in patients with a suppressed serum TSH level (these patients are likely to have an autonomous thyroxin producing adenoma as a cause of their nodule, which will show up as a hot nodule on scan) or an indeterminate cytological diagnosis, some of whom will also be found to have hot nodules (i.e., non-malignant functioning adenomas).  The rest-those with indeterminate cytological diagnosis and negative scan, and those with FNAs diagnostic of malignancy will require surgery.  20% of those with  indeterminate cytological diagnosis will prove to have malignant nodules at surgery.

Treatment of benign nodules with thyroxine therapy is no longer recommended.

Our patient was reassured that she had none of the hallmarks of a malignant nodule, but that it could not be ruled out with absolute certainty, and that she would need an aspiration to confirm its benignity.  Fine needle aspiration indeed confirmed benign colloid changes.

Take Home Points:

1. Thyroid cancer occurs with similar frequency in an isolated thyroid nodule or a multinodular goiter.

2. Most thyroid nodules are benign.

3. Certain historical and physical findings increase the likelihood of malignancy, but their absence does not rule out malignancy.

4. The first diagnostic tests to perform on a patient with a thyroid nodule are serum TSH and fine needle aspiration.

References