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Difficulty: MediumOrdering Imaging Studies

A 48-year-old woman is evaluated in the outpatient clinic after discovering a painless lump in her neck while applying lotion. She reports feeling somewhat "jittery" over the past month and has experienced a 2-kg (4.4-lb) weight loss despite maintaining her normal appetite. She has no prior medical history and takes no medications. Vital signs are normal except for a heart rate of 102/min. Physical examination reveals a smooth, firm, mobile, 1.8-cm nodule in the left lobe of the thyroid gland. No cervical lymphadenopathy is appreciated. A targeted bedside ultrasound confirms a 1.8-cm solid, circumscribed, hypoechoic nodule in the left thyroid lobe. Laboratory studies reveal:

Thyroid-stimulating hormone (TSH): 0.08 μ\mu U/mL (Normal: 0.5–5.0 μ\mu U/mL)
Free thyroxine (T4): 2.4 ng/dL (Normal: 0.9–1.7 ng/dL)

Which of the following is the most appropriate next imaging study?

  1. Radionuclide thyroid scintigraphyAnswer
  2. B
    Computed tomography of the neck with intravenous contrast
  3. C
    Magnetic resonance imaging of the neck without contrast
  4. D
    Positron emission tomography (PET) scan
  5. E
    Technetium-99m sestamibi scintigraphy

Answer

Radionuclide thyroid scintigraphy
Radionuclide thyroid scintigraphy is the correct next step because the patient has a thyroid nodule accompanied by a suppressed TSH level. According to established clinical guidelines, patients with a thyroid nodule and biochemical evidence of hyperthyroidism (low TSH) must undergo a radionuclide scan (typically using iodine-123 or technetium-99m pertechnetate). This scan determines whether the nodule is hyperfunctioning ('hot'), which carries an exceedingly low risk of malignancy and does not require fine-needle aspiration, or non-functioning ('cold'), which requires further evaluation with biopsy. Since her ultrasound has already anatomically confirmed the nodule, obtaining this functional imaging is the standard-of-care next step.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and laboratory results.
The patient has a newly discovered 1.8-cm solid thyroid nodule accompanied by symptoms of thyrotoxicosis, a suppressed TSH, and an elevated free T4.
Identifying the functional status of the thyroid gland via TSH measurement is the critical first branching point in the evidence-based evaluation of any palpable or ultrasonographically confirmed thyroid nodule.
2
Determine the algorithmic indication for further diagnostic imaging.
Because the TSH is subnormal (suppressed), the next required step is functional imaging to determine if the nodule is autonomously producing thyroid hormone.
Autonomously functioning ('hot') nodules have an extremely low risk of harboring malignancy and typically do not require fine-needle aspiration (FNA) biopsy, whereas non-functioning ('cold') nodules carry a higher malignancy risk and generally require FNA.
3
Select the appropriate imaging modality.
Radionuclide thyroid scintigraphy using iodine-123 or technetium-99m pertechnetate is the correct choice.
This specific nuclear medicine scan visualizes the spatial distribution of radioisotope uptake within the gland, effectively differentiating a toxic adenoma from multinodular goiter or Graves disease.

Key Concept

The initial evaluation of a thyroid nodule requires measuring a serum TSH. If the TSH is suppressed, indicating hyperthyroidism, the next most appropriate step is radionuclide thyroid scintigraphy to determine if the nodule is hyperfunctioning ('hot').
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Ordering Imaging Studies

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