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Among the several imaging techniques that provide clinically useful anatomic information about the thyroid gland, sonography has become the method that is most commonly employed. Previously, imaging of the thyroid required scintiscanning to provide a map of those areas of the thyroid that accumulate and process radioactive iodine. Although, scintiscanning remains of primary importance in patients who are hyperthyroid or for detection of iodine avid tissue after thyroidectomy for thyroid cancer, sonography has largely replaced it for the majority of patients who require a graphic representation of the regional anatomy because of its higher resolution, superior correlation of true thyroid dimensions with the image, smaller expense, greater simplicity, and lack of need for radioisotope administration. The other imaging methods, computerized tomography (CT) and magnetic resonance imaging (MRI) are more costly than sonography, are not as efficient in detecting small lesions, and are best used selectively when sonography is inadequate to elucidate a clinical problem. [1, 1A]
As with any test, sonography should be used to refine a differential diagnosis only when it is needed to answer a specific diagnostic question that has been raised by the clinical history and physical examination. [2] The image must then be integrated into patient management and correlated precisely with the other data.
Although sonography can supply clues about the nature of a thyroid lesion, it does not reliably differentiate benign lesions and cancer. Rather, sonography can:
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Depict accurately the anatomy of the neck in thyroid region,
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Help the student and clinician to learn thyroid palpation,
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Elucidate cryptic findings on physical examination,
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Assess the comparative size of nodules, lymph nodes, or goiters in patients who are under observation or therapy,
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Detect a non-palpable thyroid lesion in a patient who was exposed to therapeutic irradiation,
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Give clues about the likelihood of malignancy,
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Identify the solid component of a complex nodule,
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Facilitate fine needle aspiration biopsy of a nodule,
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Evaluate for recurrence of a thyroid mass after surgery,
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Monitor thyroid cancer patients for early evidence of reappearance of malignancy in the thyroid bed or lymphadenopathy,
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Identify patients who have ultrasonic thyroid patterns that suggest diagnoses such as thyroiditis.
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Refine in the management of patients on therapy such as antithyroid drugs,
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Facilitate delivery of medication or physical high-energy therapy precisely into a lesion and spare the surrounding tissue,
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Monitor in-utero the fetal thyroid for size,
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Scrutinize the neonatal thyroid for size and location,
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Screen in the field the thyroid during epidemiologic investigation.