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June 2008

Thyroid Biopsy Ultrasound-Guided Fine Needle Aspiration

Lisa A. Orloff, M.D.
Chief of Head and Neck and Endocrine Surgery
UCSF Department of Otolaryngology — Head and Neck Surgery

Thyroid nodules that can't be easily palpated present a dilemma when screening patients with suspected nodular thyroid disease or suspected recurrent thyroid cancer. In patients with thyroid nodules detected by ultrasound (US), fine needle aspiration (FNA) biopsy with ultrasound guidance can accurately assess and diagnose the majority of lesions in the head and neck region. The use of ultrasound-guided FNA (USGFNA) for thyroid nodules has a reported sensitivity of 83 percent and specificity of 77 percent.

During or after sampling, FNA specimens are reviewed by a cytopathologist. The use of USGFNA with onsite evaluation of cytology specimens by a team of physicians and pathologists has shown to provide the most accurate results and the least painful procedure.

Patient discomfort, measured by the number of required needle passes, and diagnostic errors, measured by sample inadequacy rate, can be reduced by ultrasound guidance and immediate examination of material obtained. Clinician-performed ultrasound and USGFNA can help expedite the diagnostic workup and is an alternative to performing an ultrasound and biopsy separately.

Certain preliminary FNA findings can suggest specimen adequacy as well as diagnosis.

Benign Thyroid Nodules

On FNA findings, benign thyroid nodules yield certain typical cellular and extracellular components such as visible colloid material, clusters of follicular cells often in a "honeycombed" pattern, round to oval nuclei with stippled chromatin and foamy (degenerating) cells.

Thyroid Carcinomas

Thyroid carcinomas that are identifiable on FNA by cytopathologic analysis include papillary, medullary and anaplastic carcinomas.

Papillary thyroid carcinoma typically shows large, round, irregular or grooved and often overlapping nuclei; pale nuclear chromatin; sheets of cells with papillary configuration; "pseudoinclusions"; psammoma bodies; and viscous colloid.

Medullary thyroid carcinoma shows hypercellularity, poor cell cohesion, spindle-shaped cells with elongated, eccentric nuclei, multinucleated cells, positive staining for calcitonin and positive staining with Congo red if amyloid is present.

Papillary thyroid cancer represents more than 80 percent of all thyroid malignancies. In addition to obtaining cytological diagnosis, in some cases the aspirate obtained can be examined for genetic markers such as the BRAF mutation, which may assist in surgical planning.

Thyroglobulin and Calcitonin Levels

Aspirated material can be tested for thyroglobulin or calcitonin levels. This testing is especially useful in the evaluation of potential lymph node metastases or recurrent nodules in patients with known papillary or medullary carcinoma. These levels should be correlated with simultaneous serum levels. Serum thyroglobulin (TG) is frequently used as a marker for recurrent disease in patients with well-differentiated thyroid cancer who have undergone surgical thyroidectomy with or without radioactive iodine ablation.

A shortcoming of serum TG measurement is that 12 percent or more of patients will have anti-TG antibodies that interfere with interpretation of the assay. Furthermore, demonstration of an elevated TG level does not localize the recurrent or metastatic disease. Measurement of thyroglobulin or calcitonin in the aspirate from the USGFNA of any suspicious mass can confirm the presence and simultaneously localize recurrent disease.

Follicular neoplasm of the thyroid is a cytopathologic dilemma. Follicular adenoma cannot be differentiated from follicular carcinoma by either US or FNA without surgical excision and determination of vascular or capsular invasion. On FNA, a hypercellular specimen with microfollicular pattern and nuclear polymorphism and cellular atypia will be present.

For more information, contact the Physician Referral Service at UCSF Medical Center:

Phone   (888) 689-UCSF or (888) 689-8273
Email   referral.center@ucsfmedctr.org

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