Biopsy of the Thyroid Gland
Histologic examination of thyroid tissue for diagnostic purposes requires some form of an invasive procedure. The biopsy procedure depends on the intended type of microscopic examination. Core biopsy for histologic examination of tissue with preservation of architecture is obtained by closed needle or open surgical procedure; aspiration biopsy is performed to obtain material for cytologic examination.
Core Biopsy. Closed core biopsy is an office procedure carried out under local anesthesia.
A large (about 15-gauge) cutting needle of the Vim-Silverman type is most commonly used.384 The needle is introduced under local anesthesia
through a small skin nick and firm pressure is applied over the puncture site for 5-10
minutes after withdrawal of the needle. In experienced hands, complications are rare, but
may include transient damage to the laryngeal nerve, puncture of the trachea,
laryngospasm, jugular vein phlebitis, and bleeding.385 Because of the fear of
disseminating malignant cells, biopsy was restricted for many years to the differential
diagnosis of diffuse benign diseases. With the improvement of cytology and biopsy
techniques, open biopsy carried out under local or general anesthesia has been virtually
abandoned.385
Percutaneous Fine Needle Aspiration (FNA). The development of more sophisticated staining techniques for cytologic examination, the realization that fear of tumor dissemination along the needle tract was not well founded, and especially the high diagnostic accuracy of the technique are responsible for the increasing popularity of percutaneous fine needle aspiration.385,388,388a,388b
The procedure is exceedingly simple and safe. The patient lays supine, with the neck hyperextended by placing a small pillow under the shoulders. Local anesthesia is usually not required. The skin is prepared with an antiseptic solution. The lesion, fixed between two gloved fingers, is penetrated with a fine (22- to 27-gauge) needle attached to a syringe. Suction is then applied while the needle is moved within the nodule. A non-suction technique using capillary action has also been developed. The small amount of aspirated material, usually contained within the needle or its hub, is applied to glass slides and spread. Some slides are air dried and others are fixed before staining. As biopsy of small nodules may be technically more difficult, the use of ultrasound to guide the needle is preferred.373,376 It is important that the slides be properly prepared, stained and read by a cytologist experienced in the interpretation of material from thyroid gland aspirates.
The yield of false-positive and false-negative results is variable from one center to another, but both are acceptably low. Various centers have reported that the accuracy of this technique in distinguishing benign from malignant lesions may be as high as 95%.385,388 In one clinic in which the procedure is used routinely, the number of patients operated upon decreased by one-third, whereas the percentage of thyroid carcinomas among the patients who underwent surgery doubled.389 When results are suggestive of a follicular neoplasia, surgery is required as follicular adenoma cannot be differentiated from follicular cancer by cytology alone. As the sample obtained may not always be representative of the lesion, surgical treatment is indicated for lesions highly suspicious of being malignant on clinical grounds. Other uses of aspiration biopsy include presumed lymphoma or invasive anaplastic carcinoma when biopsy may spare the patient an unnecessary neck exploration. Another application of needle aspiration is in the confirmation and treatment of thyroid cysts and autonomous thryoid nodules.389a
