Diagnostic ultrasound ( PDFDrive )

CHAPTER 19 The Thyroid Gland 709
A
B
FIG. 19.26 Anaplastic Thyroid Carcinoma. (A) Transverse image shows large hypoechoic mass (arrows) involving the entire gland, greater
on the left, which causes deviation of the trachea to the right. C, Common carotid artery; J, jugular vein; Tr, tracheal air shadow. (B) Contrastenhanced
computed tomography scan of the patient shows the large mass and its relationship to adjacent structures.
A
B
FIG. 19.27 Lymphoma. (A) Transverse image of left lobe of the thyroid shows diffuse mass enlarging the lobe and extending into the soft
tissues (arrows) surrounding the common carotid artery (c). Tr, Tracheal air shadow. (B) Contrast-enhanced computed tomography scan shows a
hypovascular mass in the left thyroid lobe and soft tissue encasement of the carotid artery.
Sonographically, lymphoma of the thyroid appears as an
extremely hypoechoic and lobulated mass. Large areas of cystic
necrosis may occur, as well as encasement of adjacent neck
vessels 37 (Fig. 19.27). On color Doppler imaging, both nodular
and difuse thyroid lymphomas may appear mostly hypovascular
or may show blood vessels with chaotic distribution and AV
shunts. he adjacent thyroid parenchyma may be heterogeneous
as a result of associated chronic thyroiditis. 38
Thyroid Metastases
Metastases to the thyroid are infrequent, occurring late in the
course of neoplastic diseases as the result of hematogenous spread
or less frequently a lymphatic route. Metastases usually are from
melanoma (39%), breast (21%), and renal cell (10%) carcinoma.
Metastases may appear as solitary, well-circumscribed nodules
or as difuse involvement of the gland. On sonography, thyroid
tumors are solid, homogeneously hypoechoic masses, without
calciications 39 (Fig. 19.28).
Fine-Needle Aspiration Biopsy
Once a thyroid nodule has been detected, the fundamental
challenge is to determine if it is benign or malignant. Short of
surgical excision, several methods for nodule characterization
are in common use, including radionuclide imaging, sonography,
and FNA biopsy. Each of these techniques has advantages and
limitations, and the choice in any speciic clinical setting depends
largely on available instrumentation and expertise.
It is generally recognized that FNA biopsy is the most efective
method for diagnosing malignancy in a thyroid nodule. 40-42 In
many clinical practices, FNA under direct palpation is the irst
diagnostic examination performed on any clinically palpable
nodule. Neither isotopic nor sonographic imaging is used
routinely, instead reserved for special situations or diicult cases.
FNA has had a substantial impact on the management of thyroid
nodules because it provides more direct information than any
other available diagnostic technique. It is safe and inexpensive
and results in better selection of patients for surgery. he successful
use of FNA in clinical practice, however, depends heavily on the
presence of an experienced aspirationist and an expert
cytopathologist.
Fine-needle thyroid aspirates are oten classiied cytopathologically
into the following four categories:
1. Negative (no malignant cells)
2. Positive for malignancy