Diagnostic ultrasound ( PDFDrive )

CHAPTER 19 The Thyroid Gland 711
A
B
C
D
FIG. 19.29 Multinodular Goiter. (A) Transverse image shows enlargement of the right lobe and isthmus by multiple conluent hypoechoic
and hyperechoic nodules. Tr, Tracheal air shadow. (B) and (C) Longitudinal images show multiple conluent nodules (arrows). (D) Longitudinal dual
image shows enlargement of a lobe by multiple nodules.
such a mass is within or adjacent to the thyroid cannot always
be made on the basis of the physical examination alone. Sonography
can readily diferentiate thyroid nodules from other cervical
masses, such as cystic hygromas, thyroglossal duct cysts, and
enlarged lymph nodes. Alternatively, sonography may help to
conirm the presence of a thyroid nodule when the indings on
physical examination are equivocal.
Sonography may be used to detect occult thyroid nodules in
patients who have a history of head and neck irradiation during
childhood as well as those with a family history of MEN II
syndrome; both groups have a known increased risk for development
of thyroid malignancy. If a nodule is discovered, a biopsy
can be performed under sonographic guidance. It is unknown,
however, whether the detection of a thyroid cancer before it
becomes clinically palpable will change the ultimate clinical
outcome for a given patient.
In the past, when thyroid nodules were evaluated primarily
with isotope scintigraphy, it was generally accepted that a “solitary
cold” nodule carried a probability of malignancy of 15% to 25%,
whereas a “cold” nodule in a multinodular gland was malignant
in less than 1% of cases. 53 However, benign goiter is multinodular
in 70% to 80% of cases, and 70% of nodules considered “solitary”
on scintigraphy or physical examination are actually multiple
when assessed with high-frequency ultrasound 21,54 (Fig. 19.29).
It has been suggested, therefore, that sonography may be used
to detect additional occult nodules in patients with clinically
solitary lesions, thereby implying that the dominant palpable
mass is benign. Such a conclusion is unwarranted, however,
because pathologically, benign nodules oten coexist with
malignant nodules. In a series of 1500 consecutive patients
undergoing surgery for papillary carcinoma, 33% had coexistent
benign nodules at surgery. 55 In addition, PTC is recognized to
be multicentric in at least 20% of cases and occult (<1.5 cm in
diameter) in up to 48% of cases. 23,53 In a previous study, almost
two-thirds (64%) of patients with thyroid cancer had at least
one nodule in addition to the dominant nodule detected sonographically.
56 Pathologically, these extra nodules can be benign
or malignant. herefore in patients with a clinically solitary
nodule, the sonographic detection of a few additional nodules
is not a reliable sign for excluding malignancy.
An ultrasound-guided FNA biopsy is performed for patients
with multinodular goiter when there is a dominant nodule. A
dominant nodule is the largest nodule or has ultrasound features
diferent from the other nodules or features suggestive of
carcinoma.
In patients with known thyroid cancer, sonography can be
useful to determine the extent of disease, both preoperatively
and postoperatively. In most patients a sonographic examination
is not performed routinely before thyroidectomy, but it can be
useful in those with large cervical masses for evaluation of nearby
structures, such as the carotid artery and internal jugular vein
for evidence of direct invasion or encasement by the tumor.
Alternatively, in patients with cervical lymphadenopathy caused
by PTC but in whom the thyroid gland is palpably normal,
sonography may be used preoperatively to detect an occult,
nonpalpable primary focus within the gland.