Diagnostic ultrasound ( PDFDrive )

CHAPTER 19 The Thyroid Gland 723
Incidence rate per 100,000
9
8
7
6
5
4
3
2
1
0
THYROID CANCER INCIDENCE AND MORTALITY
1973-2002
Incidence
Mortality
1973 1976 1979 1982 1985 1988 1991 1994 1997 2000
Year
FIG. 19.43 Thyroid Cancer: Incidence Versus Mortality. Although
the rate of occurrence of thyroid cancer has more than doubled in the
last 30 years, the mortality rate is unchanged over that period. (Adapted
from Davies L, Welch HG. Increasing incidence of thyroid cancer in the
United States, 1973-2002. JAMA. 2006;295[18]:2164-2167. 138 )
surgery for nodule excision based on positive, suspicious, or
nondiagnostic results, and most of these nodules are benign. 101,142,143
Of these surgical patients, only 15% to 32% have cancer. 101,142
herefore the majority of patients who undergo surgery for thyroid
nodule excision will have had an operation for clinically insigniicant,
benign nodular disease.
he potential cost of the FNA biopsy workup of these nodules
must be considered. For discussion purposes, assume that 1
million of the estimated 300 million people in the United States
undergo a high-frequency ultrasound thyroid examination, and
that one or more thyroid nodules are detected in approximately
40%. herefore 400,000 people will have one or more thyroid
nodules detected by ultrasound imaging. Assuming a cost of
approximately $1500 for an ultrasound-guided FNA and cytologic
analysis, $600 million could theoretically be spent to exclude or
detect thyroid cancer in this group. If 18% of these FNA biopsies
result in suspicious or nondiagnostic results, 72,000 procedures
could occur at a cost of almost $20,000 each, for an additional
cost of $1.44 billion. Finally, approximately 5%, or almost 3600
patients, could experience signiicant postsurgical morbidity,
including hoarseness, hypoparathyroidism, and long-lasting
pain. 144 Clearly, this type of aggressive management of thyroid
nodules would entail massive health care expenditures and could
have an extremely negative clinical impact. 145
4. Which incidentally discovered nodules should be pursued?
Because of the many nodules detected on ultrasound, the
therapeutic approach should allow most patients with clinically
signiicant cancers to go on to further investigations. More
important, it should allow most patients with benign lesions to
avoid further costly, potentially harmful workup. With this goal in
mind, many practices, including ours, have found that it is both
impractical and imprudent to pursue the diagnosis for most of the
small nodules detected incidentally on ultrasound. If technically
possible, we usually obtain FNA biopsy of lesions that exhibit
sonographic features strongly associated with malignancy, such
as marked hypoechogenicity, taller-than-wide shape, and thick
irregular margins, as well as lesions containing microcalciications.
Evaluation of Nodules Incidentally Detected
by Sonography
Sonographic Findings
Nodules < 1.5 cm
Nodules > 1.5 cm
Nodules that have
malignant features
(marked
hypoechogenicity,
taller-than-wide shape,
thick irregular margins,
and/or calciications or
microcalciications)
Follow-Up
Followed by palpation at
next physical examination
Evaluation, usually by
ine-needle aspiration
Evaluation by ine-needle
aspiration
DIFFUSE THYROID DISEASE
Several thyroid diseases are characterized by difuse rather than
focal involvement. his usually results in generalized enlargement
of the gland (goiter) and no palpable nodules. Speciic conditions
that produce such difuse enlargement include chronic autoimmune
lymphocytic thyroiditis (Hashimoto thyroiditis),
colloid or adenomatous goiter, and Graves disease. hese
conditions are usually diagnosed on the basis of clinical and
laboratory indings and occasionally FNA biopsy. Sonography
is seldom indicated. However, high-resolution sonography can
be helpful when the underlying difuse disease causes asymmetrical
thyroid enlargement, which suggests a mass in the
larger lobe. he sonographic inding of generalized parenchymal
abnormality may alert the clinician to consider difuse thyroid
disease as the underlying cause. FNA, with sonographic guidance
if necessary, can be performed if a nodule is detected. Recognition
of difuse thyroid enlargement on sonography can oten be
facilitated by noting the thickness of the isthmus, normally a
thin bridge of tissue measuring only a few millimeters in AP
dimension. With difuse thyroid enlargement, the isthmus may
be up to 1 cm or more in thickness.
Diffuse Thyroid Diseases
Acute suppurative thyroiditis
Subacute granulomatous thyroiditis
Hashimoto thyroiditis (chronic lymphocytic thyroiditis)
Adenomatous or colloid goiter
Painless (silent) thyroiditis
Each type of thyroiditis, including acute suppurative thyroiditis,
subacute granulomatous thyroiditis (de Quervain disease), and
chronic lymphocytic thyroiditis (Hashimoto disease) has distinctive
clinical and laboratory features. 146 Acute suppurative thyroiditis
is a rare inlammatory disease usually caused by bacterial