Diagnostic ultrasound ( PDFDrive )

722 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
Pt with nodules (%)
100
80
60
40
20
0
0 10 20 30 40 50 60 70 80 90
Age, yr
FIG. 19.40 Prevalence of Thyroid Nodules on Autopsy and
Sonography. Autopsy (blue circles) revealed thyroid nodules on average
in 49% of patients in 1955, and sonography (orange circles) detected
thyroid nodules in 41% in 1985, with both shown here as a function of
patient age. (With permission from Horlocker T, Hay I, James E. Prevalence
of incidental nodular thyroid disease detected during high-resolution
parathyroid ultrasonography. In: Medeiros-Neto G, Gaitan E, editors.
Frontiers in thyroidology. New York: Plenum; 1986. p. 1209-1312. 134 )
to patients and society from workup of these nodules may far
outweigh the beneit of detecting an occult thyroid cancer, because
the vast majority of thyroid cancers behave in a benign manner.
Speciically, patients with PTC have a 99% 10-year survival and
approximately a 95% overall 30-year survival. 55,136
2. he incidence of thyroid cancer is increasing.
Over 50 years ago, pathologists reported that clinically insigniicant
thyroid cancer was a common inding at autopsy. In the
1980s, Harach and colleagues 137 studied thinly sectioned thyroid
glands at autopsy and found that 36% had occult thyroid cancer.
hey stated that had they sectioned the glands even more inely,
almost every person would harbor a thyroid cancer. hey
concluded that occult PTC was a “normal” inding at autopsy.
Over the last three decades, the reported incidence of thyroid
cancer in North America has more than doubled. 138 his raises
the question of whether the increase represents a real increased
incidence of thyroid cancer or is simply a result of an increased
rate of detection by diagnostic imaging methods such as ultrasound.
Analyzing the data, Davies and Welch 138 found that the
increased incidence resulted from increased detection of subclinical
disease rather than from an increase in the true occurrence
of thyroid cancer. heir work showed that PTC accounts for
virtually the entire increase in incidence (Fig. 19.41). hey also
showed that the increased rate of detection is caused by small,
subclinical thyroid cancer (Fig. 19.42). Furthermore, although
the prevalence of thyroid cancer more than doubled over 30
years, the mortality rate remained unchanged (Fig. 19.43).
According to Ross, 139 “Considering the anxiety, costs and complications
sufered by many of these patients, one can reasonably
question the beneits of increased cancer detection.”
3. What are the costs of frequent use of FNA biopsy for
management of incidentally detected thyroid nodules?
If FNA biopsy were used as the automatic next step ater nodule
detection, the costs to patients and society would be great.
Whereas FNA biopsy is considered the “reference standard” for
Incidence rate per 100,000
9
8
7
6
5
4
3
2
1
0
TRENDS IN INCIDENCE OF THYROID CANCER
1973-2002
All
Papillary
Follicular
Poorly differentiated
1973 1975 1979 1982 1985 1988 1991 1994 1997 2000
Year
FIG. 19.41 Thyroid Cancer: Incidence. Graph shows the increasing
incidence of thyroid cancer in North America during the past three
decades. Note that the type of thyroid malignancy is almost entirely
papillary carcinoma. The increasing incidence results from the increased
rate of detection by diagnostic imaging methods such as ultrasound,
rather than from an increase in the true occurrence of thyroid cancer.
(Modiied from Davies L, Welch HG. Increasing incidence of thyroid
cancer in the United States, 1973-2002. JAMA. 2006;295[18]:
2164-2167. 138 )
Incidence rate per 100,000
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
PAPILLARY THYROID CANCER BY SIZE
1988-2002
0
1988 1990 1992 1994 1996 1998 2000 2002
Year
0-1.0 cm
1.1-2.0 cm
2.1-
5.0 cm
>5.0 cm
FIG. 19.42 Thyroid Cancer: Incidence by Size of Tumor. Note
that the increased incidence of thyroid carcinoma is primarily the result
of the detection of smaller tumors. (Adapted from Davies L, Welch HG.
Increasing incidence of thyroid cancer in the United States, 1973-2002.
JAMA. 2006;295[18]:2164-2167. 138 )
nodule diagnosis, it is an imperfect technique for many reasons.
First, the results are nondiagnostic in 10% to 20% of cases. 101,140
Second, there is a false-negative rate of 3% to 5%. 141 hird,
interpretative skills vary widely regarding cytopathology of the
thyroid nodule. Unfortunately, in less experienced centers, the
report of “follicular cells are present, cannot exclude follicular
neoplasm” occurs more frequently than in centers with greater
interpretive experience. his report typically leads to the need
for surgical excision. Given these considerations, an estimated
18% of all patients who have FNA biopsy ultimately undergo