Diagnostic ultrasound ( PDFDrive )

CHAPTER 19 The Thyroid Gland 713
epithelium-lined, simple thyroid cyst is extremely rare. Virtually
all cystic thyroid lesions seen with high-resolution ultrasound
demonstrate some wall irregularity and internal solid elements
or debris caused by nodule degeneration (see Figs. 19.9 and
19.10). When high-frequency gray-scale sonography and color
Doppler imaging cannot diferentiate debris and septa from
neoplastic intracystic vegetations, contrast-enhanced sonography
can sometimes resolve the problem by demonstrating the arterial
enhancement in tumoral projections and the complete lack of
enhancement of benign septa and debris (see Fig. 19.12). Comettail
artifacts are frequently encountered in cystic thyroid nodules
and are likely related to the presence of microcrystals (see Fig.
19.10). In a published series of 100 patients with this feature,
FNA biopsy was benign in all cases. 22 hese comet-tail artifacts
can be located in the cyst walls and internal septations or in the
cyst luid. When a more densely echogenic luid is gravitationally
layered in the posterior portion of a cystic cavity, the likelihood
of hemorrhagic debris is very high. Frequently, patients with
hemorrhagic debris clinically demonstrate a rapidly growing,
oten tender neck mass. he spongiform appearance of thyroid
nodules, related to the presence of tiny colloid changes, is an
extremely uncommon inding in malignant nodules, particularly
when it is associated with other indings such as well-deined
margins and isoechogenicity. his pattern is highly predictive
of a benign nodule (see Fig. 19.9).
Papillary carcinomas rarely exhibit varying amounts of cystic
change, appearing almost indistinguishable from benign cystic
nodules. 66-68 In cystic papillary carcinomas, however, the frequent
sonographic detection of solid elements or projections (≥1 cm
with blood low signals and/or microcalciications) into the lumen
can lead to suspicion of malignancy (see Fig. 19.18). Cervical
metastatic lymph nodes from either a solid or a cystic primary
papillary cancer may also demonstrate a cystic pattern; this is
likely pathognomonic of malignant adenopathy.
Shape. A taller-than-wide shape, in which the AP diameter
is equal to or less than the transverse diameter on a transverse
or longitudinal plane, is speciic for diferentiating malignant
nodules from benign nodules, likely because malignant neoplasms
(taller than wide) grow across normal tissue planes, whereas
benign nodules grow parallel to normal tissue planes. 59,65,66
Echogenicity. hyroid cancers are usually hypoechoic
relative to the adjacent normal thyroid parenchyma (see Fig.
19.15). Unfortunately, many benign thyroid nodules are also
hypoechoic. In fact, most hypoechoic nodules are benign because
benign nodules are so much more common than malignant
nodules. However, marked hypoechogenicity is highly speciic
for diagnosing malignant nodules, whereas the hypoechogenicity
oten found in benign lesions is usually less marked. 65 A predominantly
hyperechoic nodule, although relatively uncommon,
is more likely to be benign. 21 he isoechoic nodule, visible
because of a peripheral sonolucent rim that separates it from
the adjacent normal parenchyma, has an intermediate to low
risk of malignancy. Isoechogenicity has low sensitivity but high
speciicity and positive predictive value for the diagnosis of
benign nodules. 65
Halo. A peripheral sonolucent halo that completely or
incompletely surrounds a thyroid nodule is present in 60% to
80% of benign nodules and 15% of thyroid cancers. 21,69 Histologically,
it is thought to represent the capsule of the nodule, but
hyperplastic nodules that have no capsule oten have this sonographic
feature. he hypothesis that it represents compressed
normal thyroid parenchyma seems acceptable, especially for
rapidly growing thyroid cancers, which oten have thick, irregular,
and incomplete halos (see Fig. 19.15C) that are hypovascular or
avascular on color Doppler scans. Color and power Doppler
imaging demonstrates that the thin, complete peripheral halo,
which is strongly suggestive of benign nodules, represents blood
vessels coursing around the periphery of the lesion—the “basket
pattern.”
Margin. Benign thyroid nodules tend to have sharp, welldeined
margins, whereas malignant lesions tend to have irregular,
spiculated, or poorly deined margins. For any given nodule,
however, the appearance of the outer margin cannot reliably
predict the histologic features because many exceptions to these
general trends have been identiied, even if the association of
spiculated margins with malignant nodules has been demonstrated
as highly speciic. 65
Calciication. Calciication can be detected in about 10% to
15% of thyroid nodules, but the location and pattern of the
calciication have a more predictive value in distinguishing benign
from malignant lesions. 21 Peripheral shell (eggshell) calciication,
although rarely present, has traditionally been considered a
characteristic of a benign nodule (see Fig. 19.11). As recently
reported, however, thickened and interrupted peripheral
calciications, particularly if associated with hypoechoic halo,
have very high sensitivity for the diagnosis of malignant nature. 70,71
Scattered echogenic foci of calciication with or without associated
acoustic shadows are more common. When these calciications
are large and coarse (usually related to ibrosis and degeneration),
the nodule is more likely to be a benign nodule, with long disease
duration. When the calciications are ine and punctate, however,
malignancy is more likely. Pathologically, these ine calciications
may be caused by psammoma bodies, typically seen in papillary
cancers (see Figs. 19.14 and 19.15).
Medullary thyroid carcinomas oten exhibit bright echogenic
foci either within the primary tumor or within metastatically
involved cervical lymph nodes. 33 he larger echogenic foci are
usually associated with acoustic shadowing (see Fig. 19.25).
Pathologically, these densities are caused by reactive ibrosis and
calciication around amyloid deposits, which are characteristic
of medullary carcinoma. In the appropriate clinical setting (e.g.,
MEN II syndrome, increased serum calcitonin level), the inding
of echogenic foci within a hypoechoic thyroid nodule or a cervical
node can be highly suggestive of medullary carcinoma.
Kakkos and colleagues 72 found a strong association between
sonographically detected thyroid calciications and thyroid
malignancy, particularly in young patients or those with a
solitary thyroid nodule. Patients younger than 40 with calciied
nodules constitute a high-risk group, four times more likely to
harbor thyroid malignancies than patients of the same age but
without intranodular calciications. Similarly, the presence of
calciications within a solitary nodule increases the incidence of
malignancy. herefore these patients must be further evaluated or
followed.