Diagnostic ultrasound ( PDFDrive )

CHAPTER 20 The Parathyroid Glands 735
T
Tr
T
T
T
J
C
C
A
B
FIG. 20.2 Typical Parathyroid Adenoma. (A) Transverse and (B) longitudinal sonograms of a typical adenoma (arrows) located adjacent to
the posterior aspect of the thyroid (T). C, Common carotid artery; J, internal jugular vein; Tr, trachea.
However, since in current practice, most cases of primary
hyperparathyroidism are discovered in the early stages of the
disease, some controversy exists as to whether asymptomatic
patients with minimal hypercalcemia should be treated surgically,
or followed medically with frequent measurements of bone density,
serum calcium levels, and urinary calcium excretion and monitoring
for nephrolithiasis. 26 Recommendations for the management
of asymptomatic primary hyperparathyroidism have been outlined
in various articles, many of which are based on International
Workshop and National Institutes of Health (NIH) Consensus
Conference statements and subsequent updates. his area
continues to evolve, and approaches to treatment may difer
slightly among clinical practices. 24-31
SONOGRAPHIC APPEARANCE
Shape
Parathyroid adenomas are typically oval or bean shaped
(Fig. 20.2). As parathyroid glands enlarge, they dissect between
longitudinally oriented tissue planes in the neck and acquire a
characteristic oblong shape. If this process is exaggerated, they
can become tubular or lattened. here is oten asymmetry in
the enlargement, and the cephalic and/or caudal end can be
more bulbous, producing a triangular, tapering, teardrop or
bilobed shape. 19,32-34
Echogenicity and Internal Architecture
he echogenicity of most parathyroid adenomas is substantially
less than that of normal thyroid tissue (Fig. 20.3). he characteristic
hypoechoic appearance of parathyroid adenomas is caused
by the uniform hypercellularity of the gland with little fat content,
which leaves few interfaces for relecting sound. Occasionally,
adenomas have a heterogeneous appearance, with areas of
increased and decreased echogenicity. he rare, functioning
parathyroid lipoadenomas are more echogenic than the adjacent
thyroid gland because of their high fat content 35 (Fig. 20.3G). A
great majority of parathyroid adenomas are homogeneously
solid. About 2% have internal cystic components resulting from
cystic degeneration (most oten) or true simple cysts (less
oten) 36-38 (Fig. 20.3E and F, Video 20.1). Adenomas may rarely
contain internal calciication (Fig. 20.3H and I).
Vascularity
Color low, spectral, and power Doppler sonography of an enlarged
parathyroid gland may demonstrate a hypervascular pattern with
prominent diastolic low (Fig. 20.4). An enlarged extrathyroidal
artery, oten originating from branches of the inferior thyroidal
artery, may be visualized supplying the adenoma with its insertion
along the long-axis pole. 39-44 A inding described in parathyroid
adenomas is a vascular arc, which envelops 90 to 270 degrees
of the mass. his vascular low pattern may increase the sensitivity
of initial detection of parathyroid adenomas and aid in conirming
the diagnosis by allowing for diferentiation from lymph nodes,
which have a central hilar low pattern. Asymmetric increased
vascular low may also be present in the thyroid gland adjacent
to a parathyroid adenoma.
Size
Most parathyroid adenomas are 0.8 to 1.5 cm long and weigh
500 to 1000 mg. he smallest adenomas can be minimally enlarged
glands that appear virtually normal during surgery but are found
to be hypercellular on pathologic examination (Fig. 20.5, Video
20.2). Large adenomas can be 5 cm or more in length and weigh
more than 10 g. Preoperative serum calcium levels are usually
higher in patients with larger adenomas. 32
Multiple Gland Disease
Multiple gland disease may be caused by difuse hyperplasia or
multiple adenomas. Individually, these enlarged glands may have
the same sonographic and gross appearance as other parathyroid
adenomas (Fig. 20.6, Videos 20.3 and 20.4). However, the glands
may be inconsistently and asymmetrically enlarged, and the
diagnosis of multigland disease can be diicult to make sonographically.
For example, if one gland is much larger than the
others, the appearance may be misinterpreted as solitary adenomatous
disease. Alternatively, if multiple glands are only minimally
enlarged, the diagnosis may be missed altogether.
Carcinoma
Carcinomas are usually larger than adenomas. 45-47 Carcinomas
oten measure more than 2 cm compared with about 1 cm for
adenomas (Fig. 20.7). On ultrasound, carcinomas also frequently
have a lobular contour, heterogeneous internal architecture, and
internal cystic components. However, large adenomas may also