Diagnostic ultrasound ( PDFDrive )

CHAPTER 20 The Parathyroid Glands 745
renal failure. In these patients, chronic relative hypocalcemia is
the result of multiple complex factors, including decreased
synthesis of the active form of vitamin D, poor calcium and
vitamin D absorption, persistent hyperphosphatemia, and skeletal
resistance to the actions of PTH. hese factors contribute to
parathyroid hyperplasia. If untreated, secondary hyperparathyroidism
can result in bone demineralization, sot tissue calciication,
and acceleration of vascular calciication. Surgical treatment for
secondary hyperparathyroidism is less common because of the
success of renal transplantation, dialysis, and medical therapy,
including the newer calcimimetics. However, in symptomatic
patients who are refractory to these therapies, subtotal parathyroidectomy
or total parathyroidectomy with autotransplantation
are surgical options. 25,73-75
Patients with secondary hyperparathyroidism have multiple
enlarged glands. Individually, these glands may have the same
sonographic appearance as other parathyroid adenomas (see Fig.
20.6, Videos 20.3 and 20.4). However, the glands may be asymmetrically
enlarged and more lobular. Although imaging is not
usually necessary, sonography can be used to evaluate the severity
of parathyroid hyperplasia by assessing gland enlargement. 76,77
Patients with sonographically enlarged glands tend to have
signiicantly worse symptoms, laboratory values, and radiographic
signs of secondary hyperparathyroidism than patients without
gland enlargement. Sonography can also be used to aid in
localization of the enlarged parathyroid glands before surgical
resection for secondary hyperparathyroidism. Ultrasound-guided
percutaneous ethanol injection is also a treatment option for
ablation of hyperplastic parathyroid glands in patients with
refractory secondary hyperparathyroidism who are not surgical
candidates (see “Ethanol Ablation”).
PITFALLS IN INTERPRETATION
False-Positive Examination
Normal and pathologic cervical structures, such as lymph nodes,
small veins adjacent to the thyroid gland, the esophagus, the
longus colli muscles, and thyroid nodules, can simulate parathyroid
adenomas, producing false-positive results during neck
sonography.
Parathyroid Adenoma: Causes of Examination
Errors
FALSE-POSITIVE RESULTS
Cervical lymph node
Prominent blood vessel
Esophagus
Longus colli muscle
Thyroid nodule
FALSE-NEGATIVE RESULTS
Minimally enlarged adenoma/gland
Multinodular thyroid goiter
Ectopic parathyroid adenoma
One source for a false-positive ultrasound study is confusion
of cervical lymph nodes for a parathyroid adenoma. 32 Cervical
lymph nodes are usually visualized sonographically in the lateral
neck adjacent to the jugular vein and away from the thyroid.
However, lymph nodes found adjacent to the carotid artery
may occasionally simulate an ectopic adenoma. Lymph nodes
may also be visualized within the central compartment near
the inferior pole of the thyroid, simulating an inferior gland
adenoma. Enlarged cervical lymph nodes may have an oval,
hypoechoic appearance similar to parathyroid adenomas, but
they oten also have a central echogenic band or hilum composed
of fat, vessels, and ibrous tissue, which diferentiates them from
parathyroid adenomas. 78 Nonetheless, ultrasound-guided biopsy
may be necessary to distinguish a potential parathyroid adenoma
from an atypical lymph node, particularly in the postoperative
setting.
Many small veins lie immediately adjacent to the posterior
and lateral aspects of both lobes of the thyroid, and a tortuous
or segmentally dilated vein can simulate a small parathyroid
adenoma. Scanning maneuvers to help establish the structure
as a vein, not an adenoma, include (1) real-time imaging in
multiple planes to show the tubular nature of the vein; (2) a
Valsalva maneuver by the patient, which may cause transient
engorgement of the vein; and (3) spectral or color Doppler
sonography to show low within the vein.
he esophagus may partially protrude from behind the
posterolateral aspect of the trachea and simulate a mass or
parathyroid adenoma (see Fig. 20.8B). Turning the patient’s head
to the opposite side will accentuate the protrusion. Careful
inspection of this structure in the transverse plane shows that
it has the typical concentric ring appearance of bowel, with a
peripheral hypoechoic muscular layer and the central echogenic
appearance of the mucosa and intraluminal contents. Using a
longitudinal scan plane helps to demonstrate the tubular nature
of this structure. Real-time imaging while the patient swallows
will cause a stream of brightly echogenic mucus and microbubbles
to low through the lumen, which conirms that the structure is
the esophagus.
he longus colli muscle lies adjacent to the anterolateral
aspect of the cervical spine. When viewed in the transverse plane,
it appears as a hypoechoic triangular mass that can simulate
a large parathyroid adenoma located posterior to the thyroid
gland. However, scanning in the longitudinal plane will show
that this structure is long and lat and contains longitudinal
echogenic striations typical of skeletal muscle. Real-time imaging
while the patient swallows can be useful because swallowing
will cause movement of the thyroid gland and adjacent thyroid
structures, such as a parathyroid adenoma, but the longus colli
muscle, which is attached to the spine, will remain stationary.
Finally, comparison with the opposite side of the neck will
demonstrate similar symmetric indings because the longus
colli muscles are paired structures located on both sides of the
cervical spine.
hyroid nodules are also potential causes of false-positive
ultrasound and scintigraphic imaging. 32,79 If a thyroid nodule
protrudes from the posterior aspect of the thyroid, it can simulate
a mass in the location of a parathyroid adenoma (Fig. 20.16). A