Diagnostic ultrasound ( PDFDrive )

740 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
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FIG. 20.10 Ectopic Superior Parathyroid Adenoma: Tracheoesophageal Groove. (A) Transverse sonogram reveals an adenoma (calipers)
arising from the right tracheoesophageal groove located posteriorly in the neck. The patient’s head is turned to the left, which deviates the adenoma
laterally and aids in visualization. C, Common carotid artery; Tr, trachea. (B) Corresponding longitudinal sonogram shows the ectopic superior
parathyroid adenoma (arrows) posterior in the low neck adjacent to the cervical spine. (C) CT scan of the low neck/upper mediastinum in another
patient shows an ectopic adenoma (arrow) in the left tracheoesophageal groove adjacent to the esophagus (e). See also Video 20.9.
and only a portion of the mass will be visible. Turning the patient’s
head to the opposite side will accentuate the protrusion and
provide better accessibility to the retrotracheal area. his process
is then repeated on the other side of the neck to visualize the
contralateral aspect of the retrotracheal area. his process is
analogous to the maneuver that a surgeon uses to run a ingertip
behind the trachea in an attempt to palpate a retrotracheal
adenoma. Maximal turning of the head also oten causes the
esophagus to move to the opposite side of the trachea as it becomes
compressed between the trachea and the cervical spine. If the
examiner sees the esophagus move completely from one side of
the trachea to the opposite side during maximal head turning,
the esophagus has efectively “swept” the retrotracheal space and
will have pushed any parathyroid adenoma in this location out
from behind the trachea.
Mediastinal Adenoma
he most common location for ectopic inferior parathyroid
adenomas is low within the neck or in the anterosuperior
mediastinum 4,6,49,50 (Fig. 20.11). Parathyroid adenomas are
suiciently hypoechoic that they may be visualized as discrete
structures separate from the thymus and surrounding
tissues. To visualize this area optimally, the patient’s neck
is maximally hyperextended. With this technique and the
transducer angled posterior and caudal to the clavicular heads,
sonographic visualization is oten possible to the level of the
brachiocephalic veins. If the adenoma lies caudal to this level
or far anterior, just deep to the sternum, it cannot be visualized
sonographically.
Ectopic superior adenomas located in the mediastinum tend
to stay in a more posterior plane than their ectopic inferior
counterparts and are oten not visible with traditional sonography.
hey usually lie deep in the low neck or posterior superior
mediastinum, requiring use of a 5-MHz transducer for maximal
penetration. Ectopic superior adenomas may be intimately
associated with the posterior aspect of the trachea, and the
head-turning maneuver described for retrotracheal adenomas
in the neck can be applied here as well. With the patient’s neck
hyperextended and the transducer angled caudally, the posterior
mediastinum may sometimes be visualized to the level of the
apex of the aortic arch; adenomas lying caudal to this level cannot
be visualized.
Intrathyroid Adenoma
Intrathyroid parathyroid adenomas are uncommon and have
been described as either superior or inferior gland adenomas. 4,6,8
Most intrathyroid adenomas are in the posterior half of the
middle to lower thyroid, are completely surrounded by thyroid
tissue, and are oriented with their greatest dimension in the
cephalocaudal direction (Fig. 20.12, Videos 20.10 and 20.11).
Intrathyroid adenomas may be overlooked at surgery because
they are sot and are similar to the surrounding thyroid tissue
on palpation. A thyroidotomy or subtotal lobectomy may be
needed to ind an intrathyroid adenoma. Sonographically,
however, parathyroid adenomas usually are well visualized
because they are hypoechoic, in contrast to the echogenic thyroid
parenchyma, and a polar feeding vessel is oten present on color
low or power Doppler imaging. 51 he internal architecture and
appearance of these adenomas are the same as for adenomas
elsewhere in the neck. However, because intrathyroid parathyroid
adenomas can be similar to thyroid nodules in appearance,
percutaneous biopsy is oten necessary to distinguish between
these entities.
Some parathyroid adenomas lie under the pseudocapsule or
sheath that covers the thyroid gland or within a sulcus of the
thyroid, but these are not usually considered to be true intrathyroid
adenomas. hese adenomas may be diicult for the surgeon to
visualize at surgery unless this sheath is opened. 4,8 Sonographically,
these may appear the same as other parathyroid adenomas that
lie immediately adjacent to the thyroid, although the typical
thin, echogenic capsular interface oten seen between the thyroid
and a parathyroid adenoma may be absent.
Carotid Sheath/Undescended Adenoma
Rare ectopic adenomas can lie in a high position superior and
lateral in the neck, near the carotid bifurcation at the level of