Diagnostic ultrasound ( PDFDrive )

1630 PART V Pediatric Sonography
Normal Anatomy
he parotid gland is the largest salivary gland. his encapsulated
gland, containing lymphoid tissue, vessels, and nerves, wraps
around the angle of the mandible anterior to the mastoid tip
(Fig. 48.4). Most parotid tissue lies supericial to the masseter
muscle. In 20% of patients, an accessory parotid gland, which
is a nodule of salivary tissue separate from the main parotid,
can be identiied on the masseter muscle. 10 he parotid gland
contains acini that drain through the Stensen duct, a structure
that extends anteriorly to exit above the upper second molar. 11
he duct lies approximately 1 cm below the inferior margin of
the zygomatic arch. 12 he facial nerve travels within the parotid
gland, lying lateral to the retromandibular vein and posterior
belly of the digastric muscle, which is the muscle deep to the
mastoid tip. he facial nerve acts a boundary to divide the parotid
gland into supericial and deep components. he deep lobe of
the parotid, which accounts for 20% of the gland, lies adjacent
to the parapharyngeal space and beneath the angle of the
mandible.
2
3
4
FIG. 48.4 Diagram of Parotid Space. 1, Parotid gland; 2, Stensen
duct; 3, masseter muscle; 4, angle of mandible; 5, mastoid; 6, posterior
belly of digastric muscle. Arrow points between the retromandibular
vein (open circle) and external carotid artery (partly solid circle), demarcating
supericial and deep lobes. Lenticular tan structure with * is the
facial nerve.
*
1
6
5
Imaging of the parotid should be performed with a highfrequency
transducer. Usually, linear transducers of 5 to 12 MHz
are used. he entire gland should be evaluated in two perpendicular
planes. Because the facial nerve is poorly delineated on
ultrasound, the retromandibular vein, which lies directly deep
to the nerve and lateral to the external carotid artery, is an excellent
landmark to separate the supericial and deep lobes. 12,13 Typically,
the deep lobe can only be partially visualized, concealed by
acoustic shadowing of the mandibular ramus. On sonography,
the parotid gland is generally homogeneous and hyperechoic
with regard to the adjacent muscle (Fig. 48.5). he degree of
echogenicity of the gland depends on the amount of intraglandular
fatty tissue; the greater the fat content, the higher the
echogenicity.
Normal intraparotid ducts may be visualized as linear relective
structures. he Stensen duct is usually not visible in the absence
of dilation. In the parotid parenchyma, normal lymph nodes
may be observed. Most nodes are identiied at the upper or lower
pole, are oval in shape, measure 5 to 6 mm in the short axis,
and appear hypoechoic with a hyperechoic central hilum. 12
Ultrasound is especially useful in diferentiating intraparotid
lesions from extraparotid masses and separating solid and cystic
lesions in this location.
he submandibular space contains both the submandibular
glands and the sublingual glands in addition to submandibular
lymph nodes. he submandibular glands lie within the posterior
submandibular space, whereas the sublingual glands are anterior
(Fig. 48.6). he submandibular glands are bordered by the
mandible laterally and the mylohyoid muscle superiorly and
medially. A small portion of the gland may pass posterior to the
mylohyoid muscle to lie within the sublingual area. he space
anterior to the submandibular gland contains lymph nodes. he
torturous facial artery typically crosses the parenchyma laterally.
he anterior facial vein can oten be identiied along the anterosuperior
aspect of the gland. 14 Medially, the lingual artery and
vein may be evident. he Wharton duct, the excretory duct for
the gland, extends along the mylohyoid and medial part of the
sublingual gland to its oriice at the loor of the mouth. On
sonography, the submandibular glands should be examined in
M
I
RV
EC
DG
RV
A
B
FIG. 48.5 Normal Parotid Gland. (A) Transverse color Doppler ultrasound shows mildly increased echogenicity compared with adjacent
masseter muscle (M). Deep and supericial portions of the gland are separated by the retromandibular vein (RV) found lateral to the external carotid
artery (EC) and posterior belly of the digastric muscle (DG). Small, hypoechoic intraparotid lesion is consistent with normal lymph node (l).
(B) Longitudinal color Doppler sonogram shows normal parotid displaying homogeneous hyperechoic texture and retromandibular vein (RV).