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The Thyroid Gland
Holdorf
CROSS-SECTIONAL ANATOMY
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Normal Anatomy
The right and left lobes of the thyroid gland are situated in the lower part of the neck
along either side of the trachea.
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The right and left lobe of the thyroid are joined by the isthmus, which drapes over the
trachea.
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The pyramidal lobe is a normal variant extending superiorly to the isthmus.
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Normal thyroid parenchyma has a Sonographic appearance of homogeneous medium
level echoes.
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The STRAP muscles (sternohyoid and sternothyroid) of the neck are seen as thin
sonolucent lands along the anterior surface of the thyroid gland. The larger
STERNOCLEIDOMASTOOID muscles are located anteriolaterally.
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The common carotid artery and the internal jugular vein are located lateral to the
thyroid lobes.
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Posterior to the thyroid is the longus colli muscle, which is seen as a wedged-shaped
sonolucent structure adjacent to the cervical vertebrae.
KEY POINTS
 Endocrine gland, made up of specialized cells
 These cells respond to stimuli by releasing
hormones.
Thyroid facts
 Biggest gland in the neck.
 It is situated in the anterior (front) neck below
the skin and muscle layers.
 The thyroid gland takes the shape of a
butterfly, represented by the left and right
thyroid lobes which wrap around the trachea.
 The function of the thyroid gland is to make
thyroid hormones. Therefore, it regulates the
body’s metabolism.
More Thyroid facts
 The thyroid hormones are essential for
proper development .
 These hormones regulate protein, fat, and
carbohydrate metabolism, affecting how
human cells use energetic compounds.
 They also stimulate vitamin metabolism.
Indications for a Thyroid Exam
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Palpable mass in the neck
Abnormal Nuclear Medicine exam
Abnormal thyroid or parathyroid labs (Ca++)
Follow up to surgery of therapy
Pain or trauma in the neck
Difficulty swallowing or taking
History of radiation exposure
Biopsy guidance
Size
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Length: 4-6 cm (Sagittal scanning plane)
Height: 2-3 cm (Transverse scanning plane)
Isthmus: .2-.6 cm (transverse plane)
Width: 1.5-2 cm (transverse scanning plane)
In general Female > Male
Increased in size: Thyroiditis, goiter, mass
Decreased in size: Synthroid,
Radiation/Chemo therapy
Variants of the Thyroid Gland
 Variants of the thyroid Gland
 Sublingular thyroid gland: the entire gland is
behind the tongue (failure to descent)
 Agenesis of the left lobe
 Agenesis of the isthmus
 Right lobe larger than the left lobe.
The Role of Thyroid
Sonography
 Ultrasound cannot be used to tell malignant
lesions from benign. Vast majority are
benign.
 FNA is the best way to identify if a lesion is
benign or malignant.
Longus coli muscle
Sonography of the Thyroid
 The trachea, in the midline, gives a characteristic
curvilinear reflecting surface with associated reverberation
artifact due to the air within.
 The esophagus, which is seen as a target sign transversely,
is usually hidden from sonographic visualization by the
trachea. Patient swallowing can help in identifying the
esophagus. It is located to the left of midline.
 The minor neurovascular bundle is comprised of the
recurrent laryngeal nerve and inferior thyroid vessels. It is
sonographically seen as a vague hypoechoic area between
the longus coli muscle and the thyroid gland.
 The normal parathyroid glands, located on the posterior
aspect of the thyroid, are typically not visualized with
ultrasound due to their small size.
Sagittal Thyroid Imaging
Sagittal Thyroid Imaging
 Medially, you will appreciate the trachea.
 Laterally, you will appreciate the Common
Carotid.
Medially, you will notice
the longitudinal Trachea.
Laterally, you will find the
CCA
Parathyroid Gland
 Vast majority of individuals have 4
parathyroid lands
 Shape: disc or bean shaped.
 Size: Length 5-7 mm, Width 3-4 mm, AP 1-2
mm
 Variants: Size is larger if patient has only 2
glands and size is smaller if patient has > 4
glands.
 The parathyroid glands are usually not seen.
Parathyroid Glands
 Variants
 Ectopic glands: found above or below the thyroid
 Ectopic glands are also found lateral to the CCA
or even retro-esophageal
 Some patients have > 4 parathyroid glands
 Some patients have < parathyroid glands
 Parathyroid glands help the regulation of
calcium levels within the body.
Abnormal Parathyroid
 Longitudinal ultrasound of left side of neck,
showing a left superior parathyroid adenoma
which was initially mistaken to be an intrathyroid lesion.
POEM FOR A SONOGRAPHER
 “They spend all day
 with transducer in hand…
 happily collecting money
 while scanning peoples’ glands.”
Thyroglossal Duct Cyst
 Found along the path of thyroid migration,
high in the mid-neck. Due to the failure of
regression of the Thyroglossal duct.
 Superficial cystic midline mass typically seen
in adolescents associated with an upper
respiratory infection.
 Cystic dilation of Thyroglossal duct which is a
remnant of the thyroid gland migration from
pharyngeal epithelium.
Thyroid Screening
 50% of the United States population have
evidence of nodular thyroid disease, yet the
annual incidence of thyroid cancer is only
0.005%
 If 90% of thyroid cancers are papillary and
therefore curable after they become
clinically apparent, it seems practical to
pursue all of the small nodules detected
incidentally by ultrasound.
Thyroglossal Duct cyst
Thyroglossal duct cyst
 Midline neck lump in the region of the hyoid
bone.
 May be difficulty swallowing or breathing.
 Most common location is midline or slightly
off midline, between the isthmus of the
thyroid gland and the hyoid bone or just
above the hyoid bone.
SUMMARY OF ANATOMICAL SPATIAL
RELATIONSHIPS OF THE THYROID GLAND
 Strap Muscles – Anterior-to thyroid
 Sternocleidomastoid – Anteriolateral – to thyroid
 Common Carotid Artery
 /Internal Jugular vein- lateral- to thyroid
 Minor Neurovascular bundle – Posterior – to thyroid
 Longus Coli Muscle- Posterior- to thyroid
 Parathyroid Glands – Posterior- to thyroid
Hyperthyroidism
Hypothyroidism
Goiter