The Thyroid Gland Holdorf

 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.  The right and left lobe of the thyroid are joined by the isthmus, which drapes over the trachea.  The pyramidal lobe is a normal variant extending superiorly to the isthmus.  Normal thyroid parenchyma has a Sonographic appearance of homogeneous medium level echoes.  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.  The common carotid artery and the internal jugular vein are located lateral to the thyroid lobes.  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  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  Length: 4-6 cm (Sagittal scanning plane)  Height: 2-3 cm (Transverse scanning plane)  Isthmus:.2-.6 cm (transverse plane)  Width: 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

 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 intra- thyroid 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