Adrenal Gland Anatomy and Location

Adrenal Glands Anatomy and Location

• Adrenal glands and kidneys are located within the perineal space and are retroperitoneal.
• They are anterior, medial, and superior to the kidneys.
• A thick inner layer of fatty connective tissue encapsulates them.
• A thin, fibrous capsule attaches to the gland, providing support and preventing descent if the kidneys are displaced or absent.
• The right adrenal gland is shaped like a triangle or pyramid and is located superior, anterior, and medial to the upper pole of the right kidney.
• Portions of the right adrenal gland extend posterior to the IVC, and it's medial to the right lobe of the liver. The crus of the diaphragm lies medial and posterior to it.
• The left adrenal gland is crescent-shaped, located anteriomedial to the upper pole of the left kidney and is usually larger than the right.
• The aorta and crus of the diaphragm are medial to the left adrenal gland, while the tail of the pancreas is anterior.
• Each adrenal gland is supplied by three arteries: the suprarenal branch of the inferior phrenic artery, the suprarenal branch of the aorta, and the suprarenal branch of the renal artery.
• A single vein drains each adrenal gland: the right suprarenal vein drains into the IVC, and the left suprarenal vein drains into the left renal vein.

Adrenal Cortical Hormones (ACH)

• Regulated by adrenocorticotropic hormones (ACTH) of the anterior pituitary gland.
• Works together to regulate hormone production.
• A decrease in adrenal cortical function leads to increased ACTH, stimulating the adrenal cortex.
• An increase in adrenal hormones leads to a drop in ACTH secretions, decreasing activity of the adrenal cortex.
• Zona glomerulosa (outer layer) produces aldosterone.
• Zona fasciculata (middle layer) produces glucocorticoids (cortisol).
• Zona reticularis (inner layer) produces gonadocorticoids (androgens and estrogens).
• Tumors of the adrenal or anterior pituitary gland may over- or underproduce ACTH and ACH.

Adrenal Medulla

• Produces catecholamine hormones like epinephrine (adrenalin) and norepinephrine (noradrenalin).
• Epinephrine accounts for about 80% of total secretion and is physiologically more important than norepinephrine.
• Medullary hormones are not essential to life, unlike cortical hormones.
• Release of epinephrine and norepinephrine is stimulated by the sympathetic nervous system.
• The physiologic response to stress is the fight-or-flight response.

Sonographic Appearance of Adrenal Glands

• The adrenal cortex is typically hypoechoic and less echogenic than surrounding fat.
• The adrenal medulla appears as an echogenic linear structure within the adrenal gland.
• Glands vary in shape and configuration in adults.
• Adrenal glands can be visualized 90% of the time after 26-27 weeks gestation

Adrenal Masses & Pathology

• Sonographic appearance of adrenal masses does not allow differentiation between adenomas, carcinomas, pheochromocytomas, and metastases.
• Biopsy is often performed in patients with known primary malignancy to exclude metastatic disease.
• CT is the modality of choice for suspected adrenal disease. MRI and PET scans are used to refine diagnoses of adrenal pathologies.
• Ultrasound is useful for screening children from families with multiple endocrine neoplasia (MEN) syndromes, pregnant women, and poor CT candidates.
• Pathology can be divided into disorders that diminish steroid output, increase steroid production, or have no functional effect.
• Other pathologies include incidentalomas and cortical tumors like adenomas and myelolipomas.

Cushing’s Syndrome (Hypercortisolism)

• Excessive glucose production from hypersecretion of cortisol from the adrenal cortex.
• Associated with hyperadrenalism, administration of glucocorticoids (steroids), increased ACTH from pituitary adenoma, primary adrenal adenoma, and ectopic ACTH.

Conn Syndrome (Hyperaldosteronism)

• Primary aldosteronism results from excessive and uncontrolled secretion of aldosterone.
• Associated with adrenal adenomas (aldosteromas), bilateral idiopathic adrenal hyperplasia, ectopic secretion of aldosterone, and aldosterone-producing adrenocortical carcinoma.

Hirsutism

• Overabundance of hair caused by excessive androgen production.
• Results in congenital adrenal hyperplasia, Cushing’s Syndrome, ovarian and adrenal tumors, polycystic ovarian syndrome, and medications.

Incidentalomas

• General term for an unexpected mass detected during imaging for an unrelated disease.
• Subclinical Cushing syndrome is present in 5% to 20% of hypersecreting adenomas.
• Surgical treatment is usually performed for unilateral hyperfunctioning lesions like adenomas, aldosteronomas, pheochromocytomas, and adrenal hyperplasias.
• In the general population without a history of cancer, 60-94% are nonhypersecreting adenomas, 1-22% are cysts, 6-15% are myelolipomas, 0-11% are pheochromocytomas, 0-4% are adrenocortical carcinomas, and 0-2% are metastases.

Adrenal Adenoma

• Can be hyperfunctioning or nonhyperfunctioning, with most being nonhyperfunctioning.
• Most are incidentally noted while scanning the abdomen and are slow-growing.
• ACTH can cause adrenal adenomas to grow.
• Sonography is difficult to detect due to location and surrounding retroperitoneal fat.

Adrenal Cortical Carcinoma

• Rare tumors with a poor prognosis.
• Majority of patients present with Cushing’s Syndrome or metastatic involvement.
• Differentiation from benign adenoma is difficult, and tumor removal (or biopsy) is based on size (3-6cm).
• Has a tendency to invade the renal veins and the inferior vena cava.

Myelolipoma

• Benign, nonfunctioning adrenal mass containing fat and bone elements.
• Sonographically seen as hyperechoic masses in the adrenal bed and associated with propagation speed artifact.

Pheochromocytoma

• Medullary pathology originating in the adrenal medulla but may occur in ectopic locations.
• The majority are benign and secrete catecholamines like norepinephrine & epinephrine.
• Associated with multiple endocrine neoplasia (MEN), Von Hippel-Lindau disease, and neurofibromatosis type 1.

Adrenal Neuroblastoma

• Malignant tumor arising from the sympathetic nervous system.
• Commonly occurs in the adrenal medulla but can also occur in the neck, chest, or pelvis.
• The most common presentation is a palpable abdominal mass and is the most common adrenal mass of infancy & early childhood.
• Commonly occurs between 2 months and 2 years of age.
• Sonographically, it appears as a solid mass that displaces the ipsilateral kidney inferiorly into the pelvis.
• Increased blood & urine catecholamines, epinephrine, norepinephrine, and dopamine are present.
• Majority of patients present with metastatic disease.

Adrenal Metastases

• Adrenal glands are the 4th most common metastatic site after the lungs, liver, and bone.
• Lung cancer is the most common primary cancer that metastasizes to the adrenal gland.
• Differentiation from a unilateral adrenal mass (benign adenoma vs a metastatic lesion) is difficult in a patient with primary cancer.

Adrenal Lymphoma

• Non-Hodgkin’s lymphoma affecting the adrenal glands is usually associated with other sites of disease, most often retroperitoneal lymph nodes and the ipsilateral kidney.
• Adrenal involvement in widespread non-Hodgkin’s lymphoma occurs in 4% of cases.
• Involvement may be diffuse, resembling hyperplasia or mass-like.
• There is a high incidence of bilateral involvement.
• Non-Hodgkin disease is the most common type.

Adrenal Hemorrhage

• Most common in neonates due to the large size and high vascularity of neonatal adrenals, making them vulnerable to birth trauma.
• Sonographic appearance varies due to blood coagulation.
• Normal evolution of hematoma ends with pseudocyst formation.
• If a mass is identified adjacent to the adrenal glands of a newborn, it is most likely a hemorrhage.
• The most common adrenal mass in a newborn is adrenal hemorrhage.

Thyroid Development

• Develops from invagination in the floor of the primitive pharynx around 5 weeks gestation.
• Epithelial cells separate which form pharyngeal connections.
• Vesicle becomes a solid mass of epithelial cells and severs connection with pharyngeal cavity.
• Thyroglossal Tract (Duct) leaves a trace of epithelial cells, left along superior to inferior path, that solidify and atrophy around 7 weeks gestation.
• Divides into 2 lobes connected by isthmus and Thyroid cartilage is formed.

Thyroid Size

• In adults approximately 15 to 20 grams.
• Each lobe is 40 to 60 mm in length and 13 to 18 mm anteroposterior (AP).
• Isthmus is 4 to 6 mm thick.

Thyroid Vasculature

• Four arteries: superior and inferior thyroid arteries
• Peak velocity of major arteries: 20 to 40 cm/second Three veins: thyroid plexus (anterior

Thyroid Function

Maintains Body Metabolism, Physical and Mental Growth ,Lipolysis and Fatty Acid Mobilization—lowers blood serum cholesterol

Thyroid Hormones

• Hormones are released to perform thyroid function, these include: Triiodothyronine (T3), Thyroxine (T4) and Calcitonin or Thyrocalcitonin (C cells)
• T3 and T4 synthesis depends on availability of iodine and T3 has greater metabolic effect. Calcitonin or Thyrocalcitonin (C cells) Lowers plasma calcium by inhibiting release from bones

Thyroid Feedback System

• Hypothalamus releases thyrotropin-releasing hormone (TRH).
• Pituitary Gland produces thyroid-stimulating hormone (TSH).
• Production of Hormones Leads to Increased Circulation, Increased Metabolism. Inhibits TRH and TSH

Thyroid Conditions

There are three main thyroid conditions which can be identified via laboratory values including: Hyperthyroidism, Hypothyroidism and Euthyroid.

Thyroid - Cold Nodules

• Common among women of increased age with decreasing iodine intake.
• Cold nodules demonstrated in nuclear medicine studies referred for sonographic examination.
• FNA is required to distinguish between thyroid nodules and Adenoma

Thyroid - Adenoma

• Benign, glandular epithelium, fibrous capsule
• Most solitary, slow growing
• Accounts for 5% to 10% thyroid nodules
• Toxic hyperfunctioning adenoma may provoke thyrotoxicosis
• Wide variation of sonographic appearances—most common are solitary, well-circumscribed, oval/circular mass with uniform low echogenicity
• Color Doppler will produce a—“spoke and wheel

Thyroid - Nontoxic Goiter

• Enlarged gland without producing nodularity and without evidence of a functional disturbance.
• Calcifications, fibrosis, degenerative cysts, and hemorrhage result in heterogeneous appearance.
• Multilobulated, asymmetrically enlarged gland
• Doubles in size (40 g) to a massive enlargement which the thyroid weighs a few hundred grams. Sonographic features associated with increased risk for malignancy include; Hypoechogenicity, Presence of microcalcifications, Increased vascular flow and Irregular boarders.

Thyroid - Hashimoto

• Most common thyroid function disorder
• Most common cause is Iodine Insufficiency
• Lymphatic Thyroiditis (Autoimmune)—Hashimoto
• Secondary causes less frequent including pituitary or hypothalamic disease

Thyroid - Hashimoto Appearance

• Course texture, Multiple ill-defined hypoechoic areas separated by thick fibrous strands and a Diffusely abnormal gland.
• Best indication of diffuse enlargement is an isthmus measurement >1 cm AP and Color Doppler—Hypervascularity

Thyroiditis

• Sonographic appearance of acute or subacute is diffusely enlarged hypoechoid thyroid gland with normal or decreased vascularity due to edema.
• Second most common endocrinopathy in women of reproductive age
• Maternal physiologic changes during pregnancy include; Increase TBG, Increased HCG and a Partial inhibition of pituitary gland that yields a transient decrease in TSH between 8 and 14 weeks of gestation
• Reduced plasma iodine also occurs which causes an Increased thyroid size in 15% of women as well as Postpartum thyroiditis (PPT).
• Sonographically will show Decreased echogenicity and diffuse enlargement

Thyroid Carcinoma: General

• Most nodules are benign; 5% to 6.5% are Malignant
• Papillary carcinoma most prevalent followed by follicular, medullary, anaplastic, and Hurthle cell cancer.

Thyroid Carcinoma: Suggestive Criteria (Requires FNA)

• Solitary location
• Occurs in Younger patient
• More common Males History of radiation exposure

Thyroid Carcinoma: Elastography

• Elastography describes a mechanical tissue characteristic that prevents displacement of stiffer tissue when placed under pressure such as with compression from an ultrasound probe.
• Elastography evaluates stiffness; malignant nodules tend to be more stiff
• There are different types of Strain imaging such as Color elasticity, and Shear wave imaging

Thyroid Carcinoma: Papillary

• Papillary carcinoma most common (accounts for 75%–85%).
• More common in those aged 20–50 years of age, and More prevalent among females.
• Least aggressive of thyroid carcinomas and Clinical presentation can be: a Painless, palpable nodule, Enlarged cervical lymph nodes or Cervical lymphadenopathy in the absence of a palpable nodule.

Thyroid Carcinoma: Medullary

• Neuroendocrine neoplasm derived from parafollicular cells—sporadic or familial forms and is around 5% of all thyroid carcinoma.
• Serum calcitonin tumor marker will be present in mass in neck sometimes associated with dysphagia or hoarseness.
• Aggressive and patients suffer from symptoms related to endocrine secretion
• Sonographic appearance should show: Hypoechoic solid mass, Microcalcifications, Lymph nodal metastases and Hepatic metastases.

Anaplastic Carcinoma and Lymphoma

• Rare