The Adrenal Glands

Amber Wooten

OBJECTIVES

Identify the sonographic role in the evaluation of the adrenal glands.
Describe the embryologic development of the adrenal glands.
Discuss the anatomy and physiology of the adrenal cortex and medulla.
List the hormones secreted by the adrenal cortex and medulla.
Identify conditions caused by hyposecretion and hypersecretion of adrenal hormones.
Identify the normal sonographic appearance of the adrenal glands.
Describe adrenal gland scanning technique, patient positions, and scanning pitfalls.
Discuss the differential diagnosis for solid adrenal masses.
Discuss alternative imaging modalities used to evaluate the adrenal glands.

GLOSSARY

adrenal cortex
outer parenchyma of the adrenal gland that makes up 90% of the organ’s weight and secretes corticoids including cortisol and aldosterone

adrenal medulla
inner portion of the adrenal gland that secretes the catecholamines epinephrine and norepinephrine

adrenocorticotropic hormone (ACTH)
hormone secreted by the pituitary gland that causes the adrenal gland to produce and release corticosteroids

endoscopic ultrasound (EUS)
an ultrasound transducer on a thin flexible endoscope is inserted in the mouth or anus to visualize the walls of the upper or lower digestive tract and surrounding organs

multiple endocrine neoplasia (MEN) syndrome
a group of autosomal dominant disorders characterized by benign and malignant tumors of the endocrine glands

In contrast with other examinations of the abdomen, transabdominal sonographic imaging is not the first-choice imaging modality for screening adrenal glands or detecting adrenal pathology. Examination of the adrenal glands challenges the skills of novice and experienced sonographers alike and requires a working knowledge of exact adrenal anatomic locations and landmarks. However, combining planar flexibility and improved beam-resolution capabilities of modern ultrasound equipment with maneuvering the patient into multiple positions increases the likelihood of producing quality sonographic images of the adrenal glands.¹, ² and ³ In addition, since the mid-1990s, endoscopic ultrasound (EUS) and intraoperative ultrasound (IOUS) have developed as tools for high-resolution sonography evaluation of suprarenal and retroperitoneal masses. Using a 7.5-MHz transducer positioned 1 to 2 cm from the adrenal gland, EUS and IOUS are particularly useful for detecting adrenal metastases and staging cancer.⁴^,⁵ As new technologies are introduced for transabdominal imaging, such as three-dimensional/four-dimensional (3D/4D) imaging and elastography, these tools also become available for EUS and IOUS applications.⁶^,⁷

This chapter provides an overview of relevant anatomy, embryology, scanning techniques, functional and morphologic adrenal pathology, and the sonographic appearance
of the normal gland as well as adrenal pathology. As a sonographer, it is important to develop critical-thinking and problem-solving skills for sorting out the origin and extent of abdominal masses, including those of suprarenal and retroperitoneal origin. Related techniques are discussed. In addition, EUS, IOUS, computed tomography (CT), magnetic resonance imaging (MRI), and associated nuclear medicine imaging procedures are presented as related to adrenal imaging. Owing to technical improvements in all the diagnostic imaging modalities and the increased use of these modalities, more clinically silent or unexpected masses are being detected. The general term for an unexpected mass detected during an imaging procedure being performed for unrelated disease is “incidentaloma.” This term may be applied to any unexpected mass occurring anywhere in the body. Adrenal incidentaloma (AI) has become a common term in the medical literature and represents a diagnostic challenge that includes discovery of masses, which range from benign, nonfunctional lesions to malignant tumors such as pheochromocytomas, adrenocortical carcinomas, or metastases from other primary cancers.⁸ Sonographers have a role both in the initial detection of AIs and in gathering diagnostic information regarding newly discovered AIs.

ANATOMY

Embryology

The adrenal gland consists of two distinct parts: the cortex and the medulla. Each develops from different embryonic tissues, forms different anatomic and functional structures, and combines within a common capsule.⁹^,¹⁰ The result is two endocrine glands in one organ. Most glands of the body develop from epithelial tissue. In contrast, the adrenal cortex is derived from the mesoderm of the same region that gives rise to gonadal tissue.⁹^,¹⁰ The central tissue or adrenal medulla is functionally part of the sympathetic nervous system developed from the neural crest cells that also give rise to postganglionic sympathetic neurons.⁹, ¹⁰ and ¹¹ As a result, some adrenal medullary pathology may appear ectopically along the paths of these sympathetic neurons usually near the celiac axis, whereas ectopic adrenocortical tissue may be located inferiorly along the path of gonadal tissue migration.⁹, ¹⁰ and ¹¹ In addition, extra-adrenal chromaffin cells also normally deposit near the aortic bifurcation to form the organ of Zuckerkandl.¹⁰, ¹¹ and ¹²

Cortex

During gestational weeks 5 and 6, the fetal cortex is first recognized bilaterally as a groove between the developing dorsal mesentery and gonad.⁹^,¹⁰ During weeks 7 and 8, the cells arrange into cords with dilated blood spaces, forming a thin capsule of connective tissue that encloses the gland⁹^,¹⁰ and develops an intimate relationship with the superior pole of the kidney. If the kidney does not develop normally, there will be a discoid distortion in the shape of the adrenal gland.⁹^,¹⁰ Initially, the fetal adrenal gland is larger than the kidney and 10 to 20 times the relative size of the adult adrenal gland.⁹^,¹⁰ During the remainder of fetal life, the cortical tissue is composed of two zones comprising 75% to 80% of the bulk of the gland.¹⁰^,¹¹ By week 8, the cortex produces precursors to androgen, estriol, and corticosteroids.⁹^,¹⁰ After birth, the inner zone undergoes involution, whereas the thinner outer zone continues to develop into the adult adrenal cortex, which takes on a yellow color.⁹, ¹⁰, ¹¹, ¹² and ¹³ By the age of 3 years, the cortex differentiates into three zones: (1) zona glomerulosa, (2) zona fasciculata, and (3) zona reticularis. Each zone develops different cellular arrangements and becomes functionally specialized, producing mineralocorticoids, glucocorticoids, and gonadocorticoids, respectively⁹, ¹⁰, ¹¹ and ¹²^,¹⁴ (Fig. 15-1).

Medulla

Specific ectodermal cells ascend from the neural crest, migrate from their origin, and differentiate into sympathetic neurons of the autonomic nervous system.⁹, ¹⁰ and ¹¹ Some of these primitive autonomic ganglia differentiate even further into endocrine cells, designated chromaffin cells, and migrate to form a mass on the medial surface of the fetal adrenal cortex.⁹, ¹⁰ and ¹¹ Soon, these chromaffins, or pheochrome cells, invade the developing cortex, establishing the primordium of the adrenal medulla.⁹^,¹⁰ On cut section, the medulla has a red, brown, or gray color depending on the level of blood perfusion.¹⁵ As mentioned previously, chromaffin cells also form the organ of Zuckerkandl.¹⁰, ¹¹ and ¹²

Relational Anatomy

Like the kidneys, the adrenal glands are retroperitoneal. They are generally anterior, medial, and superior to the kidneys.⁹^,¹⁰^,¹³^,¹⁵ The cortex and medulla are encapsulated by a thick inner layer of fatty connective tissue.¹²^,¹³ A thin, fibrous outer capsule attaches to the gland by many fibrous bands, providing the adrenals with their own fascial supports so that they do not descend if the kidneys are displaced or absent.⁹^,¹² The glands are attached to the anteromedial aspect within renal fascia (also referred to as Gerota fascia), and abundant adipose tissue (perinephric fat) surrounds each gland, separating it from the kidneys¹¹^,¹²^,¹⁶ (Fig. 15-2).

Right Adrenal

The right adrenal gland is located posterior and lateral to the inferior vena cava (IVC), medial to the right lobe of
the liver and lateral to the crus of the diaphragm.⁹^,¹⁰^,¹³^,¹⁵^,¹⁶ The right adrenal gland has been described as sitting like a triangular cap on the anterior, medial, and superior aspects of the superior pole of the right kidney.

FIGURE 15-1 Adrenal gland. The anatomic sectional illustration of the adrenal gland demonstrates the medulla surrounded by three differentiated zones of the cortex.

FIGURE 15-2 Relational anatomy. The illustration demonstrates the anteromedial relationship of the adrenal glands to the kidneys. IVC, inferior vena cava.

The anterior surface of the right adrenal gland is shaped like a pyramid. Two areas make up the anterior surface: the medial area is narrow and lies posterolateral to the IVC and the lateral, somewhat triangular, portion is in contact with the liver.⁹^,¹⁰^,¹³^,¹⁵^,¹⁶ The superior end of the lateral area is devoid of the peritoneum as it comes in contact with the bare area of the liver, and the inferior portion is covered by reflected peritoneum from the inferior layer of the coronary ligament¹²^,¹³^,¹⁵ (Fig. 15-3).

A curved ridge separates the posterior dorsal surface into superior and inferior parts. The superior convex portion rests on the diaphragm, and the inferior concave portion is in contact with the superior-anterior surface of the right kidney¹⁵ (Fig. 15-3).

FIGURE 15-3 Topographic anatomy. There is a difference in the surface anatomy of right and left adrenal glands. IVC, inferior vena cava.

Left Adrenal

The left adrenal gland appears draped in an elongated, crescent, or semilunar shape on the medial aspect of the left kidney’s superior pole.⁹, ¹⁰, ¹¹, ¹² and ¹³^,¹⁵^,¹⁶ The left gland is larger than the right, and extension to the left renal hilus is a normal variant.

The anterior portion can be separated into superior and inferior parts. The superior area is situated posterior to the peritoneal wall of the lesser sac and is covered by the peritoneum of the omental bursa, which separates the gland from the cardiac portion of the stomach.¹⁵ The inferior area is not covered by the peritoneum and lies posterior and lateral to the pancreas⁹^,¹⁰^,¹²^,¹³^,¹⁵^,¹⁶ (Fig. 15-3). The splenic artery and vein course between the pancreas and the left adrenal gland.

The posterior surface is in close proximity to the splanchnic nerves.⁶^,¹⁵ It is divided into a medial and a lateral area by a vertical ridge. The larger lateral area rests on the kidney and the medial posterior area on the crus of the diaphragm¹²^,¹³^,¹⁵ (Fig. 15-3).

Systemic and Lymphatic Vessels

Similar to other endocrine glands, the adrenals are among the most vascular organs of the body.¹³^,¹⁵^,¹⁶ The vasculature of the adrenal gland is distinguished from other organs in that the arteries and veins do not actually course together. The abundant arterial supply may contain as many as 50 to 60 small terminal arterioles, whereas the venous blood is channeled almost completely through a single, large venous trunk.¹²^,¹³^,¹⁵^,¹⁶

Arteries

Three arteries supply each gland: the superiorly located suprarenal branch of the inferior phrenic artery, the superior and medially located branch of the aorta, and the inferiorly located suprarenal branch of the renal artery¹²^,¹³^,¹⁵^,¹⁶ (Fig. 15-4).

These arteries are distinctively classified into three types: short capsular arterioles, intermediate cortical arteries (long branches that go through the cortex to the medulla), and the medullary sinusoids.¹⁵

Veins

In each adrenal gland, a central vein runs the length of the gland and exits at the hilum.¹² The right suprarenal vein empties directly into the posterior aspect of the IVC as a short (4 to 5 mm) vessel, which exits the gland on the mid-anteromedial surface.¹²^,¹⁵ The left suprarenal vein drains directly inferior and medial into the left renal vein.¹²^,¹⁵ Frequently, the left inferior phrenic vein and the left suprarenal vein join before emptying into the left renal vein¹²^,¹⁵ (Fig. 15-4).

Lymphatics

Lymph channels drain from the adrenal cortex and medulla to the hilar area.¹⁵ Following the arterial pathways, larger lymphatic vessels drain into para-aortic and lumbar lymph nodes, which drain to the cisterna chyli, thoracic duct, and eventually into the subclavian vein, whereas a few lymphatic vessels drain into the posterior mediastinal lymph nodes.¹²^,¹⁷

FIGURE 15-4 Adrenal gland vascular anatomy. The illustration shows the three arteries supplying blood and the venous drainage for the right and left adrenal glands. IVC, inferior vena cava.

PHYSIOLOGY

Just as their origin and structure are unique, the function and control of hormones differ for these two different glands in one organ. Adrenal pathology and some medications have the potential to disrupt the level of adrenal hormone secretion and associated regulatory mechanisms.¹¹^,¹⁴^,¹⁸, ¹⁹ and ²⁰ Hormones produced by the adrenal cortex, such as cortisol, are essential to life and must be replaced if both adrenal glands are removed.¹¹^,¹⁴^,¹⁸, ¹⁹ and ²⁰

Cortex

The cortex makes up 90% of the adrenal gland. By 3 years of age, the cortex develops into three epithelial layers, each one evolving functionally into very specialized zones, producing steroid hormones consistent with their mesodermal source. The zona glomerulosa, the outer layer directly beneath the connective tissue covering, makes up 15% of the cortex and produces aldosterone, a mineralocorticoid.⁹^,¹⁰^,¹³^,¹⁴^,¹⁶ The zona fasciculata, the middle layer, comprises 75% of the cortex and the zona reticularis, the inner layer, accounts for the remaining 10% of the cortex⁹, ¹⁰ and ¹¹^,¹³^,¹⁶ (Fig. 15-1). Cortisol, a glucocorticoid, and two gonadocorticoids, estrogen and androgen, are produced by the zona fasciculata and zona reticularis.⁹^,¹⁰^,¹³^,¹⁴^,¹⁶

Hormone secretion is often controlled by the negative feedback mechanisms.¹⁴ Low blood concentrations of a hormone trigger the hypothalamus to secrete the primary regulating factor, corticotrophin-releasing hormone (CRH), which triggers the anterior lobe of the pituitary to release adrenocorticotropic hormone (ACTH).¹⁴ As blood concentrations of ACTH increase, adrenal hormone activity increases, producing a higher concentration of hormones, such as cortisol, in the bloodstream. This increased concentration of the adrenal hormone inhibits CRH and ACTH and, ultimately, hormone synthesis. When the blood concentration of one or more of the adrenal hormones drops to low levels, the cycle is repeated.¹⁴^,¹⁸ Adrenocortical hormone secretion, function, and regulation are summarized in Table 15-1.

Medulla

Originating from ectodermal cells, the medulla secretes catecholamine hormones, similar to the posterior pituitary and thyroid glands. The medulla’s chromaffin (pheochrome) cells, the hormone-producing portion, surround large blood-filled sinuses.⁹^,¹⁰^,¹³^,¹⁶

Epinephrine (adrenalin) and norepinephrine (noradrenalin) are the two principal hormones synthesized by the medulla. Epinephrine constitutes about 80% of the total secretion, and its action is more important than norepinephrine. Release of both hormones is usually stimulated through the sympathetic nervous system.¹¹^,¹⁴

Adrenal nerve stimulation results in prompt discharge of medullary hormones without materially influencing cortical secretion.¹¹^,¹⁴ Hormone secretion is controlled directly by the autonomic nervous system, and innervation by the preganglionic fibers allows the gland to respond to the neural stimulus.¹⁴ The anticipation or presence of stress or pain causes the hypothalamus to signal the sympathetic preganglionic neurons to stimulate the chromaffin cells to increase output of epinephrine and norepinephrine.¹¹^,¹⁴ Functionally, the medulla is a large sympathetic ganglion, which triggers action via hormone release instead of through axons.¹¹^,¹⁴ The body responds by (1) accelerating the heart rate and constricting the vessels, causing increased blood pressure; (2) accelerating the rate of respiration and dilating the respiratory passage; (3) decreasing the rate of digestion to make available more blood to the muscles, increasing the efficiency of muscle contraction; and (4) increasing the blood sugar level to provide energy, thus stimulating cellular metabolism.¹¹^,¹⁴ This physiologic response to stress is better known as the fight-or-flight response.¹¹^,¹⁴^,¹⁸ Hypoglycemia, hypotension, hypoxia, hypovolemia, and exposure to temperature extremes may also stimulate medullary secretion of epinephrine and norepinephrine.¹¹^,¹⁴ Like the glucocorticoids of the adrenal cortices, these hormones help the body resist stress; however, unlike the cortical hormones, the medullary hormones are not essential to life.¹¹^,¹⁴

FUNCTION TESTS

There are many different kinds of laboratory tests to evaluate adrenocortical function. They can be divided into two types: tests that determine the absolute values in serum and urine versus tests that check the interdependency of the various hormones. Table 15-2 summarizes the significance of increased and decreased variance from normal laboratory values for various serum and urine tests.

TABLE 15-1 Adrenal Hormone Secretion, Function, and Regulation⁷^,¹¹^,²¹

Layer	Hormone	Function	Regulation
Zona glomerulosa	Aldosterone is responsible for 95% of mineralocorticoid hormone activity	Regulates sodium and potassium levels, which affect fluid and electrolyte homeostasis, including extracellular fluid volumes; primary activation through the renin-angiotensin system	Complex process; release triggered by dehydration, sodium deficiency, hemorrhage or elevated potassium levels ACTH has minor role in stimulation secretion.
Zona fasciculata	Glucocorticoids, including cortisol or hydrocortisone (most abundant), cortisone, and corticosterone	Major effect on metabolism of lipids, proteins, and carbohydrates; encourages fat storage; when more energy is required, assists in gluconeogenesis, which helps resist both mental and physical stress; hormones trigger anti-inflammatory and immunosuppressive responses	High stress or low blood concentration (negative feedback mechanism)
Zona reticularis	Regardless of gender, secretes both male and female gonadocorticoids (estrogens and androgens)	Promotes normal development of bones and reproductive organs; affects secondary sex characteristics but not as much as hormones from ovaries and testes	Low blood concentration (negative feedback mechanism)
ACTH, adrenocorticotropic hormone.

TABLE 15-2 Tests of Adrenal Function⁷^,¹¹^,²¹

Sample Source	Steroid	Variation	Clinical Implications and Accompanying Conditions
Serum	Adrenocorticotropic hormone (ACTH, corticotropin)	Increase	Addison disease, ectopic ACTH syndrome, pituitary adenoma, pituitary Cushing syndrome, primary adrenal insufficiency, and stress; drugs causing elevation: amphetamine sulfate, calcium gluconate, corticosteroids, estrogens, ethanol, lithium carbonate, metyrapone, and spironolactone
Serum	Adrenocorticotropic hormone (ACTH, corticotropin)	Decrease	Primary adrenocortical hyperfunction (owing to tumor or hyperplasia) and secondary hypoadrenalism; drugs causing suppression: dexamethasone
Serum/urine	Aldosterone	Increase	Adrenal tumor (adenoma), aldosteronism (primary, secondary), bilateral adrenal gland hyperplasia, cirrhosis, chronic obstructive lung disease, congestive heart failure, Conn syndrome (with decreased renin), stress, hemorrhage, hyponatremia, hypovolemia, idiopathic cyclic edema, inadequate renal perfusion causing continual activity of the renin-angiotensin system (renin level is also high), nephrosis (lower nephron), nephrotic syndrome, renovascular hypertension (with hypokalemia), low-sodium diet, and excessive licorice consumption; drugs causing elevation: corticotropin, diuretics that promote sodium excretion, fludrocortisone, and potassium
Serum/urine	Aldosterone	Decrease	Addison disease, primary hypoaldosteronism, salt-wasting syndrome (high-sodium diet), septicemia, stress, diabetes mellitus, and pregnancy-induced toxemia; drugs causing suppression: fludrocortisone and methyldopa
Serum/urine	Cortisol	Increase	Pituitary tumor causing ACTH-dependent increase (Cushing disease), Cushing syndrome causing ACTH-independent increase, adrenal gland hyperplasia, pregnancy-induced hypertension, exercise, severe hepatic disease, hyperpituitarism, hypertension, hyperthyroidism, infectious disease, obesity, acute pancreatitis, pregnancy, severe renal disease, burns, shock, stress (severe heat, cold, trauma, psychological), surgery, and amenorrhea (urine); drugs causing elevation: long-term corticosteroid therapy (virilism), corticotropin, estrogens, oral contraceptives, and vasopressin
Serum/urine	Cortisol	Decrease	Addison disease from primary hypofunction of the cortex or secondary to hypofunction of the pituitary gland, iatrogenic adrenal insufficiency, adrenogenital syndrome, AIDS, chromophobe adenoma, craniopharyngioma, hyperkalemia, hypoglycemia, hyponatremia, hypophysectomy, pituitary necrosis, renal-glomerular dysfunction (urine), and Waterhouse-Friderichsen syndrome; drugs causing suppression: withdrawing corticosteroids after long-term administration, dexamethasone, dexamethasone acetate, and dexamethasone sodium phosphate
Urine	17-Ketogenic steroids (17-KS)	Increase	Adrenogenital syndrome, Cushing syndrome, adrenal carcinoma, burns, hirsutism, hyperadrenalism, infectious disease, obesity, pregnancy, surgery, and virilization; drugs causing elevation: cephalothin, corticosteroids, digoxin, meprobamate, oral contraceptives, penicillin, phenothiazine, and spironolactone
Urine	17-Ketogenic steroids (17-KS)	Decrease	Addison disease, cretinism, hypoadrenalism, hypopituitarism, Simmonds disease, postovary or testicle removal, and wasting away diseases in general; drug intake includes ampicillin, dexamethasone, estrogens, glucose, morphine, phenytoin, prednisone, and prednisolone

Of the limited tests available for testing medullary function, 24-hour urine samples are typically used for catecholamines.¹¹^,¹⁴^,¹⁸^,²⁰ Metanephrines are measured in urine, whereas dopamine may be assessed via urine or blood samples.¹⁸^,²⁰ With hypertension, pheochromocytoma, or neuroblastoma, urine levels of catecholamine, vanillylmandelic acid (VMA), or both may be elevated.¹¹^,¹⁴^,¹⁸^,²⁰

Multiple tests are designed to determine the true functions and interdependency of the hypothalamus, pituitary, kidneys, and adrenals, including stimulation and suppression testing for ACTH, aldosterone, and cortisol.¹¹^,¹⁴^,¹⁸^,¹⁹

SONOGRAPHIC SCANNING TECHNIQUE

Preparation

Usually, patients receive no preparatory instructions for sonography of the adrenal glands, but when there is suspicion of a mass or metastases or a need to image any retroperitoneal anatomy sonographically, it is recommended that the patient fast approximately 6 to 8 hours before the examination.

Scanning Protocol

Evaluation of adrenals may be approached with the patient in supine or decubitus positions. Common protocols typically begin with transverse scanning, followed by longitudinal and/or coronal assessment. Slight or small scanning maneuvers are used to obtain desired images. One of the imaging goals for adrenal sonography is to document unilateral versus bilateral pathologic involvement. As with most sonographic examinations, width and anteroposterior measurements in transverse sections and length measurements from the longitudinal/coronal sections are required. Various breathing excursions and suspended inspiration may be used to optimize visualization of both adrenal glands.

The sonographer should select the highest-frequency transducer that will provide adequate penetration, given an adrenal depth range of 4 to 12 cm, depending on the patient’s size.²¹ Selection of a transducer with a small footprint will also facilitate scanning through intercostal spaces.¹^,³ Magnifying the field size may improve visualization of small structures. Scanning the patient in a prone position is uncommon, although this method is useful to show the spatial relationship between a large adrenal mass and the adjacent kidney.

Right Adrenal

For imaging the right adrenal, the liver and sometimes the right kidney are useful acoustic windows (Fig. 15-5). Successful utilization of the liver as an acoustic window depends on hepatic size and attenuation characteristics (Fig. 15-6). Starting with transverse scans using an intercostal approach, the section of the IVC located medial and anterior to the upper pole of the kidney should be found.¹^,² The plane should be directed toward the lateral and posterior aspects of this portion of the IVC while also keeping the ultrasound beam perpendicular to the spine. The adrenal gland should be seen in this location anterior to the crus of the diaphragm. The entire right adrenal gland is evaluated by scanning transversely from the renal hilus and proceeding superiorly (Fig. 15-5).

FIGURE 15-5 Right adrenal gland scan technique. With the patient in a supine position, a series of transverse images are obtained through the intercostal spaces of the right adrenal gland, using the liver and kidney as acoustic windows. LK, left kidney; RK, right kidney.

Longitudinal or coronal scanning of the right gland can be accomplished with several approaches¹^,³ (Fig. 15-6). A higher success rate has been reported when utilizing the liver as an acoustic window and scanning the patient in a left lateral decubitus position.⁶^,²²^,²³ From an intercostal window, the transducer is angled anterior toward the IVC and posterior toward the right kidney until the entire gland is visualized in the longitudinal or coronal plane (Fig. 15-7).

Left Adrenal

The left adrenal gland is more difficult to locate and document. Conventionally, the left adrenal has been imaged with the patient in the right decubitus position, using the spleen or left kidney as an acoustic window²¹^,²²^,²⁴ (Fig. 15-8). Identifying the left adrenal and its alignment is first done in the transverse plane. The left adrenal should lie between the left kidney and the aorta, with the pancreatic tail and splenic vein marking the superior margin of the gland.²⁵

Longitudinal or coronal scans may be easier to obtain with the patient in a right anterior oblique position using a left posterior oblique scanning plane. First, in the transverse plane, the aorta medial and anterior to the upper pole of the left kidney or the spleen should be located, until the axis of the left kidney and the position of the aorta are determined and the left adrenal gland is identified between these structures²²^,²³ (Fig. 15-9A). With the patient in the same position, the transducer should be rotated into the longitudinal/coronal plane. When imaging the left adrenal gland, the transducer may have to be oriented obliquely (Fig. 15-9B).

In the mid-1980s, Krebs and colleagues²¹^,²⁴ introduced an alternative approach to improve localization and delineation of the left adrenal gland. The patient is placed in a 45-degree left posterior oblique position, termed the cava-suprarenal line position.²¹^,²⁴^,²⁶ The transducer is placed on the patient’s right side, allowing the acoustic beam to pass through a double vascular acoustic window, the IVC, and the aorta²¹ (Fig. 15-10). The protocol starts with transverse scans until the left adrenal gland is located; longitudinal views follow. With this position, the success rate is 90%, compared with 60% in the same patient population using the conventional approach.²¹^,²⁴

FIGURE 15-6 Transverse sectional planes of the right adrenal gland. The sectional transverse illustration demonstrates the relationship of the adrenal glands to other anatomic structures. Longitudinal images of the right adrenal gland as obtained with the patient in a supine position, using the liver as an acoustic window. (A) and (B) can be obtained on most patients, whereas (C) requires a prominent left liver lobe.

FIGURE 15-7 Left lateral decubitus technique. With the patient in a left lateral decubitus position, the right adrenal gland may be easier to visualize as the inferior vena cava (IVC) moves forward and the aorta (Ao) moves over the crus of the diaphragm. LK, left kidney; RK, right kidney.

FIGURE 15-8 Right lateral decubitus technique. Using the spleen or the left kidney (LK) as an acoustic window, transverse images of the left adrenal gland can be made with the patient in a right lateral decubitus position. Ao, aorta; IVC, inferior vena cava; RK, right kidney.

FIGURE 15-9 Right anterior oblique technique. A: With the patient lying in a right anterior oblique position, the left kidney (LK) and aorta (Ao) are aligned in a transverse plane until the left adrenal gland is located. B: After the left adrenal gland is identified in the transverse plane, longitudinal images of the entire gland are easier to obtain. IVC, inferior vena cava.

FIGURE 15-10 Cava-suprarenal line position. The cava-suprarenal line position uses the inferior vena cava (IVC) and aorta (Ao) as a double vascular acoustic window for visualizing the left adrenal gland.³⁵, ³⁶ and ³⁷ LK, left kidney; RK, right kidney.

Pitfalls

The size, location, and pathology of the adrenals and of surrounding structures impose significant limitations on sonographic visualization. Cirrhosis with fatty infiltration of the liver and obesity interfere with adequate penetration. Shadowing from the ribs and narrow intercostal spaces also make this approach challenging.

The right adrenal gland may be obscured by gas and food in the second portion of the duodenum. It is important to differentiate the crus of the diaphragm as a tubular structure located medial to the right adrenal, because it can be mistaken for a normal gland.²⁷ The right adrenal gland is usually displaced posteriorly when the retroperitoneal fat line is displaced by liver disease.²⁷^,²⁸

Structures that converge in the area of the left adrenal may mimic this gland: the esophagogastric junction, stomach, gastric diverticula, splenic vessels, portosystemic collateral vessels, tail of the pancreas, prominent hepatic lobes, medial lobulations of the spleen, superior lobulations of the kidney, or adjacent tumors.¹^,³^,²⁷^,²⁹, ³⁰, ³¹ and ³² A more posterolateral approach or the cava-suprarenal line position may be indicated for proper visualization of the left adrenal gland.²¹^,²⁴

NORMAL SONOGRAPHIC ANATOMY

Fetal adrenal glands are quite large, and 90% of the time at least one can be imaged after 26 to 27 weeks of gestation.³³ In adults, the adrenal glands are much smaller. The glands are generally located anterior, medial, and superior to the kidneys and vary in shape and configuration.¹¹^,³² Their size varies from 3 to 6 cm long, 2 to 4 cm wide, and 3 to 10 mm thick; the adult adrenals weigh 4 to 14 g.¹^,³^,²²^,²³^,³²^,³⁴ Transabdominally, the cortex and medulla are usually sonographically indistinguishable, because the normal internal texture appears homogeneous and hypoechoic.³² The glands are usually surrounded by highly echogenic fat, and in some patients, only the echogenic fat can be identified in contrast to an anechoic adrenal gland.³² Higher-resolution transducers such as those used for endoscopic and intraoperative applications are able to routinely detect the hyperechoic medullary echoes against the hypoechoic cortical echoes and the hyperechoic halo of fatty tissue.⁴^,¹⁷

Right Adrenal

The right adrenal gland is identified superior to the kidney and lateral to the right crus of the diaphragm.²³^,³² On transverse sections, the gland is described as having a triangular, trapezoid, or inverted Y or V shape, with the tail extending from the anteromedial aspect of the right kidney³^,³⁰^,³²^,³⁵ (Fig. 15-11A). In a longitudinal plane scanning the medial aspect of the gland, the anteromedial ridge appears as a curvilinear or S-shaped structure and is visualized posterior to the IVC, slightly above or at the level of the portal vein.¹^,²²^,²³^,³²^,³⁵ Moving laterally in longitudinal planes through the right adrenal gland, the anterior and posterior wings spread open and the gland takes on an inverted Y or V shape³⁵ (Fig. 15-11B, C). The anterolateral portion is medial and posterior to the right lobe of the liver and posterior to the duodenum.³² Care should be taken to differentiate the right adrenal gland from the more medial hypoechoic/anechoic tubular right crus of the diaphragm.

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