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Biologic aggressiveness of thyroid cancers. Two risk groups have been defined for patients with well-differentiated thyroid cancer, based on an analysis by the Lahey Clinic and the Mayo Clinic.

Low-risk group. This group consists of women who are younger than 50 years of age and men who are younger than 40 years of age with intrathyroidal papillary carcinoma or follicular carcinoma with minimal vascular or lymphatic invasion, both of which are less than 5 cm in size and are not associated with distant spread.

Unless both lobes are grossly involved with tumor, patients in this group do as well with near -total thyroidectomy as with total thyroidectomy. The remaining thyroid remnant may be ablated postoperatively with 131 I.

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After surgery, patients should receive exogenous thyroid hormone for life to suppress endogenous TSH production.

With comparable treatment, the recurrence rate and death rate in this group have been found to be significantly lower than in the high-risk group.

High-risk group. This group consists of patients of any age with evidence of distant spread or with extrathyroidal papillary carcinoma, follicular carcinoma with significant vascular invasion (tumors greater than 5 cm in size), or women who are older than 50 years of age and men who are older than 40 years of age with either papillary or follicular carcinoma.

In this group, the tumors are much more aggressive and require a more aggressive initial approach because local recurrences are more difficult to treat and the mortality rate is significantly greater. Thus, total thyroidectomy is indicated in these patients.

Lymph node dissection of palpable nodes should be more extensive than in the low -risk groups.

Radioiodine ablation of any tissue showing radioiodine uptake postoperatively should be performed, and exogenous thyroid hormone should be administered to suppress TSH production.

Types of thyroid malignancy

Papillary carcinoma

Incidence

Papillary carcinoma accounts for 80% of all thyroid cancers in children and 60% in adults.

It affects women twice as often as men and is the most common histologic type found in patients who have a history of radiation exposure.

Characteristics

The tumor is characterized by a slow rate of growth and spread to regional lymphatics in 50% of the cases. It spreads by way of the bloodstream in fewer than 5% of cases.

Tumors range in size from occult (less than 1.5 cm in diameter) to tumors that involve an entire lobe or both lobes.

In 40% of cases, the tumor is multicentric in origin.

Microscopic multicentric lesions rarely develop into clinical carcinoma.

Macroscopic multicentric lesions will usually be biologically similar to papillary cancer.

Some tumors are well encapsulated with minimal invasion of adjacent normal thyroid. Others are poorly encapsulated with invasion to perithyroidal structures.

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Prognosis

Prognosis is excellent with occult or well-encapsulated intrathyroidal carcinoma. Patients with these tumors have a 20 -year survival rate of better than 90%.

Prognosis is poor when the tumor is poorly encapsulated and extends by extrathyroidal invasion. The 20 -year survival rate is less than 50%.

Prognosis is also poorer as the patient's age increases beyond 40 years.

Survival does not appear to be adversely affected by lymphatic spread.

Follicular carcinoma

Incidence

Follicular carcinoma accounts for approximately 20% of all thyroid malignancies. It is more common in areas of the world where iodine -deficiency goiter is in evidence.

It also affects women twice as often as men.

Its relative frequency increases after 40 years of age.

Characteristics

Follicular carcinoma spreads primarily through the bloodstream by way of angioinvasion. It rarely spreads to regional lymph nodes except for locally invasive nodules that extend into the perithyroidal tissue.

The tumor is slow growing and usually unifocal.

When found cytologically to be combined with papillary elements, it is biologically similar to papillary carcinoma.

Prognosis

Prognosis is good when there is minimal vascular invasion, with a better than 80% 20 - year survival rate.

Prognosis is poor when there is gross invasion, with a less than 20% 20 -year survival rate.

Medullary carcinoma

Incidence

Medullary carcinoma of the thyroid accounts for fewer than 10% of all thyroid cancers.

It occurs at all ages without predilection for either sex.

It most commonly occurs sporadically but also can be genetically transmitted.

When it occurs sporadically, it usually appears as a solitary lesion.

When transmitted genetically, it may occur as a solitary lesion or may be a part of multiple endocrine neoplasia (MEN) syndrome type II; (see Chapter 17, I B 2, C 2, D 2).

Characteristics

Early spread to the lymphatics is characteristic, and spread by way of the bloodstream is also common.

There are two types of medullary carcinoma that are indistinguishable histologically:

Those characterized by aggressive, rapid growth, rapid spread, and early metastasis

Those characterized by slow growth and a prolonged course despite metastasis

Because these tumors arise from the C cells of the thyroid, they produce thyrocalcitonin.

This hormone can be detected by radioimmunoassay in early stages of tumor development.

In patients with hereditary MEN type II, the disease can be detected in this way before the development of clinically evident malignancy.

Prognosis is poorer than for papillary or follicular carcinoma and is related to the stage of the tumor at the time of its initial diagnosis.

Stage I medullary carcinoma has a 50% 20 -year survival rate.

Stage II has a less than 10% 20 -year survival rate.

Death results from generalized metastasis.

Medullary thyroid carcinoma occurring in MEN syndrome is curable by total thyroidectomy if detected and treated before the development of clinically evident malignancy.

Anaplastic carcinoma

Incidence

This tumor accounts for fewer than 10% of all thyroid cancers.

It is most common between the ages of 50 and 70 years and shows no predilection for either sex.

Characteristics

Anaplastic carcinomas are characterized by small cells, giant cells, or spindle cells.

They usually arise from a pre -existing, well-differentiated thyroid neoplasm, such as a follicular lesion.

They grow rapidly into local structures, such as the trachea and esophagus, and metastasize early by way of the lymphatics and the bloodstream, so they are usually incurable at the time of initial presentation.

Prognosis

Prognosis is poor with a fatal outcome in almost all instances, regardless of the type of treatment.

When treatment appears successful, the lesion may well have been a lymphoma instead of a small cell anaplastic carcinoma, and the histologic nature of the neoplasm should be confirmed by electron microscopy or immunohistochemistry.

Lymphoma and lymphosarcoma

Incidence. This tumor accounts for fewer than 1% of all thyroid malignancies and affects mostly women 50–70 years of age.

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Characteristics

Fine -needle aspiration alone may not be able to establish this diagnosis. Core biopsy or open biopsy may be required.

Pathologically, these are usually small cell tumors and may be difficult to distinguish from small cell anaplastic carcinoma except by electron microscopy.

The lesion may occur primarily in the thyroid gland as an extranodal growth, or it may be part of a generalized lymphomatous process.

The local type is best treated by radiation therapy, whereas the diffuse type will probably require systemic multidrug chemotherapy. Unless the tumor is small and confined to the thyroid lobe, surgical excision is generally not indicated.

Prognosis is variable and depends on the cell type and whether the tumor is local or diffuse.

II Adrenal Gland

A Introduction

The adrenal glands are the source of several tumors, benign and malignant, and of hyperplasias, primary and secondary. Some of these lesions produce syndromes due to the overproduction of normal adrenal hormones, including Cushing's syndrome, Conn's syndrome, and pheochromocytomas. The diagnosis and treatment of these disease states require a thorough knowledge of the production, action, and metabolism of the adrenal hormones.

Embryology. The adrenal gland consists of two distinct parts, the cortex and the medulla , each of which has a different embryologic origin.

The adrenal medulla originates from ectodermal cells of neural crest origin.

These cells migrate from the sympathetic ganglion and combine to form the medulla, which is surrounded by mesodermal cortex.

Additional collections of adrenal medullary tissue can form. These are most frequently found in the paraganglia, in the organ of Zuckerkandl just below the origin of the inferior mesenteric artery, and in the mediastinum.

The adrenal cortex is derived from mesodermal cells near the genital ridge.

These cells coalesce to form a complete layer around the ectodermal cells that will form the adrenal medulla.

Occasionally, these cells become separated from the main cortex and form adrenocortical rests. These are most commonly found in the ovary or testis and near the adrenal glands and kidneys.

Anatomy. There are two adrenal glands, each one lying on the medial aspect of the superior pole of a kidney. The normal combined weight of the two glands is about 10 g.

Histology. Three distinct areas can be recognized in the cortex.

The zona glomerulosa is the outer zone, where the production of mineralocorticoids such as aldosterone takes place.

The zona fasciculata is the intermediate zone, where cortisol and the other glucocorticoids are produced.

The zona reticularis is the inner zone, where androgens and estrogens are made.

Vasculature of the adrenal glands

Arterial supply to the adrenals varies but arises from three primary sources (i.e., the phrenic artery, aorta, and renal artery).

Venous drainage is more constant. There is usually a large single vein on each side of the body. The right adrenal vein drains into the vena cava, and the left adrenal vein empties into the left renal vein. Small accessory veins can occur.

Adrenal portal system. Venous blood from the cortex, containing high levels of glucocorticoids, drains into the medulla, helping to induce the enzyme phenylethanolamine -N- methyltransferase. This enzyme methylates norepinephrine to form epinephrine.

B Adrenal hormones and catecholamines

Steroid hormones. The adrenal cortex produces three main classes of steroid hormones: the glucocorticoids, the mineralocorticoids, and the sex steroids (androgens and estrogens).

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Glucocorticoids. The most important glucocorticoid physiologically is cortisol. Production of cortisol takes place primarily in the zona fasciculata. There is a diurnal variation, with the highest levels occurring around 6:00 A.M. and the lowest levels at 8–12 P.M.

Regulation

Adrenocorticotropic hormone (ACTH; corticotropin) is produced by the anterior pituitary gland. ACTH stimulates the production of cortisol by the adrenal. Cortisol , in turn, exerts a negative feedback on ACTH production at the hypothalamic-pituitary level.

Corticotropin-releasing factor (CRF) is produced by the hypothalamus and stimulates the release of ACTH from the pituitary.

Free cortisol is the active hormone. Normally, most circulating cortisol is bound to corticosteroid -binding globulin (CBG). When large amounts of cortisol are produced, the binding sites become saturated, and the levels of free hormone will increase.

Metabolism. Cortisol is metabolized in the liver by conjugation with glucuronide. This renders it water soluble for urinary excretion. The level of urinary 17 -hydroxycorticosteroids reflects glucocorticoid production and metabolism. However, in states of hypercortisolism, the urinary free cortisol is more accurate.

Mineralocorticoids. The major mineralocorticoid produced by the adrenal gland is aldo-sterone , which is produced in the zona glomerulosa of the adrenal cortex.

Regulation

Aldosterone production is regulated chiefly by the renin -angiotensin system and changes in plasma concentrations of sodium and potassium.

Renin is released by the juxtaglomerular cells of the kidney in response to a decrease in blood pressure.

Renin converts angiotensinogen (made in the liver) to angiotensin I.

Angiotensin I is converted to angiotensin II by angiotensin -converting enzyme , which is produced by endothelial cells.

Angiotensin II stimulates the adrenal cortex to release aldosterone.

Aldosterone production is minimally controlled by ACTH.

The sympathetic nervous system can also stimulate the release of aldosterone.

Metabolism. Aldosterone is metabolized in a similar manner to cortisol. It is excreted in the urine in small quantities and can be measured by radioimmunoassay.

Sex steroids. Androgens and estrogens are produced in the zona reticularis of the adrenal cortex. The urinary level of 17 -ketosteroids reflects the androgen production. Estrogens can also be measured in the urine.

Catecholamines. The adrenal medulla is the site of catecholamine production, including dopamine, norepinephrine, and epinephrine.

Regulation. Catecholamine production is under the control of the sympathetic nervous system.

Metabolism

The pathways of catecholamine production and metabolism in the adrenal medulla are summarized in Figure 16 -4. Dopamine can also be metabolized by an alternate pathway to homovanillic acid (HVA).

The levels of metanephrine, normetanephrine, vanillylmandelic acid (VMA), and the individual catecholamines can be measured in the urine to evaluate the function of adrenal tumors.

C Congenital virilizing adrenal hyperplasia

Pathogenesis

If an enzyme is missing from the pathway of cortisol production, the consequent shortage of cortisol will cause an increase in ACTH activity, and adrenal hyperplasia will result. The cortisol precursors will then be shunted into the production of androgens.

Although several different enzymes can be congenitally absent, the most common defect is a block in hydroxylation at C-21 of the cortisol molecule.

Clinical presentation

Virilization results from the hormonal defect. In the female, this produces pseudohermaphroditism, and in the male, macrogenitosomia precox.

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FIGURE 16-4 Pathways of (A) catecholamine production and (B) metabolism.

In a minority of cases, the block is more complete, and a severe salt-losing state with vascular collapse results from the aldosterone deficiency.

Diagnosis. The diagnosis can be suspected from the characteristic virilization and the excess levels of 17 - ketosteroids in the urine.

Treatment

The metabolic deficiency is treated with steroid replacement.

In females, plastic surgical procedures are often necessary to correct the genital deformities.

An accurate sex assignment must be made in female pseudohermaphrodites by means of karyotyping and Barr body analysis.

D Adrenocortical insufficiency (Addison's disease)

This condition is important to the practicing surgeon because patients who have Addison's disease are not capable of undergoing the stress of surgery without receiving corticosteroid support.

Types. Addison's disease may be primary or secondary.

Primary adrenocortical insufficiency results in diminished or absent function of the adrenal cortex because of adrenal pathology. Causes include:

An autoimmune attack on the adrenal gland

Bilateral adrenal tuberculosis

Adrenal fungal infections

Bilateral adrenal hemorrhage, which can occur:

Secondary to meningococcal septicemia

Postpartum

In patients on anticoagulant therapy

Secondary adrenocortical insufficiency is due to atrophy of the adrenal cortex secondary to a decreased pituitary production of ACTH. Causes include:

ACTH suppression by corticosteroid drugs , which is the most common cause of adrenal insufficiency encountered in the surgical patient

Primary pituitary pathology , which is a less common cause