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Diseases of the adrenal medulla

The adrenal medulla consists of specialized nerve cells (neuroendocrine). It serves as the main source of catecholamines - epinephrine, norepinephrine, dopamine. Neurosecretory cells have a round or oval shape, developed cytoplasmic membrane and cytoplasm, containing catecholamine vesicles surrounded by a membrane. These cells are located in a well-vascularized fiber-poor stroma, which also contains fusiform and supporting cells. Since secretory cells are part of the neuroendocrine system, they are able to synthesize a variety of biologically active amines and peptides, such as histamine, serotonin, renin, chromogranin A, and neuropeptide hormones. After fixation in solution (for example, Zenker), the cytoplasmic granules turn brown as a result of the oxidation and polymerization of catecholamines (chromaffin reaction). Although neuroendocrine cells (for example, in a tumor) can produce a positive chromaffin reaction, this does not always indicate the release of accumulated catecholamines, i.e. positive reaction does not always indicate the presence of secretion.

There is also a widely scattered extraadrenal system of clusters and nodules from similar neuroendocrine cells, which, together with the medulla of the adrenal glands, are a paraganglionic system. These extraadrenal paraganglia are closely related to the autonomic nervous system. Histologically, all paraganglia consist of cells that are very similar to the cells of the adrenal medulla. Although many of them are functioning, some are in an inactive state. Some of the paraganglia, especially the carotid bodies, have chemoreceptors capable of reacting to the oxygen content and carbon dioxide in the blood.

Norepinephrine acts as a local neurotransmitter, mainly in sympathetic postganglionic neurons. Only small amounts of norepinephrine (adrenaline) are secreted into the vascular system. It interacts with a- and p-adrenergic effector cells associated with membrane specific receptors. The latter then activate secondary messengers and a cascade of enzymatic reactions that provide systemic action of epinephrine (for example, an increase in the strength and speed of heart contractions and vascular spasm).

The most significant diseases of the adrenal medulla are tumors - pheochromocytomas, neuroblastomas, ganglioneuromas and their variants.

Pheochromocytoma. This is a relatively rare tumor in which hypertension develops, associated with the release of catecholamines and disappearing after the removal of the tumor. Although pheochromocytoma occurs only in 0.1-0.3% of patients with hypertension, the disease can be fatal if the tumor is not recognized. Sometimes a tumor produces other biogenic steroids or peptides and may be associated with Cushing's syndrome or other endocrinopathy.

About 85% of pheochromocyte are formed in the medulla of the adrenal glands, the rest - in any extra-adrenal paraganglia, most often under the diaphragm. The extra-adrenal tumors, if they are chromaffin-negative, are also called paragangliomas, thus distinguishing them from functioning pheochromocytes. 85–90% of pheochromocytes arise sporadically; the remaining 10–15% develop in various hereditary syndromes (Hippel — Lindau, Sturge — Weber, Recklinghausen). The occurrence of pheochromocytoma is characteristic of syndromes of multiple endocrine neoplasia (see below).

Although non-familial pheochromocytomas are most common in adults between the ages of 40 and 60, and mostly in women, with hereditary syndromes they can develop in childhood and more often in males. Most tumors in hereditary syndromes are bilateral (70%).

There is an assumption that pheochromocytoma in its development passes through the stages of diffuse hyperplasia, nodular hyperplasia and, finally, neoplasm.
Conventional intramedullary tumors are accompanied by diffuse hyperplasia of the adrenal medulla on the opposite side.

A pheochromocytoma is most often a single tumor, but in hereditary syndromes it can be multiple. The mass of the tumor varies from 1 g to 4000 g, an average of about 100 g. The size of the tumor correlates poorly with the severity of clinical manifestations. On the cut, the tumor tissue is pale gray or brown in color with areas of hemorrhage and necrosis, cysts, especially in large tumors. When a fixer with dichromate is used (Zenker or Helly solutions), the tumor becomes brownish-black due to catecholamine oxidation.

The tumor consists of mature medullary cells that contain abundant basophilic cytoplasm with secretory granules, best seen when tissue is fixed in dichromate or electron microscopy. Less commonly, the dominant cell type is fusiform or small. The functional activity of the tumor is not associated with an abundance of granules. The cells are located in the form of wide trabeculae, separated by thin-walled sinusoids, often lined by the tumor cells themselves, or in the form of small alveoli, enclosed in a fibrovascular stroma emanating from the tumor capsule. In the same tumor, different structures can be found simultaneously. The sizes of cells and their nuclei can vary considerably; there are giant and bizarre cells. Figures of mitosis are rare.

Since malignant and benign pheochromocytomas may have a similar histological structure, the presence of metastases is an absolute criterion for malignancy. Metastases to the lymph nodes, liver, lungs and bones are more common, after which patients live for no more than 3 years.

Hypertension is the dominant clinical feature of pheochromocyte. The increase in pressure is due to a sudden release of catecholamines, which can cause exacerbation of chronic cardiovascular insufficiency, pulmonary edema, myocardial infarction, ventricular fibrillation, and hemorrhage in the brain. Heart complications are characteristic, they are called catecholamine cardiomyopathy, or catecholamine heart disease. Changes in myocardium ischemic, occur after vascular spasm caused by catecholamines or as a result of direct toxic effects. Histologically, there are areas of myocytosis, necrosis of myofibrils, interstitial fibrosis, and sometimes inflammatory infiltration of mononuclear leukocytes.

Tumors of non-adrenal paraganglia. Despite the rarity and small size of paraganglion tumors, they have great clinical significance, since 10-40% of them are malignant, and about 10% produce extensive metastases, leading to death. These tumors are found about 10 times less pheochromocyte. Most of them appear in the 2nd or 3rd decade of life. These tumors are much more common than adrenal tumors, multicentric (15–25% of cases).

Tumors have a diameter of 1-6 cm, dense, brown-red color in the section, often tightly soldered to nearby vessels. Histologically, paragangliomas consist of well-differentiated neuroendocrine cells with fuzzy boundaries, so that they can appear as syncytium. The cells are located in the form of small clusters or cords separated by a developed fibrovascular stroma. Some tumors are similar to adrenal pheochromocytoma. In the cells of most tumors, dark neurosecretory granules are found that contain catecholamines. Sometimes these cells are fusiform. Mitoses are usually rare, but anaplastic and polymorphic tumors contain numerous mitoses. The incidence of malignant growth (up to 40%) in paraganglionic tumors is significantly higher than in pheochromocytes. Most anaplastic tumors can produce extensive metastases and lead to death.

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Diseases of the adrenal medulla

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  3. Diseases of the adrenal cortex
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  12. Adrenal pathology
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