Diagnostic programs for thyroid diseases

In order to carry out rational treatment, it is necessary to determine the morphological changes in the thyroid gland and the level of endocrine function of all glands that regulate iodine metabolism in the body.

The patient examination program should be coordinated with the main clinical and radiological syndromes. It is advisable to highlight the following syndromes:

1. diffuse enlargement of the thyroid gland - diffuse goiter (euthyroid or toxic);
2. toxic nodular goiter (toxic adenoma of the thyroid gland);
3. benign space-occupying lesion in the thyroid gland;
4. malignant space-occupying lesion in the thyroid gland;
5. hypothyroidism.

In most cases, radionuclide research begins with distinguishing between hyper-, eu- and hypothyroid states using radioimmunological determination of the level of thyroid hormones in the blood. An increased concentration of T4 and T3 is characteristic of hyperthyroidism, a decreased concentration is characteristic of hypothyroidism.

First of all, total thyroxine is determined, i.e. the total amount of the hormone (both bound to the transport protein - TSH, and in a free state in the blood - CT4). The normal concentration of T4 in the blood fluctuates between 70 and 150 nmol/l. A concentration below 70 nmol/l indicates hypothyroidism, and above 150 nmol/l - hyperthyroidism. Since the main active fraction of T4 is its unbound part, determining its concentration is important for establishing the activity of thyroxine. In healthy people, the concentration of CT4 in the blood is vanishingly small, only 10-20 nmol/l. As with determining total thyroxine, a decrease in the content of CT4 indicates hypothyroidism, and an increase - hyperthyroidism.

Determining the level of T3 is less important than T4. Total T3 and free T3 (CT3) are determined. Normally, the content of T3 is 1.3 - 9.5 nmol/l, CT3 - 3-10 nmol/l. Exceeding the required values is characteristic of hyperthyroidism, a decrease - of hypothyroidism. Data on the content of T4 is more reliable, but determining the concentration of T3 allows us to identify a special form of hyperthyroidism - the so-called T3 - thyrotoxicosis. It is not so rare - in 5-10% of patients with thyrotoxicosis.

In clinical practice, there are cases when, with a normal concentration of T, a decrease in the content of T3 is noted. In such cases, "low T3 syndrome" is diagnosed. It develops with various systemic diseases, liver and kidney failure, malignant tumors, starvation, burns, and extensive surgical interventions.

To assess the functional state of the thyroid gland, it is important to determine not only the content of T3 and T4, but also the concentration of TSH. In healthy people, it is 0.36-0.42 μmol / l. The TSH level increases during pregnancy, in newborns, with the use of estrogens and oral contraceptives. A decrease in the TSH level is observed in kidney diseases, the use of androgens and prednisolone. Calculation of the ratio of total thyroxine to TSH has acquired a special role in the clinic. The T4 / TSH indicator allows you to clearly differentiate between eu-, hypo- and hyperthyroid states, even with a change in the concentration of transport proteins. A number of other indices have also been proposed. Among them, the "integral index" (II): II = (ST) + CT4) / STSH, where CT5 is the normalized value of the total T3 level (2.38 nmol / l x 100%); ST is the normalized value of total thyroxine (90.0 nmol/l x 100%), STSH is the normalized value of thyrotropin (4.46 mU/l x 100%).

If it is impossible to conduct a radioimmunological analysis, and also if it is necessary to establish the state of the intrathyroid stage of iodine metabolism, thyroid radiometry is performed.

Diffuse goiter

A distinction is made between diffuse enlargement of the entire thyroid gland in the absence of individual palpable nodes and diffuse-nodular goiter when one or more nodes develop in the enlarged organ. In both forms, the function of the gland can be normal, enhanced, or weakened.

Radiographs of diffuse goiter reveal an enlarged thyroid gland with preserved acoustic structure. The echogenicity of the glandular tissue is usually reduced, but at the same time, coarser structures are distinguished - connective tissue strands against the background of follicular reorganization. Scintigrams confirm a diffuse uniform enlargement of the gland. The contours of the gland are always convex. Increased image intensity is observed with increased function of the thyroid tissue. In large goiters, focal formations, including cysts, are often detected. In thyroiditis, the gland is also enlarged, but the RFP is distributed unevenly, although there are usually no clearly defined nodes.

Sometimes the thyroid gland is located behind the sternum ("substernal goiter"). The shadow of such a goiter appears on radiographs and especially on tomograms. Scintigrams allow it to be distinguished from a tumor formation in the mediastinum.

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Toxic nodular goiter

In case of nodular lesions of the thyroid gland, it is advisable to begin the examination with sonography. Ultrasound scanning allows confirming the presence of nodes in the gland, establishing their macromorphological structure, and distinguishing them from cysts. The next stage of differentiation of nodular formations is scintigraphy. Most nodular formations, with the exception of toxic adenoma, give a defect in the accumulation of radiopharmaceuticals on the scintigram - a "cold" focus. The substrate of the "hot" focus is usually toxic adenoma - a benign formation in which a clinical picture of thyrotoxicosis is observed. Toxic adenoma of the thyroid gland is focal hyperplasia of the thyroid tissue. During sonography, it is detected as a single clearly quoted node with reduced echogenicity, on scintigrams it causes a "hot" focus. At the same time, other parts of the gland do not accumulate radiopharmaceuticals or there is very little of it in them. A stimulation test serves as evidence of toxic adenoma: after the introduction of thyrotropin, an image of all other parts of the thyroid gland appears on the scintigrams.

Often, in case of toxic adenoma, a "suppression" test is also used. It allows to establish whether the function of the thyroid gland and adenoma depends on the concentration of the pituitary hormone circulating in the blood - thyrotropin. For this purpose, the patient is administered thyroid hormones - T3 or T4. If the function of the gland and the nodular formation in it depends on the pituitary gland, then a significant, up to 50%, decrease in the accumulation of the radiopharmaceutical is noted on repeated scintigrams. At the same time, autonomously functioning nodes, including toxic adenoma, do not respond to the administration of thyroid hormones.

Benign nodular formation

The thyroid gland contains various benign formations: cysts, adenomas, nodes in some forms of colloid goiter, areas of limited thyroiditis, cicatricial fields. All of them on scintigrams determine the area in which the radiopharmaceutical does not accumulate or accumulates very weakly, i.e. a "cold" node. Based on the results of a radionuclide study, it is difficult, and sometimes impossible, to establish its origin. In this case, clinical data, sonography and biopsy results help in diagnosis.

By the nature of the structure, benign formations are divided into solid, cystic and mixed. A solid node consists of dense tissue, a cystic node is a cavity with liquid contents, and a mixed node includes both dense tissue and cysts.

Sonograms allow to immediately identify all cystic formations. A cyst is defined as a round or oval body with smooth contours and is characterized by uniform echo-negativity. Follicular adenoma looks like a formation of a regular round shape with reduced echogenicity with some heterogeneity of structure. The outlines of the adenoma are usually smooth. Denser areas in it are determined by increased echogenicity; in such cases, a rim of reduced echogenicity around can be seen, caused by peri-nodular edema of the thyroid tissue. A "cold" lesion in limited thyroiditis produces an area of low echogenicity with unclear outlines and small additional structures inside.

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Malignant space-occupying lesion

A cancerous node in the thyroid gland is usually solitary. On scintigrams, it usually appears as a "cold" lesion. Its ultrasound image is difficult to interpret, as it varies depending on the tumor structure. Most often, sonograms show a node of low echo density with fairly clear but uneven contours. However, there are tumors with increased echogenicity. The image of the node is non-uniform: areas of varying echogenicity stand out against its background. There is no echo-negative rim around the tumor. Instead, very small calcifications in the form of short lines or foci are often visible along the periphery of the node.

Hypothyroidism

There are four forms of hypothyroidism: primary, secondary, tertiary, and iodine-deficiency. In primary hypothyroidism, hormone formation in the thyroid gland itself is disrupted; in secondary hypothyroidism, the thyrotropic function of the pituitary gland is reduced. Tertiary hypothyroidism is caused by suppression of the hypothalamus. Finally, iodine-deficiency hypothyroidism develops with insufficient iodine in food and water.

In the differential diagnosis of primary and secondary hypothyroidism, the thyrotropin test is decisive. When conducting it, the level of thyrotropin in the blood is determined twice - before and 30 minutes after rapid intravenous administration of thyrotropin. In the case of normal functioning of the pituitary gland, the concentration of thyrotropin increases by 15%.

Parathyroid adenoma

The parathyroid glands control all calcium metabolism in the body. Hyperfunction of one or both glands leads to primary hyperparathyroidism. The level of parathyroid hormone in the blood is determined by radioimmune testing. This is a very sensitive reaction, which makes it possible to establish hyperparathyroidism before changes in the bones appear on X-rays. In approximately 80% of cases, hyperparathyroidism is associated with the development of a single parathyroid adenoma. Secondary hyperparathyroidism is usually explained by hyperplasia of both glands in chronic kidney disease.

The primary task of a radiologist is to detect parathyroid adenoma. This can be done using sonography, computed tomography, magnetic resonance imaging, and scintigraphy.

On sonograms, a typical adenoma is well-defined and produces an image of decreased echogenicity. It is defined between the posterolateral edge of the thyroid gland and the common carotid artery. The size of the adenoma is usually up to 1.5 cm.

For radionuclide detection of adenoma, ^99m Tc-pertechnetate must be administered. The scintigraphic image with pertechnetate is "subtracted" from the image obtained on a series of scintigrams with thallium.

Increased function of the parathyroid glands leads to a disruption of mineral metabolism, primarily calcium. The patient develops hyperparathyroid osteodystrophy (Recklinghausen's disease). It has a clear radiographic picture. Conventional radiographs show systemic osteoporosis. It is gradually accompanied by stratification and thinning of the cortical bone layer. Single and multiple cysts may appear in different parts of the skeleton. Often, shadows of kidney stones can be discerned from the images.

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