Substernal goiter is an enlargement of the thyroid gland, in which the lower pole or a significant part of the organ is localized below the jugular notch of the sternum. The cause of pathology are the same factors that cause other types of goiter: iodine deficiency, hereditary predisposition, poor ecology. The disease is manifested by shortness of breath, dysphagia, cava syndrome and signs of thyrotoxicosis. Radiography and MRI of the mediastinum, radionuclide examination, thyroid hormone tests are carried out to diagnose a substernal goiter. Surgical treatment is the removal of nodular formations, which, according to indications, is supplemented with hormone replacement therapy.
ICD 10
E01 E04 E05
Meaning
Substernal goiter (сhest, retrosternal) refers to a large group of diseases that are manifested by an increase in the size of one or both lobes of the thyroid gland (thyroid gland). According to various statistics, it makes up from 1% to 10% of all cases of goiter. The disease occurs more often in people over 60 years of age who have more than 15 years of experience in thyroid pathology. The disease is characterized by an unfavorable course and often causes complications, therefore it requires a rational selection of therapy and timely surgical intervention.
Causes
Most often, goiter is formed in conditions of iodine deficiency, which is caused by living in areas endemic to iodine deficiency, a lack of iodine in food, impaired absorption of trace elements in the intestine. Iodine deficiency causes 90-95% of cases of thyroid enlargement. Pathology begins to develop in childhood or at a young age, by the age of 50-60, the goiter acquires a chest localization.
Regarding other causes and risk factors, doctors have no consensus. The appearance of toxic adenomas is associated with a hereditary predisposition: mutations of the TSH receptor gene and the adenylate cyclase cascade protein subunit. Some scientists consider substernal goiter in the elderly as a variant of involutive changes in the organ. Among the independent risk factors are smoking, increased radiation background, taking certain medications.
Pathogenesis
Hyperplasia of the gland tissues is caused by the presence of cells with high growth potential. They form locally dominant foci in the parenchyma of the organ and become a morphological substrate for the growth of nodes. Endogenous growth factors, such as thyroid-stimulating hormone, insulin-like growth factor-1, are of great importance in the mechanism of the development of volumetric neoplasms.
The main source of the development of a substernal goiter is considered to be a low-lying thyroid gland, which gradually descends behind the sternum in the process of its increase. The atypical location is facilitated by a powerful anterior neck muscle, which is especially pronounced in muscular men of endomorphic physique. The movement of the node during swallowing and its own heaviness contribute to the growth of tissues along the path of least resistance – towards the mediastinum.
In most cases, the goiter is located in the anterior mediastinum on the right. Its right—sided localization is a pathognomonic sign that is used by doctors for differential diagnosis with other types of tumors. Right-sided goiter can also develop from the left lobe of the thyroid gland, since large vessels in the left half of the mediastinum shift the organ in the opposite direction. The location of the goiter on the left and in the posterior mediastinum is extremely rare.
Classification
According to the mechanism of development, primary and secondary retrosternal goiter are distinguished. The primary form is 1% of cases and arises from ectopic thyroid tissue. The remaining 99% is occupied by the secondary form that occurs when the normally located gland is lowered behind the sternum. According to the location relative to the mediastinal organs, there is an anterior and posterior mediastinal goiter. In practical endocrinology, the classification of the disease by degrees is important (according to A.F. Romanchishen, 1993):
- The neoplasm is located on the neck, but tends to spread to the chest area.
- The thyroid gland begins to descend behind the sternum, at the moment of swallowing it can be completely brought to the surface of the neck.
- The enlarged thyroid gland is not displayed on the neck during swallowing, so its chest part is inaccessible for finger examination.
- The main part of the gland is localized behind the sternum, only the upper pole of the organ is available for palpation in the neck area.
- Hyperplastic thyroid tissue is located behind the chest, mediastinal dystopia of the organ is possible.
Symptoms
Clinical manifestations of the disease associated with compression of surrounding organs. Respiratory disorders come out on top. Shortness of breath attacks develop in 60% of patients as the first sign of pathology. Breathing difficulties increase in the supine position without a pillow, when bending forward, during physical exertion. The severity of respiratory disorders depends on the size of the enlarged thyroid gland and its localization.
In addition to shortness of breath, patients have wheezing noisy breathing, there are periodic bouts of coughing. Compression of the upper digestive tract causes difficulty swallowing, a constant feeling of a lump in the throat. Some patients complain of nausea and vomiting that occur during meals. The defeat of the recurrent nerve and the vocal apparatus causes hoarseness, hoarseness of the voice.
Manifestations of thyrotoxicosis are observed in only 15% of patients. They are associated with increased production of thyroid hormones in hyperplastic parts of the gland. Endocrine disorders are manifested by nervousness, irritability, acceleration of thought processes and speech. It is characterized by an inability to concentrate on current tasks, insomnia, tremor of the fingers.
Hyperthyroidism is manifested by an acceleration of metabolism, which leads to weight loss with a preserved appetite. Protein-energy deficiency increases against the background of swallowing difficulties with large sizes of the retrosternal goiter. Some patients complain of excessive sweating, a rise in body temperature, poor tolerance of heat and stuffiness. It is possible to increase the heartbeat, increase blood pressure, the appearance of various forms of arrhythmias.
Complications
Tracheal compression is recognized as one of the most dangerous consequences of substernal goiter. With hemorrhage in the nodes, rapid enlargement of the gland is possible, which leads to sudden asphyxia and death of the patient if emergency medical care is not provided. Due to compression of the nerves coming from the sympathetic cervical ganglion, Gorner’s syndrome develops. It includes drooping of the eyelid, narrowing of the pupil, decreased sweating.
A large goiter causes the syndrome of the superior vena cava, which is manifested by a violation of blood circulation in the upper parts of the trunk. With cava syndrome, there is swelling and cyanotic staining of the skin of the face, neck, upper extremities and upper half of the trunk. Shortness of breath, cough and dysphagia increase. There are severe chest pains, which are aggravated in the supine position. Against the background of venous hypertension, pulmonary and esophageal bleeding is possible.
Diagnostics
With an increase in the size of the thyroid gland, patients are examined by an endocrinologist. At the initial consultation, the specialist needs to establish complaints and anamnesis of the disease, find out risk factors, palpate the neck area and determine the degree of goiter, if it is available for physical examination. The second stage of diagnostics includes laboratory and instrumental methods:
- Chest X-ray. The study in two projections determines the presence and diameter of the retrosternal goiter, the deviation of the trachea as an additional sign of a mediastinal tumor. The X-ray mode shows the movement of the volumetric formation during swallowing, which is characteristic of an enlarged thyroid gland.
- Ultrasound of the thyroid gland. Sonography is informative for cervical-thoracic localization of neoplasm, when part of the goiter is available for scanning. Using the duplex scanning mode, the state of blood flow in the gland and the surrounding large vessels is studied.
- MRI of the mediastinum. Magnetic resonance imaging is prescribed to clarify the anatomical features of the identified neoplasm, to visualize its relationship with other mediastinal structures.
- Thyroid scintigraphy. Radionuclide diagnostics is necessary to assess the location and amount of functioning thyroid tissue. The study is necessarily carried out before the operation in order to make a decision on the preservation of a part of the thyroid gland.
- Additional instrumental methods. Examination of the larynx is necessary for hoarseness of the voice and suspected compression of the recurrent nerve. Chest pain and cough may require a CT scan of the lungs, bronchoscopy. Cardiological symptoms require an ECG and ultrasound of the heart.
- Hormonal profile. To determine the thyroid status of the patient, blood tests are conducted for thyroid hormones (thyroxine, triiodothyronine) and pituitary (thyroid-stimulating hormone). To exclude the autoimmune nature of the disease, an analysis for antibodies to thyroglobulin is prescribed.
Differential diagnosis
Since the retrosternal localization of goiter is much less common than the typical location, other types of mediastinal neoplasms are excluded when making a diagnosis. Differential diagnosis with neurinomas, thymomas, lymphomas is carried out. Exclude dermoid cysts, teratomas and secondary carcinomas. Differential diagnostic of substernal goiter signs include the absence of a connection between the neoplasm and the thyroid gland, immobility when swallowing.
Treatment
Surgical treatment
Taking into account the high risks of respiratory tract compression and life-threatening complications, conservative tactics are considered inappropriate. A confirmed diagnosis of a retrosternal goiter is an absolute indication for surgical intervention. In case of unilateral lesion, hemithyroidectomy is recommended, which allows you to save part of the thyroid tissue. Bilateral lesion requires radical thyroidectomy.
The technique of the operation is selected by the doctor individually after receiving the results of the examination. With the euthyroid form of goiter, patients do not need special training. In case of critical hormonal disorders, it is necessary to achieve a state of euthyroidism before surgery. To improve the long-term prognosis, before the removal of the gland, the correction of concomitant diseases of the cardiovascular system is carried out.
Pharmacotherapy
With the preservation of a part of the thyroid tissue that is capable of producing thyroid hormones, patients do not need drug therapy. Thyroxine replacement treatment is indicated for total thyroidectomy, after which the patient develops iatrogenic hypothyroidism. In this case, a lifetime intake of individually selected doses of the hormone is prescribed under the control of TSH levels and with regular examinations by an endocrinologist.
Prognosis and prevention
Although the posterior location of the goiter is recognized as prognostically unfavorable, a timely operation eliminates the risk of suffocation and other complications. In the future, a dispensary observation by an endocrinologist is required at least 1 time a year with the delivery of hormone tests. Prevention of the disease consists in the elimination of iodine deficiency, quitting smoking, avoiding occupational hazards, especially radiation exposure.