Intrathoracic goiter
Advanced Thoracic Surgery, Akademisyen Kitabevi, ss.205-214, 2021
- Yayın Türü: Kitapta Bölüm / Araştırma Kitabı
- Basım Tarihi: 2021
- Yayınevi: Akademisyen Kitabevi
- Sayfa Sayıları: ss.205-214
- Sağlık Bilimleri Üniversitesi Adresli: Evet
Özet
Intrathoracic goiter refers to a condition where the thyroid gland grows larger than its normal size based on the patient's age and gender. The enlargement of the thyroid gland usually occurs in the front part of the neck, due to it not being limited by weak neck muscles, subcutaneous tissue, or skin. If the enlargement of the thyroid gland continues downwards and enters the thoracic cavity, it is called intrathoracic, substernal, or retrosternal goiter. In fact, intrathoracic and nodular goiter are not different entities but rather anatomical variations of each other. The reason for these various descriptive terms is the lack of a precise definition of intrathoracic goiter and a lack of consensus on its definition. The most commonly accepted definition of intrathoracic goiter includes the condition where the goiter extends below the thoracic inlet or where more than 50% of its mass is located below the sternal notch.Globally, there are over 80,000 patients who undergo surgical procedures for inflammatory, neoplastic, and endocrine abnormalities of the thyroid gland. This accounts for almost 5% of all resected mediastinal tumors and is usually found in the pretracheal area as an extension of the thyroid goiter in the neck. The incidence of intrathoracic goiter varies significantly between 0.2% and 45% depending on the criteria used to define such goiters. The prevalence of intrathoracic goiter in the general population is unknown due to a lack of epidemiological studies. With the widespread use of imaging, more cases of intrathoracic goiter are expected to be considered clinically. It is more commonly diagnosed after the age of 50 and is four times more common in women.Intrathoracic goiter presents specific challenges in preoperative evaluation and surgical management. The classical indications for surgery include pressure and cosmetic effects, and a higher than expected incidental malignancy rate is found in multinodular goiters with retrosternal and intrathoracic extensions.The causes of goiter are diverse, including genetic, toxic (smoking), natural, iodine deficiency, hormonal or infiltrative pathology, and inflammatory disorders of the thyroid gland such as autoimmune thyroiditis. Iodine deficiency is generally accepted as an important environmental factor contributing to increased thyroid nodularity.The origins of intrathoracic goiter can be divided into two groups. The first group is true, primary intrathoracic or ectopic goiter. This occurs congenitally in the mediastinum independent of the thyroid gland in the neck. It has been found that the blood supply comes from the thyroid ima artery, aorta, subclavian artery, or internal mammary artery, but it does not have a direct connection to the cervical thyroid gland. This group accounts for less than 1% of surgically removed goiters. The other most common group defines acquired intrathoracic goiter, which initially originates from the cervical thyroid gland and descends into the mediastinum over time. Occasionally, a cervical goiter that descends into the chest loses its connection with the thyroid tissue in the neck and appears as a separate entity in the chest. An intrathoracic goiter can only be connected to a cervical goiter through a fascial extension.The mass of the goiter is anatomically limited by the thyroid and cricoid cartilage above, the prevertebral fascia at the back, and the cervical fascia and sternocleidomastoid muscles at the front, with the weakest supporting structure being the thoracic inlet. Since there is no anatomical structure between the lower part of the thyroid and the substernal region, the growth of the gland can only occur downwards. The tendency of the mass to be pulled downwards during swallowing, negative pressure in the thorax during respiration, and gravity contribute to the extension of the thyroid gland into the thorax. Other factors that may be associated with the development of intrathoracic goiter include a short neck, short cervical trachea, and well-developed neck muscles.