What is Substernal Goiter (enlarged thyroid gland)?
A goiter is a term for an enlarged thyroid gland. The thyroid is a gland which lies at the base of the neck and it can grow forward or to the sides. It’s covered by thin muscles, a layer of fatty tissue, and skin. This allows it to grow without meeting much resistance. When it gets bigger, it’s usually easy to see and feel. However, body size and shape can sometimes make this a bit tricky.
Sometimes, the thyroid can grow downwards, passing into the chest cavity. This is known as a “substernal goiter”, also called a “retrosternal goiter”. This can occur with one or both parts (lobes) of the thyroid gland. When this happens, it can cause the windpipe (trachea), and less commonly the food pipe (esophagus) or blood vessels, to be squashed or pushed to the side. Studies have shown that the windpipe is compressed in about 35% to 73% of substernal goiters.
Around 10% of substernal goiters are found at the back of the chest cavity (posterior mediastinum). And out of that 10%, 90% are on the right side, because the left-sided subclavian arteries (the artery that supplies blood to the left arm) and the aortic arch (the main artery that brings oxygenated blood from the heart to the rest of the body) don’t leave room for enlargement on the left side.
Some studies define a substernal goiter as any part of the thyroid that extends beneath the opening to the chest (thoracic inlet), while others say there needs to be 50% or more of the thyroid below this opening. The difference in these definitions is why study results might vary. If the lower part of the thyroid goes back above the thoracic inlet when the patient stretches their neck, this is seen as a positional abnormality and is not considered a substernal goiter.
What Causes Substernal Goiter (enlarged thyroid gland)?
Substernal goiter, also known as a type of thyroid enlargement, occurs in the same way as a cervical goiter, which is a swelling in the neck. This enlargement tends to move downwards from the neck into the chest area. Substernal goiters receive their blood supply mainly from the lower thyroid artery in the neck, indicating their origin.
Only in very rare cases (about 2% of the time) does thyroid tissue, which is referred to as ‘ectopic’, grow directly in the chest, causing a substernal goiter.
Sometimes, neck goiters that have descended into the chest area appear to be separate from the thyroid tissue in the neck, making it seem like isolated cases inside the chest. There might be a connection between a substernal goiter and a cervical goiter through a fascial extension, a type of tissue that helps organs stay in place.
Risk Factors and Frequency for Substernal Goiter (enlarged thyroid gland)
Substernal goiter, a type of thyroid condition, is not commonly found because there aren’t enough studies on it. However, with the increased use of medical imaging, doctors are expecting to find more cases. People over the age of 50, especially females, are more likely to be diagnosed with substernal goiter. Interestingly, in a recent report, around 7% of people who had thyroid surgery also had a substernal goiter.
- Substernal goiter’s prevalence in the general population is unclear due to a lack of studies.
- Due to more use of medical imaging, doctors expect to detect more cases.
- This condition is often diagnosed in people over the age of 50 and is four times more common in women.
- In a recent surgical review, about 7% of patients who had thyroid surgery were found to have substernal goiter.
Signs and Symptoms of Substernal Goiter (enlarged thyroid gland)
People with substernal goiter often don’t show any symptoms and it might only be discovered during a routine chest X-ray, CT, or MRI. When symptoms do occur, they are usually due to the thyroid gland pressing on nearby structures. For example, patients may experience breathlessness during physical activity, a feeling of choking, coughing and stridor, which is a high-pitched, wheezing sound usually heard when breathing in. Other symptoms can include difficulties in swallowing, a hoarse voice, visibly enlarged veins in the neck, or symptoms of superior vena cava syndrome, which is a group of symptoms caused by blockage of the superior vena cava (the large vein that carries blood from the upper half of the body back to the heart).
- Breathlessness during physical activity
- Feeling of choking
- Coughing
- Stridor (a high-pitched, wheezing sound usually heard when breathing in)
- Difficulties in swallowing
- Hoarse voice
- Visibly enlarged veins in the neck
- Symptoms of superior vena cava syndrome
In some cases, patients can also experience symptoms of over- or under-production of thyroid hormones (hyperthyroidism or hypothyroidism). If the thyroid gland is compressing the trachea, there might be an audible noise when breathing in. The Pemberton sign can be used to examine patients for substernal goiter. This sign is positive if patients develop facial congestion, bulging of neck veins, hoarse voice, or breathe heavily after raising their arms above their head for about a minute. An effect called “corking” can cause symptoms in some patients with substernal goiters. It either happens when the thyroid gland descends into the chest cavity or the chest opening moves upwards. Symptoms from “corking” may occur when patients with substernal goiter move their neck.
Testing for Substernal Goiter (enlarged thyroid gland)
Your thyroid stimulating hormone (TSH) level is typically checked first if your doctor suspects an issue with your thyroid. If the TSH level is abnormal, other hormones like total or free T4 and T3 may be tested to further assess your thyroid’s functioning. Looking at antibodies called anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin can also provide information about a condition called Hashimoto’s thyroiditis, which can exist alongside a goiter (an enlarged thyroid).
A thyroid ultrasound is usually done to examine the part of the goiter present in the neck. However, this method can’t be used to study the part of the goiter that extends into the chest, as the ultrasound waves can’t penetrate bone or travel well through air in the lungs.
An X-ray of the chest might show a mass called an upper mediastinal mass and reveal if your windpipe (or trachea) is deviated or compressed due to the goiter.
Although X-rays provide some information, a computed tomography (CT) scan or a magnetic resonance imaging (MRI) of the chest is preferred. These can accurately measure the size and extent of the goiter and reveal how it relates to other structures in your body. Be aware that a special dye (or iodinated contrast) used in some CT scans might interfere with following thyroid scans until it’s cleared from your body.
If you’re having trouble swallowing (or dysphagia), tests like barium esophagography or upper endoscopy can be considered. However, these aren’t part of the routine check-ups.
Interestingly, even if you don’t have any symptoms, a breathing test known as a pulmonary function test may still show abnormalities. This is because the goiter can affect both your in-breath and out-breath flows, suggesting an obstruction in your upper airway. It’s a useful test as it can help differentiate from other breathlessness causes, like chronic obstructive pulmonary disease (COPD).
Worth knowing is that thyroid cancer has been noted in 0-19% of cases with this type of goiter. A more recent guideline puts the risk of cancer in these cases at around 9% to 13%. Even though, a test called fine-needle aspiration is typically used to check for thyroid cancer, it’s not recommended for these goiters. This is because the test poses a risk of causing bleeding inside the goiter or puncturing a lung (known as pneumothorax). So, it’s best avoided in these cases.
Treatment Options for Substernal Goiter (enlarged thyroid gland)
If a patient has an underactive or overactive thyroid, prompt treatment is important. Surgery is typically the recommended treatment for substernal goiter, a condition where the thyroid gland grows downward into the chest, especially if the patient is experiencing symptoms. However, for those not having symptoms, the approach to treatment isn’t straightforward and can vary.
In these situations, if the patient doesn’t have problems with breathing or significant compression of the windpipe due to the goiter, they can be observed over time. This monitoring would track any changes in the size of the goiter, the diameter of the windpipe, and thyroid function. However, during this observation period, it’s important that the patient stays clear of iodine-containing supplements, multivitamins, and medications, as well as iodinated contrast agents used in certain imaging procedures, to avoid inducing an overactive thyroid.
If the goiter grows or compresses the windpipe over time, or if the patient develops an overactive thyroid, surgery will be necessary. Patients with an overactive thyroid may need to take certain medications before surgery to ensure a safe procedure.
Some experts advocate for early surgical intervention even for those without symptoms, due to concerns about potential future goiter growth and compression of structures in the chest. The idea is that surgery might become riskier or more complicated if delayed.
Research has shown that when compression of the windpipe progresses to 35% or more, surgery often results in significant improvement of symptoms.
Attempts to control the growth of the goiter with levothyroxine (a medication that is similar to thyroxine, a hormone produced by the thyroid) are generally ineffective. Radioactive iodine treatments are also not recommended, even if the patient has an overactive thyroid.
The surgery usually performed is a total thyroidectomy, removing the entire thyroid gland, usually through a cervical (neck) approach. In some cases, however, the goiter may extend farther into the chest, requiring different surgical approaches like partial sternotomy or thoracotomy.
When deciding the best treatment for a patient, it’s critical to consider various factors including their symptoms, clinical findings, risks, and benefits. While surgery is required in cases where the goiter is causing severe symptoms or threatening vital structures in the chest, the decision isn’t as clear for those without symptoms. That’s why it’s essential to try and strike a balance between careful observation and proactive surgical intervention.
What else can Substernal Goiter (enlarged thyroid gland) be?
When identifying the cause of a possible medical issue, doctors might need to consider the following potential conditions:
- Thymoma and thymic carcinoma (types of tumors found in the thymus, a small organ that forms part of the immune system.)
- Bronchogenic cyst (a congenital cyst consisting of fluid-filled sacs that are formed during the fetal stage.
- Lymphoma (cancer of a part of the immune system called the lymphatic system.)
- Teratoma and germ cell tumors (an abnormal growth of cells, which can contain many different types of tissues.)
- Pericardial cyst (a rare, harmless cyst on the membrane around the heart.)
- Ganglioneuromas and other neurogenic tumors of the posterior mediastinum (a benign tumor that can occur anywhere along the sympathetic nervous system, often found in a part of the torso called the mediastinum.)
What to expect with Substernal Goiter (enlarged thyroid gland)
There hasn’t been any research conducted on the natural progression of substernal goiter, which is a kind of enlarged thyroid that lies beneath the breastbone. This means that there are no studies comparing the outcomes of simply monitoring the condition versus having surgery. The idea that a substernal goiter will continue to grow and eventually lead to symptoms or severe difficulty in breathing if left untreated has also not been demonstrated in any research studies.
Possible Complications When Diagnosed with Substernal Goiter (enlarged thyroid gland)
Substernal goiter, or a large swelling in your neck due to an abnormally large thyroid, can affect the windpipe, the veins in your neck, and other structures inside your chest. If a substernal goiter continues to grow, it can cause serious breathing problems, which can be life-threatening. For instance, if the goiter suddenly gets bigger because of bleeding or if a neck infection worsens, it can squeeze your airway and make it hard to breathe.
Also, researchers have found that people with substernal goiter are more likely to have thyroid cancer, specifically papillary thyroid cancer. The study found that, out of the people operated for substernal goiter, 72% had the cancer in their chest area, while 28% had it in their neck. When looking at each individual nodule rather than the person as a whole, the occurrence of papillary thyroid cancer was significantly more common in substernal goiter compared to neck goiter (31% versus 19% probability).
Furthermore, substernal goiter can cause other problems like phrenic nerve paralysis, Horner’s syndrome (which is caused by compression of the nerve chain in the neck), jugular vein thrombosis (a blood clot in the neck), cerebrovascular steal syndrome (a condition where blood is rerouted from one area of the body to another), and superior vena cava syndrome (a blockage of the vein that carries blood from the head and arms to the heart).
Possible Complications:
- Problems with surrounding structures in the chest
- Life-threatening breathing issues
- Papillary thyroid cancer
- Phrenic nerve paralysis
- Horner syndrome
- Jugular vein thrombosis
- Cerebrovascular steal syndrome
- Superior vena cava syndrome
Preventing Substernal Goiter (enlarged thyroid gland)
Put simply, preventing a condition called goiter can also prevent the development of a similar condition known as substernal goiter. A goiter is an abnormal enlargement of the thyroid gland, and if it’s not prevented or treated, it tends to keep growing. This ongoing growth can eventually lead to the collection of nodules, or small lumps, and can change from a non-harmful goiter to a harmful multinodular goiter. As time passes, the goiter becomes larger, and a bigger goiter often results in lower levels of a hormone known as TSH. It’s believed that certain physical factors contribute to the growth of the thyroid gland into a new area called the upper mediastinum.
So, the only way to prevent a substernal goiter is to prevent a goiter from developing in the first place. The best preventive measures at an individual level involve maintaining appropriate iodine intake according to one’s age or condition (150 micrograms per day for adults and teenagers, 220 for pregnant women, 290 for breastfeeding mothers, 90-120 for 1 to 11-year-old children, 110-130 for infants) and avoiding certain goiter-inducing substances in one’s diet or medication. However, please note that goiters caused by autoimmune thyroid disease, or certain genetic disorders, need medical help and can’t be prevented.
The best way to guard against goiters involves being knowledgeable about the importance of sufficient dietary iodine, avoiding goiter-promoting substances, and making sure to have regular health check-ups every year.
