What Is the Isthmus?

What Does the Isthmus Have to Do With Your Health and Cancer?

The isthmus connects each side of the thyroid.
The isthmus connects each side of the thyroid. Purestock/Getty Images

Most people have a hard time pronouncing isthmus, let alone tell you the definition. Perhaps you know that a narrow strip of land surrounded by water that connects two pieces of larger land is referred to as an isthmus (pronounced is-muh s), but you may be wondering what an isthmus has to do with your health.

Isthmus and Your Health

In medicine, the isthmus commonly refers to tissue that forms a bridge between the two lobes of the thyroid, but can reference other points in the body as well, such as isthmus of the eustachian tubes and isthmus of the uterus.

The thyroid is a butterfly-shaped gland in the front of the neck, under the larynx (or voice box). It is the isthmus that connects the "butterfly wings" or lobes together. The thyroid gland regulates metabolism by secreting hormones that affect calcium levels in the blood, and the heart rate, body temperature, and energy levels.

Thyroid Cancer and the Isthmus

Diseases can affect the thyroid, where the size or activity may become abnormal. A healthy thyroid is about the size of a US quarter and can't usually be seen or felt through the skin. A swollen thyroid (called a goiter) on the other hand may look or feel like a lump in the front of the neck.

The thyroid may have trouble producing and secreting the right amount of hormones the body needs. Too much thyroid hormone (hyperthyroidism) may cause weight loss or feeling overheated and sweaty. It may also may cause chest pain, cramps, and diarrhea.

If the thyroid hormone level is too low (hypothyroidism), weight gain, feeling cold, and dry skin and hair may be symptoms.

Any symptoms of abnormal thyroid activity may lead your doctor to test you for abnormal levels (too low or too high) of thyroid-stimulating hormone (TSH) in the blood or for abnormally high levels of calcium.

To fully assess your health, your doctor may start with:

  • A Physical exam (of the neck, thyroid, voice box, and lymph nodes in the neck to check for unusual growths (nodules) or swelling)
  • Blood tests
  • Ultrasonography (An ultrasound device which uses sound waves to identify nodules)
  • Radionuclide scanning (A scan that uses a small trace of radioactive material to make nodules show up on a picture)
  • Biopsy

If a biopsy indicates the presence of cancer cells in the thyroid, parts of the thyroid gland may have to be removed (called a thyroidectomy) to treat the disease. There are several different types of thyroidectomies based how much of the gland has to be removed.

The isthmus may be removed during a thyroidectomy to treat thyroid cancer. The removal of the isthmus is called an isthmusectomy.

Types Of Thyroidectomies

  1. Total thyroidectomy (removal of the entire thyroid gland)
  2. Thyroid lobectomy (removal of a whole lobe)
  3. Partial thyroid lobectomy (partial removal of a lobe)
  4. Thyroid lobectomy with isthmusectomy (removal of the isthmus, in addition to a lobe)
  5. Subtotal thyroidectomy (removal of a whole lobe, isthmus and a partial lobe)


Endocrine Web. Thyroid Cancers. 

Endocrine Surgery and Oncology UCSF. Thyroidectomy. 

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