Cancer and the Isthmus of Thyroid

Structural tissue often impacted during thyroid cancer

Female doctor examining male patient's glands in clinic
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To many, the word "isthmus" refers to a narrow strip of land surrounded by water which connects two pieces of larger land.

When used in a medical capacity, it suggests something similar: a narrow organ, passage, or piece of tissue that connects two larger parts. It can be applied to the ears (isthmus of the Eustachian tubes), uterus (isthmus of the uterus), brain (isthmus of cingulate gyrus) and thyroid gland (isthmus of the thyroid).

It is in this latter capacity — as part of the thyroid — that the function of the isthmus takes on greater significance during cancer treatment.

The Role of the Isthmus of the Thyroid

The isthmus is the tissue that forms a bridge between the two lobes of the thyroid and serves as a covering for two rings of the windpipe (trachea). The thyroid itself is a butterfly-shaped gland in the front of the neck situated just beneath the larynx.

The thyroid gland regulates the body's metabolism by secreting hormones that regulate temperature, growth, muscle strength, appetite, and the health of your heart, brain, kidneys, and reproductive system. The isthmus is there purely to support and stabilize these organs.

Complications of the Thyroid Glands and Isthmus

A healthy thyroid is about the size of a quarter and usually can't be felt or seen through the skin. By contrast, a swollen thyroid (called a goiter) may look or feel like a lump in the front of the neck.

The thyroid can sometimes have problems secreting the right amount of hormones into the body. Too much hormone (a condition called hyperthyroidism) can cause weight loss, sweatiness, chest pain, cramps, and diarrhea. Too little (hypothyroidism) and a person can gain weight, feel cold, and have dry skin or hair.

Complications of the isthmus include agenesis (the absence of the isthmus due to a birth defect) or direct injury (usually in association with one or both lobes).

Any abnormalities in thyroid function will lead your doctor to measure the levels of thyroid-stimulating hormone (TSH) in your blood. Other evaluations can include:

  • a physical exam of the neck, thyroid, trachea, and lymph nodes to check for swelling or unusual growths
  • ultrasonography, an imaging device that uses ultrasonic sound waves
  • radionuclide scanning which uses a trace amount of radioactive material to highlight the nodules during imaging
  • biopsy of thyroid tissue

Removal of the Thyroid and Isthmus

If a biopsy indicates the presence of cancer in the thyroid, parts of the thyroid gland may have to be removed. This procedure, called a thyroidectomy, can involve the removal of one or both lobes. If the cancer is invasive (spreading beyond the site of the original tumor), the isthmus may also need to be removed in a procedure called an isthmectomy.

There are several different types of thyroidectomy based how much of the gland is to be removed:

  • Total thyroidectomy (removal of the entire thyroid gland)
  • Thyroid lobectomy (removal of a single lobe)
  • Partial thyroid lobectomy (partial removal of a lobe)
  • Thyroid lobectomy with isthmectomy (removal of a lobe and the isthmus)
  • Subtotal thyroidectomy (removal of an entire lobe, isthmus and a partial lobe)

Source

  • Mathur, A. and Doherty, G. "Chapter 1: Thyroidectomy and Neck Dissection." Current Procedures: Surgery. 2010; New York: McGraw-Hill.

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