You have one thyroid gland. It sits in the front of your neck, just below the Adam’s apple, and wraps around the windpipe in two halves connected by a thin bridge of tissue. Because those two halves (called lobes) look distinct on imaging or during surgery, it’s easy to wonder whether they count as separate glands. They don’t. The thyroid is a single organ shaped like a butterfly, with a right lobe, a left lobe, and a connecting strip called the isthmus.
Why It Looks Like Two Glands
Each lobe of the thyroid sits on either side of the windpipe, extending from roughly the level of the thyroid cartilage (the firm bump in your throat) down to about the sixth ring of the trachea. The isthmus, the narrow band connecting them, lies across the second and third tracheal rings. On an ultrasound or CT scan, the two lobes can appear quite separate, especially if the isthmus is thin. But they share the same blood supply, the same nerve connections, and the same embryonic origin. Functionally and anatomically, it’s one gland.
The Hidden Third Lobe
Up to about 44 to 50 percent of people have something extra: a small fingerlike projection of thyroid tissue extending upward from the isthmus, called the pyramidal lobe. It’s a remnant of the path the thyroid traveled during fetal development, when it migrated from the base of the tongue down to its final position in the neck. The pyramidal lobe is often too small to feel on a physical exam, but surgeons find it in nearly half of all thyroid operations. It doesn’t change the gland count. It’s simply a normal anatomical variation of the same single thyroid.
Ectopic Thyroid Tissue
In rare cases, small deposits of thyroid tissue end up in unexpected places. This happens when bits of the gland get left behind during that fetal migration from the tongue to the neck. These deposits, known as ectopic thyroid tissue, show up in fewer than 1 percent of people who undergo thyroid surgery. They’ve been found in the base of the tongue, below the jaw, along the side of the neck, and even in the chest. These aren’t extra thyroid glands in any meaningful sense. They’re stray clusters of thyroid cells, often too small to produce significant amounts of hormone on their own.
Born With Only One Lobe
On the other end of the spectrum, some people are born missing an entire lobe. This condition, called thyroid hemiagenesis, occurs in roughly 0.05 to 0.5 percent of the population. The left lobe is absent about 80 to 87 percent of the time, for reasons researchers still don’t fully understand. Many people with hemiagenesis never know it until an imaging scan reveals the missing lobe. The remaining lobe often compensates by growing slightly larger and producing enough hormone to keep the body running normally, though these individuals do have a higher chance of developing thyroid problems over time.
What the Thyroid Actually Does
Your single thyroid gland produces two main hormones that regulate metabolism, the process your body uses to convert food into energy. The gland releases a largely inactive form (T4), which other organs then convert into the active form (T3) that directly influences your cells. Together, these hormones affect heart rate, body temperature, weight, and energy levels. In infants, they’re critical for brain development.
The thyroid also produces a separate hormone called calcitonin, which helps regulate calcium levels in the blood. Calcitonin plays a much smaller role in daily metabolism compared to the main thyroid hormones.
Don’t Confuse Them With Parathyroid Glands
Tucked behind the thyroid are four tiny, separate glands called the parathyroid glands. About 80 percent of people have exactly four, two embedded in each lobe of the thyroid. Despite their name and location, the parathyroids are entirely different organs with a different job: they regulate calcium and phosphorus levels in the blood and bones. Some people have parathyroid glands in unusual locations, such as along the esophagus or in the chest, but these are still parathyroid glands, not thyroid tissue.
What Happens When Part of It Is Removed
Because the thyroid has two distinct lobes, surgeons can remove just one (a lobectomy) or the entire gland (a total thyroidectomy). If only one lobe is taken out, the remaining lobe often produces enough hormone on its own, and many patients avoid the need for daily hormone replacement medication. Studies have shown that people who keep one lobe tend to have more stable hormone levels in the year following surgery compared to those who lose the entire gland. If the whole thyroid is removed, lifelong hormone replacement becomes necessary.