The human body, ever-mysterious, yields a surprise 12/07/2020
This illustration shows the location of the newly-identified tubarial glands. Image credit: Netherlands Cancer Institute.
Modern anatomy books display three major salivary glands: one set near the ears, another below the jaw and a third under the tongue. But this year, Dutch scientists may have found a new pair at the top of our throats - basically, in the center of our heads.
At about one and a half inches long on average, the glands are surprisingly big. And their discovery raises a practical consideration: doctors need to avoid blasting them when doing radiation therapy.
A larger consideration: This is the first discovery of a new gland in some 300 years (Lydiatt and Boucher, 2012). We clearly don't know as much about the human body as we thought we did, so we all need to stay humble!
How we found them
The new glands appeared in an area called the nasopharynx. As far as scientists knew, the only salivary glands there were microscopically small, among up to 1,000 evenly spread through the moist tissue in the nose, mouth, and top of the digestive tract. These minor, minuscule salivary glands provide the main lubricant in the mouth in the form of saliva that contains chemicals preventing bacterial infections (Holmberg et al., 2014, Paula et al., 2017). But the new gland is much larger and eventually may be classified as the fourth major salivary gland.
The first hint of its existence emerged while a Netherlands radiation oncologist, Outer Vogel, was looking at special imaging that probed for damage to salivary glands after patients received radiotherapy for cancer in the head, neck, or brain. It’s important to avoid these injuries, which can leave patients with digestive and speech problems or a tendency to oral infections.
Vogel was using a technique designed to catch cancer cells by binding to a chemical called prostate-specific membrane antigen, a useful marker for prostate cancer. He and his team had found it also identifies salivary gland cells, which express the same chemical. Low levels of the antigen occur in many noncancerous body tissues and fluids, including the mammary glands, pancreas, thyroid gland, breast milk, placenta, amniotic fluid, and semen (Olsson et al., 2004).
When Vogel first saw signs of the unexpected cells, he called for backup help. A team of more than a dozen researchers examined scans of more than 100 patients with prostate or urethral gland cancer. They found signals indicating the salivary gland in those other patients, and that the glands came as a pair. Dissecting two human cadavers, the team found the salivary gland tissue in the dead people as well (Kwon et al., 2020, Valstar et al., 2020). The new structures looked something like known glands that lie below the tongue and hooked onto large ducts.
Why might we have missed these glands before?
Other salivary glands are visible during surgery but these could only be seen during a nasal endoscopy when doctors insert a tube with a tiny camera to take pictures of the nose and sinuses. The special imaging technique also allowed Vogel to distinguish the tissue as salivary glands, which he named the “tubarial glands” after their location, above a structure called the torus tubarius.
The discovery could be good news for patients with head and neck cancers or tumors in the tongue or throat. Often when they undergo radiation therapy, they end up with chronic dry mouth and swallowing problems. Doctors already try to avoid the major salivary glands during radiation treatment, which is the very task Vogel was working on. Now they will try to avoid the just-discovered ones as well.
Anatomy knowledge is changing
As imaging and other medical techniques become more sophisticated, who knows what we’ll see? Five years ago, scientists found a network of vessels extending from the lymphatic system into a membrane that envelops the brain and the spinal cord, a possible explanation for how immunity affects our brains and mental health (Devlin, 2015).
Then we learned more about the tissues that connect the intestines to the abdominal wall. They turn out to be continuous rather than fragmented.
In 2018, a third discovery emerged. Scientists announced the discovery of fluid-filled spaces in connective tissues lining the digestive tract, lungs, and urinary systems, tissues once thought to be a dense wall of collagen (Benias et al., 2018).
Studying these structures may lead us to useful insights about how our bodies work in sickness and in health (Kumar et al., 2019). What other discoveries about human anatomy may lie before us? We will keep you posted. In the meantime, when salivating over the prospect of a seared salmon fillet, remember to thank the contribution of your long unknown and unsung tubarial glands!
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