A team of doctors in the Netherlands may have discovered a new pair of salivary glands located in humans' heads, according to a study recently published in the journal Radiotherapy and Oncology—a development that would mark the first discovery of a new human organ in nearly three centuries, Katherine Wu reports for the New York Times.
Wu reports that, according to any modern anatomy book, humans have three major types of salivary glands: one set located near the ears, another set located under the jaw, and a third set located below the tongue.
Salivary glands perform many tasks, including lubricating our mouths, carrying food chemicals to the microscopic cells responsible for sensing them, fighting germs, speeding up wound closures, and making it easier for us to spit and swallow, Wu notes. According to Matthijs Valstar, a surgeon and researcher at the Netherlands Cancer Institute and an author of the new study, our salivary glands produce a quart of spit each day, which play a role in "a lot of things that make you enjoy life."
But our salivary glands also are very sensitive, and a single misguided zap could permanently hurt the delicate tissue, Wu reports. As such, doctors who administer radiation therapy take several precautions to avoid damaging them, she notes.
Now, Valstar and his colleagues believe they may have discovered new salivary glands. "[W]e think there is a fourth," Valstar said.
For the study published last month, the researchers examined scans from a machine designed to visualize tissues in high detail and dissected tissue from two cadavers. The researchers focused on 100 subjects with prostate or urethral gland cancer, but the patient sample included just one woman.
When the researchers viewed the images, they noticed two unfamiliar structures tucked away under the base of the human skull, where the nasal cavity meets the throat. The researchers described the structures as a pair of flat, spindly glands that were a few inches long and draped inconspicuously over the tubes connecting the ears to the throat.
After noticing the unfamiliar glands on the scans, the researchers dissected tissue from two cadavers. The researchers not only found the glands, but they discovered that the glands were similar to the salivary glands below the tongue. The newly found glands were connected to large draining ducts, which suggested that they were funneling fluid from one place in the body to another, the researchers said.
Wouter Vogel, a radiation oncologist at the Netherlands Cancer Institute and an author of the study, said he understands how anatomists may have missed the fourth pair of salivary glands for all this time. The glands' "location is not very accessible, and you need very sensitive imaging to detect" them, Vogel said. In comparison, the body's other, larger salivary glands are located closer to the surface of the skin and may be poked and prodded, he explained.
If the researchers' findings are confirmed, it would mark the first time in about 300 years that a new human organ was discovered, Wu reports.
Valerie Fitzhugh, a pathologist at Rutgers University who wasn't involved in the study, said although the study was small, "it seems like they [researchers] may be onto something." And "[i]f it's real, it could change the way we look at disease in this region," she said.
For instance, Vogel said the discovery may help researchers understand why people who undergo radiation therapy for head and neck cancers often report having chronic dry mouth and issues swallowing. He explained that, since doctors were unaware of the obscure glands, "nobody ever tried to spare them" from damage tied to radiation.
But some observers aren't yet convinced that Vogel and his colleagues have, in fact, discovered a fourth set of salivary glands.
Alvand Hassankhani, a radiologist at the University of Pennsylvania, said he's hesitant to call the structures the researchers discovered "new organs," because people have nearly 1,000 minor salivary glands dispersed around the lining of their mouths and throats. Hassankhani said it's possible the researchers may have detected minor glands rather than a fourth set of major salivary glands.
Yvonne Mowery, a radiation oncologist at Duke University, said she'd be "quite shocked that we are in 2020 and have a new structure identified in the human body." She added, "To have it one clinical data set is never enough."
Fitzhugh noted that the study has some limitations, including its small patient population and lack of diversity, as well as the imagining techniques used by the researchers, which Fitzhugh said is tailored to identify tumorous growths in a specific patient population.
Fitzhugh recommended that the researchers consider widening their experiment to include a new group of patients and other imagining methods. "You'd like to see more balance," she said (Wu, New York Times, 10/19).
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