The medical researchers first came across the body part, which they propose naming tubarial glands, during a scan designed to look for tumorous growths.
"We thought it wasn't possible to discover this in 2020," Mr Valstar said.
"It's important it's replicated and it should be done with different series of patients. It's important to have confirmation of new medical findings."
The glands cannot be seen with conventional methods of medical imaging like ultrasound, CT scans or MRI, the study authors said.
The "unknown entity" was only identified when the doctors were using an advanced and new type of scan called PSMA PET/CT that has been used to detect the spread of prostate cancer.
PSMA PET is shorthand for prostate-specific membrane antigen imaging using positron emission tomography.
Salivary glands show up clearly on this highly sensitive kind of imaging.
"As far as we knew, the only salivary or mucous glands in the nasopharynx are microscopically small, and up to 1000 are evenly spread out throughout the mucosa. So, imagine our surprise when we found these."
Many great scientific discoveries "come as a surprise — an incidental finding," Joy Reidenberg said, a professor of anatomy at the Icahn School of Medicine at Mount Sinai in New York City, who wasn't involved in the study.
"Luckily, these researchers were tuned into the data, and were anatomically savvy enough to note the unusual brightness in a region that was not thought to contain any salivary glands," Ms Reidenberg said.
"As the famous (late French biologist) Louis Pasteur once said: 'Chance favours the prepared mind.'"
It was a matter of debate whether the tubarial glands were a completely new organ or could be considered part of the salivary gland organ system, according to the study.
"These findings support the identification of the tubarial glands as a new anatomical and functional entity," the study said, published in the journal Radiotherapy and Oncology.
The glands could be newly discovered, "but it is difficult to exclude that these might represent groups of minor salivary glands," Dr Valerie Fitzhugh said, the interim chair of pathology at Rutgers New Jersey Medical School and Rutgers Robert Wood Johnson Medical School. Dr Fitzhugh wasn't involved in the study.
Because the study concentrated on a small number of patients who were mostly male and used specific rather than standard tests, examination of more women and healthier patients would allow for better data, Dr Fitzhugh said.
Overall, there is "still much to learn about the human body," she said, "and technology is allowing us to make these discoveries. This might be the first of some exciting discoveries within the body."
Radiotherapy can damage salivary glands, which can lead to dry mouth and trouble swallowing, speaking and eating.
"For most patients, it should technically be possible to avoid delivering radiation to this newly discovered location of the salivary gland system in the same way we try to spare known glands," study author Wouter Vogel said.
"Our next step is to find out how we can best spare these new glands and in which patients.
"If we can do this, patients may experience less side effects which will benefit their overall quality of life after treatment."