Seromucinous Hamartoma: Understanding Your Pathology Report

Section Editor: Jason Wasserman MD PhD FRCPC
July 15, 2026

A seromucinous hamartoma is a rare, noncancerous (benign) growth found in the nasal cavity or sinuses. The term hamartoma refers to a mass composed of an abnormal mixture of cells and tissues that normally belong in the area but have grown in a disorganized manner. “Seromucinous” refers to the combination of serous (watery) and mucinous (mucus-producing) glandular cells that make up the growth. A seromucinous hamartoma is not a cancer. It does not invade surrounding tissues or spread to other parts of the body, and it typically grows slowly. Its main importance is that, under the microscope, it can closely resemble a slow-growing cancer, so it needs to be correctly identified by a pathologist.

This article will help you understand the findings in your pathology report, what each term means, and why it matters for your care.

What causes a seromucinous hamartoma?

The exact cause of a seromucinous hamartoma is not known. These growths are thought to arise from disorganized development of the glands and tissues that normally line the nasal cavity and sinuses. They are not linked to any known environmental exposure or lifestyle factor, and they do not appear to be inherited. Some people with a seromucinous hamartoma also have long-standing sinus inflammation or nasal polyps, and the two are sometimes found together, but it is not clear whether one causes the other.

Where are seromucinous hamartomas found?

A seromucinous hamartoma most often arises in the back part of the nasal cavity, particularly from the posterior nasal septum (the wall of cartilage and bone that divides the two sides of the nose) or the nasopharynx (the upper part of the throat behind the nose). Less commonly, it develops on the side wall of the nasal cavity or in one of the paranasal sinuses. These growths are usually small and localized, typically measuring between about half a centimeter and six centimeters. They are most often found in middle-aged and older adults.

What are the symptoms?

Many seromucinous hamartomas cause no symptoms at all and are found incidentally, meaning they turn up unexpectedly during imaging or surgery performed for another reason, such as chronic sinus problems or nasal polyps. When symptoms do occur, the most common is nasal obstruction on one side, meaning difficulty breathing through that nostril. Other symptoms may include nosebleeds, nasal discharge, or a sensation of fullness in the nose. Larger growths can cause more noticeable blockage or discomfort.

How is the diagnosis made?

The diagnosis of a seromucinous hamartoma is made after a pathologist examines tissue under the microscope. The tissue may be obtained by biopsy during nasal endoscopy, or the growth may be removed entirely and examined. Imaging studies such as CT and MRI may be performed first, and they typically show a well-defined mass in the back of the nasal cavity without any destruction of surrounding bone, a reassuring finding that helps separate this growth from cancer.

Under the microscope, a seromucinous hamartoma is made up of a mixture of small serous (watery) and mucous (mucus-producing) glands. The glands are lined by normal-looking cells, but their arrangement is crowded and disorganized, which is typical of hamartomas. The surrounding tissue may show fibrosis (scar-like tissue) or mild inflammation. Importantly, there are no signs of cancer, such as invasion into surrounding tissues, destruction of bone, or abnormal-looking cells.

Because the crowded glands can look similar to those of a slow-growing cancer called low-grade non-intestinal-type sinonasal adenocarcinoma, telling these two apart is the main diagnostic challenge with this growth. The pathologist relies on the orderly, normal-looking cells, the lack of invasion, and the overall architecture to make the distinction, and may use immunohistochemistry, a test that uses specially labeled antibodies to detect proteins in cells, to help. A seromucinous hamartoma may also be found alongside a related growth called respiratory epithelial adenomatoid hamartoma, and some growths show features of both.

Surgical margins

A surgical margin is the edge of the tissue that the surgeon cuts through when removing a growth. Margins are described in your report only after the entire seromucinous hamartoma has been removed, not after a small biopsy. Because this growth is noncancerous, the report may simply state that it was completely removed, and margins are not always commented on.

Negative margin — No abnormal tissue is present at the cut edge. This suggests the growth was completely removed.
Positive margin — Abnormal tissue is present at the cut edge. Because this growth is benign and rarely recurs, a positive margin is much less concerning than it would be for cancer, but it may prompt closer follow-up.

What happens after the diagnosis?

A seromucinous hamartoma is noncancerous, so no cancer treatment is needed. Growths that cause symptoms are usually removed completely with surgery, most often performed endoscopically through the nose. This is typically curative, and recurrence after complete removal is rare. Growths found incidentally and causing no symptoms may simply be watched.

Perhaps the most reassuring part of this diagnosis is what it rules out. Because a seromucinous hamartoma can resemble a slow-growing cancer under the microscope, confirming that the growth is a hamartoma means no further cancer treatment, staging, or surveillance is required. Your care team, usually an ear, nose, and throat (ENT) surgeon, will discuss whether any follow-up is needed based on your symptoms and how the growth was removed.

Questions to ask your doctor

Where in my nasal cavity or sinuses was the growth located?
Was my growth completely removed, or was only a sample taken?
Was the diagnosis confirmed by a pathologist under the microscope?
Was there any concern that this could have been a cancer, and how was that ruled out?
Do I need any treatment now that the diagnosis is known?
What is the chance that this growth will come back?
Do I need any follow-up appointments or imaging?
Do I have any other conditions, such as nasal polyps or chronic sinusitis, that also need treatment?
What symptoms should prompt me to contact my doctor?
Was there anything unexpected in my pathology report?