Sinus Mucous Retention Cyst on a Scan: Is It Serious?

A sinus mucous retention cyst is a small, rounded swelling filled with fluid that forms in the lining of a sinus. It is usually benign, often found by chance on a CT, MRI or dental scan done for another reason, and most need no treatment when they cause no symptoms.

The maxillary sinuses sit in the cheekbones, beneath the eyes on either side of the nose. They are the largest sinuses, and the floor of the maxillary sinus is where these cysts are most often seen. A report may also call the finding a retention cyst, a pseudocyst or a rounded soft-tissue opacity.

This guide is for adults reading a report that mentions a sinus cyst. It explains common terms and questions to raise. It cannot tell you what your own scan shows or whether you need treatment.

A small cyst on a report is not an emergency. Some symptoms, however, should not wait for a routine appointment, whatever the scan says. Cleveland Clinic advises seeking medical attention right away for signs of a serious sinus infection, including:

• a fever above 103°F (40°C);
• confusion or other changes in mental state;
• vision changes, especially with pain or swelling around the eyes;
• a stiff neck or seizures.

Book a prompt appointment rather than waiting for routine follow-up if you notice new symptoms on one side that do not go away. The NHS lists a persistently blocked nose on one side, nosebleeds, mucus with blood in it, double vision, a watering or bulging eye, facial pain or numbness that does not go away, loosening teeth or a lump on the face or roof of the mouth as symptoms to get checked.

The NHS notes that these symptoms are very common and are often caused by other conditions. They are listed here because they should be assessed in person, not because a retention cyst is expected to cause them.

They are common. A 2014 letter in the journal Hippokratia cited a general-population rate of 1.4% to 9.6%. A 2025 review of 3,092 head MRI scans, done for neurological reasons, found retention cysts in 5.7% of people, and most cysts were on one side only. Reported rates vary widely with the type of scan and the group studied.

Because many scans of the head include the sinuses, these cysts often appear on reports for headaches, dizziness, dental work or other problems that have nothing to do with the sinuses.

The 2025 authors note their study lacked symptom data, so these figures describe how often cysts are seen on scans, not how often they cause problems. A percentage from a study cannot tell you anything specific about your own cyst.

Usually not. The authors of the 2014 CT study found that most cysts caused no symptoms and concluded that medical treatment was not necessary for them. Over about three years of follow-up, most cysts did not change in size, a small portion grew gradually and a few disappeared on their own.

The 2025 MRI study likewise described observation as appropriate for cysts without symptoms. Surgery, usually done endoscopically through the nose, was discussed for cysts that cause symptoms, grow steadily or get in the way of a planned procedure such as a dental implant sinus lift.

Do not start sprays, rinses or other medicines to shrink a cyst without advice. If a medicine has already been prescribed for another reason, do not stop or change it without talking to the prescriber.

The 2014 letter states that not every retention cyst needs referral to an ear, nose and throat (ENT) specialist. Review is more likely to help when the finding and your symptoms point the same way. The published studies mention situations such as:

• symptoms that could match the cyst, such as facial or cheek pain, headache, nasal blockage or repeated sinus infections;
• a cyst that is large, is growing on repeat imaging or appears to block the sinus drainage opening;
• a planned dental or sinus procedure near the cyst;
• a one-sided finding close to tooth roots, where the authors suggest dental and radiological assessment because tooth infection can involve the maxillary sinus;
• a report that leaves the diagnosis uncertain or suggests something other than a simple cyst.

A retention cyst is a single, well-defined swelling within the lining. Mucosal thickening is a more general swelling of the lining and is covered in a separate guide. Nasal polyps are soft growths, usually on both sides, that often come with long-term blockage and reduced smell, and they are diagnosed with a camera examination as well as imaging.

Chronic sinusitis is a clinical diagnosis based on symptoms lasting at least 12 weeks, supported by examination and imaging. A cyst on a scan, without matching symptoms, does not mean you have sinusitis.

Take the written report to your appointment. These questions can help you leave with a clear plan.

• Which sinus is the cyst in, how big is it, and does the report describe it as a simple retention cyst?
• Could it explain any of my symptoms, or is it most likely unrelated to why I had the scan?
• Was a dental cause considered, and should I see a dentist?
• Is any repeat scan or follow-up needed, and if so, when and who arranges it?
• Would an ENT review change anything for me?
• Which new symptoms should make me contact you sooner?

On SameCase, patients and verified doctors share de-identified cases. Reading how other people with a similar scan finding described their symptoms, and which questions they asked, can help you prepare for your own appointment. Similar cases cannot diagnose you or tell you what your scan means. Your clinician, who can see your full report and history, makes those decisions.