Sinus thickening seen by chance on a head scan

What the report means

Mucosal thickening. The lining of a sinus looks thicker than usual. It is the most common sinus finding on head scans, and is most often seen in the maxillary sinuses behind the cheeks. (HUNT MRI 2014)
Retention cyst or polyp. A small rounded swelling of the lining, again mostly in the maxillary sinus. Most are on one side only. (HUNT MRI 2014)(Rot 2025)
Fluid. A fluid level in a sinus. In a population study it was rare, seen in 6% of scans. (HUNT MRI 2014)
Opacification. A general word for any of these: part of the sinus is not filled with air. (HUNT MRI 2014)
MRI shows more than CT. In one study of head scans, MRI picked up sinus changes more often than CT. (Nazri 2013)

How common it is in people with no symptoms

Two in three. In 982 adults aged 50 to 66 who had a head MRI for a Norwegian health survey, not for a medical reason, 66% had some sinus shadowing and 49% had mucosal thickening. In the maxillary sinuses, 25% had changes smaller than 4 mm. Polyps and retention cysts were seen in 32%. (HUNT MRI 2014)
Brain MRIs done for other reasons. In 839 brain MRIs, 45.5% showed one or more sinus findings. (Ozdemir 2019) In 3,092 head MRIs, 64.5% had normal sinuses, 26.4% had thickening under 5 mm, 3.8% had a cyst alone, 3.2% had moderate and 2.1% had severe changes. (Rot 2025)
More often in men. All three MRI studies found sinus changes or cysts more often in men than in women. (HUNT MRI 2014)(Ozdemir 2019)(Rot 2025)

When it matters

The scan alone does not decide. Sinusitis is diagnosed from symptoms and an examination of the nose and face, sometimes with imaging. (MedlinePlus) The population study had no symptom data, and its authors say the meaning of these findings is often uncertain and that over-reporting can cause worry. (HUNT MRI 2014)
Symptoms of sinusitis. The NHS lists pain, swelling and tenderness around the cheeks, eyes or forehead, a blocked or runny nose, a reduced sense of smell, green or yellow mucus and a high temperature. Other symptoms include headache, toothache, bad breath, a cough and pressure in the ears. (NHS)
Seeing a GP. The NHS says to see a GP if symptoms do not get better after 3 weeks, or keep coming back. It says a GP may refer to an ear, nose and throat (ENT) specialist when symptoms are only on 1 side of the face, keep coming back, or last more than 3 months. (NHS)
One-sided cysts near the teeth. The authors of the large MRI study say a fuller check matters most for cysts on one side close to the tooth roots. (Rot 2025)
Worry is real. See after an abnormal screening result.

Other things a brain scan may show

The same scan may mention other chance findings, each with its own page: small meningioma, pineal cyst, brain shrinkage (atrophy) and white matter changes.

Who it applies to

Adults told that a brain or head CT or MRI done for another reason shows thickening, a cyst, a polyp or fluid in the sinuses. Children, people already being seen for sinus disease, and a scan done because of sinus symptoms are outside this page.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 (your local urgent care line elsewhere) if you have sinus symptoms and are very unwell, painkillers do not help or symptoms get worse, or you have a weakened immune system. (NHS) NICE says people with sinus symptoms need hospital care if they have swelling or redness around the eye, a displaced eye, double vision or new problems seeing, swelling over the forehead, signs of meningitis, a severe headache at the front of the head, or new nerve problems such as weakness. (NICE NG79)

Routine age-based screening

A sinus finding on a head scan does not replace the routine screenings for your age. See screenings by age and gender.

Where they differ:

How common it is. Rates range from about a third to two thirds of scans, depending on who was scanned, the scan type and the cut-off used. (HUNT MRI 2014)(Ozdemir 2019)(Rot 2025) One smaller study gave 14.8% to 37% on CT and 29.5% to 85.2% on MRI, depending on the score cut-off. (Nazri 2013)
Season. One study found sinus findings more often in winter (50.6%) than summer (40.3%) (Ozdemir 2019); the population study found no seasonal difference. (HUNT MRI 2014)
Age. Two studies found no link with age (Ozdemir 2019)(Nazri 2013); the largest found retention cysts less often at 61 to 75 and 76 to 90 than at 31 to 60. (Rot 2025)
Follow-up. The large MRI study says there is no agreed view on whether cysts found by chance need more tests or monitoring when there are no symptoms. (Rot 2025)

Your doctor decides what your result means for you.

Questions people ask

Is sinus thickening on a brain MRI common?

Yes. In 982 Norwegian adults aged 50 to 66 who had a head MRI for research, not because of symptoms, two out of three had some sinus shadowing and one out of two had mucosal thickening. (HUNT MRI 2014)

Does sinus thickening on a scan mean I have sinusitis?

Not on its own. Sinus changes are common in people with no sinus symptoms. Sinusitis is diagnosed from your symptoms and an examination of your nose and face, sometimes with imaging. Your doctor decides what your result means for you. (HUNT MRI 2014) (MedlinePlus)

What is a retention cyst in the sinus?

A small rounded swelling of the sinus lining, most often in the maxillary sinus behind the cheek. In 3,092 head MRIs, 5.7% showed one, more often in men, and most were on one side only. The authors call these findings common and often benign. (Rot 2025)

Does age change how common sinus findings are?

Studies differ. One study of 839 brain MRIs and a smaller CT and MRI study found no link with age, while a larger MRI study found retention cysts less often in people over 60 than in people aged 31 to 60. (Ozdemir 2019) (Nazri 2013) (Rot 2025)

When should I see a doctor about my sinuses?

The NHS says to see a GP if sinus symptoms do not get better after 3 weeks or keep coming back, and to ask for an urgent appointment if you are very unwell, symptoms get worse, or you have a weakened immune system. (NHS)