About a CT scan of the sinuses
The sinuses are air-filled spaces in the bones of the face, around and behind the nose and eyes. They are lined with a thin layer of tissue that makes mucus, which drains into the nose through small channels. A sinus CT (computed tomography) scan uses X-rays and a computer to make thin cross-section pictures of the sinuses and the thin bones between them.
Most sinusitis is short-lived, is diagnosed from your symptoms, and does not need a scan. A sinus CT is the main scan for long-term (chronic) sinusitis, when symptoms such as a blocked nose, facial pain and reduced sense of smell last more than 12 weeks and have not improved with treatment such as nasal sprays. It shows:
- which sinuses are blocked or inflamed, and whether the drainage channels are open
- nasal polyps and other causes of blockage, such as a bent nasal septum
- the detailed anatomy of the thin bones, which ENT surgeons use as a “map” to plan and safely carry out sinus surgery (functional endoscopic sinus surgery, FESS); some centres use the scan for image-guided surgery
- bony changes from long-term infection and some complications of sinusitis
To look at growths, or whether a problem has spread to the eye socket or brain, a sinus MRI is usually better at showing soft tissue. For the bones of the face after an injury, see face CT.
What happens during the scan
You lie on your back on the scanner bed with your head resting in a cradle, and pads may be used to help you keep still. Only your head goes into the scanner, which is a short, open ring. The radiographer controls the scanner from the next room, but can see, hear and talk to you throughout. The scan itself takes less than a minute. Contrast dye is not usually needed; where contrast is needed, it is charged separately.
Is CT safe?
CT uses X-rays, which are a type of ionising radiation. A sinus CT uses a low-dose technique and gives a lower dose than a CT of the head (about 2 mSv). Centres use techniques to reduce the dose to the eyes. The risk from a single scan is very small, and every CT scan is checked by a radiologist or radiographer to make sure the benefit of the scan outweighs the risk, as required by the Ionising Radiation (Medical Exposure) Regulations. If you have had other CT scans recently, tell us when you book.
What the scan can show
A CT scan of the sinuses can help to look at:
- chronic sinusitis
- nasal polyps
- blocked sinus drainage channels
- a deviated nasal septum and other anatomy
- planning for sinus surgery
- bony changes and some complications of sinusitis
When to get urgent help: call 999 or go to A&E if you have sinus symptoms with swelling or redness around the eye, changes to your vision, a severe headache, confusion or a stiff neck.
Preparing for your scan
No special preparation is needed, and you can eat and drink normally. Remove glasses, earrings, hair clips and removable dental work before the scan. If you have a cold or a recent infection, tell us, as the scan is best done when you are well. Upload any letters from your GP or ENT specialist when you book.
Wear loose, comfortable clothing without metal zips, poppers or buttons, and leave jewellery at home, as metal in the scan area can affect the pictures. You may be asked to change into a gown. Unlike MRI, CT is not affected by pacemakers or most metal implants, and the scanner is a short open ring rather than a tunnel, so it is usually easier for people who feel anxious in enclosed spaces.
Tell the team before your scan if you are, or might be, pregnant or breastfeeding, if you have kidney problems, diabetes (especially if you take metformin), asthma, thyroid problems or allergies, or if you have had a reaction to contrast dye before. If you need contrast, you may be asked for a recent kidney blood test result.
Frequently asked questions
Do I need a scan for sinusitis?
Usually not. Most sinusitis gets better on its own within 2 to 3 weeks. A CT may be suggested if symptoms last more than 12 weeks despite treatment, keep coming back, or if surgery is being considered.
Is CT or MRI better for the sinuses?
CT is the main scan for chronic sinusitis and planning surgery, as it shows the thin bones best. MRI shows soft tissue better and is used to look at growths and complications. Your referrer will say which is needed; if you are unsure, contact us before booking.
Should I have the scan when I have a cold?
It is best to wait until a cold or short-term infection has cleared, as it can make the sinuses look worse than they usually are. Your specialist may also ask you to complete a course of treatment first.
Do I need a referral?
Because CT uses radiation, each scan has to be justified by a qualified professional before it can go ahead. Upload a referral from your GP or consultant when you book if you have one. If you do not, select “no referral” and the scanning centre will review your request and confirm the next steps with you, which may include arranging a referral.
Sources
- NHS – Sinusitis (sinus infection)
- NHS – Nasal polyps
- RadiologyInfo.org – CT of the Sinuses
- NHS – CT scan
- UKHSA – Patient dose information: guidance
The information on this page has been gathered from various sources and is provided for general information only. It is not medical advice. TOP MRI is not liable for the accuracy or completeness of this information. Please speak to your doctor or the scanning centre about your own situation.