Chronic sinusitis in a cat means signs that have run 4 weeks, or come back 3 times in 12 months. At that point the useful question is no longer which antibiotic but which anatomy is broken, and a 2-view skull film cannot answer it. A CT scan booked after 3 to 4 weeks of failed medical care and before any biopsy settles the anatomy in 15 to 25 minutes of table time; the 8-week review is what tells you whether the plan worked.
When acute becomes chronic
An acute viral upper respiratory infection clears in 7 to 10 days, sometimes 14. Chronic is 4 weeks of continuous discharge, or 3 separate episodes in 12 months with sneezing in between. Score 5 signs at every visit: discharge from 1 or both nostrils, sneeze bursts of 5 to 20 at a time, noise on breathing at rest, appetite, and weight. By week 4, structural disease is common enough that imaging belongs in the first plan, not at the end of a third course of treatment.
Why CT instead of a skull film
A radiograph gives 2 overlapping flat images of a skull 4 to 5 cm across, while the turbinates inside are 0.5 to 1 mm thick and vanish into the overlap. CT gives 0.5 to 1 mm slices in 3 planes and shows the sinus walls, the turbinate scrolls, the 3 roots of the upper fourth premolar, and any bone erosion of 1 mm or more. The scan itself takes 6 to 10 minutes, the anaesthetic 25 to 40 minutes, and most cats go home the same day after 60 to 90 minutes of recovery.
The CT time points
Three moments matter, and a fourth is optional. The scan is not an emergency test; it is a decision tool that has to be placed where it changes what happens next.
| Time point | Days from first sign | What happens | Minutes under anaesthesia | Decision it opens |
|---|---|---|---|---|
| First exam | 0-7 | History, nasal airflow, oral exam | 0 | Start a 3 to 4 week medical trial |
| Baseline CT | 28-42 | Scan, then rhinoscopy if the scan shows disease | 25-40 | Structural cause found or excluded |
| 8-week review | 56 | Rescore 5 signs; repeat scan only if worse | 0-25 | Continue, switch, or biopsy |
| 6-month recheck | 180 | Repeat CT after surgery or fungal treatment | 15-25 | Close the case or re-treat |
Preparing the cat for the scan
Food off for 8 to 12 hours, water off for 2 hours. A cat with poor nasal airflow gets 5 minutes of pre-oxygenation before induction, because the airway it shares with the sinus disease is the one being imaged. Position prone with the head straight and the hard palate parallel to the table; a 10 degree tilt shifts the frontal sinus out of plane. Ask for 2 acquisitions, bone and soft tissue windows, at 1 mm and then 0.5 mm through the affected side. Keep the disc, because the 8-week comparison only works if the same window and the same slice thickness are used.
What the scan has to answer
Five questions, in this order. Which sinuses are opacified: frontal, maxillary, or sphenoid. One side or both. Are the turbinates intact, thinned, or gone. Is there bone erosion of 1 mm or more, which points to fungus, tumour, or an aggressive process rather than simple inflammation. Is a tooth root involved, most often the upper fourth premolar. A sixth finding, a foreign body of 1 to 5 mm, is small enough to be missed on a plain film and obvious on a 0.5 mm slice.
The 8-week assessment
Week 8 is long enough for a medical plan to show an effect and short enough that a cat does not lose weight for a quarter of a year. Score 5 signs from 0 to 3 at day 1 and again at day 56: discharge volume, sneezes counted over 10 minutes, airflow felt on a cold mirror held under each nostril, breathing noise at rest, and appetite. A total drop of 3 points or more means the plan is working and continues to week 12. A total that has not moved means the diagnosis or the plan is wrong. A total that has risen means scope and biopsy at once, not another course.
If nothing has changed by week 8
Rhinoscopy with 3 to 5 biopsy pieces of 1 to 2 mm, taken from the turbinate and from any mass, is the next step. Fungal culture needs 10 to 21 days, so send it at the same time rather than after the histology comes back. Ask for dental films of the upper fourth premolar if the CT showed a widened root. In cats over 8 years, a mass is the finding to exclude first, and a second CT with contrast 4 to 6 weeks later shows whether a lesion has grown.
Home care that moves the numbers
Saline, 2 to 3 ml per nostril twice a day, given with the head slightly down. Nebulise for 10 to 15 minutes once or twice a day, and run a humidifier in a small room for 15 minutes rather than all day. Wipe the nares twice a day so the crust does not block the airflow you are scoring. Keep the room at 20 to 22 degrees Celsius and away from litter dust. Count sneezes for 10 minutes once a week and write the number down, because that count is the most reliable thing you can bring to the 8-week review.
When to call the vet today
Bleeding from 1 nostril that lasts more than 5 minutes, swelling under the eye, an eye pushed forward, noise on breathing at rest, a fever of 39.5 degrees Celsius, or 300 g of weight lost in 4 weeks are all same-week problems and mostly same-day. A cat that also vomits 2 or more times a week has a second problem, covered in IBD and chronic vomiting and in this chronic vomiting plan; treating the nose will not fix it.
Five steps for this week
- Write down the start date of the discharge, so week 4 and week 8 have a fixed reference point.
- Count sneezes for 10 minutes and photograph the discharge, once a week.
- Start saline twice a day now, and keep it going through the imaging, because it changes the score.
- Book the CT for week 4 to 6, with a biopsy consent signed in advance in case the scan shows a mass.
- Check the cost estimate before booking, since scan, scope, and histology are billed as 3 separate lines.
Terms mentioned in this article
Frequently asked
How long should treatment run before a CT scan?
Three to 4 weeks of a structured plan, which is enough time for simple inflammation to respond. If discharge, sneezing, or airflow are unchanged at that point, book the scan rather than starting a second course, because the answer is usually structural.
Is a CT scan safe for a cat with a blocked nose?
It needs a general anaesthetic, so the airway has to be assessed first. Pre-oxygenation for 5 minutes, a short 6 to 10 minute scan, and recovery of 60 to 90 minutes make it a same-day procedure in most cats, including those with poor nasal airflow.
What happens at the 8-week review?
Five signs are scored from 0 to 3 and compared with day 1: discharge, sneezes over 10 minutes, airflow, breathing noise, and appetite. A drop of 3 points or more means continue; no change means the diagnosis is wrong; a rise means rhinoscopy and biopsy the same week.