After your scan
Cannula Site Swollen or Painful — After Your Scan
Swelling or pain where the cannula went in is usually caused by contrast leaking outside the vein or by vein inflammation. Most cases are mild. A few need urgent care. The red flags below tell you which.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed September 2026
- Two common causes — Contrast leaking outside the vein (extravasation) or inflammation of the vein wall itself (phlebitis). Both cause swelling and discomfort at the site.
- Usually mild and self-limiting — Most cases involve a small area of swelling and manageable discomfort that settles within 24 to 48 hours.
- Remove rings immediately — If the hand or arm is swelling, remove rings, bangles, and your watch now, before swelling makes this harder.
- Some signs need urgent review — Skin colour change, spreading swelling, or any loss of feeling in the hand needs same-day care, not a wait-and-see approach.
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Swelling or pain at the cannula site after a scan is usually caused by contrast leaking outside the vein — called extravasation — or by inflammation of the vein itself, called phlebitis. Most cases are mild and settle within a day or two. Elevate your arm, remove any rings from that hand, and watch for the red flags listed below.
If a symptom below applies to you, do not wait for a callback. Call 1800-202-8726 or go to your nearest emergency department.
What to do right now for mild symptoms
- Raise your arm above the level of your heart and keep it there for the first hour.
- Remove all rings, bangles, and your watch from the affected hand now.
- Apply a cool, damp cloth to the site for 20 minutes at a time.
- Keep the arm rested and avoid lifting anything with it.
- Check the site every 30 minutes for the first two hours — you are looking for spreading swelling or skin colour change.
- Call your imaging centre or oncology team if swelling spreads or pain increases rather than settles.
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What caused this and what should you expect?
Most contrast-enhanced scans use a cannula in the arm vein. Extravasation happens when a small amount of contrast fluid leaks into the surrounding tissue instead of staying in the vein. Phlebitis is inflammation of the vein wall itself, which can develop hours after the scan is complete.
In mild extravasation, the body absorbs the leaked fluid over one to two days. The area may stay tender and bruised for a few days after that. This is uncomfortable but not dangerous when the signs of serious injury are absent.
If you are unsure whether your symptoms are mild or concerning, call the imaging centre where you had the scan. They can advise over the phone and tell you whether you need to be seen.
How to tell mild from concerning
| Feature | Monitor at home | Call your team today |
|---|---|---|
| Swelling | Small, localised, not spreading | Spreading up the arm or increasing hour on hour |
| Pain | Mild, improves when arm is raised | Severe, or worsening despite elevation |
| Skin colour | Normal, possibly slightly pink | White, mottled, dark, or blistered |
| Feeling in hand | Normal sensation in all fingers | Tingling, numbness, or weakness in any finger |
| Improves with elevation | Yes, within an hour or two | No clear improvement after raising the arm |
| Typically starts | During or immediately after the injection | Can appear hours later — more common with phlebitis |
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Common questions
Frequently asked questions
Is contrast fluid dangerous if it leaks into the tissue?
In small amounts, it is not usually dangerous. The body absorbs leaked contrast fluid, and most people have only temporary swelling and discomfort. Larger amounts can irritate the tissue more significantly and in rare cases cause skin damage, which is why skin colour change, spreading swelling, or loss of feeling need immediate emergency assessment. Any doubt is worth a same-day call to the imaging centre.
The site is bruised but not particularly painful — do I still need to call?
Bruising alone, without spreading swelling or any of the red flags on this page, does not usually need urgent assessment. Check that the bruise is not spreading and that you have full sensation and movement in your hand and fingers. If both are true and the discomfort is mild, monitoring at home is reasonable. Call if the bruise spreads quickly, becomes significantly more painful, or you develop any of the warning signs in the first section.
How long will the swelling and soreness last?
Mild swelling from a small extravasation typically settles within 24 to 48 hours. The area may remain bruised and tender for a few days after that. Phlebitis can take a little longer to resolve and may leave a firm, cord-like feeling along the vein for a week or two. If symptoms are still present and not improving after 48 hours, let your oncology team know rather than continuing to wait.
Can this happen again with future scans?
It can, though most contrast injections are completed without extravasation. If it has happened to you, mention it before your next scan. The radiographer or nurse may choose a different vein, use a smaller cannula, or inject more slowly. Having had one episode does not mean it will happen again, but knowing about it lets the team take extra care at the next procedure.