Advice after your nerve block for surgery
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What is a Magseed?
The Magseed is a metallic seed, smaller than a grain of rice, that can be accurately placed in a breast lesion prior to surgery.
Many breast lesions are too small for the surgeon to be able to feel. Previously, a wire would be placed into the lesion, which the surgeons would then use to locate the tissue to be removed during the operation. Using a Magseed instead of a wire enables the lesion to be localised in advance, unlike a guidewire insertion which would have been placed on the morning of your surgery.
At the time of surgery, a magnetic probe is used to locate the Magseed. The Sentimag sensing machine makes sounds of different pitches and gives a reading to let the surgeon know how close they are to the Magseed within the lesion. The Magseed is then removed along with the lesion.
Magseed can also be useful for patients prior to undergoing Neoadjuvant Chemotherapy. The Magseed can be placed into the tumour at the begining of treatment and once treatment is completed the Magseed is already in situ, enabling the surgeon to accurately remove the tumour bed.
Magseed insertion is a minimally invasive procedure which is generally very safe. This procedure is performed under either ultrasound or Mammographic control.
How do I prepare for the Magseed insertion?
No special preparations are required. You can eat and drink normally before and after the procedure (unless you are due for surgery on the same day).
It is advisable to wear separate top and bottoms, as you will be asked to undress from the waist up. Avoid wearing deodorant, powder, lotion or perfume on your breasts or underarms on the day of your appointment, as these may affect the x-ray image.
You may bring a friend or relative; however, they may not be allowed into the examination room. There are no childcare facilities. If you do need to bring your children with you, please bring along an adult who can supervise them when your examination is being carried out.
What happens during the Magseed insertion?
The Radiologist will explain the procedure and answer any questions you may have and ensure you are happy to proceed.
Ultrasound guidance
You will lie on the ultrasound couch. After the breast has been scanned the skin is cleaned with a sterilising solution before an injection of local anaesthetic is given to numb the area. A small nick is made in the skin and a hollow needle is inserted.
Ultrasound is used to guide the needle to the exact location. A plunger on the end of the needle pushes the Magseed into the correct area. The needle is removed, and firm pressure applied to the area to reduce bruising.
A mammogram is then taken to check the position of the Magseed. The wound is then covered by a dressing.
Under Mammographic control
The Radiographer will position you in the mammography machine; you will either be seated or lying down, and the breast will be compressed. Once the area has been precisely located, your skin will be cleaned with a sterilising solution before local anaesthetic is injected to numb the area.
A small cut is made in the skin and the hollow needle is inserted to the correct area. a plunger at the end of the needle pushes the Magseed into position.
The needle is removed, and firm pressure applied to the area to reduce bruising. You may experience some discomfort during this procedure, but most patients tolerate it very well.
A mammogram is then taken to check the position of the Magseed. The wound is then covered by a dressing.
What is the aftercare?
The dressing should be kept clean and dry for the next 48 hours, after which you can remove it yourself. You will also need to avoid any strenuous activity (such as exercise, vacuuming and lifting heavy objects) and swimming for the next 48 hours.
As the local anaesthetic wears off, your breast may feel sore and uncomfortable; if required, you can take painkillers such as Paracetamol. Always take the tablets according to the instructions on the packet. Do not take Aspirin or Ibuprofen.
Are there any side-effects?
Side effects may include:
- Pain at the site of the incision and biopsy once the local anaesthetic has worn off.
- Bruising to the breast and around the site of the incision.
- Bleeding: if the wound starts to bleed, sit down, and apply firm pressure with the tips of your fingers for 10 minutes.
- Infection, there is always a very small chance, as with any wound, that it may become infected.
Any further questions?
If you have any further questions regarding this procedure or require any further advice, please contact the Mammographers on 0300 614849.
Contact us
If you have any queries relating to this information, please contact the Radiology service.
About this information
Service:
Radiology
Reference:
PILS.5
Approval date:
15 April 2026
Review date:
1 April 2029
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Important note
This page provides general information only. It is developed by clinical staff and is reviewed regularly every 3 years for accuracy. For personal advice about your health, or if you have any concerns, please speak to your doctor.