Dermatology (Skin conditions)

Mohs Micrographic Surgery

What is Mohs surgery?
This is a method of surgically removing skin cancers, most often basal cell carcinoma (also known as rodent ulcer) and squamous cell carcinoma. Basal cell carcinoma and squamous cell carcinoma are the two most common types of skin cancer. Basal cell carcinoma most often affects the face, commonly the nose. Squamous cell carcinoma most often affects the skin that has had the most sun exposure over the years, commonly the bald scalp, cheeks, forehead or ears. Please ask for a leaflet about these tumours if you require more information and have not already seen these.

What is different about Mohs surgery?
The procedure is different to other surgical techniques because at the time of tumour removal the complete tumour margin is mapped and examined under the microscope (first stage) to ensure that tumour is not present at the edges of the removed skin. We draw a map of the operation site if tumour is still present we can identify where by using the map. If there is tumour present at the edge then a further piece of skin needs to be removed, at that specific site. This process is repeated until no tumour is found.

What are the advantages of Mohs surgery?
The advantages are the high cure rate and removal of tissue only where there are cancer cells present. This prevents the unnecessary removal of normal tissue. The technique is well suited for sites and situations where preserving as much normal tissue as possible is important such as tumours of the eyelids, nose, lips, ears and in young people. Mohs surgery is also good for skin cancers which are difficult or impossible to see with the naked eye such as those that have come back after previous treatment and those that have been incompletely removed at the first attempt.

How is it done?
Mohs micrographic surgery can be done using frozen tissue (frozen tissue Mohs surgery) where all the stages are generally done in one day, or using formalin fixed tissue (fixed tissue Mohs surgery) where the excision stages are done over several days.

Frozen tissue Mohs surgery
First, the skin is numbed with a local anaesthetic injection. The visible tumour is first removed and then a margin of skin around this is removed. A map is carefully drawn so that the surgeon knows the exact location of the skin margins. This removed margin of skin is processed in the laboratory to see if any tumour remains. A dressing is applied to the wound and the patient will be able to go back to the waiting area. The first stage is now over for the patient. The wait is to allow the removed margin of skin to be processed by the laboratory and the slides checked under the microscope by the surgeon. It will take approximately one hour for the laboratory to process a small tissue specimen; a large specimen will take longer. If tumour is seen at the edge of the removed margin of skin then further skin will need to be removed. The process is the same as before except that only the areas where tumour is present need to be excised so in many cases this means it is a shorter procedure. Because the effects of the anaesthetic may have worn off by this time more anaesthetic will be injected. The process is repeated for as many stages as necessary until no more tumour is found at the edge of the removed skin and there is no tumour remaining.

Fixed Tissue Mohs Surgery

For some tumours we need to prepare the skin specimens in a different way. This is called fixed tissue Mohs surgery. The important difference from the frozen tissue technique is that the interval between stages is 1-2 days rather than 1-2 hours.

Will I feel any pain?
The local anaesthetic is usually effective for two hours, after which some discomfort may be present. If necessary two paracetamol tablets may be taken every six hours. You may also be asked to take a short course of antibiotics before or after the operation and this will be discussed with you.

Can I be sedated?
You could ask your general practitioner to prescribe a mild sedative that you can take by mouth before the procedure. We do not use sedative injections.

What happens when the entire tumour has been removed?

Generally there are three options:

  • At some sites the wound can be left and with careful dressing it will heal naturally leaving a perfectly good result. If this is done you will be shown how to look after the wound and given the necessary materials.
  • The wound is repaired by the Mohs surgeon. This is done after the tumour has been removed. The repair will be done under local anaesthetic and you will be able to go home afterwards.
  • The third possibility is that the resulting wound is repaired by another surgeon, either an oculoplastic surgeon, plastic surgeon or the dermatologist or doctor who referred you in the first place. This closure procedure will usually be done a few days after the Mohs excision day. In each case the best option for you will determine what method is used.

Is there anything I need to do?

  • Bring a list of your medications
  • Tell us about any allergies you have to medicines, rubber, anaesthetics, iodine, Elastoplasts.
  • Smoking makes healing of the skin more difficult and there is a greater chance of infection and poor healing if you smoke. You should aim to stop smoking two weeks before and two weeks after surgery.
  • Read our leaflet, ‘Patient information prior to having a skin surgical procedure’. This gives a more general outline of what happens in the Skin Surgery unit.

Will anything else happen?
Photographs of the procedure are usually taken for possible use in audit, teaching, or publication. Your permission for this will be requested beforehand. You will not be recognisable in the photographs and a name will not be attached.

How long does all this take?
Frozen tissue Mohs surgery: It could take all day. It depends on how big your tumour is, how much tissue has to be processed, how many excision stages are required to remove all the tumour cells and the type of wound repair. Please bring something to read. Refreshments can be purchased in the hospital snack bar and cafe, or you could bring a packed lunch with you.

Fixed tissue Mohs surgery: Each visit for surgery will usually be for one to two hours. There is usually 1-2 days between each stage.

Can I bring someone with me?

That is a good idea. You may be unable to drive if the dressing covers or partially covers your eye and you may feel a bit ‘groggy’. However, space is limited and we do not want you to bring more than one accompanying person with you. In particular, bringing a child with you would be entirely inappropriate.

Is there anything else I need to bring?

  • You will need to bring your own tablets if you need to take tablets for other conditions
  • Food and drink will be required. These can be purchased from the hospital snack bar or cafe or you can bring a packed lunch with you.
  • It is a good idea to bring some pain killers with you. We normally recommend paracetamol just after surgery as this will make the wound less painful when travelling home.
  • Something to read whilst you wait for the result

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