Named after Dr Frederic Mohs, who developed it in the 1930s, Mohs' micrographic surgery is undertaken to remove skin cancers, primarily basal cell carcinomas. It is the treatment of choice for lesions on the face or the neck.
It is the ideal surgical approach for cancers in cosmetically sensitive or difficult sites to obtain clearance from – such as the nose, eyelids, lips or ears. There is the possibility that if these cancers are simply excised with a margin, they will not be completely removed and further surgery will be needed at a later date.
Mohs is also undertaken for more difficult cancers – as in the case of those which have recurred, large lesions or those invading nerves.
Mohs’ surgery is undertaken as a day case procedure under local anaesthetic. The visible skin cancer is outlined with a marker pen and the area is anaesthetised. The lesion is excised with a very narrow margin of healthy skin around and underneath it.
The excision site and the sections of tissue that have been removed are drawn in a ‘map’ by the surgeon. This will enable the surgeon to have a precise knowledge of where the removed tissue was located should further removal be required. The area involved is then dressed and the patient moves to the waiting room while the specimen is examined microscopically. This may take several hours and refreshments are provided during this time.
If any tumour remains, for example if it was larger than it appeared on the surface, further surgery may be required and the patient will return to theatre for this until complete elimination of the cancer has been achieved.
If, on the other hand, complete clearance is demonstrated, the next step will be wound closure. Very small wound sites may be dressed and left to heal naturally but normally the edges will be stitched together and sometimes a small area of skin from an adjacent site may be needed to complete the closure.
Sometimes, in the case of surgery around the eye, wounds may be dressed and closure undertaken at a subsequent appointment by an oculoplastic surgeon (eye specialist) and in the case of ear or nose surgery, a plastic surgeon.
In the case of a cancer on the eyelid margin, for example, if this were excised with the normal 4 mm margin around it, it would involve removal of practically the entire eyelid and make reconstruction extremely difficult.
However, with Mohs’ micrographic surgery, very narrow margins are involved which are then inspected microscopically until it can be demonstrated that the cancer has been completely removed. This spares tissue and has an exceptionally high cure rate, both for new and recurrent tumours. It also produces the smallest scar possible.