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7.1 What are the main considerations for determining which patients should be selected for Mohs micrographic surgery procedures?
Consideration of the following issues will determine a patient’s suitability for Mohs micrographic surgery:
* Recurrent tumours for which other treatments have failed
* Incompletely excised tumours particularly in cases of deep margin involvement
* Tumour subtypes can influence whether the patient is suitable for Mohs micrographic surgery; thus, in the case of BCC, tumours which are multicentric or morphoeic. In the case of SCC, those tumours that are undifferentiated or poorly differentiated and acantholytic.
* Some anatomical sites on the face are more likely to have higher recurrence rates than other areas and are therefore more suitable for Mohs micrographic surgery. In the case of BCC, the ‘H’ area or mask of the face, and in the case of SCC, those lesions in periorbital or auricular areas, as well as those occurring around mucosal sites or those arising in scarred tissue sites.
7.2 What are the key factors to consider when designing and setting up a Mohs laboratory?
The laboratory needs to be:
- Juxtaposed to the clinical theatres, and ideally away from direct patient areas.
- It is often the room where much discussion, both technically and medically, is likely to be going on. It is the nerve centre for process! Adjacent to the room containing the histological equipment, the laboratory should ideally have an annex with a dedicated viewing microscope for the surgical teams to assess slides.
- A multiheaded microscope to enable discussion amongst medical staff and also to facilitate teaching and training.
- Good laboratory layout which should adhere to good efficient, ergonomically orientated design and layout (Lean principles apply)
- Provision of key amenities including:
- Adequate external sunlight (windows)
- Adequate ventilation and air flow.
- Running tap water
- Good overhead lighting
- Appropriate shelving and cupboard space
- Good non-slip flooring
- Lockable doors with good general security (equipment is expensive and should be protected at all times!)
- Adequate health and safety indicators and supportive signage
- Provision of all the key pieces of equipment required
- Back-up equipment in cases of emergency, which should also be in close proximity and readily available.
7.3 Name the key features of the cryostat that should be present for performing Mohs procedures adequately.
The key factors should include:
- Adequate internal chamber space (remember you may have up to 20–30 blocks in the chamber at any one time)
- Appropriate size of the overall dimensions of the cryostat. Some modern cryostats have very rounded exteriors which can take up more space within the laboratory than is ideal. Space requirements in the Mohs laboratory are paramount considerations.
- An X/Y axis. Not all cryostats have this feature. This enables you to re-orientate an embedded block, in case one part of the tissue is being cut more deeply or unevenly than another. Adjustment of the X/Y axis will enable the missing tissue block component to be cut following re- alignment.
- Adequate cooling plate (heat extraction device) This will speed the process of hardening and freezing the embedded tissue
- Automated retraction of the object holder arm
- Wheel lock to ensure there is no movement when placing or removing tissue from the object holder.
- Adequate lighting within the chamber to see all areas of the chamber
- Provision of ultraviolet light options for rapid decontamination.
7.4 Describe the factors that can cause aberrant staining outcomes and how do you avoid them.
Generally, staining will be compromised, largely leading to patchy staining if sections are:
- To thick or thin
- Excessively dried out prior to staining
- Inadequately fixed
- Residual OCT remains in the sections during staining