๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Mohs micrographic surgery
Mohs micrographic surgery
MMS involves tangential removal of tissue and immediate processing with frozen section histology in order to ensure that 100% of the tumor margin has been histologically examined and excised. It has the distinct advantage of ensuring almost complete histologic removal of the tumor in real time, and provides the least possible damage to adjacent normal tissues. Many studies have demonstrated both the safety and efficacy of MMS in the treatment of NMSC. The strength of the technique is that it has the lowest documented recurrence rate of any surgical treatment method and maximizes tissue sparing.37โ39 For a full discussion of MMS, see Chapter 29.
MMS is the treatment of choice for skin cancers on functionally or cosmetically sensitive areas, though it may be used anywhere the body. In general, MMS is indicated for NMSC in high-risk locations. It is also appropriate for larger tumors, incompletely excised tumors, tumors with aggressive histologic subtypes or indistinct clinical borders, and tumors in cosmetically or functionally sensitive areas.
The fresh frozen tissue technique40 is performed by tangentially excising the tumor with a small amount of normal surrounding tissue. Orienting marks are made on the specimen and the corresponding site on the patient. The surgical specimen is then flattened in a manner that allows the three-dimensional margin to be cut in a twodimensional plane and rapidly frozen. This allows the entire margin to be viewed in a microscopic section. The tissue is cut using a cryostat and the margin is mounted on one or more slides, then stained and examined by the Mohs surgeon. Typically, a hematoxylin and eosin (H&E) stain is used when examining NMSC, though other special stains exist that are specific to different types of tumors. Positive margins are marked on an operative map, and additional tissue can then be removed to ensure the greatest possible tissue sparing. Processing of the tissue, histologic examination, and reexcision are repeated in stages until a negative margin is obtained.
Assuming that 100% of the epidermis and deep margin are visualized, once there are no positive margins, complete removal of the tumor has been achieved.41 The resulting defect from the excision can be repaired, allowed to heal by secondary intention, reconstructed, or referred to a colleague for reconstruction. Occasionally during the course of MMS, tumors will be encountered that are unresectable. This typically will not be apparent until many stages are performed or in cases of perineural invasion. When surgical margins cannot be obtained or complete resection cannot be achieved, it is helpful to map out the positive margins so that future surgery or radiotherapy can be targeted most accurately.
Indications for MMS have evolved as the technique has become more widely adopted and more actively sought out by patients. Appropriate use guidelines were developed by performing a thorough review of all available literature from 1940 to
2011 to help guide clinicians in determining when MMS is medically necessary.42 A rating system was developed to guide clinical decision making and ensure rational use of MMS depending on patient characteristics, type of NMSC, tumor characteristics, and clinical scenario.
MMS has been very well-studied for the treatment of NMSC, and has the highest cure rate of all treatment modalities for BCC and SCC. A review of the Australian Mohs database showed 5-year recurrence rates of primary BCC and SCC to be 1.4% and 2.6%, respectively.38 In addition, it found the 5-year recurrence rates of recurrent BCC and SCC treated with MMS to be 4% and 5.9%, respectively.38,43 Other large retrospective studies have shown that MMS has lower recurrence rates than any other treatment modality in both SCC and BCC, likely because all of the tissue margins are examined.37 Though MMS may be more costly than excision or EDC, several studies have highlighted its cost effectiveness, particularly because it can be performed in the office, the surgeon also acts as the pathologist, and it has an extremely high cure rate.44