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Microscopically controlled surgery (MCS)

2010; Wiley; Volume: 8; Issue: 11 Linguagem: Inglês

10.1111/j.1610-0387.2010.07314.x

1610-0387

Christoph Löser, Rainer Rompel, Helmut Breuninger, Matthias Möhrle, Hans‐Martin Häfner, Christian Kunte, Jessica C. Hassel, Ulrich Hohenleutner, Maurizio Podda, Günther Sebastian, Jürg Hafner, Birger Konz, Roland Kaufmann,

Reconstructive Facial Surgery Techniques

Guidelines are systematically developed recommendations that are designed to assist clinicians and healthcare practitioners in making decisions concerning appropriate the treatment of patients with specific clinical conditions. Guidelines apply to “standard situations”, taking into account current scientific knowledge. Continual revisions and, if necessary, updates must be made based on the state of scientific knowledge and feasibility in everyday practice. Guidelines are not intended to restrict the choice of methods available to physicians. Nor does following the recommendations set forth in a guideline guarantee diagnostic or treatment success. Guidelines are not intended to be exhaustive. It is up to the physicians to determine the most appropriate method of treatment on an individual basis. Microscopically controlled surgery (MCS) aims to insure complete removal of a malignancy (R0 resection) with histological confirmation while sparing as much of the adjacent tissue as possible. The subclinical extent of skin cancer is often difficult to assess prior to therapy or based on macroscopic appearances alone. There is thus a risk of choosing a margin of safety that is either too large or too small. Complete removal of a tumor is the only way to insure a cure. Microscopically controlled surgery is performed in conjunction with various histological processing methods to ensure complete surgical removal of the tumor. In all procedures, the excised tissue is marked for precise topographical orientation. These procedures differ in terms of surgical technique as well as in the method of histological sectioning to confirm complete removal (R0 resection). Histological techniques may be performed in single, dual, or multiple interventions. Immediate closure of the wound is possible, especially if it does not interfere with precise topographical orientation or any potentially necessary re-excisions. For removal of large tumors or tumors at problematic sites, a suitable protective bandage may be used for temporary coverage before final closure. Later closure of the defect may be with plastic reconstruction, free skin grafting, or the wound may be allowed to close by secondary healing. If histological analysis reveals tumor extending to the margins of excision, the affected border zone or wound base is identified at the excision site and re-excision is performed with the aim of R0 resection. With regard to histological analysis, a distinction is made between procedures that show the margins with no gaps and those that have diagnostic gaps. Methods with no gaps have the highest sensitivity for an R0 resection. Yet whether they have a significant influence on tumor-free survival has not yet been confirmed by prospective, randomized clinical studies. The usefulness of the chosen technique depends on the expertise and experience of the surgeon and histologist, who are occasionally one and the same person. This procedure was introduced in 1941 in the United States by F. Mohs, initially as chemosurgery. Originally Mohs used a fixative zinc chloride paste prior to performing the actual excision in a procedure that was very painful. In 1974 Tromovitch published on the cryostat technique in which excision was performed under local anesthesia and histological analysis was done with a rapid sectioning cryostat technique. Mohs called the procedure “microscopically controlled surgery.” This procedure is currently used only in certain specialized clinics, mainly in the United States. The terms “Mohs’ micrographic surgery” and “Mohs’ surgery” are also found in the literature. The technique is suitable for use only by specially trained dermatologic surgeons. One key difference between this procedure and others (see 2.2) has to do with the incision. Following local curettage of exophytic components, an incision is made under local anesthesia at a 45 degree angle around the tumor. The scalpel is angled away from the tumor so that the circular excision removes an upside-down tissue cone. Depending on its size, the specimen may then be divided. The tissue is then pressed onto a slide so that the angled margin is level with the base. Next the tissue is embedded and the resulting block is cut in a cryostat horizontally from the margin. For topographical orientation, a scalpel may be used to place cuts in the tissue in situ. These tiny incisions remain as slight indentations on the specimen and around the margins of the wound; they are also visible in the microscopic specimen. Dye marking is also common. Using automatic staining, the surgeon, who basically functions as his or her own dermatohistopathologist, can assess the sections within the hour and immediately perform any necessary re-excision. Correct interpretation of the histological sections depends greatly on processing and requires highly qualified laboratory personnel. Inadequate embedding or incision can produce incomplete or incorrectly oriented margins. Reproducibility with re-excision is usually not possible. Given the complexity and time involved, this procedure is prone to error. A significant drawback of using an angled incision is the incision of tumor components extending into the lower dermis. Increasing the excision margins to avoid this results in an unnecessarily large defect. In addition, the oblique incision can also complicate adaptation of the wound margins. In principle, three-dimensional incision margins of the removed tissue are fully shown in two-dimensional histological sections. Thus they may also be subsumed under the term three-dimensional histology, which is discussed in the following. One variation on Mohs’ surgery is an incision performed parallel to the skin's surface (the “Münchner” method) (Burg and Konz 1975). Unlike Mohs’ technique, the tissue is not removed in a cone shape, but rather is cylinder-shaped with perpendicularly cut margins. Histological processing is performed in a cryostat which enables assessment of the whole tumor. Micrometer-wide sequential sections are prepared (maximum 10 = 0.001 mm) resulting in numerous parallel sections. By evaluating sequential sections from the base of the tumor up to the epidermis, the three-dimensional growth pattern of the tumor can be assessed. For large tumors that do not fit on the cryostat slide, the tissue may be divided into individual blocks and marked topographically. Histological processing is necessarily also more time consuming. This method is suitable for histologically confirmed epithelial tumors, especially basal cell carcinomas and recurrent disease. The “Münchner method” is less well suited for histological evaluation of superficial precancerous lesions such as lentiginous melanocytic tumors or Paget or Bowen disease, given that pathological cell structures are difficult to assess in the cryostat sections. Various, similar alternatives to the above-mentioned techniques are described in the literature: La Galette (Drepper 1963) histology of the margins of excised tissue, with no gaps, or “Tübinger tort” (Breuninger 1982), Flunder or muffin technique (Breuninger 1994, Möhrle 2006), square procedure (Johnson 1997), quadrant method (Smeets 2005), and the Wallgraben or perimeter technique (Blum 2004, Mahoney 2005). Although some of these terms are used synonymously, they in fact refer to different techniques with distinct advantages and disadvantages. All of these methods involve three-dimensional margins and show the tissue without any gaps. In addition to the central section, the histo-pathologist also evaluates whether tumor components are visible at the margins. For the purpose of simplification, the term 3-D histology has been proposed for all of these methods. Methods of microscopically controlled surgery (MCS). (Illustration: Professor Dr. Helmut Breuninger, Tübingen). In all 3-D histology techniques the tumor is removed en bloc. The incision is made perpendicularly to the surface of the skin which is preferable for defect closure. Only in the perimeter or Wallgraben technique is a margin of tissue excised around the in situ tumor. In the square procedure, a square excision is made to remove the tumor using a double-bladed scalpel. This facilitates separation of the margins. In the La Galette procedure re-excision is made from the margins and base in situ following a preliminarily narrow tumor excision. In other techniques the margins and the base are separated from the excised tissue. Intraoperatively an incision or thread is placed for marking, usually at 12:00 o’clock (most central cranial point). The margins and base of the tumor are embedded, without staining, in histology cassettes, either by the surgeon or laboratory personnel. For small excisions (up to 2 cm in diameter) the margins and the underside may be cut and leveled (muffin technique). A representative section taken from a central portion of the tumor can aid diagnostic classification. Dye marking facilitates orientation of the sections. Usually formalin fixation of tissue is performed followed by paraffin embedding. Cryostat processing (with the above-mentioned advantages and disadvantages) is also possible. Using the paraffin technique with rapid tissue fixation in a 60° C formalin solution for 2 hours, the histological sections can be ready the next day. The preparation of the margins and base (“Tübinger tort”, quadrant technique) can also be performed by a histopathological laboratory on tissue that has been fixed, but is more time consuming. First, the separated margin and base are placed in paraffin. Next, the wax-like tissue may be heated to 65° C with the outer side slightly bent to make it level. This procedure allows the specimen to be sent to a laboratory for histological analysis. In the peripheral method, far fewer incision margins must be assessed. Similar to Mohs technique, it is not possible to evaluate the distance between the tumor and the incision margin. This very common method is also subsumed under MCS. The incision is made using sequential vertical cuts with a scalpel, lending it the name bread-loaf technique. Representative sections are then made from the tissue slices. When the sections are 1 mm or larger, diagnostic gaps must be presumed, and thus depending on the number of slices, it may appear that an R0 resection has been achieved. This method is especially suited for small excisions measuring less than 20 mm in diameter. The use of thin sections can allow higher sensitivity. For large excisions, however, sensitivity is lower given that the diagnostic gaps increase – unless a large number of very thin sections are made, making this method much more time consuming. An advantage of this technique is that it enables thorough assessment of the tumor architecture and the tumor-free zone as far as the incision border. For follow-up surgery for R1 resections or difficult tumors, one of the peripheral techniques (3-D histology) that does not involve any gaps between tissue slices may also be used (Table 1). MCS is indicated for tumors at difficult sites in which a tissue-sparing surgical technique is needed or when there is aggressive growth and a local R0 resection must be ensured. Common indications include basal cell carcinoma (especially infiltrative types), recurrent basal cell carcinomas, or neural infiltrating variants, as well as spinocellular carcinomas that have infiltrated the subcutis or have moderate to poor differentiation. Dermatofibrosarcoma protu-berans, lentigo maligna, lentigo maligna melanoma, acral lentiginous melanoma, and Merkel cell carcinoma are also indications as are erythroplasia of Queyrat, extramammary Paget disease, and Bowen disease. The paraffin section method is preferred in most cases, given then tumor extensions may be better evaluated than with rapid sectioning cryostat procedures. This applies in particular to spinocellular carcinoma, Merkel cell carcinoma, and extramammary Paget disease. MCS with 3D-histology of paraffin sections with no gaps between the tissue is especially important for recurrent tumors, dermatofibrosarcoma protuberans, lentigo maligna melanoma, and acrolentiginous melanoma. MCS should be used for malignant tumors at problem sites or when it is expected that more complex closure techniques will be needed and thus complete tumor removal must be ensured prior to wound closure. The more problematic the tumor and the affected site, the more important is the choice of highly sensitive procedures that can confirm an R0 resection with a high degree of sensitivity (3D histology). Visualization of the lateral and basal margins, without any gaps between tissue slices, is independent of the diameter of the excised tumor. In tumors that have infiltrated the bone, the procedure is only of limited use, if at all. If it is used, it is very complicated. Osseous components must be decalcified and can then be histologically examined. Selection of any of the above-named MCS procedures is based on the expertise of the cooperating surgeon and histologist. The “personal union” of the surgeon and histologist is even relevant in certain countries for invoicing for Mohs’ surgery. Ideally, the surgeon can also assess the incisions and ensure any clinical-histopathological correlation. In peripheral margin techniques, the surgeon can perform the processing of the margins immediately after surgery to aid the histological laboratory. The evaluation is generally made by the histopatho-logist, or in special cases, by surgeons trained in histological analysis. All methods used in microscopically controlled surgery must be documented using drawings (e.g., surgeon's protocol, requirements of histology and histological analysis) and histological sections so that the steps taken can be readily reconstructed if need be. Microscopically controlled surgery for the removal of malignant skin cancer requires a qualified, specially trained surgeon working closely together with a histopathologist who is also familiar with MCS methods. The selection of the appropriate procedure depends on the experience of the users. To confirm a local R0 resection of tumors with infiltrative growth at problem sites and for sparing of tissue, microscopically controlled surgery represents a safe and proven method, particularly when there are no gaps between the tissue taken at the incision margins. Expert group of the German Society for Dermatosurgery (DGDC) Dr. med. Christoph Löser, Ludwigsha-fen; Prof. Dr. med. Rainer Rompel, Kassel; Prof. Dr. med. Matthias Möhrle, Tübingen; Dr. med. Hans-Martin Häfner, Tübingen; Dr. med. Christian Kunte, München; Dr. med. Jessica Hassel, Mannheim; Prof. Dr. med. Ulrich Hohenleutner, Regensburg; PD Dr. med. Maurizio Podda, Darmstadt; Prof. Dr. med. Günther Sebastian, Dresden; Prof. Dr. med. Jürg Hafner, Zürich; Dr. med. Birger Konz, München; Prof. Dr. med. Roland Kaufmann, Frankfurt; Prof. Dr. med. Helmut Breuninger, Tübingen Guideline coordination Dr. med. Christoph Löser Created on: 05/2006 Last update: 03/2008 First revision: 03/2009 Next scheduled update: 03/2017 Level: 1