slide from the staining solution, the side with the specimen should be carefully noted. One must be absolutely sure that the clearing reagent and the mounting media are compatible. The mounting media should be nonaqueous as it lasts longer and does not desiccate as quickly as aqueous media. The correct size of coverslip must also be chosen and applied to the slide. The mounting media can be applied to the cover slip or to the slide. The end result is to not have any air bubbles on the slide, while preserving the integrity of the specimen [1]. Following transport and initial processing of the slides, the specimen is now ready to be analyzed by the Mohs micrographic surgeon.

Summary: Conclusion

•The major goal during tissue transport and initial processing is to maintain the proper specimen orientation. The sample should be cut into as few sections as possible to minimize error orientation. After being sectioned in the microtome, it is stained, most commonly with hematoxylin and eosin. After the coverslip is placed on the slide, the analysis can be made by the Mohs surgeon.

12.3Conclusion

The major goal during tissue transport and initial processing is to maintain the proper specimen orientation. After the specimen is removed from the surgical site and hemostasis is complete, the Mohs map can be drawn. The specimen can then be transported to the histopathology laboratory. It should be cut into as few sections as possible, that way orientation error is minimized. Colored ink is generally used to maintain orientation. Optimum cutting temperature (OCT) is used to attach the specimen to the microtome chuck. After being sectioned in the microtome, the specimen is stained, most commonly with hematoxylin and eosin. After the coverslip is placed on the slide, the slides are ready to be analyzed by the Mohs surgeon.

Reference

1.Steinman HK. Specimen Transport and Preliminary Tissue Processing. In: Mohs Surgery: Fundamentals and Techniques. Gross KG, Steinman HK, Rapini RP, editors. Saint Louis: Mosby; 1999. p. 91–96.

A.M. Hassanein (*)

Medical Director, Florida Pathology, Dermatologic Sugery & Aesthetics Institute,

The Villages, FL, USA e-mail: ßoripathol@aol.com

H.A. Hassanein

Department of Microbiology and Biomedical Sciences, University of South Florida College of Medicine Tampa, FL, USA

e-mail: hatem.h@gmail.com

Summary: Introduction

¥The Mohs surgeon should communicate with the laboratory personnel to ensure the production of high-quality Mohs slides.

¥The Mohs surgeon should be aware of all the technical issues related to the Mohs laboratory, since technical errors represent the most common cause of local recurrence after MMS.

13.1Introduction

The success of MMS is contingent upon high-quality frozen tissue sections for histopathologic interpretation. The Mohs slide is the product of the Mohs surgeonÕs performance and the laboratory personnelÕs experience. Strong communication between the Mohs surgeon and the laboratory personnel is a key for production of high-quality Mohs slides. For example, some Mohs surgeons do not bevel the Mohs layers. This will require special tissue processing such as compression with Miami spatula to produce slides showing a complete tissue with epidermis. The low recurrence rate and the tissue-sparing beneÞt associated with MMS require accurate interpretation of the frozen sections by the Mohs surgeon [1]. Mohs surgeons should be aware of all the technical issues related to the Mohs laboratory. Frozen tissue section processing results in approximately 10Ð20% tissue shrinkage. The Mohs surgeon should pay attention to any discrepancy in the size of the tissue on the slide compared to the tissue excised. Discrepancy in the tissue size or large holes could be due to missing tissue and is deÞnitely associated with incomplete margin. Technical errors represent the most common cause of local recurrence after MMS [2].

Summary: Histopathologic Scanning

of Mohs Slides

¥Histopathologic scanning of Mohs slides should include all tissue sections on the slide.

¥Mohs surgeons should evaluate all the tissue on the slides in a systematic way by examining all of the peripheral margin (i.e., the epidermis) and the deep margin. This should entail evaluation of 100% of the margin.

¥Overlooking a piece of tissue or evaluating a suboptimal slide with missing tissue or containing a hole may result in tumor recurrence.

¥Routine scanning should be performed under the low power (20× and 40×) magniÞcation. Positive areas of a residual tumor can be easily seen upon scanning. Any suspicious areas should be examined under high-power (100× and 200×) magniÞcation.

13.2Histopathologic Scanning of Mohs Slides

The MMS layer is typically a thin slice of skin that is removed by curvilinear excision. Sections are usually divided into subunits to facilitate ßattening of the tissue so that the epidermis (the peripheral margin) and the deep margins lie on the same plane. Consequently, Mohs slides contain only margins and interpretation of Mohs slides entails literally 100% evaluation of specimen margins [3, 4]. This is in contrary to routine dermatopathology slides that are meant mostly for diagnostic reasons. Routine surgical pathology, grossing and processing of excisional specimens show only less than 1% of the actual margin. When you examine a Mohs slide, you are actually evaluating the entire bottom and the whole periphery of the specimen.

Mohs slides should be examined in numerical order corresponding to the map. Any residual tumor identiÞed can be located with its exact site on the map based upon the colors of the margins (Chap. 12). Mohs slides should be routinely scanned under the low power (20× and 40×) magniÞcation. If microscopic evaluation reveals malignancy at one point in the slides, it should be assumed that the corresponding point in the patient is positive. Scanning of Mohs slides should be done the same way dermatopathologists examine their slides. A routine and systematic way of evaluation of cutaneous structures should be followed. We always teach our new dermatopathology fellows to scan slides at low power in the same fashion a photocopier machine or scanner does. One should scan slides starting at one side of the specimen and sweep, up and down until reaching the other side. Practically speaking, it is advisable to go up and down, perpendicular to the epidermis, after evaluating the epidermis itself and consequently the dermo-epidermal junction. The latter is of utmost importance in scanning Mohs slides for melanoma.

The time needed to scan Mohs slides depends upon the experience of the Mohs surgeon; it is usually a few seconds. Positive areas of residual tumor can be easily seen on scanning. If any suspicious areas are found, high-power (100× and 200×) examination is needed. The Mohs surgeon should scan and examine all the sections on the slide. The histotechnician usually puts multiple tissue sections on one slide. This helps

speciÞcally if a part of one section is missing or folded and also helps track a particular suspicious structure that is mimicking cancer.

Higher magniÞcation facilitates evaluation of certain structures and small groups of malignant cells. For instance, perineural invasion deÞnitely needs highpower examination. Dense inflammatory infiltrate is said to be the pathologistÕs enemy. Higher-power examination of dense inßammatory inÞltrate is important to rule out any hidden individual cells, groups of tumor cells or perineural invasion. Patients with chronic lymphocytic leukemia and solid-organ transplant recipients have a 36% and 13% incidence, respectively, of dense inßammatory inÞltrates seen in Mohs slides; as opposed to 1% seen in controls [5]. Dense inßammatory inÞltrate does not normally obscure residual tumors of BCC [6] or SCC [7]. In the authorÕs

experience, high-power evaluation and/or recuts usually resolve any problem interpreting dense inßammatory inÞltrate. Permanent sections should always be obtained in these cases as a frozen section control. It is important to note that these permanent sections (frozen section control) are routinely obtained for all frozen sections performed in the surgical pathology department. It is advisable to do them only in controversial Mohs cases and in cases of aggressive cancers such as melanoma, sebaceous carcinoma, and merkel cell carcinoma. On the other hand, dense inßammatory inÞltrate can be reactive or represent a chronic skin disease. This is not uncommon in Mohs slides of facial tumors that may show a variable degree of rosacea. The presence of multinucleated giant cells and/or granulomas within the lymphohistiocytic inÞltrate is helpful in identifying rosacea (Fig. 13.1).