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Surgical pearl: large single sections in Mohs micrographic surgery
PEARLS Stuart J. Salasche, MD Surgical Pearls Editor
Mark G. Lebwohl, MD Medical Pearls Editor
Surgical Pearl: Large single sections in Mohs micrographic surgery Hugh M. Gloster, Jr, MD Cincinnati, Ohio
M
ohs micrographic surgery is a highly effective surgical modality for the treatment of certain cutaneous malignancies. The “fresh-tissue technique,”1 which is currently used by most Mohs micrographic surgeons, involves the saucerization excision of a neoplasm followed by the preparation of horizontal frozen sections, sequential microscopic examination of all frozen section tissue specimens, mapping of the excised tissue, and reexcision of persistent tumor until all margins are clear. Mohs micrographic surgery, which insures maximal cure rates and the conservation of normal tissue, may also be a meticulous and time-consuming procedure. In 1998, this author and Taylor2 described a method of embedding and mounting multiple, small tissue specimens on one glass slide, which can reduce the number of glass slides used to mount frozen sections and increase the rapidity with which frozen sections can be prepared and examined during Mohs micrographic surgery. This article describes the use of large single sections, another efficient, time-saving technique for preparing histologic sections for Mohs micrographic surgery. Tissue specimens excised for Mohs micrographic surgery are typically divided into 2 or more sections before being horizontally sectioned, stained, and mounted on slides for microscopic examination. The specimen is divided so that it will fit on the cryostat chuck disk and so that the lateral and deep margins can easily be flattened into a single plane. The single-section method, originally described by Randle et al,3 saves time by omitting the division of the specimen into smaller sections, thus, reducing the number of tissue specimens that must be cut by the technician and interpreted by the surgeon. AccordFrom the University of Cincinnati. Reprints not available from the author. J Am Acad Dermatol 2003;48:506-8. Copyright © 2003 by the American Academy of Dermatology, Inc. 0190-9622/2003/$30.00 ⫹ 0 doi:10.1067/S1090-9622(03)0078-6
506
ing to Randle et al,3 the single-section method is most useful for small or thin specimens (eg, eyelid tumors). Conversely, large tumors or thick specimens are typically divided into 2 or more specimens so that they may fit on the cryostat chuck and to facilitate flattening the lateral and deep margins in the same horizontal plane. This article describes a method of processing large and thick specimens by the single-section method. The first step is to aggressively remove the bulk of the tumor either by curettage, scalpel excision, or shave excision. Shave excision with a bowed half razor blade is our preferred method of debulking, which produces a thin section that is easier to flatten, freeze, and cut (Fig 1). To preserve orientation, nicks are placed at 12, 3, 6, and 9 o’clock. The tumor is removed in a thin, saucerized fashion by beveling the scalpel blade 45 degrees. The excisional specimen is then placed on a glass slide and the surface is scored with partial-thickness cuts to relax the tissue so that, as it freezes, the epidermal and deep margins can be gently flattened with forceps into the same plane that is represented by the surface of the glass slide. The 12, 3, and 9 o’clock nicks are then color-coded with dyes, the map is drawn, and the specimen (that rests on the slide) is placed into the cryostat. Optimum cutting temperature (OCT) embedding compound is poured on the tissue and the cryostat chuck, and allowed to freeze to about ⫺24°C. After placing the slide and the tissue on the chuck, the slide is separated from the specimen by warming the slide with the thumb. At this point, the undersurface of the specimen and the epidermal margin are embedded in OCT medium in the same plane in preparation for horizontal sectioning with the microtome (Fig 2). OCT medium, if allowed to adequately freeze, may extend beyond the edges of the chuck. Thus, the diameter of the cryostat chuck is not a size-limiting factor, because specimens larger than the chuck may be successfully embedded in OCT, mounted on the chuck, and horizontally sectioned. It may also be necessary to allow larger specimens to freeze for a
Pearls 507
J AM ACAD DERMATOL VOLUME 49, NUMBER 3
Fig 1. Excisional specimen (4 ⫻ 2 cm) of basal cell carcinoma that has been debulked by shave excision of exophytic portion of tumor.
Fig 2. Specimen (4 ⫻ 2 cm) is embedded in optimum cutting temperature medium and mounted on cryostat chuck. Undersurface and epidermal margin are in single plane in preparation for horizontal sectioning with microtome.
longer period of time (5-10 minutes). Smaller specimens are frequently sectioned first to permit adequate freezing of larger tissue. Once the OCT has adequately frozen, the tissue may be cut with the microtome and mounted on a glass slide for microscopic examination (Fig 3). The section incorporates the entire peripheral and deep margin, permitting
the surgeon to examine 100% of the margins. The only factor limiting the size of the specimen that may be cut as a single section is the length and diameter of the glass slide (typically 2.5 ⫻ 7.5 cm) on which the specimen is mounted. In other words, the specimen may not be larger than the glass slide. To date, the largest specimen the author has cut using this
508 Pearls
J AM ACAD DERMATOL SEPTEMBER 2003
Fig 3. Specimen has been mounted on glass slide for microscopic examination.
technique has been 4.5 ⫻ 2.1 cm. Also, as with smaller specimens, depending on the fat content, it may be necessary to cut larger specimens slightly thicker (10-15 m instead of the usual 5-10 m-thick sectioning) so that incomplete sections do not occur. In conclusion, the use of large single sections is an efficient technique for preparing histologic sections for Mohs micrographic surgery. This method omits subdivision of excisional specimens, which saves time and reduces the risk for technical errors by decreasing the number of specimens that must be cut, stained, and coverslipped by the technician and interpreted by the surgeon. The single-section method may also decrease the risk of false-positive margins that may occur during the division of the specimen into multiple sections, when epidermal malignant cells may be inadvertently pushed into the undersurface plane. In contrast to the original single-section method described by Randle et al3 in 1993, this technique is not limited to small or thin specimens. Large and thick tumors and specimens containing cartilage may be processed in this manner, provided that they are adequately debulked
Direct all Surgical Pearl submissions to Dr Stuart J. Salasche, 5300 N Montezuma Trail, Tucson, AZ 85750.
before excision and can be flattened into a single plane. This technique may be difficult for specimens from fatty areas where the dermis is thick (eg, the back and posterior aspect of the neck). Rapid freezing of specimens from such areas frequently renders the epidermis brittle and easily damaged by the microtome. Furthermore, if it is necessary to cut thicker sections, the technician may be more likely to cut into the tumor and obtain a false-positive margin. This complication can be avoided by having the technician mount several sections of initial cuts from the first portion of the tissue block for histologic examination. REFERENCES 1. Mikhail GR. Mohs micrographic surgery. Philadelphia: WB Saunders; 1991. 2. Gloster HM, Taylor AF. Surgical pearl: the use of multiple different tissue specimens on the same glass slide to enhance the efficiency of frozen section preparation in Mohs micrographic surgery. J Am Acad Dermatol 1998;39:107-8. 3. Randle HN, Zitelli J, Brodland DG, Roenigk RK. Histologic preparation for Mohs micrographic surgery—the single section method. J Dermatol Surg Oncol 1993;19:522-4.
Direct all Medical Pearl submissions to Mark G. Lebwohl, Mount Sinai Medical Center, One Gustave L. Levy Place, Box 1048, New York, NY 10029.
Mark G. Lebwohl, MD Medical Pearls Editor
Surgical Pearl: Large single sections in Mohs micrographic surgery Hugh M. Gloster, Jr, MD Cincinnati, Ohio
M
ohs micrographic surgery is a highly effective surgical modality for the treatment of certain cutaneous malignancies. The “fresh-tissue technique,”1 which is currently used by most Mohs micrographic surgeons, involves the saucerization excision of a neoplasm followed by the preparation of horizontal frozen sections, sequential microscopic examination of all frozen section tissue specimens, mapping of the excised tissue, and reexcision of persistent tumor until all margins are clear. Mohs micrographic surgery, which insures maximal cure rates and the conservation of normal tissue, may also be a meticulous and time-consuming procedure. In 1998, this author and Taylor2 described a method of embedding and mounting multiple, small tissue specimens on one glass slide, which can reduce the number of glass slides used to mount frozen sections and increase the rapidity with which frozen sections can be prepared and examined during Mohs micrographic surgery. This article describes the use of large single sections, another efficient, time-saving technique for preparing histologic sections for Mohs micrographic surgery. Tissue specimens excised for Mohs micrographic surgery are typically divided into 2 or more sections before being horizontally sectioned, stained, and mounted on slides for microscopic examination. The specimen is divided so that it will fit on the cryostat chuck disk and so that the lateral and deep margins can easily be flattened into a single plane. The single-section method, originally described by Randle et al,3 saves time by omitting the division of the specimen into smaller sections, thus, reducing the number of tissue specimens that must be cut by the technician and interpreted by the surgeon. AccordFrom the University of Cincinnati. Reprints not available from the author. J Am Acad Dermatol 2003;48:506-8. Copyright © 2003 by the American Academy of Dermatology, Inc. 0190-9622/2003/$30.00 ⫹ 0 doi:10.1067/S1090-9622(03)0078-6
506
ing to Randle et al,3 the single-section method is most useful for small or thin specimens (eg, eyelid tumors). Conversely, large tumors or thick specimens are typically divided into 2 or more specimens so that they may fit on the cryostat chuck and to facilitate flattening the lateral and deep margins in the same horizontal plane. This article describes a method of processing large and thick specimens by the single-section method. The first step is to aggressively remove the bulk of the tumor either by curettage, scalpel excision, or shave excision. Shave excision with a bowed half razor blade is our preferred method of debulking, which produces a thin section that is easier to flatten, freeze, and cut (Fig 1). To preserve orientation, nicks are placed at 12, 3, 6, and 9 o’clock. The tumor is removed in a thin, saucerized fashion by beveling the scalpel blade 45 degrees. The excisional specimen is then placed on a glass slide and the surface is scored with partial-thickness cuts to relax the tissue so that, as it freezes, the epidermal and deep margins can be gently flattened with forceps into the same plane that is represented by the surface of the glass slide. The 12, 3, and 9 o’clock nicks are then color-coded with dyes, the map is drawn, and the specimen (that rests on the slide) is placed into the cryostat. Optimum cutting temperature (OCT) embedding compound is poured on the tissue and the cryostat chuck, and allowed to freeze to about ⫺24°C. After placing the slide and the tissue on the chuck, the slide is separated from the specimen by warming the slide with the thumb. At this point, the undersurface of the specimen and the epidermal margin are embedded in OCT medium in the same plane in preparation for horizontal sectioning with the microtome (Fig 2). OCT medium, if allowed to adequately freeze, may extend beyond the edges of the chuck. Thus, the diameter of the cryostat chuck is not a size-limiting factor, because specimens larger than the chuck may be successfully embedded in OCT, mounted on the chuck, and horizontally sectioned. It may also be necessary to allow larger specimens to freeze for a
Pearls 507
J AM ACAD DERMATOL VOLUME 49, NUMBER 3
Fig 1. Excisional specimen (4 ⫻ 2 cm) of basal cell carcinoma that has been debulked by shave excision of exophytic portion of tumor.
Fig 2. Specimen (4 ⫻ 2 cm) is embedded in optimum cutting temperature medium and mounted on cryostat chuck. Undersurface and epidermal margin are in single plane in preparation for horizontal sectioning with microtome.
longer period of time (5-10 minutes). Smaller specimens are frequently sectioned first to permit adequate freezing of larger tissue. Once the OCT has adequately frozen, the tissue may be cut with the microtome and mounted on a glass slide for microscopic examination (Fig 3). The section incorporates the entire peripheral and deep margin, permitting
the surgeon to examine 100% of the margins. The only factor limiting the size of the specimen that may be cut as a single section is the length and diameter of the glass slide (typically 2.5 ⫻ 7.5 cm) on which the specimen is mounted. In other words, the specimen may not be larger than the glass slide. To date, the largest specimen the author has cut using this
508 Pearls
J AM ACAD DERMATOL SEPTEMBER 2003
Fig 3. Specimen has been mounted on glass slide for microscopic examination.
technique has been 4.5 ⫻ 2.1 cm. Also, as with smaller specimens, depending on the fat content, it may be necessary to cut larger specimens slightly thicker (10-15 m instead of the usual 5-10 m-thick sectioning) so that incomplete sections do not occur. In conclusion, the use of large single sections is an efficient technique for preparing histologic sections for Mohs micrographic surgery. This method omits subdivision of excisional specimens, which saves time and reduces the risk for technical errors by decreasing the number of specimens that must be cut, stained, and coverslipped by the technician and interpreted by the surgeon. The single-section method may also decrease the risk of false-positive margins that may occur during the division of the specimen into multiple sections, when epidermal malignant cells may be inadvertently pushed into the undersurface plane. In contrast to the original single-section method described by Randle et al3 in 1993, this technique is not limited to small or thin specimens. Large and thick tumors and specimens containing cartilage may be processed in this manner, provided that they are adequately debulked
Direct all Surgical Pearl submissions to Dr Stuart J. Salasche, 5300 N Montezuma Trail, Tucson, AZ 85750.
before excision and can be flattened into a single plane. This technique may be difficult for specimens from fatty areas where the dermis is thick (eg, the back and posterior aspect of the neck). Rapid freezing of specimens from such areas frequently renders the epidermis brittle and easily damaged by the microtome. Furthermore, if it is necessary to cut thicker sections, the technician may be more likely to cut into the tumor and obtain a false-positive margin. This complication can be avoided by having the technician mount several sections of initial cuts from the first portion of the tissue block for histologic examination. REFERENCES 1. Mikhail GR. Mohs micrographic surgery. Philadelphia: WB Saunders; 1991. 2. Gloster HM, Taylor AF. Surgical pearl: the use of multiple different tissue specimens on the same glass slide to enhance the efficiency of frozen section preparation in Mohs micrographic surgery. J Am Acad Dermatol 1998;39:107-8. 3. Randle HN, Zitelli J, Brodland DG, Roenigk RK. Histologic preparation for Mohs micrographic surgery—the single section method. J Dermatol Surg Oncol 1993;19:522-4.
Direct all Medical Pearl submissions to Mark G. Lebwohl, Mount Sinai Medical Center, One Gustave L. Levy Place, Box 1048, New York, NY 10029.