Microscopic evaluation of peripheral margins. (a) Melanoma in situ involving the inked peripheral margin of a specimen (×20). (b) Atypical nevus excised with a margin of un-involved skin (×10)
Shave Biopsies/Shave Excisions (Saucerizations, Tangential Excisions)
Shave biopsies represent a sampling of epidermis and superficial dermis taken in a plane parallel to the epidermal surface. Deeper shaves may include superficial reticular dermis, but subcutis is almost never sampled by this technique. Deeper shave biopsies (tangential excisions/saucerizations) intended to completely remove a lesion are marked with indelible ink along the entire margin sparing only the epidermal surface. Depending on the size, shave biopsies may be bisected along the long axis or serially sectioned. The tissue is then embedded on edge so that the inked peripheral and deep margin is entirely represented in the histological section. Larger shaves may be divided between cassettes so that the tip (third dimension) margins can be evaluated independent of sections from the middle of the lesion.
Elliptical (and Cylindrical) Excisions
Excisions are, by definition, specimens intended to excise a lesion. As such, assessment and reporting of margins is usually required. Most excisions are elliptical; however, cylindrical specimens may be taken from certain anatomic sites where optimum lines of surgical closure are not clinically evident prior to the procedure. In this case, additional detached tips (“dog ears”) may be submitted separately, and should be treated as true “tip” margins. Larger excisional specimens often are oriented to identify a specific anatomic site on the patient such that a positive margin may be treated locally and less aggressively. Any surface lesion should be described noting its size, circumscription, color(s), and proximity to the peripheral margins.
Un-oriented specimens are marked with indelible ink along the entire peripheral and deep surgical margin similar to a shave biopsy. The ellipse (or cylinder) is then serially sectioned along the entire specimen (bread-loafed) to produce parallel sections perpendicular to the epidermal surface. Each section should be no greater than 2–3 mm in thickness to facilitate optimum tissue fixation and to allow examination of a larger area of surgical margin. Any lesion present on the cut surface should be noted, especially satellite lesions outside of the prior biopsy site in larger excisions.
Larger oriented specimens are treated somewhat differently than un-oriented excisions.
A suture often is used to orient an excisional specimen. The suture may be placed at one end (on a tip) and/or along one long axis (edge). Occasionally, two sutures may be used (different colors or lengths to differentiate). Some surgeons use a standard designation of “Short suture—Superior, Long suture—Lateral” to simplify communication with the laboratory. Others may place a nick/slice along one border to designate orientation, but this practice is not advised as formalin fixation may result in tissue shrinkage that obscures the mark .
Regardless of the method used to identify a specific margin, specimens are differentially inked to reflect the orientation. The easiest way to orient an excisional specimen is by quadrant using a clock face for landmarks. Assuming that a marking suture at one tip of an ellipse is designated 12 o’clock, the specimen can be divided into 12–3, 3–6, 6–9, and 9–12 o’clock quadrants. Each quadrant could then be marked with a different color of indelible ink along the peripheral and deep surgical margin.
Another approach using only three colors of ink produces similar results. The 12–3 and 3–6 o’clock quadrants are differentially inked, whereas the 6–9–12 o’clock half is marked with one color. As such, the 12 o’clock half can be distinguished from the 6 o’clock half based on the unique pairing of the ink colors.
Very Large Re-excision Specimens
Very large excisional specimens, often taken for treatment of broad malignant melanomas, pose a unique challenge. These specimens may be marked with ink to reflect orientation similar to a small excision, but serial sectioning may result in pieces of tissue still too large to fit into a cassette for tissue processing. In this scenario, the prior biopsy site and residual primary tumor should be removed en bloc, serially sectioned, and entirely submitted as if it was an elliptical excision. Peripheral margins closet to the en bloc excision are then serially sectioned to document the peripheral margins. En face peripheral margins may be employed for extremely large specimens in which serial sections perpendicular to the primary lesion are still too large. En face sections, however, are not optimum for evaluating margins of lentigo maligna as distinction from melanocyte hyperplasia reflective of the background actinic changes may be difficult without use of additional special studies such as immunohistochemistry [7, 8].
Interpretation of Surgical Margins
Each of the procedures described above produces a specimen that can be assessed for adequacy of local therapy. Chapter 2 will address the reporting of melanocytic lesions including recommendations for adequacy of surgical margins. Surgical margins can be evaluated for most specimens regardless of biopsy/surgical technique. A microscope fitted with a calibrated ocular micrometer facilitates measurement of distance between the lesion and the surgical margin. Larger excisions may be measured with a ruler after marking the coverslip above the peripheral extension of the lesion under low magnification. These measurements may be reported directly or incorporated with a recommendation for further therapy based upon current consensus [9–19].