A frozen section, tissue that is snap-frozen and immediately sectioned in a cryostat, is indicated when the results of the study will affect intraoperative management of the patient. Permanent sections, tissue that is processed into paraffin prior to sectioning, are always preferred in ophthalmic pathology because of the inherent small size of the samples and the superior morphological preservation achieved with this technique (see Chapter 2). If the tissue sample is too small, it could be lost during frozen sectioning.
The most frequent indication for a frozen section is to determine whether the resection margins are free of tumor, especially in eyelid carcinomas. When tissue is submitted for margin evaluation, appropriate orientation of the specimen, correlated with documentation (through drawings of the excision site, labeled margins, or margins of the excised tissue that are tagged with sutures or other markers), is crucial; see Figure 2-2 in Chapter 2. Two techniques can be used for assessing the margins in eyelid carcinomas (eg, basal cell carcinoma, squamous cell carcinoma): (1) routine frozen sections (as discussed previously); and (2) Mohs micrographic surgery (Fig 3-6), which preserves normal tissue while obtaining clear margins. Eyelid lesions, especially those located in the canthal areas, require tissue conservation in order to maintain adequate cosmetic and functional results.
Figure 3-6 Frozen section and Mohs micrographic surgery techniques. A, To prepare a frozen section, the surgeon excises the lesion, typically a malignancy, with surgical margins denoted for the pathologist. For an eyelid margin lesion, the surgeon often performs a pentagonal wedge eyelid resection. The pathologist samples the nasal, temporal, and inferior margins to assess for the presence of tumor. A central cross section may be performed to demonstrate the distance of the tumor from the inferior surgical margin. An elliptical excision of a skin tumor can be evaluated by frozen section using the bread-loaf technique, in which multiple cross sections are prepared. B, In Mohs micrographic surgery performed on an eyelid margin tumor, the surgeon excises the visible lesion. Then, additional thin shavings of tissue are prepared by frozen section from the bed of the residual defect, allowing the surgeon to evaluate en face margins. In another variation of Mohs surgery, the surgeon performs an elliptical excision of the visible tumor. Frozen en face sections are obtained from the undersurface and the edges of the excised lesion. The tumor locations are marked on a map for a subsequent second-stage excision.
(Illustration developed by Tatyana Milman, MD, and rendered by Mark Miller.)
Another indication for obtaining frozen sections is to determine whether adequate diagnostic tissue has been obtained by the surgeon. As frozen sections are a time-intensive and costly process, they should be used with discretion.
See the section on eyelid disorders in BCSC Section 7, Oculofacial Plastic and OrbitalSurgery, for more information.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.