Principles of Frozen Section Specimens

Frozen sections are used during surgery mainly to assess the margins of resected tissue for residual tumor. They can also be used to confirm a suspected diagnosis or relate to the surgeon a type of tissue (eg, nerve vs scar). When assessing margins, it is important to submit a tissue specimen outside the resection periphery. If a separate tissue specimen is taken from the main resection specimen itself, it will appear on the permanent sections that the tumor was closer to the resection margin than it actually was (Fig 1-2). This will be recorded as a close or positive margin on the final pathology report and may precipitate additional treatment recommendations unnecessarily.

When frozen sections of the main specimen are required, the specimen should be marked with sutures, or the edge should be inked to direct the pathologist to areas of concern (Figs 1-3a and 1-3b). In addition, clearly noted orientation should be included on the pathology request, noting anterior, superior, medial, and lateral edges. Dental terms such as mesial, distal (meaning dental distal rather than the opposite of proximal), lingual, buccal, and labial should be avoided. These terms are unfamiliar and confusing to general pathologists, and although oral and maxillofacial pathologists understand them, they are rarely the ones involved in interpreting frozen sections; anatomical orientations more consistent with all surgical specimens are preferred. It is also useful to provide a sketch of the specimen with the same orientation sutures or inked edges on the drawing. This can be accomplished without violating sterile scrub by using a sterile marking pen and the paper in which sterile gloves are packaged (Fig 1-3c).

Frozen sections also may be obtained from a margin in bone even though hard tissue requires decalcification before processing. Because most tumors advance through bone within the marrow cavity, this area rather than the cortex is the preferred area to sample (Fig 1-4a). A frozen section can therefore be obtained by curetting the marrow cavity from the native bone at each resection margin (Fig 1-4b). This is almost always a fibrofatty tissue that does not require decalcification. If the pathologist believes that the curettings are still too "gritty" to microtome without decalcification, then at least a touch preparation or cytologic slide (Figs 1-4c and 1-4d) can be prepared from the specimen.

Fig 1-2. Frozen sections should be taken from the host tissue edge rather than from the specimen tissue edge.

Fig 1-3a. Excision of a surface lesion should be guided by outlining the excisional periphery with a sterile marking pen.

Fig 1-3b. Sutures at an excisional specimen with long-long ends, short-long ends, and short-short ends denoting specific margins.

Fig 1-3c. The excised specimen should be adequately tagged at reference margins and annotated to the pathologist. A diagram such as this to accompany the specimen is ideal.

Fig 1-4a. The resection margin of a benign tumor in bone is based on a sound knowledge of the tumor's invasive properties, the radiographic and/or CT scan margin, and the clinical observation of the tumor's edge.

Fig 1-4b. Because both benign and malignant tumors advance further within the marrow space than in the cortex, curettings from the marrow space can be used as frozen sections or for cytology.

Fig 1-4c. Cytology of normal-appearing epithelial cells. Note the small nuclei, abundant cytoplasm, and regular cell outlines.

Fig 1-4d. Cytology of abnormal cells with large nuclei, resulting in a reversal of the nuclear-cytoplasmic ratio.