about –20 to –30 °C. The specimen is placed in a gel-like embedding medium, usually OCT which consists of polyethylene glycol and polyvinyl alcohol; this compound is known by many names and when frozen has the same density as frozen tissue. At this temperature, most tissues become rock-hard. Usually a lower temperature is required for fat or lipid rich tissue. Each tissue has a preferred temperature for processing. Subsequently, it is cut frozen with the microtome portion of the cryostat, the section is picked up on a glass slide and stained (usually with hematoxylin and eosin, the H&E stain). The preparation of the sample is much more rapid than with traditional histology technique (around 10 minutes vs 16 hours). However, the technical quality of the sections is much lower. The entire laboratory can occupy a space less than , and minimal ventilation is required compared to a standard wax embedded specimen laboratory. Steps of cryotomy: Uses The principal use of the frozen section procedure is the examination of tissue while surgery is taking place. This may be for various reasons. In the performance of Mohs surgery, it is a simple method for real-time margin control of a surgical specimen. If a tumor appears to have metastasized, a sample of the suspected metastasis is sent for cryosection to confirm its identity. This will help the surgeon decide whether there is any point in continuing the operation. Usually, aggressive surgery is performed only if there is a chance to cure the patient. If the tumor has metastasized, surgery is usually not curative, and the surgeon will choose a more conservative surgery, or no resection at all. If a tumor has been resected but it is unclear whether the resection margin is free of tumor, an intraoperative consultation is requested to assess the need to make a further resection for clear margins. In a sentinel node procedure, a sentinel node containing tumor tissue prompts a further lymph node dissection, while a benign node will avoid such a procedure. If surgery is explorative, rapid examination of a lesion might help identify the possible cause of a patient's symptoms. It is important to note, however, that the pathologist is very limited by the poor technical quality of the frozen sections. A final diagnosis is rarely offered intraoperatively. Rarely, cryosections are used to detect the presence of substances lost in the traditional histology technique, for example