Frozen sections are performed as a stat procedure during surgery as a guide to surgical therapy. The frozen section is used to determine if margins around a tumor are clear and if adequate tissue for a complete diagnosis has been obtained. Frozen sections are often performed on axillary lymph nodes in patients with breast cancer. These are called sentinel nodes and the findings in these lymph nodes may determine if an axillary lymph node dissection is performed.
A relevant portion of tissue, perhaps with margins, is taken from the specimen (this may include the entire specimen). This tissue is placed on a base of frozen material and sectioned with a cutting blade. These thin sections of tissue are removed from the cryostat (the large very cold instrument used for cutting tissue), fixed briefly in formalin, and taken through a series of hematoxylin and eosin stains. The tissue is cover slipped and examined immediately and a frozen sections diagnosis is rendered to the operating surgeon by the pathologist.
The tissue to be examined is frozen within the cryostat, enabling the tissue to be sectioned without the necessity of long hours of fixation in formalin, followed by tissue permeation for hours by multiple solvents, and eventual imbedding of tissue in paraffin. This process of fixation generally takes about 24 hours. The cryostat enables a frozen section to be prepared in about 15 minutes.
The frozen section has its limits. It is prepared quickly so the tissue is not fixed and firm for sectioning. The process does not permit the same quality of detail that the pathologist generally sees in the routine fixed section. In general, special stains and procedures are not available with frozen sections as they are with routine sections. However, it is a quick and useful guide to assist the surgeon in determining immediate surgical therapy, generally while the patient is under anesthesia.