Frozen section procedure

Overview
The frozen section procedure is a pathological laboratory procedure to perform rapid microscopic analysis of a specimen. It is used most often in oncological surgery. The technical name for this procedure is cryosection.

The intraoperative consultation is the name given to the whole intervention by the pathologist, which includes not only frozen section but also gross evaluation of the specimen, examination of cytology preparations taken on the specimen (e.g. touch imprints), and aliquoting of the specimen for special studies (e.g. molecular pathology techniques, flow cytometry). The report given by the pathologist is usually limited to a "benign" or "malignant" diagnosis, traditionally shouted into an intercom.

Procedure
The key instrument for cryosection is the cryostat, which is essentially a microtome inside a freezer. The surgical specimen is placed on a metal chuck and frozen rapidly to about −20 °C. At this temperature, most tissues become rock-hard. 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.

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:
 * 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 surgical 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 lipids. They can also be used to detect some antigens masked by formalin.

History
The frozen section procedure as practiced today in medical laboratories is based on the description by Dr Louis B. Wilson in 1905. Wilson developed the technique from earlier reports at the request of Dr William Mayo, surgeon and one of the founders of the Mayo Clinic. Earlier reports by Dr Thomas Cullen in at Johns Hopkins Hospital in Baltimore also involved frozen section, but only after formalin fixation, and pathologist Dr William Welch, also at Hopkins, experimented with Cullen's procedure but without clinical consequences. Hence, Wilson is generally credited with truly pioneering the procedure (Gal & Cagle, 2005).