Cryotomy (Frozen Sections)

introduction

Frozen sectioning is performed on tissues where the need for rapid examination of the tissue does not allow sufficient time for conventional fixation and processing procedures (such as intra-operative frozen sections or Mohs micrographic surgeries), or when the tissue elements to be demonstrated would be destroyed by such procedures (such as with methods for lipids, enzymes, etc).

Specimens for frozen sections are most often tissue received fresh and individual slides are quickly fixed with formalin before staining, although they may also be performed on fixed unprocessed tissues.  Once specimens are received, they are accessioned into the frozen section log.  The same quality practices and procedures are used as for accessioning routine fixed specimens, except that the code FS is used to indicate to the pathologist that the slides will be created from frozen sections.  Instead of paraffin blocks created with traditional processing, the tissue is oriented and embedded in a water soluble gel that supports the tissue by quickly freezing onto a metal disk.  Rapid freezing is essential with frozen sections to avoid the formation of ice crystal artifact.  When water molecules are allowed a greater degree of expansion during cooling, the resulting crystals displace tissue elements and leave open artifact spaces behind once removed.  These spaces can hinder a diagnosis, and so must be minimized by cooling the tissue as quickly as possible.

Sections are cut using a cryostat, which is essentially a rotary microtome that operates inside a low-temperature controlled environment.  Once cut sections are affixed to glass slides, they are able to be stained with the desired method.   Cutting temperatures can vary with the tissue type but on average, cryotomy is performed at approximately -20C.  Tissues with a higher lipid content required colder temperatures (-25C to -30C), and harder, denser tissues prefer temperatures that are higher (-10C to -15C).

Due to the urgent nature of frozen sections (the patient is often still in surgery waiting for results), the technologist must be able to work quickly and keep the workstation neat and organized at all times.

Safety Precautions

Since fresh tissue is most often used, appropriate precautions for blood borne illnesses must be taken.  This includes use of PPE (gloves, goggles, lab coat), avoiding the creation of aerosols by not using freezing sprays etc, and by regular and approved disinfection of the cryostat and accessories.  Waste and debris from fresh tissues are to be disposed of as anatomical waste (red bags).