Frozen Section

The number of frozen sections appears to be declining in the United Kingdom, due in part to improved preoperative diagnosis of breast lumps and many other tumours by FNA, needle core or endoscopic biopsy. This is in contrast to the situation in North America where frozen sections and intra-operative consultations are very common.

The use of frozen section should be restricted to those cases where the result will change the intra-operative management of the patient.

Frozen sections are used in a wide variety of clinical situations

• confirmation of excised tissue, e.g., parathyroidectomy versus lymph node or a thyroid nodule.

• evaluation of a suspicious lymph node, liver or lung nodule as part of an operative staging procedure, or prequel to consideration of radical surgery.

• determination of a lung, pancreatic or ampullary mass prior to proceeding to lobectomy or a Whipple's procedure.

• clearance of resection margins, e.g., gastrectomy, pulmonary lobectomy or resections for squamous cell carcinoma of the upper aerodigestive tract.

• diagnosis of suspicious abdominopelvic masses at laparotomy, e.g., ovarian tumours.

Specimens for frozen section are best examined using a safety cabinet. As the tissue is not fixed, full precautions must be taken against blood-borne Category Three infections. Thin fragments of tissue (no more than 2-3 mm thick and no wider than the diameter of the chuck) should be removed by a scalpel and placed on the surface of a metal chuck in a blob of embedding medium such as OCT compound (Tissue Tek) so that the tissue is covered. The chuck is rapidly cooled by standing it in a small volume of liquid nitrogen or using a proprietary aerosol spray such as CryoSpray Freezer Spray (Cell Path PLC). The sections are then cut using a microtome and cryostat and stained routinely by haematoxylin and eosin.

Touch imprints can be made by gently smearing the fresh tissue against a glass slide. This is allowed to air dry and then stained by Giemsa or proprietary stains such as Diff Quick. This can be very useful in the evaluation of lymph nodes and many tumours providing complementary cytological detail that cannot be appreciated on frozen section. Immunocytochemistry and FISH may be performed on touch imprints of tumours made onto suitable adhesive coated slides (e.g., APES).

Relative contra-indications to frozen section include certain infections such as suspected tuberculosis or where the frozen section is unlikely to yield a clinically useful result and may compromise the final diagnosis (e.g., an impalpable breast lesion containing microcalcification picked up at screening). Some diagnoses cannot be readily made on frozen section; classical examples being the distinctions between follicular carcinoma and adenoma of the thyroid and lymph node hyperplasia and follicular lymphoma.

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