Expansion
Margins, tissue identification, and confirming malignancy during surgery
Expansion
Method: tissue is frozen and cut on a cryostat, stained and reported within 15 to 20 minutes, without fixation or paraffin embedding.
Indications
- Resection margin assessment, as in breast, head and neck and Mohs surgery
- Tissue identification: confirming parathyroid rather than thyroid or lymph node
- Establishing whether a lesion is malignant when this changes the operation
- Confirming that adequate diagnostic tissue has been obtained
- Assessing sentinel lymph nodes in some protocols
- Lipid demonstration, which requires frozen tissue since processing dissolves fat
Limitations
- Ice crystal artefact and poor cytological detail
- Small sample, so sampling error
- Unreliable for lymphoma, follicular thyroid lesions (where capsular invasion must be assessed on the whole capsule) and for grading
- Not for fatty tissue, calcified tissue or bone
The governing principle is that frozen section should only be requested when the answer will change the operation in progress. Otherwise the specimen should go for standard processing, which gives far better morphology and allows immunohistochemistry.