Blocks for histology Figure 433

• marrow and proximal margin of resection.

• any scars related to previous surgery or open biopsy.

• representative blocks of involved soft tissues.

• representative blocks of tumour obviously around or in major vessels.

• blocks to evaluate the tumour characteristics and extent of necrosis for assessing response to chemotherapy.

• the extent of tumour necrosis is roughly estimated by calculating the tumour necrosis present in a whole bone slab 0.4 cm thick. Having bivalved the affected bone this 0.4 cm longitudinal slab is obtained by cutting along the plane of maximum tumour diameter. The slab is drawn out and the whole slab cut into blocks for histology. These blocks are individually labelled and are correspondingly noted and labelled on the written diagram. About 20-40 blocks are required to achieve this properly (Figure 43.3).

• the blocks are properly fixed in formalin prior to decalcification. It is most important that blocks, especially these relatively large bone blocks, are well fixed as the acid used in

Figure 43.3. Taking blocks from a bone slab containing sarcoma.

decalcification can destroy the cell morphology. Often about 48 hours fixation is required.

• decalcification is obtained using 10% formic acid. This may take several days.

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