Sentinel node biopsy

This is currently an experimental technique {2057} that is under active evaluation by prospective clinical trials and it is not practised at all centres. It is a technique used primarily for staging a clinically N0 neck. in an effort to avoid a neck dissection. If a clinically N0 neck is followed untreated until tumour development occurs, the prognosis can be very poor {57,977}. Studies on the incidence of occult metastases in N0 necks {753} have shown tumour spread in only a small minority of patients. Therefore, if neck dissection is undertaken either prophylacti-cally or as a staging procedure, on patients with N0 necks, a large majority will have unnecessary surgery, as the neck will be found to be free from tumour. The sentinel node is the first draining lymph node from a tumour. It is assumed that if the sentinel node can be shown to be free from tumour, then the lymphatic basin is free from tumour and neck dissection is not required. By contrast, sentinel node positive patients can be selected for further therapy. Sentinel nodes are identified by a combination of lym-phoscintigraphy and injection of blue dye in the tumour bed and then sampling draining nodes identified. In reality, more than one sentinel node is found in many cases {2345} indicating that tumours drain to more than a single first echelon node, presumably from different parts of the tumour.

Sampled sentinel nodes should be fully examined by the pathologist. This usually involves bisecting the node in the largest diameter and then undertaking extensive sampling. Some pathologists undertake frozen sections on bisected fresh nodes. If this is done it is important to use a technique whereby the cut surface is frozen on a flat surface and only early sections are examined. This is to ensure that as little node as possible is examined at this stage in order not to compromise full examination of the node. Paraffin processed blocks are then examined with H and E sections of the early sections of the blocks. If these show no tumour, more detailed sampling with immunocytochem-istry for cytokeratins and sampling through the block is required. True serial sectioning is impracticable for routine use. A compromise is step sectioning at intervals of 150pm with examination of H and E sections and AE1/3 reacted sections {2202}. The importance of these sections is that suspicious areas on immunocytochemistry can be identified in the H and E sections. These may be viable tumour cells, but other possible causes of cytokeratin positivity, such as inclusion of normal salivary gland epithelium or thyroid follicles, either occult metastases or lateral aberrant thyroid, need to be identified. Another not infrequent finding is areas of cytokeratin posi-tivity which on H and E appear as densely eosinophilic apparently non-viable tumour cells.

Fig. 4.12 A Verrucous carcinoma (VC) of the gingiva. B VC of the ginigva, spreading laterally to involve the cheek mucosa.

Interpretation of sentinel nodes can demand considerable pathological expertise. The outcome of the pathological assessment may be the presence of metastasis; micrometastasis, less than 2mm diameter tumour deposits, or isolated tumour cells {2477}. Micrometastasis has been defined {1073} as cells which have arrested and implanted. These may be in contact with a vessel or lymph sinus wall or may be extravascular. Single or small clusters of cells within lymph or blood vessels, but not in contact with the wall are defined as isolated tumour cells.

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