Regional Lymph Nodes

The number of lymph nodes evaluated and the number involved by metastasis should always be stated in the pathologic report. Around 7-14 lymph nodes should be evaluated for radical resection, as it has been shown that a lower number does not predict for negativity [3]. If fewer than 12 nodes are found, additional methods (i.e., visual enhancement techniques) should be considered [25]. A smaller number of nodes is acceptable for palliative resection or after neoadjuvant radiotherapy.

Tumour nodules in the perirectal fat without histologic evidence of residual lymph node involvement have two different possibilities. They are classified as metastasis (in the N category as lymph node replacement by tumour) if the nodule has the form and smooth contour of a lymph node (Fig. 8a). If the nodule has an irregular contour, it should be considered as an expression of vascular invasion either microscopic (V1) (Fig. 8b) or macroscopic (V2).

Micrometastases (tumour measuring greater than 0.2 mm but less than or equal to 2.0 mm in the greatest dimension) are classified as N1. The report should specify that it is an N1 (mic) or Ml (mic) micrometastases [25].

The biologic significance of isolated tumour cells within nodes (defined as single tumour cells or small clusters of tumour cells measuring 0.2 mm or less) isolated by immunohistochemical or molecular techniques is still not clear. Isolated tumour cells should be classified as N0 [33].

Twelve lymph nodes is still considered the minimal number, but recent studies have shown [63] that no precise value correlates to an accurate staging; the possibility of finding a positive node simply increases with the number of nodes evaluated [64].

Routine assessment of regional lymph node metastasis is limited to the use of conventional pathologic techniques (gross assessment and histo-logic examination). Current data are not sufficient to use special/ancillary techniques (such as immunohis-tochemistry, flow cytometry, polymerase chain reaction) to detect micrometastases or isolated tumour cells [25].

Fig. 8a, b. Tumour nodules in perirectal fat. a Nodules with smooth contour: lymph node metastasis. b Nodules with irregular contour: vascular invasion (V1)

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