Preoperative Lymphoscintigraphy

The techniques and results of cutaneous lymphoscintigraphy are discussed in detail in Chapter 3, but several aspects of the procedure need to be emphasized here because they are directly relevant to the planning and execution of surgery to identify and remove sentinel nodes. High-quality preoperative lymphoscintig-raphy is invaluable to ensure that sentinel lymphadenectomy is accomplished expeditiously and to minimize the amount of dissection of the relevant lymph node field (or fields) which must be performed. As well, lymphoscintigraphy provides preoperative identification of drainage pathways to unexpected node fields [3-5]. Some have suggested that preoperative lymphoscintigraphy is necessary only for melanomas in sites from which the lymphatic drainage might be ambiguous. It has now become clear, however, that there are few, if any, sites in the body from which lymphatic drainage pathways are able to be predicted with complete confidence [6,7]. Even in sites that appear to have predictable drainage such as the extremities, occasional ectopic lymph nodes will be identified by lymphoscintigraphy.

If preoperative lymphoscintigraphy is performed, information about the exact number and location of sentinel lymph nodes which must be found and removed is known to the surgeon before the operative procedure of sentinel node biopsy commences (Fig. 1). This means that the patient can be made aware of the site or sites of the proposed surgery and can give appropriately informed consent for the operation. The information obtained from the preoperative lympho-scintigram further facilitates the sentinel lymphadenectomy procedure by identifying patients in whom the rate of lymphatic flow from the primary melanoma site to the draining lymph nodes is unusually slow [8-10]. This allows modification of the standard blue dye injection protocol, with earlier dye injection to increase the probability that it will have reached the node field by the time of surgical exposure.

Yet another benefit of carefully performed preoperative lymphoscintigra-phy is that if the images are acquired with the patient in the planned operative position and appropriate lateral and/or oblique views are obtained, the depth of each sentinel node beneath the skin surface can be indicated with precision, and its location in relation to the mark previously made on the overlying skin by the nuclear medicine physician will be accurate [5]. This is particularly useful for biopsy of axillary sentinel nodes in obese patients, where locating them can otherwise be particularly difficult and time-consuming. With the patient supine and the arm positioned at a 90° angle to the body for both preoperative lymphoscintigraphy and surgery, operative sentinel node localization is greatly facilitated.

If lymphoscintigraphy is performed the day before a planned sentinel lymphadenectomy procedure, there will be sufficient residual radioactivity in sentinel lymph nodes to allow them to be identified at the time of surgery using a

Axilla Sentinel Node Procedure
Figure 1 Patient with primary melanoma site in right loin showing lymphatic draining pathways to a single sentinel node in the right axilla and three sentinel nodes in the right groin. The skin markings were made at the time of preoperative lympho-scintigraphy.

hand-held gamma probe [11,12]. This can greatly simplify logistics and reduce radiation exposure to both patient and operating theater staff by avoiding the need for a second injection of a radioisotope in the immediate preoperative period. It also provides better discrimination between sentinel and nonsentinel nodes and is particularly useful when the primary injection site is close to the draining lymph node field (as is often the case for head and neck melanoma) [12].

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