Sentinel Node Biopsy for Melanoma of the Trunk; Wide Local Excision

The lymphatic drainage patterns from lesions located on the trunk are less predictable than those of the extremities. Therefore, when sentinel node biopsy for melanoma is indicated, it is important that lymphoscintigraphy be performed to include imaging through the inguinal, axillary, and cervical nodal basins. It is not uncommon to see drainage to more than one of these areas, which will require multiple sentinel lymph node biopsies. The location of these nodal basins and the primary tumor will then determine whether all areas can be addressed in one position, or whether the patient will need to be repositioned (such as a midback lesion that drains to bilateral axillae).

STEPS IN PROCEDURE

Sentinel Node Biopsy

Send patient to nuclear medicine for injection of Tc-99m–labeled sulfur colloid in four quadrants around lesion/previous biopsy site
Review lymphoscintigrams and discuss results with nuclear medicine staff; determine nodal basins with accumulation of Tc-99m
In the operating room, use hand-held gamma counter to identify sites of nodes
Inject 0.5-mL isosulfan blue dye in each of four quadrants around lesion/previous biopsy site
Position patient appropriately for removal of primary and/or sentinel nodes
Prep and drape these sites
Make 2- to 3-cm incision directly over area with highest counts in nodal basin, oriented so that it could be excised should complete node dissection be performed later
Dissect through subcutaneous tissues, directed by gamma probe and blue dye; take in situ count
Identify hot or blue nodes, remove, take ex vivo count and post excision count in basin; if >10% of in situ, then search for additional node(s) with probe
Close incision in two layers

Wide Excision

For 0.75- to 1-mm lesions, 1-cm margins, orient along Langer lines to reduce tension
For 1- to 4-mm Breslow depth, 2-cm margins
Make ellipse around lesion to facilitate primary closure
Excise skin and fat down to or to include muscle fascia
Close primarily in two layers

HALLMARK ANATOMIC COMPLICATIONS

Missed sentinel node
Lymphocele
Wound infection/disruption

LIST OF STRUCTURES

Axillary lymph nodes
Inguinal lymph nodes
Cervical lymph nodes

Biopsy of Suspected Melanoma

The diagnosis of melanoma begins with an adequate biopsy. Current guidelines recommend complete excisional biopsy whenever possible. For large or cosmetically important areas, punch biopsy is acceptable, but is associated with higher rates of both sampling error and understaging. Shave biopsy does not accurately assess the depth of invasion, and is not recommended. For excisional biopsy, the entire lesion is excised sharply to a depth of approximately 10 mm, with 1- to 3-mm lateral margins of normal appearing tissue. The orientation of the biopsy incision is important to facilitate closure after wide local excision (should this be necessary), and the incision is closed primarily.

Sentinel Node Biopsy (Fig. 120.1)

Technical Points

In addition to wide local excision, sentinel node biopsy is currently recommended for melanomas with depth 0.75 to 1 mm
with high-risk features such as ulceration or mitotic rate ≥1/mm², and for all intermediate thickness melanomas 1 to 4 mm in depth. Sentinel lymph node biopsy may also be indicated for staging thick melanomas (with depth greater than 4 mm).

Figure 120.1 Sentinel node biopsy. A: Injection of tracer at site of primary lesion. B: Scintigram showing drainage to ipsilateral axillary node. C: Scintigram showing drainage to left axillary and right inguinal nodes. D: Typical drainage patterns indicate dividing lines at the midline and at L2, but there is considerable individual variation.

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