Lymphoscintigraphy and sentinel lymph node biopsy for melanoma

Keywords: Lymphoscintigraphy, melanoma, sentinel node

INTRODUCTION

The assessment of the sentinel lymph node(s), the draining lymph node(s) nearest the site of the primary malignant melanoma, has become an important staging and prognostic modality in the management of malignant melanoma. (1, 2)

The identification of the sentinel lymph node has evolved over a period of time. It has changed from using only vital dyes, 3 to pre-operative radioisotope lymphatic mapping and intra-operative use of hand-held gamma probes. (4, 5, 6)

At Middlesborough, we combine all of the above techniques to identify and biopsy the sentinel lymph node. We carry out preoperative lymphatic mapping using technetium (Tc99) colloid, intra-operative vital blue dye injection and use a handheld gamma probe to locate the node(s).

PATIENT SELECTION

We adopt the selection criteria used by the Multicentre Selective Lymphadenectomy Trial co-ordinated by Morton et al (1999). (7)

• Primary cutaneous melanomas having a Breslow thickness of one millimetre and at least Clarke's level three or
• Breslow thickness of less than one millimetre and at least Clarke's level four or
• Allergy to the radiopharmaceutical colloid. This is an absolute contraindication. Patients, who for other reasons are not fit for surgical procedure(s) and/or anaesthesia may also be excluded.

PREOPERATIVE PREPARATION

This is a day case procedure with a provision for an overnight stay, if required.

Sentinel lymph node biopsy is easily performed using local or general anaesthesia (the groin is easy to examine under a local anaesthetic).

LYMPHOSCINTIGRAPHY

Lymphatic mapping is the first of this three-part investigation. No anaesthetic is required for this component of the assessment. It is performed in the Department of Nuclear Medicine by the surgeon and a medical physicist. The procedure is carefully explained to the patient who then lies on the imaging table with the appropriate anatomical site exposed. The surgeon injects 0.4mll (20 megaBecquerels) of technetium (Tc 99) unfiltered sulfur colloid intradermally in to four quadrants (0.1ml each) around the melanoma scar.

The patient is then positioned under the scanner (Figure 1) and dynamic images obtained (Figure 2).

Figure 1 Patient lying under the scanner

This early phase dynamic scanning shows the lymphatic channels and the sentinel node(s) as they appear in sequence. This is carried out for 20 minutes. The patient is then asked to walk about in the hospital for approximately one hour.

Figure 2 Lymphoscintigram (dynamic image)

A late phase scanning of the basin is done ninety minutes after the injection. The sentinel node(s) is (are) usually clearly demonstrated at this phase (Figure 3).The location of the node(s) is then marked out on the skin surface guided by a radio-opaque lead marker.

Figure 3 Sentinel lymph nodes (late phase), at 15 minutes (left) and 90 minutes (right)

INTRADERMAL BLUE DYE INJECTION

This is done on the operating table in theatre while the patient is under anaesthesia (if general anaesthesia is used) or before the local anaesthetic infiltration. Vital blue dye (0.1 ml) is injected in to each of four quadrants around the melanoma scar (Figure 4). The surgeon scrubs and gowns while the operation site is prepared, thus, allowing time for the dye to reach the sentinel lymph node via the afferent lymphatics. This process takes 10-20 minutes in the lower limb and up to 30 minutes in the upper limb.

Figure 4 Four-quadrant injection of dye

SENTINEL LYMPH NODE BIOPSY

The handheld gamma probe (covered in a sterile sheath) is run over the region of the sentinel lymph node(s) and a surface marking made over the putative node(s) (point of maximal counts against background, using the audible siren tone of the probe). The incision (at the marked site is so positioned that it forms part of the incision for any future block dissection of the regional nodes.

A careful dissection is carried out through soft tissues with strict haemostasis so as to demonstrate a blue lymphatic channel and lymph node (Figure 5).

Figure 5 Blue lymphatic channel and lymph node

The 'hot' node(s) is(are) confirmed by the hand held gamma probe and then excised; and an ex-vivo count of radioactivity is obtained using the gamma probe (Figure 6). All excised nodes are sent for histopathological examination and assessment of invasion by the melanoma cells.

Figure 6 Ex-vivo count of radioactivity in an excised lymph node

CONCLUSION

Sentinel lymph node biopsy is a very useful diagnostic and staging tool in experienced hands. A learning curve of 30 cases is normally needed to achieve a consistently high accuracy. Using the blue dye alone, a success rate of 90-95% can be achieved. This rises significantly to 99% with the addition of a radiopharmaceutical tracer. (8, 9)

There are no prospective data on the therapeutic benefit of sentinel lymph node biopsy-directed therapy to date. However, in a disease in which the mainstay of management (cutaneous and nodal disease) in surgery, early identification and removal of micrometastasis can only be a positive way forward.

REFERENCES

1. Kelly MC, Ollila DW, Morton DL. Lymphatic mapping and sentinel lymphadenectomy. Sem Surg Oncol 1998 June; 14: 283-90
2. North JH Jr, Spellman JE. Role of sentinel node biopsy in the management of malignant melanoma. Oncology (Huntington) 1996; 10: 1237-42
3. Lingam MK, Mackie RM, McKay AJ. Intraoperative identification of sentinel node in patients with malignant melanoma. Br J Cancer 1997; 75: 1505-8
4. Norman J Jr, Cruse W, Ruas E et al. The expanding role of lymphoscintigraphy in the management of cutaneous melanoma. First Place Winner: Conrad Jobst award. American Surgeon 1989; 55: 689-94
5. Gennari R, Stoldt HS, Bartolomei M et al. Sentinel node localisation: Anew prospective in the treatment of nodal melanoma metastases.International Journal of Oncology 1999; 15(1): 25-32
6. Thompson JF, Uren RF, Shaw HM et al. Location of sentinel lymph nodes in patients with cutaneous melanoma: new insights into lymphatic anatomy. J Am Coll Surg 1999; 189: 195-204
7. Morton DL, Thompson JF, Essner R et al.Validation of the accuracy of intraoperative lymphatic mapping and sentinel lymphadenectomy for early-stage melanoma: a Multicentre Selective Lymphadenectomy Trial Group. Annals of Surgery 1999; 230;453-63
8. Bostick P, Essner R, Glass E et al.Comparison of blue dye and probe-assisted intraoperative lymphatic mapping in melanoma to identify sentinel nodes in 100 lymphatic basins. Archives of Surgery 1999; 134; 43-9