Dynamic lymphoscintigraphy and image fusion of SPECT and pelvic CT-scans allow mapping of aberrant pelvic sentinel lymph nodes in malignant melanoma

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Abstract

To date, there are no reliable criteria to identify those patients with melanoma-infiltrated sentinel lymph nodes (SLNs) of the groin who might benefit from an extended lymphadenectomy, including the pelvic lymph nodes. We hypothesised that there are pelvic lymph nodes that receive lymph directly from the primary tumour, thus being at an increased risk for metastasis. In order to determine the frequency of radioactively labelled pelvic lymph nodes and the kinetics of their appearance, we introduce here a combination of dynamic lymphoscintigraphy, single photon emission computed tomography (SPECT) and image fusion of SPECT and pelvic Computed Tomography (CT)-scans. By dynamic lymphoscintigraphy and intraoperative gamma probe detection, superficially located inguinal SLNs (median 2 nodes) could be identified in all of the 51 patients included in this analysis. The histological search for micrometastases was positive in 16 patients (median Breslow thickness of the primary melanoma 2.5 mm). In 29 patients, SPECT and the image fusion technique were additionally performed. Radioactively labelled pelvic lymph nodes were detected in 20 individuals, 6 of them presenting aberrant pelvic SLNs that, on dynamic lymphoscintigraphy, had appeared simultaneously with the superficial SLN(s). Of the 6 patients in whom radioactive pelvic lymph nodes were excised together with the superficial SLN(s), only one had positive superficial SLNs. In this patient, the aberrant pelvic SLN proved to be tumour-positive. In 9 patients, there was no radiotracer uptake in the pelvic lymph nodes at all. Image fusion of SPECT and pelvic CT-scans is an excellent tool to localise exactly the pelvic tumour-draining nodes. The significance of radioactively labelled pelvic lymph nodes for the probability of pelvic metastases should be analysed further.

Introduction

Presently, in many clinical institutions intraoperative lymphatic mapping and sentinel node biopsy has become a standard procedure for patients with primary cutaneous malignant melanoma and clinically negative regional lymph nodes. The sentinel lymph node (SLN) is defined as the first lymph node draining the primary tumour, i.e. the first lymph node that is at risk from metastatic cells. The histological status of the SLN has been found to be an indicator representative of the whole lymph node basin. Moreover, it has turned out to be the strongest predictor for tumour recurrence and survival 1, 2, 3, 4. The original procedure of intraoperative lymphatic mapping, developed by Morton and colleagues [5], is performed using vital blue dye.

More recently, the addition of intraoperative gamma probe detection to blue dye mapping has been shown to improve the rate of SLN identification compared with the use of blue dye alone (for review see [6]). However, often multiple radioactive nodes are detected by gamma detection probe. It is not always clear whether these additional lymph nodes represent true SLNs, or rather second-echelon lymph nodes having collected radiocolloid particles that have passed through the SLN(s). Moreover, it also remains unknown whether radioactively labelled non-SLNs are at an increased risk of metastatic involvement, compared with lymph nodes with no radiotracer uptake.

Until now, the appropriate extent of groin dissection is controversial. A so-called superficial groin dissection consists of en bloc removal of all lymph nodes within the femoral triangle, the lymph nodes above the inguinal ligament and the nodes anterior and medial to the common and superficial femoral vessels up to Cloquet's node within the femoral canal. The more extended ilioinguinal dissection additionally includes the deeper lymphatics of the iliac, hypogastric and obturator vessels (also called “deep” or “pelvic” nodes). There are, however, no reliable criteria to determine which patients with positive superficial inguinal SLNs will have additional pelvic metastases and, therefore, might benefit from an extended ilioinguinal lymphadenectomy.

Several surgeons have hypothesised that the histological status of Cloquet's node, situated in the femoral canal, can significantly reflect the tumour status of the pelvic basin [7]. Others have shown that this lymph node is often missing and that its sensitivity to predicting the status of the pelvic lymph nodes is low [8].

Afferent lymphatic channels leading directly to the pelvic nodes have been described (Fig. 1) [9]. So far, no previous study has dealt with details of the pelvic lymphatic drainage in patients with cutaneous malignant melanoma. Performing SLN biopsies using a hand-held gamma probe, we have often found radioactivity underneath the abdominal fascia along the iliac vessel, beyond the Cloquet's node. Moreover, in some cases we have observed blue lymphatic channels draining directly to the deep iliac nodes. Thus, an unknown amount of radioactively labelled non-SLNs or even true SLN should be located in the deeper lymphatics along the iliac, hypogastric and obturator blood vessels. Applying dynamic lymphoscintigraphy, single photon emission computed tomography (SPECT) together with pelvic Computed Tomography (CT)-scans (image fusion technique), the present study aims to determine the frequency of radioactively labelled pelvic lymph nodes as well as the kinetics of their appearance in order to provide the basis for future studies on micrometastasis to the pelvis.

Section snippets

Patients

At the Georg-August-University of Göttingen from May 1997 to January 2002, 51 patients with primary cutaneous melanoma of the leg or the lower part of the body underwent lymphatic mapping and 50 of them received inguinal SLN biopsy. Patients' data, including clinical characteristics, lymphoscintigraphic findings, and histopathological microstaging, were entered prospectively into an electronic database. By physical examination and staging evaluation these patients showed no evidence of

Patients' characteristics

The study population consisted of 17 men and 34 women with a median age at diagnosis of 61 years (range 26–84 years). 47 of the patients had leg-located primary tumours, whereas in 4 patients the primary was located at the lower part of the trunk. The mean Breslow thickness was 3 mm (Standard Error (SE) 2.1 mm), the median tumour thickness 2.4 mm (range 0.6–10.8 mm). Twenty of the primary melanomas (39%) showed histological ulceration.

Lymphoscintigraphic findings

In each patient, at least one superficial inguinal SLN could

Discussion

Although presently a complete lymph node dissection is considered to be the correct treatment for patients with proven regional lymph node metastases of malignant melanoma, there is still no general agreement upon the appropriate extent of groin dissection (inguinal versus ilioinguinal dissection). In patients with clinically enlarged groin metastases, the iliac lymph nodes have been found to be positive in approximately 30% of histological specimens 11, 12, 13 and, thus, most authors have

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