Original ContributionRole of High-Resolution Ultrasound and PET/CT Imaging for Preoperative Characterization of Sentinel Lymph Nodes in Cutaneous Melanoma
Introduction
Positron emission tomography (PET) is a relatively modern, complex and expensive imaging technology, which can detect metastases by an altered metabolism. Images are obtained from positron emitting radioactive tracers that are administered intravenously. 18F-fluorodeoxyglucose (FDG) is most frequently used because of the enhanced glucose consumption by tumors (Larson et al. 1981). Combining computed tomography (CT) with PET imaging as an integrated examination has brought extra benefits by performing an accurate anatomic localization, shorter examination time, improved patient comfort and convenience (von Schuthess et al. 2006). In various oncologic diseases, it has become a very important technique giving detailed information about diagnostic or prognostic issues (Larson and Schwartz 2006; Blodgett et al. 2007). PET combined with computerised tomography (PET/CT) is frequently used in the initial staging and restaging of common cancers such as non-small cell lung cancer, colorectal cancer, breast cancer and lymphomas (Silverman et al. 1998; Nieweg 1994). Addressing the value in patients with cutaneous melanoma (CM), various studies have illustrated the potential of PET/CT in detection of distant metastases, especially visceral ones (Reinhardt et al. 2006; Gritters et al. 1993). In contrast to the large amount of publications in other fields like breast cancer or PET/CT and follow-up, our study is one of the first addressing the comparison of PET/CT and HRUS in the preoperative characterisation of peripheral lymph nodes (LN) focusing on sentinel lymph nodes (SLN). So far, a single PET study claims that micrometastases in SLNs can also be identified by PET imaging alone before surgery (van Diest 1999). The smallest tumor deposit to be detected by PET is a frequently investigated and discussed question. It has convincingly been shown that PET can locate tumors smaller than 1 cm, which is known to be the limit of the CT scan (Pieterman et al. 2000). The spatial resolution of PET imaging equipment commonly in service at this time is 5–6 mm diameter (Gritters et al. 1993).
On the other hand, HRUS as a cheap (average costs per patient about 80–100€, pending on the addition of color Doppler sonography for detection of lymph node vascularisation pattern) and noninvasive imaging method has been frequently used in the staging of melanoma patients pointing to a possible detection of intranodal tumor deposits in the range of 3 mm in diameter (Rossi et al. 2003; Starrit et al. 2005; Hocevar et al. 2004; Sanki et al. 2009; Voit et al. 2009; Mueller et al. 2009; Schuler et al. 2010). In contrast, the average costs for a PET/CT examination in Germany are 1200€ (Plathow et al. 2008). The overall costs of SLNB including the detection of the SLN by lymphoscintigraphy had been estimated to range from 4000€ to 5000€ per patient on the basis of the German DRG-system (Mueller et al. 2009). Although neither PET/CT nor HRUS can replace SLNBs, the question of detection of smallest metastatic deposits in SLNs might be interesting for general diagnostic statements concerning nodal disease in cutaneous melanoma.
The aim of our study was to compare sensitivity and specificity of HRUS and FDG-PET/CT in the preoperative characterization and identification of metastatic involvement of SLNs in CM.
Section snippets
Patients
From January 2009 to January 2011, 123 patients (56 females and 67 males, mean age 55.2 ± 13.3 years) with invasive CM (tumor thickness ≥1.0 mm) received SLNB at the Department of Dermatology and Allergy, University of Bonn, Germany. A retrospective computer-aided search of preoperatively performed staging procedures revealed 20 (out of 123) patients presenting with high-risk melanomas in whom PET/CT had been performed for exclusion of systemic metastases in addition to HRUS. HRUS was performed
Results
From 123 patients, 333 SLNs were removed surgically, with a mean of 2.7 (range 1–7) SLNs per patient. Of the 333 SLNs excised, 53 (16%) were positive in 39 patients (31.7% of all 123 patients had a positive SLN) according to histopathologic investigation. In the subgroup of 20 patients resembling our study group, 59 SLNs were removed surgically, with a mean of 2.95 (range 1–6) SLNs per patient. Of the 59 SLNs excised, 17 (28%) were positive in 12 patients (60.0% of these 20 patients had a
Discussion
The detection of metastases in regional lymph node basins of patients with CM is one of the most important issues concerning the prognosis of this disease (Carlson et al. 2003; Garbe et al. 1995; van Akkoi et al. 2010). This is true for follow-up situations but also for primary staging of patients with elevated tumor thickness or further risk factors. Therefore, multiple efforts had been made in the past to identify reliable staging procedures. Without doubt, SLNB followed by histopathologic
Conclusion
Without doubt HRUS is not an appropriate substitute for SLNB, but, on the basis of the current investigation, it could be superior to PET/CT imaging in this indication. Preoperative PET/CT reveals to be no adequate screening method for SLNs in melanoma patients and cannot replace SLNB. Although SLNB is most exact for correct primary nodal staging of melanoma patients with the possibility to identify even single-cell metastases, HRUS is strongly recommended for the preoperative identification of
Acknowledgments
The study was supported by a grant from the German Cancer Aid (Program for the Development of Interdisciplinary Oncology Centers of Excellence in Germany), Bonn, Germany.
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