Metastatic cutaneous malignant melanoma: Spectrum of imaging findings and the role of multimodality imaging

[Staging of cutaneous malignant melanoma by CT]

Malignant melanomas are a challenge in radiological imaging diagnostics as they may metastasize into every organ and tissue. Cross-sectional imaging, in particular positron emission tomography computed tomography (PET/CT) and whole body magnetic resonance imaging (MRI), are considered the standards in the staging of melanomas. Because of its excellent availability CT, however, remains a widely employed staging modality. Familiarity with the manifold CT morphology of metastasized melanomas as it is described here is essential when interpreting dedicated CT and in addition useful when interpreting PET/CT results. In individual cases CT can assist in the detection of transient metastases. In the detection of locoregional lymph node metastases CT has a median sensitivity and specificity in meta-analyses of at best 61 % and 97 %, respectively, which is inferior to the performance of ultrasound (96 % and 99 %, respectively). According to meta-analyses, in the assessment of systemic tumor spread CT can detect the majority of metastases with a sensitivity and specificity of 51-63 % and 69-78 %, respectively, which is inferior to MRI and PET/CT. Therefore, if an exact staging is required for critical management decisions, MRI or PET/CT should be employed whenever possible.

Isolated cerebral susceptibility artefacts in patients with malignant melanoma: metastasis or not?

OBJECTIVE

While staging patients with malignant melanoma, cerebral susceptibility artefacts on T2*-weighted/susceptibility-weighted imaging (SWI) sequences without a correlate on contrast-enhanced T1-weighted images can be confusing. Without intravenous contrast enhancement, cavernomas, microhaemorrhages and melanin-containing metastases represent possible differential diagnoses for these findings. The purpose of this study was to find out, how often such lesions correspond to metastases.

METHODS

Brain MR images (1.5 T) of 408 patients with malignant melanoma but without cerebral metastases in the initial staging by MRI were reviewed retrospectively. Eighteen patients (5 female, 13 male) with malignant melanoma and signal intensity loss on T2*/SWI were included in our study. The average observation period was 19.6 months (6-46 months, 2006-2009).

RESULTS

In each of these 18 patients between one and seven hypointense lesions on T2*/SWI were found. None of these lesions developed into metastasis.

CONCLUSION

Focal areas of susceptibility artefacts in the brain parenchyma without corresponding abnormalities in contrast-enhanced T1 weighted images are unlikely to represent brain metastases.

KEY POINTS

• In melanoma patients early diagnosis of metastatic brain lesions is mandatory. • Melanin content and haemorrhage are potential reasons for MRI characteristics of melanoma metastases. • Susceptibility-weighted MRI visualises melanin and blood products. • Isolated cerebral susceptibility artefacts do not convert into melanoma metastases. • SWI/T2* sequences cannot replace Gd-enhanced sequences.

RANK is expressed in metastatic melanoma and highly upregulated on melanoma-initiating cells

Melanoma accounts for ∼ 79% of skin cancer-related deaths, and the receptor activator of NF-κB (RANK)-receptor activator of NF-κB ligand (RANKL) pathway has been shown to be involved in the migration and metastasis of epithelial tumor cells. In this study, we demonstrate that RANK was significantly increased in peripheral circulating melanoma cells, primary melanomas, and metastases from stage IV melanoma patients compared with tumor cells from stage I melanoma patients. However, upregulated RANK expression was not found in stage IV melanoma patients with bone metastases compared with stage IV melanoma patients without bone metastases, providing a possible explanation for the clinical observation that melanoma cells do not preferentially metastasize to bone tissue. Strikingly, RANK-expressing melanoma cells from peripheral blood, primary tumors, or metastases of stage IV patients coexpressed ATP-binding cassette (ABC) B5 and CD133, both markers characteristic of melanoma-initiating cells, suggesting a tumor stem cell-like phenotype. In support of this hypothesis, RANK-expressing melanoma cells showed a reduced Ki67 proliferation index compared with RANK(-) melanoma cells from the same patient and are able to induce tumor growth in immunodeficient mice. Together, our data demonstrate that RANK expression is increased in metastatic melanoma and highly upregulated on melanoma-initiating cells, suggesting that RANK might be involved in the development and maintenance of melanoma-initiating cells and possibly in metastatic spreading.