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.