Correlation of MRI signal characteristics of intracranial melanoma metastases with BRAF mutation status

Abstract

BRAF V600 mutations (BRAFmut) are associated with more pigmentation in primary melanomas, but data on melanin content of metastases are limited. This study compares signal characteristics of BRAFmut and BRAF-wildtype (BRAFwt) intracranial melanoma metastases (IMM). MRI brain examinations at first diagnosis of IMM were identified, all performed at 3-Tesla including 1 mm volumetric pre- and postcontrast T1-weighted imaging and susceptibility-weighted imaging (SWI). Individual metastases were assessed by a neuroradiologist, stratified by size (≥10 mm, ‘larger’, vs. 2–9 mm, ‘small’; up to 10 per group); presence of intrinsic T1-hyperintensity (T1H) and, if present, whether confidently attributable to melanin as opposed to haemorrhage; evidence of haemorrhage; presence of central necrosis. A total of 267 IMM in 73 patients were assessed (87 larger IMM, 180 small). The proportion of larger IMM was similar in both groups (31% BRAFmut and 36% BRAFwt). In small IMM, MRI evidence of melanin was more common in BRAFmut patients (42% vs. 26%; P = 0.038). Haemorrhage was more common in larger IMM (51%, vs. 20% of small IMM; P < 0.0001), but did not differ based on BRAF status. Central necrosis was more common in larger IMM (44% vs. 7%; P < 0.0001) and in BRAFmut IMM (23% vs. 11%; P = 0.011). In the BRAFmut cohort, central necrosis was more common in patients without previous anti-BRAF therapy (33% vs. 7%; P = 0.0001). T1H attributable to melanin is only slightly more common in BRAFmut IMM than BRAFwt. Higher rates of central necrosis in BRAFmut patients without previous anti-BRAF therapy suggest that anti-BRAF therapy may affect the patterns of IMM growth.