Purpose: Susceptibility-weighted imaging (SWI) has significantly increased our sensitivity in detecting hemorrhagic brain lesions. We sought to explore the prevalence of intratumoral hemorrhage as detected by SWI in brain metastases from melanoma and breast cancer.
Methods: Lesions with a size of 0.1 cm were categorized as micrometastases, whereas larger lesions were categorized as macrometastases. Susceptibility-weighted imaging findings on locations corresponding to enhancing lesions were categorized as either positive or negative based on presence/absence of signal dropout. The percentage of SWI positivity was then estimated as a function of lesion size. Two-tailed Fisher exact test was performed to examine differences in the contingency tables.
Results: Magnetic resonance imaging studies from 73 patients with 1173 brain metastases, which enhanced on postcontrast T1-weighted imaging (T1WI) were selected for analysis. Of these lesions, 952 had SWI data available, and 342 of 952 were micrometastases. Only 10 of the 342 micrometastases and 410 (67.2%) of the 610 macrometastases were SWI positive (P < 0.0001). When examined by tumor type, 76.9% (melanoma) versus 55.6% (breast cancer) were SWI positive (P < 0.0001), regardless of tumor size. All melanoma lesions (8/8) and only 1 of 15 breast cancer lesions larger than 1.5 cm were SWI positive.
Conclusion: With the use of combined SWI and contrast-enhanced high-resolution T1 imaging, we found that presence of intratumoral brain hemorrhage is uncommon in micrometastases but common in metastases greater than 0.1 cm from breast cancer or melanoma. Large metastases commonly harbored hemorrhage, and this occurred more frequently in patients with melanoma than with breast cancer.