Background
A variety of studies have been published on both the frequency and utility of brain imaging for detecting melanoma brain metastasis. However, uncertainty remains in the subset of asymptomatic patients who have regional metastasis at the time of selective sentinel lymph node biopsy (SLNB). In many cases, patients receive brain imaging with magnetic resonance imaging (MRI) when regional metastatic disease is found during SLNB. These imaging studies have historically been reported as low-yield for distant metastasis. If the diagnostic yield for MRI tends to be low, based on data, we sought to calculate that maximal incidence melanoma brain metastasis at the time of positive SLNB in our CPMC melanoma database.
Materials and Methods
136 patients with brain MRIs were identified from our prospectively maintained databases of individuals who underwent SLNB for primary melanoma with metastasis to SLNs. The study was conducted as part of an IRB-approved, retrospective analysis of a population of patients at a tertiary care referral center. The primary outcome measure was detection of distant metastasis on MRI brain imaging. A probabilistic model was then applied to the observed data to predict the maximal incidence of melanoma brain metastasis at the time of positive SLNB in asymptomatic melanoma patients.
Results
None (0.0%) of the brain MRIs detected metastatic disease in 136 melanoma patients at the time of positive SLNB. Using the developed probabilistic model, estimates of the incidence of brain metastasis at the time of diagnosis of melanoma with a positive SLN were calculated. For an approximated error tolerance of 0.05 the maximal incidence of melanoma brain metastasis at the time of positive SLNB was calculated as less than 2.2%; for a more stringent error tolerance of 0.01, the maximal incidence of was calculated at less than 3.3%.
Conclusions:
Brain MRI rarely reveals distant metastasis at the time of SLNB. Based on the MRI data, there is a low incidence of melanoma metastasis to the brain at the time of positive SLNB. The use of MRI for patients at the time of positive SLNB should be reserved for symptomatic patients or those who undergo clinical trials that require baseline brain MRI.