Background
Several studies have been published on the appropriate radiographic studies for detecting stage IV disease in patients with melanoma at initial presentation. Of particular interest are those asymptomatic patients who undergo selective lymph node biopsy and are found to have regionally metastatic melanoma to a sentinel lymph node. Commonly, patients undergo PET/CT and/or brain MRI at the time that metastasis to a sentinel lymph node is found. The diagnostic yield of these imaging studies is uncertain with false positives being of particular concern.
Materials and Methods
Of 1389 patients identified from a database of individuals who underwent selective sentinel lymphadenectomy for primary melanoma we studied 212 with at least 1 sentinel lymph node positive for metastatic melanoma who had a PET/CT and/or brain MRI. The study was conducted as an IRB-approved, retrospective analysis of a population of patients at a tertiary care referral center. The main outcome measure was diagnostic yield of the imaging studies.
Results
The results of 0.6% of the imaging studies were positive for metastatic disease, 92.6% were negative, and 6.7% were indeterminate. Indeterminate results were confirmed to be negative by additional studies ranging from repeated imaging to invasive procedures. The yields are as follows: PET/CT 0.7% and brain MRI 0%; the false positive rate for PET/CT was 7.2%.
Conclusions:
PET/CT and brain MRI rarely reveal systemic metastasis at the time of sentinel lymph node biopsy. In the case of PET/CT, the false positive rate is up to 10 times the true positive rate indicating that the use of PET/CT (and brain MRI) as routine imaging modalities at the time initial detection regional melanoma metastasis should be reconsidered in otherwise asymptomatic patients.