Long-term follow-up of vanishing tumors in the brain: How should a lesion mimicking primary CNS lymphoma be managed?

ObjectivesThe spontaneous disappearance of a tumor is referred to as a vanishing tumor. Most vanishing tumors in the brain are eventually diagnosed as malignant tumors or multiple sclerosis. However, their long-term clinical course remains unclear. This study aims to elucidate the management of vanishing tumors in the brain.Patients and methodsWe defined a vanishing tumor as a case in which the tumor spontaneously disappeared or decreased to less than 70% of the initial tumor volume before definitive diagnosis and treatment (other than steroid treatment). Ten cases of vanishing tumors are reviewed.ResultsNine patients underwent biopsy at least once. Five patients, all of whom had malignant tumors (primary central nervous system lymphoma: 4, germinoma: 1) that recurred in 4–45 months (median: 7 months), underwent a second biopsy after the reappearance of the tumors. Five patients (tumefactive demyelinating lesion: 1, undiagnosed: 4) who had no relapse are alive, and their median follow-up time is 44 months. No cases have yet been reported of malignant brain tumors that recurred more than 5 years after spontaneous regression.ConclusionsPatients with vanishing tumors should be followed up carefully by magnetic resonance imaging for at least 5 years, even after the disappearance of an enhancing lesion.