Abstract
The increase in the rate of mRNA vaccination against coronavirus disease 2019 (COVID-19) worldwide has been accompanied by reports of an increase in the side effects of the vaccine. In the field of neurosurgery, several cases of venous thrombosis have been reported as possible complications after COVID-19 vaccination. However, no such side effects have been reported in patients with brain tumors, and COVID-19 vaccination is considered safe for this patient population. In this report, we present the cases of two patients with brain tumors who experienced intratumoral hemorrhage as a possible side effect of the COVID-19 vaccine. In the first case, a 54-year-old man who had received CyberKnife treatment for a vestibular schwannoma eight years prior presented with tongue discomfort, right-side facial numbness, and dizziness since the day after his COVID-19 vaccination. MRI revealed intratumoral hemorrhage of the vestibular schwannoma. The second patient was a 60-year-old woman who presented with a sudden-onset headache and vomiting that had started three days after her COVID-19 vaccination. CT revealed a meningioma with intratumoral hemorrhage. Both patients had undergone surgery prior to this presentation, and their symptoms had improved. They had no risk factors for intratumoral hemorrhage, suggesting that it may be a side effect of the mRNA vaccine against COVID-19. Although the causal relationship is unclear, acute inflammation with predominantly lymphocytic infiltration and thrombogenicity after COVID-19 vaccination may damage the fragile microcirculation of the tumor.