The FLUO.CER.TUM study is a prospective observational clinical trial conducted at the IRCCS Foundation Neurological Institute Carlo Besta in Milan, Italy. It investigates the intraoperative use of intravenous sodium fluorescein as a fluorescent tracer to assist in the surgical resection of suspected malignant tumors of the central nervous system (CNS). These tumors typically present as contrast-enhancing masses on pre-operative MRI or CT scans. Malignant brain tumors are notoriously difficult to fully resect due to challenges in distinguishing tumor margins from healthy tissue. Sodium fluorescein, a dye that accumulates in areas where the blood-brain barrier is disrupted, offers a promising solution by enhancing tumor visualization during surgery. When used with a dedicated surgical microscope equipped with a fluorescence filter, fluorescein can help surgeons identify and remove more tumor tissue, potentially improving patient outcomes. The study aims to evaluate the effectiveness and safety of fluorescein-guided surgery in a real-world clinical setting. Approximately 800 patients of any age and gender, with suspected aggressive CNS lesions, will be enrolled. Each patient will receive 5 mg/kg of sodium fluorescein intravenously at the induction of anesthesia. Surgery will be performed using fluorescence-guided techniques, and patients will undergo pre- and post-operative imaging to assess the extent of resection. Clinical and neurological evaluations will also be conducted to monitor outcomes and any adverse effects. The primary objective is to qualitatively assess the intraoperative fluorescence characteristics of CNS tumors. Secondary objectives include measuring the extent of tumor resection, evaluating post-operative neurological function, and documenting any side effects related to fluorescein administration. The study adheres to ethical standards, including informed consent and approval by an ethics committee, and will be conducted in accordance with Good Clinical Practice guidelines and the Declaration of Helsinki. Data will be anonymized and securely stored, with results potentially published following appropriate review and approval.