Primary central nervous system lymphoma (PCNSL) accounts for approximately 5% of primary brain tumors and its incidence has been increasing recently, especially in the elderly. Most PCNSLs are histologically large B-cell non-Hodgkin's lymphomas, occurring in solitary or multifocal lesions in the brain, and growing rapidly. Biopsy is the gold standard for establishing the diagnosis and classification of PCNSL, but it is relatively invasive and difficult to perform in some cases. Differential diagnosis by means of imaging such as MRI and PET is not always easy, because it often closely resembles other malignant brain tumors and inflammatory diseases. In recent years, new diagnostic techniques have been attempted, such as the detection of IL-10, a cytokine and chemokines, and the detection of MYD88 or CD79B gene mutations using cell-free DNA in cerebrospinal fluid. Multidrug chemotherapy (rituximab, high-dose methotrexate, procarbazine, vincristine followed by high-dose cytarabine ; R-MPV-A therapy) has been effective in treating patients and significantly prolongs survival. However, no treatment has been established for recurrent or refractory PCNSL. BTK (Bruton's tyrosine kinase) inhibitors, which were approved by insurance in 2020, are expected to be incorporated with re-challenges of chemotherapy and radiation therapy. High-dose chemotherapy, combined with autologous hematopoietic stem cell transplantation, is also considered an important treatment strategy for young patients.

  Metastatic brain tumors develop in 10-40% of patients with cancer, and their incidence has steadily increased. The therapeutic strategy for these tumors includes surgery, radiotherapy, and systemic treatments. Neurosurgeons play a crucial role in multidisciplinary care teams dedicated to managing these tumors. The management of patients with metastatic brain tumors has become increasingly complex due to advancements in systemic therapies, radiation oncology, and neurosurgery. Surgical resection of metastatic brain tumors can provide immediate relief from neurological symptoms and yield histopathological diagnosis in cases of unknown primary malignancy. While whole brain radiation therapy has been crucial for the treatment of metastatic brain tumors, recent clinical trials revealed that this therapy could be replaced by stereotactic radiosurgery/radiotherapy. In addition, systemic therapies, such as targeted or immunotherapeutic agents, have proven effective for specific patients with metastatic brain tumors. A personalized approach is necessary to determine the optimal therapeutic strategy for each patient. Therefore, multidisciplinary teams are needed for addressing the needs of patients with metastatic brain tumors. Understanding the current standard treatments is essential to provide optimal care, maintain quality of life, and improve overall survival.

  With the advancement of molecular diagnostics for brain tumors, the classification of pediatric brain tumors requires genetic investigation. While molecular diagnostics aid in predicting prognosis and therapeutic response, contentious issues persist.

  Medulloblastoma has long been subjected to molecular classification based on expression and/or methylation profiles. However, debates persist regarding its classification. Here, we review the molecular classifications of medulloblastoma.

  The WHO classification stratifies SHH medulloblastomas into two groups based on TP53 mutation status. Germline TP53 mutations are confirmed as a poor prognosis marker, whereas the impact of somatic TP53 mutations remains controversial. Further investigation is imperative for somatic TP53 mutations. Although the pathogenesis of Group3 and Group4 medulloblastomas had not been well understood, single-cell expression analysis and the discovery of mutations in core binding factor alpha complex have facilitated their cell of origin and pathogenesis. Group3 and Group4 medulloblastomas arise from the progenitor cells of the cerebellar rhombic lip at distinct developmental stages by arrested development. Despite various subtype classifications have been proposed to refine medulloblastoma classification, their utility requires continued validation.

  Molecular diagnosis enhances patient management but remains a topic of controversy. It is crucial to comprehend the rationale, significance, and limitations of each classification for both basic and clinical research. With a further understanding of the molecular underpinnings of medulloblastoma, molecular classification may be revised. Therefore, it is imperative to be familiar with the most recent consensus.

  Ependymomas are the third most common brain tumors in children, after medulloblastomas and astrocytoma. Recent advances in an understanding of the molecular biological processes of the brain has allowed for molecular classification of ependymomas along with histological classification. Ependymomas with similar histological types can exhibit completely different molecular biological characteristics depending on the site of occurrence, such as supratentorial, infratentorial, or spinal cord. And these have different prognosis. The primary therapeutic approach for these tumors involves complete surgical resection followed by radiation therapy. However, the efficacy of chemotherapy is unclear. An unfavorable prognosis is noted in cases where gross total resection is not achieved, often leading to local recurrence or dissemination of the tumor.

  Currently, chemotherapy represents pre- and post-operative supplementary treatment. Nevertheless, other novel molecular discoveries and functions can be of significance in substituting the current ependymoma treatment.

  This review includes the 2021 WHO molecular classification of ependymomas and an overview of treatment strategies and recent findings related to pediatric ependymomas.

  Metastatic breast cancer tends to occur 5 or more years after the initial treatment of primary tumors. Neurosurgeons often treat breast cancer as skull or brain metastasis. However, the clinical and molecular features of skull and brain metastases of breast cancer remain unclear. To identify these characteristics, we retrospectively investigated data from patients with skull or brain metastasis of breast cancer treated at our hospital (skull metastasis, three cases ; brain metastasis, eight cases). We focused on the latency until recurrence, expression patterns of the estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and Ki-67 index in each sample. Our results showed that ER/PR-positive and HER2-negative patients had skull metastasis with long latency (average : 13.7 years ; range : 8-17 years), whereas ER/PR-negative and HER2-positive patients had brain metastasis presenting earlier relapse compared with skull metastasis (average : 3.8 years ; range : 1-6 years). The Ki-67 index was significantly lower in skull metastasis than in brain metastasis (average Ki-67 index of skull metastasis : 8% [range : 3-16%] ; brain metastasis : 38% [range : 17-50%] ; p＜0.05). Our results suggested that skull and brain metastases in breast cancer have distinct molecular characteristics.

  As a carotid body tumor grows and surrounds the cervical carotid bifurcation, internal carotid artery reconstruction may be necessary. In this case, an 18-year-old woman presented with bilateral carotid body tumors and a larger tumor was detected on the right side. The tumor exhibited strong adhesion to the carotid bifurcation, encircling it. The external carotid artery was harvested as an interposition graft. Subsequently, the graft was anastomosed to both the internal and common carotid arteries, strategically crossing over the tumor. Furthermore, the tumor, along with the carotid bifurcation, was resected. The reconstruction of the internal carotid artery was then accomplished using the interposition graft. When reconstruction of the internal carotid artery is necessary for resection of the tumor along with the carotid bifurcation, the external carotid artery proves valuable as an interposition graft.

  Claw hand deformity (CHD) occurs in severe ulnar neuropathy, requiring early surgical treatment ; however, its prognosis is often reported to be poor. A 72-year-old woman presented with right CHD due to marked atrophy of the intrinsic hand muscles and abnormal ulnar sensation in the upper extremity. Imaging of the cervical spine showed no obvious lesions, such as compression of the spinal cord or stenosis of the nerve roots of C8 and T1, forming the ulnar nerve. Electrophysiological examination of the peripheral nerves revealed a lower trunk disorder of the right brachial plexus and ulnar neuropathy at the elbow, leading to a diagnosis of DCS. A two-stage surgery was planned. First, the patient underwent a supraclavicular approach to decompress the brachial plexus by resecting the anterior and middle scalene muscles and removing the first rib. Ulnar nerve dissection of the right elbow was performed after 9 days. Postoperatively, the patient underwent 4 months of rehabilitation of the cervico-omo-scapular region and fingers, which enabled extension of the right third to fifth fingers and improved the abduction limitation of the fifth finger. With accurate identification of the affected areas by electrophysiology and precise surgical treatments, improvement in motor dysfunction can be expected, even in patients with CHD and muscle atrophy.