Minimally Invasive Cisterna Magna Injection Model for Leptomeningeal Metastasis Studies in Mice

Leptomeningeal metastasis (LM), the spread of cancer cells into the cerebrospinal fluid (CSF)-filled leptomeninges, is a rare yet devastating complication of advanced solid tumors. Patients with LM often have a poor prognosis, with survival measured in weeks to months. Developing in vivo models that accurately replicate the complexities of LM is essential for understanding its cellular and pathological mechanisms and evaluating potential therapies. Murine LM models are typically created through intra-cardiac, carotid artery, or cisterna magna injection of tumor cells. However, intra-cardiac or carotid injections often result in substantial extracranial and brain tumor burden, complicating bioluminescent imaging and leading to mortality unrelated to LM. Meanwhile, conventional cisterna magna injection requires invasive procedures, such as skin incision and muscle dissection, making it both traumatic and resource intensive. Here, we describe a minimally invasive procedure for tumor cell injection into the leptomeningeal space through the cisterna magna without the need for a skin incision. This approach reduces extracranial tumor formation, minimizes surgical trauma, and shortens the time and postoperative care required compared to other surgical methods. Importantly, it consistently induces LM with minimal brain parenchyma infiltration, as confirmed by two-photon microscopy and histological analysis. This streamlined approach offers an efficient and reliable model for studying LM in preclinical research.