System and method for accessing and treating a patient's cerebrospinal fluid. The system comprises a device with at least one implantable single or multilumen catheter, configured for placement along a patent's cerebrospinal fluid pathway, with at least one domed subcutaneous reservoir and/or pump connected to the catheter(s). The device can also be equipped with control circuitry and controllable valves. The devices allow for drug administration and/or simultaneous, bidirectional cerebrospinal fluid access and exchange. The catheter(s), may be coupled with medical probes that transmit sensor data to the device's processor, which can be configured transmit and receive data and instructions. The catheters may also be configured with guide devices to facilitate implantation. Various configurations, from single dome to multiple dome devices are taught, along with various applications such as epidural and other cerebrospinal drug administration, and various medical diagnostic applications.