Cerebrospinal fluid
Some problems can cause CSF to leak out through a hole or tear in the dura mater (the layer of the meninges that is next to the skull and the bones of the spinal cord).  CSF leaks are usually a complication of a lumbar puncture or certain kinds of surgery on the head, neck, or brain.  However, an injury to the head or spine can also cause a CSF leak.  Sometimes, doctors cannot find a cause for a CSF leak.