BACKGROUND: In the search for a better preoperative knowledge of the position of 
probes and electrodes, we assessed the feasibility and the usefulness of 
transcranial sonography during surgery for the implantation of stimulation 
electrodes into the subthalamic nucleus (STN) of patients with Parkinson's 
disease.
METHODS: Transcranial sonography was carried out during stereotactic surgery in 
8 patients with Parkinson's disease who had a suitable temporal bone window on 
the side receiving the electrode. Test stimulation parameters were 130 Hz, 0.1 
ms, up to 0 to 4.5 V.
RESULTS: The test probe with a diameter of 0.8 mm was visualized through the 
temporal preauricular window. The correct anatomic position of the electrode tip 
could be indirectly assessed thanks to the topographic relationship of the STN 
with the hyperechogenic substantia nigra and the nucleus ruber. The tip position 
of the final electrode was easily documented. A laterality of 10.5 to 11.5 mm, 
verified by teleradiographic ventriculography and plain films, was correlated 
with the best response of symptoms of Parkinson's disease to electrical impulses 
delivered to the STN.
CONCLUSIONS: Transcranial sonography is easily feasible during stereotactic 
surgery. In combination with the clinical effects of electrostimulation on the 
symptoms of Parkinson's disease and with stereotactic x-ray images, it enables 
the assessment and the documentation of the correct position of implanted STN 
electrodes in real time.