Submitted on: 14 March 1998.
Revised on: 01 May 1998.
Accepted on: 30 May 1998.
___________________Egyptian Journal of Neurosurgery
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Submitted on: 26 June 2000.
Revised on: 12 August 2000.
Accepted on: 08 October 2000.
___________________Egyptian Journal of Neurosurgery
Submitted on: 08 July 2000.
Revised on: 23 August 2000.
Accepted on: 02 September 2000.
___________________Egyptian Journal of Neurosurgery