THis assumes you have a WEB.SITEMAP file and a Menu1 using the sitemap as the datasource.

CODE BEHIND OF CALLING PAGE

Protected Sub Menu1_MenuItemDataBound(ByVal sender As Object, ByVal e As MenuEventArgs) Handles Menu1.MenuItemDataBound
        If e.Item.Text = "Your Menu Node Title" Then
            If CBool(Session("MyPermissions")) = False Then
                e.Item.Parent.ChildItems.Remove(e.Item)
            End If
        End If
End Sub

Web SiteMap Remove Menu Node is best used in a Master Page