Magic render var from taxo parent

_preprocess_node(&$variables) {

  $terms = field_get_items('node', $variables['node'], 'field_topic');
  $parents = taxonomy_get_parents($terms[0]['tid']);
  $parent = array_shift($parents);

  $variables['top_topic'] = field_view_value('node', $node, 'field_topic', array('tid' => $parent->tid));
}