find absolute parent of a page hierarchy

I created a menu using get_pages() and specifying the parent id. This parent id has children and sub-children and sub-subchildren. I need each of these (sub)children to have the parent id displayed .

The code i made ony works for children, not for sub/ sub-sub children

$pages = get_pages('child_of=16&parent=16&sort_column=menu_order&sort_order=asc&title_li=&exclude=73');
    foreach($pages as $page) {

    <li <?php echo ($post->ID == $page->ID)? 'class="current_page_item"': ''; ?>><a>ID) ?>"><?php echo $page->post_title ?></a>

    <?php

    }
    ?>

I’m a bit puzzled on how to achieve that in wordrpress. Any suggestion is welcomed!