// Get menu description as global variable
function add_menu_description( $item_output, $item, $depth, $args ) {
    global $description;
    $description = $item->post_content;
    return $item_output;
}
add_filter( \'walker_nav_menu_start_el\', \'add_menu_description\', 10, 4);

// Submenu walker to add image
class submenu_walker extends Walker_Nav_Menu {
    function start_lvl( &$output, $depth = 0, $args = array() ) {
        if(0 == $depth) {
            global $description;
            $output .= \'<ul class="sub-menu">\'.
                \'<li class="row marginbottom1">\'.
                    \'<div class="col-sm-8 col-lg-9">\'.
                    \'<div class="menu-title">\'.
                            //$item->title.
                        \'</div>\'.
                        \'<div class="menu-description">\'.
                            $description.
                        \'</div>\'.
                    \'</div>\'.
                    \'<div class="col-sm-4 col-lg-3"><div class="menu-image img-rounded"></div></div>\'.
                \'</li>\';
        } else {
            $output .= \'<ul class="sub-menu">\';
        }
    }
}