使用apache_request_headers()

I'm trying to use apache_request_headers() to get some request headers. I'm trying to get this output into one $ApacheHeaders:

<?php
$headers = apache_request_headers();

foreach ($headers as $header => $value) {
    echo "$header: $value <br />
";
}
?>

When I try calling it again like:

OTHER_PLACE => "{\"Extra headers $header: $value <br />\"}",

I'm not getting the same result as using echo. How can I join all this into one $ApacheHeaders to get the same result as echo?

Example:

   OTHER_PLACE => "{\"Extra headers $ApacheHeaders\"}",
$headers = apache_request_headers();
$ApacheHeaders = '';
foreach ($headers as $header => $value) {
    $ApacheHeaders .= "$header: $value <br />
";
}
echo $ApacheHeaders;