Alert for orphaned files (.mdf, .ldf & .ndf)

Question

Hi, 
Has anyone got any code that can scan all attached drives/directories for database files and compare them to what the instance says are attached files?  I have some code which works but you have specify the directories to monitor.  
I know that I could do this in C# quite easily but I'm wondering if it could all be done in T-SQL. Also could I run into permissions issues if the process is scanning all directories. 
This is the SQL code I have 
CREATE PROCEDURE [dbo].[UspReport_OrphanedDatabaseFile]
@FileLocation VARCHAR(512)
AS
BEGIN
SET NOCOUNT ON;
-- create temporary table to capture file names from directory.
if object_id('tempdb..#folderandfileinfo') is not null
BEGIN 
  DROP TABLE #folderandfileinfo;
  END; 
create table #folderandfileinfo
  cid int identity(1,1) primary key clustered,
subdirectory varchar(255),
depth int,
 isfile int
exec master..xp_dirtree @FileLocation, 1, 1;
select
  @FileLocation AS [Path Location] ,
  subdirectory AS [Orphaned Data Files] 
from
  #folderandfileinfo
where
  subdirectory like '%df' -- compares ONLY to .mdf, .ndf, and .ldf
  and subdirectory not in
  select right(smf.physical_name, charindex('\', reverse('\' + smf.physical_name)) - 1) 
  from
  sys.master_files smf join sys.databases sd on smf.database_id = sd.database_id
order by
  subdirectory asc;
END

Answer 1

What if you have several SQL Server instances on one machine (as I have)? You would have to check all instance with all found files?
What if other file extentions are used? MDF/NDF/LDF are common, but not a must, you can use any other file ext.
Hi, 
Good points.  
Typically there is only one instance per server here (apart from the DEV server).  I can live with the procedure returning hits on non db files.  Basically if any are reported then I would investigate and delete if required.