Connection between Spondylolisthesis & Chiari Malformation?

I recently described in my last post about some strange click/tap/pop sound along with some pain in the lower, left area of my skull. (read most recent post before this to understand)

I only got one reply of advice/opinion, mentioning Arnold Chiari Malformation.. So I decided to look it up to do some research on it... I read many different articles which all sort of stated similar facts: symptoms, causes, treatment, etc...

For causes, I read Quote "It can be caused by structural defects in the brain and spinal cord that occur during fetal development, whether caused by genetic mutations or lack of proper vitamins or nutrients in the maternal diet." Unquote..
AND..
Quote "It can also be caused later in life if spinal fluid is drained excessively from the lumbar or thoracic areas of the spine either due to injury, exposure to harmful substances, or infection.
Unquote..

What I'm wondering, is about the 2nd "quote", 'due to injury' - what kind of injuries? And 'exposure to harmful substances' - as in drugs? chemicals? both?

I know I should be asking a doctor, but I can't afford to right now... I'm just seeking advice, opinions (professional or personal), or any information, URLs, etc.. that can give me some information..

Thank you for taking the time to read this & reply.

[stellavip]

ALSO, I forgot to mention, I found a very old post from THIS site, dated from 1998, asking something similar, with a response, I just don't understand it really.. heres the link if interested..

http://www.medhelp.org/posts/Neurology/Connection-Between-Spondylolisthesis-Spondylolysis-Chiari-Malformation/show/896423

thank you, again

[selmaS]

  Hi, u may want to pop over to the Chiari forum here on MedHelp-
http://www.medhelp.org/forums/Chiari-Malformation/show/257?controller=forums&action=show&id=257&camp=msc

  And we will try to answer ur questions there : )

    "selma"