Check for Element existence within a predicate

Hello,

Is it possible to check whether a node exist from within a predicate.
what I am trying to do is:

<xsl:if test="count(parent::aaa/preceding-sibling::bbb/ppp[@id = $pId
and not(exists(extraChildNode))]/zzz) &gt; count(yyy)">

So I want to count the "zzz" child elements of "ppp" but only for the
"ppp" element that does not have "extraChildNode" as a child.

Thanks,
J