I desperately need to filter FeedItems where Type = 'ContentPost' and at least one of the following fields is LIKE '%Commission Report%', but they all appear to be unsupported in a query call: Body, ContentDescription, ContentFileName, Title. It looks like querying Description and Name is supported in Attachment, why can't I query anything useful related to a FeedItem?

Can anyone offer a suggestion on how to go about doing this? Here is my extension:

public with sharing class pcrControllerExtension {
private final id pdcid;
public pcrControllerExtension(ApexPages.StandardController stdController) {
pdcid = ((Producer_Document_Center__c)stdController.getRecord()).id;
}

public String getFileList() {
    String strHTMLTable = '<table>';
    Integer i = 1;
        for(FeedItem fi:[Select Id, Body, Title, RelatedRecordId FROM FeedItem
        WHERE ParentId =:pdcid AND Type = 'ContentPost' AND ContentFileName LIKE '%Commission Report%' Order By CreatedDate Desc])
        {
            strHTMLTable = strHTMLTable + '<tr><td>No.' + i + ' </td><td><a href="' + URL.getSalesforceBaseUrl().toExternalForm()+ '/' + fi.RelatedRecordId + '" target="_blank" >' + fi.Title+ '</a></td></tr><BR>';
            i++;
        }
    strHTMLTable = strHTMLTable + '</table>';
    return strHTMLTable;
    }
}