How can the appraised value of a home be ok with a mortgage lender yet be too high for a PMI company?

The conventional mortgage with 90% ltv for a home I am buying next week has been approved by the mortgage company based on the appraisal the mortgage lender sent out however the PMI company believes the home is worth about $15000 less than the appraiser says it is worth. What gives? If this breaks the deal can I get my money back for the appraisal? ($395) The home is in Pike county, PA