The top of dryer is hot, the vent pipe from dryer to the wall is to hot to touch. What is the cause of .

In a normal dryer hot air is circulated through clothes and out the vent ----> outside

It sounds like your dryer has lint build up that is stopping this from happening

This can be a fire hazzard -- you need to clean out out dryer and vent...

http://www.laundry-alternative.com/clean_dryer_vent.html

How to Clean a Clothes Dryer Vent - wikiHow (http://www.wikihow.com/Clean-a-Clothes-Dryer-Vent)