Usually, small cells connect to a central gateway which may consolidate 10,000's or even 100K's of units.
Some small cell architectures use a local controller to co-ordinate a number of small cells, such as in a large office building or campus. These servers allow close interworking of the radio, reducing the number of handovers as smartphones/mobile devices move throughout the building and also offloading excess signalling traffic from the core network.
Local controllers may also offer a range of network services, such as tighter integration with the Enterprise.