"Haemangiopericytoma is a term formerly used to describe a continuum of mesenchymal tumours with elevated cellularity found throughout the body in soft tissue and bone. After many years of controversy, haemangiopericytomas have been shown to not only share histological features similar to solitary fibrous tumours but also a similar genetic alteration; i.e. a genomic inversion of 12q13 locus resulting in fusion of NAB2 and STAT6 genes, the latter expressed and able to be assessed using immunohistochemistry techniques 4."