Reactive heterotopic ossification. Its patterns on MRI.

The purpose of this report is to analyze common features of reactive heterotopic ossification, zone phenomenon and involution. Eleven cases evaluated with plain radiography and MRI were classified based on the location: intramuscular, periosteal, and intermediate (mainly the insertion site of muscles). Zone phenomenon tends to be complete in the intramuscular type and incomplete in the periosteal type. Involution is also more evident in the intramuscular type.