Leontiasis ossea is largely a historical term used to describe a number of conditions that result in the affected patient’s face resembling that of a lion. Although it is most frequently associated with craniofacial fibrous dysplasia, it has a broader meaning encompassing other lesions that have similar appearance. 

The distinction is made between true leontiasis ossea (craniofacial fibrous dysplasia) and other conditions having similar external appearance (mimics); however it would be safe to say that as a term it is no longer of clinical use, primarily due to its negative connotations, and should be avoided. 

In addition to craniofacial fibrous dysplasia the following conditions may mimic leontiasis ossea:

When one of these differentials is the cause of this distinctive craniofacial phenotype, the name of the underlying condition is sometimes used in combination with leontiasis ossea, e.g. “Pagetic leontiasis ossea” or “uremic leontiasis ossea”.

Source: https://radiopaedia.org/articles/leontiasis-ossea

Image: Skull with Leontiasis Ossea