Cerebellar heterotopia in the orbit.

An infant with slowly progressive proptosis was found to have heterotopic cerebellum in her left orbit. Although cerebellar cell rests are common, to our knowledge none has been found previously in the orbit. It probably arose either from abnormal germ cell migration or from aberrant germ cell differentiation. Orbital heterotopia probably can be classified in the larger category of orbital encephaloceles because of similarities in presentation, clinical course, and treatment, although there can be differences in the embryologic mechanisms of their development.