Elevation of hemidiaphragm is a radiological finding seen in conditions such as diaphragmatic eventration, lobar lung collapse, subphrenic mass or abscess and phrenic nerve paralysis. 

Diaphragmatic eventration typically affects only a segment of the hemidiaphragm, compared to paralysis where the entire hemidiaphragm is typically affected. The atrophic changes of the left hemidiaphragm, combined with the lack of a sharp peak strongly suggests phrenic nerve paralysis rather than diaphragmatic eventration.

In this case, no history of previous trauma or current tumor in the neck or chest. No history of previous surgical intervention. Cervical spondylotic changes are noted. The etiologic possibilities are previous infection that may have affected the phrenic nerve or phrenic nerve paralysis due to compression by the cervical spondylosis.