A patient presented with unilateral proptosis which was compressible and increases on bending forward. No thrill or bruit was present. MRI shows a retro orbital mass with enhancement. The likely diagnosis is -

Proptosis on bending forward is typical of intermittent proptosis. Orbital varices constitute about 90% of cases of intermittent proptosis). So, it is seen in venous malformation, i.e., orbital varixes (not AV malformation). AV malformation (carotid - cavernous fistula) and encephalocele cause pulsatile exophthalmos.