computed tomographic angiography ( cta ) is a non - invasive mean of investigating isolated third nerve palsy to exclude intracranial aneurysm . however
, third nerve palsy can be also associated with dural carotid cavernous fistulae ( ccf ) with anterograde inferior petrosal sinus drainage , which may occur without cta features of superior ophthalmic venous dilatation and orbito - ocular congestion . here , we present two cases missed by cta . a 68-year - old woman with a history of hypercholesterolemia and on statin therapy presented with progressive ptosis and diplopia over five days .
physical examination showed left painful complete third nerve palsy without orbito - ocular congestive signs .
cta showed a 2.5 mm left internal carotid artery ( communicating segment ) outpouch but did not show any other vascular pathology .
digital subtraction angiography ( dsa ) confirmed the above finding as a left internal carotid artery infundibulum and also showed left dural carotid cavernous fistulae with drainage into the right inferior petrosal sinus .
follow - up magnetic resonance angiography ( mra ) at 5 months showed persistent carotid - cavernous fistulae . similarly ,
63-year - old woman with no medical comorbidity presented with ptosis and diplopia over five days . physical examination showed right painful partial third nerve palsy with mydriasis and without orbito - ocular congestive signs .
dsa was carried out and found right dural ccf ( figure 1a  d ) .
common causes of isolated third nerve palsies include diabetes mellitus and communicating segment internal carotid artery aneurysm .
the above two cases illustrate that cta may not detect posterior - draining dural carotid cavernous fistulae when radiological signs of grossly engorged anterior cavernous sinus and a dilated superior ophthalmic vein are absent . in future
, mra may act as a noninvasive diagnostic tool for these cta - negative posterior - draining dural carotid cavernous fistulae as illustrated by the first patient .
embolization can also result in rapid and complete resolution of third nerve palsy in 88% of affected patients .
figure 1digital subtraction angiography found right dural carotid cavernous fistulae fed by dural branches of bilateral internal carotid artery ( ica ) and drained through right inferior petrosal sinus .
( a ) right ica injection , ap projection ; ( b ) right ica injection , lateral projection ; ( c ) left ica injection , ap projection ; ( d ) left ica injection , lateral projection . digital subtraction angiography found right dural carotid cavernous fistulae fed by dural branches of bilateral internal carotid artery ( ica ) and drained through right inferior petrosal sinus . ( a ) right ica injection , ap projection ; ( b ) right ica injection , lateral projection ; ( c ) left ica injection , ap projection ; ( d ) left ica injection , lateral projection .
 computed tomographic angiography ( cta ) is a well - established non - invasive investigation for this neurological presentation to exclude intracranial aneurysms . 
 however , dural arteriovenous fistulae with anterograde venous drainage only can be missed by cta . 
 here we reported two patients with painful complete third nerve palsy and dural carotid cavernous fistulae with anterograde venous drainage only missed by cta . 
 the natural history and management option are discussed . in patients with persistent symptoms or without vasculopathic risk factors , magnetic resonance angiography ( mra ) or digital subtraction angiography ( dsa ) 
 should be considered to exclude the diagnosis . 
Case report