You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
dural arteriovenous fistulas ( davfs ) are abnormal arteriovenous shunts , which develop in the dura mater , usually within or near the walls of a dural sinus and are most common in the cavernous and transverse or sigmoid sinuses4,6 ) .
anatomically , the cavernous sinus ( cs ) is an extradurally located sinus , while other dural sinuses are located between two dural walls in the cranial cavity3,7 ) .
a variety of strategies for treatment of aggressive davf of the cs have been reported in the literature , including transvenous and/or transarterial embolization , radiation therapy , and surgery .
recent studies have demonstrated that gamma knife radiosurgery ( gkrs ) is a safe , less - invasive , and effective treatment for low - flow davf of the cs when used alone or in combination with other treatment modalities3,6,7,13,17 ) . here
, the authors report a case of paradoxical exacerbation of symptoms resulting from obstruction of the venous outflow after gkrs for treatment of a davf of the cs .
a previously healthy 59-year - old female presented with progressive right proptosis , chemosis , and ocular pain for two weeks .
there were no abnormal findings , including cranial nerve palsy , on the neurological examination .
brain magnetic resonance images provided a clue indicating davf of the right cs without edematous cerebral lesions ( fig .
cerebral catheter angiography showed a right - sided davf of the cs supplied by the dural branches of the internal and external carotid arteries bilaterally , corresponding to a barrow type c davf .
cortical venous reflux was observed via the petrosal vein in the right posterior fossa ( fig .
2 ) . for treatment , a transfemoral route via ipsilateral jugular vein and inferior petrosal sinus was attempted repeatedly , however , the microcatheter could not be passed through the tortuous inferior petrosal sinus .
accordingly , the patient underwent gkrs at a marginal dose of 17 gy on the prescription 50% isodose line and a maximal dose of 34 gy with a volume of 611.2 mm . no obvious change in her ocular symptoms
was observed after gkrs . at one month after gkrs , she developed increasing ocular pain and occipital headache , and was readmitted to our hospital .
she was not able to sleep less and less because headache was getting worse . however , no obvious change in her ocular symptoms such as proptosis and chemosis was observed , compared with the time of discharge .
t2-weighted magnetic resonance images showed a diffuse hyperintensity of the right cerebellar hemisphere ( fig .
urgent cerebral angiography showed partial obliteration of the fistula and loss of drainage via the right superior and inferior ophthalmic veins .
therefore , prompt transarterial embolization was attempted with the aim of symptom palliation . under local anesthesia , a microcatheter was superselectively navigated into the feeders arising from both external carotid arteries via the middle meningeal artery , ascending pharyngeal artery , and internal maxillary artery .
immediate postembolization angiograms showed total occlusion of the external carotid artery feeders and disappearance of the cortical venous reflux in the right cerebellar hemisphere ( fig .
5 ) , while the fistula supplied from the left internal carotid artery remained minimally .
the patient showed rapid resolution of the pain and gradual improvement of other ocular symptoms .
conservative management , including manual compression of both carotid arteries , was continued following this endovascular procedure .
no symptoms suggestive of recurrence developed during the clinical follow - up period of seven months .
davfs of the cs are somewhat different from other davfs , which drain into the transverse , sigmoid , or superior sagittal sinus . cavernous sinus davfs are associated with a low risk of intracranial hemorrhage , unless cortical venous drainage is present , which occurs less frequently7 ) .
a variety of strategies for the treatment of aggressive davfs of the cs have been reported in the literature , including transvenous and/or transarterial embolization , radiation therapy and surgery .
gkrs is reported mainly for those davfs with a high treatment risk involving surgical excision or embolization , as well as for lesions that fail more traditional modalities or require further adjunctive therapy4,11 ) .
gkrs targets the arterial feeders of the davf 's nidus to induce diminishing shunting and eventually obliteration .
although it is not entirely clear how gkrs achieves obliterations , one theory points to radiation - induced small muscle expansion , adventitial fibrosis , and an intimal response leading to small vessel occlusion11 ) .
another potential theory is that an inflammatory process in the adjacent dura causes external pressure on small arteries , leading to reduced blood flow and thrombosis4 ) .
davfs of the cs are known to show a much more rapid response to gkrs than davfs that drain to sinuses other than the cs .
clinical improvements after gkrs are known to occur as early as two months after the procedure1,12,13,16 ) .
as reported by the largest study of davfs treated by gkrs , published by wu et al.17 ) , symptom improvement occurred as early as six weeks after gkrs .
the angiography - documented obliteration rate after gkrs as a first - line treatment was 75% in the study reported by wu et al.17 ) and 91% in the study by barcia - salorio et al.1 ) . in a study of 20 cases of davfs of the cs , pollock et al.15 )
reported a clinical improvement rate of 95% ( 19 of 20 patients ) and an angiography - documented complete obliteration rate of 87% ( 13 of 15 patients ) . according to other published papers on gkrs for treatment of davfs of the cs , administration of a high dose ( margin dose > 18 gy ) resulted in an occlusion rate of more than a 72% throughout variable follow - up periods1,4,8,14,15,17 )
such a high radiation dose is very similar to that used elsewhere in gkrs for treatment of arteriovenous malformations5 ) . in our case ,
when a high radiation dose was delivered to the delineated target , the optic apparatus , which is known to be sensitive to radiation , was exposed to less than 10 gy .
a major disadvantage is the necessary latency period until obliteration could be achieved with radiosurgery .
conversely , the treatment latency of radiosurgery could be an advantage in preventing the risk of venous hypertension and infarction involved with sudden complete obliteration by endovascular methods .
chiou et al.2 ) observed normalization of the reverse pulsatile flow in the superior ophthalmic vein at months after gkrs for davfs of the cs , indicating a gradual change of haemodynamics .
nevertheless , acute obstruction of the venous outflow at just one month after gkrs , like the current case , is a rare event .
lau et al.10 ) reported on a patient with worsening proptosis and ophthalmoplegia caused by transient superior ophthalmic vein thrombosis of a davf of the cs after gkrs .
the cavernous sinus normally receives drainage from the superior and inferior ophthalmic veins as well as superiorly from the sphenoparietal sinus , sylvian veins , and cortical veins .
the cavernous sinus drains posteriorly through the inferior petrosal sinus and superior petrosal sinus to the jugular bulb , inferiorly through the pterygoid plexus via emissary veins , and contralaterally through the contralateral cavernous sinus9 ) . in the current case , the right superior and inferior ophthalmic veins as the main venous outflow were occluded without diminishing shunting early after gkrs , resulting in serious cerebellar congestion due to drainage obstruction .
it has been postulated that obstruction of the main venous outflow may be due to concurrent thrombus formation in the ophthalmic veins and in the anterior cavernous sinus , which depicts the mechanism of paradoxical worsening of symptoms before clinical improvement , after receiving gkrs .
we report on a case of paradoxical exacerbation of symptoms resulting from obstruction of the venous outflow after gkrs for treatment of a davf of the cs , and include clinical features and a review of the literature .
a 59-year - old female presented with progressive right proptosis , chemosis and ocular pain . 
 an imaging work - up including conventional catheter angiography showed a right - sided dural arteriovenous fistula of the cavernous sinus , which drained into the right superior petrosal sinus , right superior ophthalmic vein , and right inferior ophthalmic vein , and cortical venous reflux was seen via the right petrosal vein in the right posterior fossa . 
 after failure of transvenous embolization , the patient underwent gamma knife radiosurgery ( gkrs ) . at one month after gkrs , she developed increasing ocular pain and occipital headache . 
 repeat angiography showed partial obliteration of the fistula and loss of drainage via the superior and inferior ophthalmic veins with severe congestion , resulting in slow flow around the right cerebellar hemisphere . 
 prompt transarterial embolization relieved the patient 's ocular symptoms and headache . 
 we report on a case of paradoxical exacerbation of symptoms resulting from obstruction of the venous outflow after gkrs for treatment of a dural arteriovenous fistula of the cavernous sinus .