radiation - induced aneurysm is a rare complication for head and neck cancer , and the pathogenesis is not fully understood.1 
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 8 but the mechanism is likely to be similar to that of radiation - induced chronic vascular damage.9 
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  several authors have reported  30 cases of radiation - induced intracranial aneurysms with subsequent rupture.1 
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 8 
 13 these aneurysms were diagnosed from 10 months to 21 years after radiation therapy . so far , only seven cases of aneurysm after stereotactic radiosurgery ( srs ) and/or stereotactic radiotherapy ( srt ) have been described.14 
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 20 all of these patients underwent repeated radiotherapies in various combinations . we present two cases of catastrophic epistaxis due to a ruptured internal carotid artery ( ica ) aneurysm induced by repeated srt for an anterior skull base tumor and successfully treated by endovascular surgery . srt for skull base tumors may be very effective to control these tumors . however , these cases suggest that the development of a radiation - induced aneurysm should be considered a possible serious complication in the case of repeated srt . a 29-year - old man was referred to our institution for the treatment of a large ewing primitive neuroectodermal tumor ( pnet ) that occupied the right orbit and ethmoid and maxillary sinus with right progressive visual loss in four years earlier ( fig . postoperatively , the patient underwent adjuvant chemotherapy and srt with a dose ranging from 45 to 54.9  gy in 15 fractions that produced a complete response . therefore , the second srt was performed with a dose ranging from 53.5 to 62.3  gy in 15 fractions that resulted in the partial response . however , 42 months after surgery , tumor relapse was revealed in the right orbit that remarkably had eroded the sphenoid bone . he underwent the third srt with a dose ranging from 52.8 to 60.0  gy in 15 fractions . magnetic resonance imaging ( mri ) demonstrated the tumor had almost disappeared after srt ( fig . a ) axial t1-weighted magnetic resonance image with gadolinium ( mri - gd ) before the surgery revealed the tumor in the orbit and ethmoid sinus adjacent to the right internal carotid artery ( ica ) . ( b ) axial mri - gd after the third stereotactic radiotherapy demonstrated remarkable shrinkage of the tumor . ( c ) computed tomography scan on emergent admission due to massive epistaxis revealed the hematoma at the middle cranial fossa and pneumocephalus . ( d ) right internal carotid angiogram showed a right petrous ica aneurysm ( arrow ) with slight stenosis of the adjacent ica ( arrowhead ) . ( e ) left internal carotid angiogram after the endovascular treatment revealed the tolerable cross - flow via the anterior communicating artery . the patient was admitted to our hospital with complaints of significant epistaxis with hypovolemic shock 6 months after the final srt . a computed tomography scan revealed a hematoma at the middle cranial fossa and paranasal sinuses , and pneumocephalus ( fig . cerebral angiography showed a right petrous ica aneurysm with slight stenosis of the adjacent ica ( fig . because of rebleeding during the cerebral angiography , we urgently performed endovascular parent - artery occlusion without balloon test occlusion ( bto ) to save his life . cerebral angiography after the endovascular treatment showed complete disappearance of the aneurysm with a tolerable cross - flow via the anterior communicating artery ( acoa ) ( fig . he recovered fully and was discharged 3 weeks after surgery without new neurologic deficits . but 6 months after endovascular treatment , he died from an untreatable tumor relapse . a 61-year - old man was admitted to our hospital for the treatment of a left large sphenocavernous meningioma in 1999 at 48 years of age . the tumor was partially resected via the orbitozygomatic approach without removal of the cavernous mass . the left cavernous tumor had gradually grown 23 months after the initial surgery and was treated by srs using gamma knife . the tumor margin was covered by the 50% isodose line , and 12  gy were delivered to the margin . the left cavernous ica was located within the radiation field . however , the rest of the tumor continued to grow to the infratemporal fossa ( fig . two surgeries , using the infratemporal fossa approach and transsphenoidal approach , were required to remove the extracranial tumor without removal of the cavernous tumor 83 months after the first operation . the following month , the patient underwent srt using cyber knife with a dose ranging from 30.0 to 47.6  gy in five fractions that produced a complete response ( fig . coronal t1-weighted magnetic resonance image with gadolinium ( mri - gd ) after stereotactic radiosurgery revealed tumor recurrence in the cavernous sinus and the left infratemporal fossa surrounding the left internal carotid artery ( ica ) . ( b ) mri - gd after stereotactic radiosurgery and stereotactic radiotherapy demonstrated an almost disappearance of the tumor . ( c ) left internal carotid angiogram demonstrated a small aneurysm at the left cavernous ica ( arrow ) . ( d ) right internal carotid angiogram after the endovascular treatment showed enough collateral flow via the anterior communicating artery . the patient was admitted to our hospital with complaints of massive epistaxis 77 months after the last srt . cerebral angiography showed a small aneurysm located at the cavernous portion of the left ica ( fig . 2c ) . bto of the left ica demonstrated the presence of collateral flow via the acoa without a reduced regional cerebral oxygenation state on the occluded side under the monitoring of near - infrared spectroscopy . cerebral angiography after the endovascular treatment showed complete disappearance of the aneurysm with enough collateral flow via the acoa ( fig . a 29-year - old man was referred to our institution for the treatment of a large ewing primitive neuroectodermal tumor ( pnet ) that occupied the right orbit and ethmoid and maxillary sinus with right progressive visual loss in four years earlier ( fig . postoperatively , the patient underwent adjuvant chemotherapy and srt with a dose ranging from 45 to 54.9  gy in 15 fractions that produced a complete response . therefore , the second srt was performed with a dose ranging from 53.5 to 62.3  gy in 15 fractions that resulted in the partial response . however , 42 months after surgery , tumor relapse was revealed in the right orbit that remarkably had eroded the sphenoid bone . he underwent the third srt with a dose ranging from 52.8 to 60.0  gy in 15 fractions . magnetic resonance imaging ( mri ) demonstrated the tumor had almost disappeared after srt ( fig . a ) axial t1-weighted magnetic resonance image with gadolinium ( mri - gd ) before the surgery revealed the tumor in the orbit and ethmoid sinus adjacent to the right internal carotid artery ( ica ) . ( b ) axial mri - gd after the third stereotactic radiotherapy demonstrated remarkable shrinkage of the tumor . ( c ) computed tomography scan on emergent admission due to massive epistaxis revealed the hematoma at the middle cranial fossa and pneumocephalus . ( d ) right internal carotid angiogram showed a right petrous ica aneurysm ( arrow ) with slight stenosis of the adjacent ica ( arrowhead ) . ( e ) left internal carotid angiogram after the endovascular treatment revealed the tolerable cross - flow via the anterior communicating artery . the patient was admitted to our hospital with complaints of significant epistaxis with hypovolemic shock 6 months after the final srt . a computed tomography scan revealed a hematoma at the middle cranial fossa and paranasal sinuses , and pneumocephalus ( fig . cerebral angiography showed a right petrous ica aneurysm with slight stenosis of the adjacent ica ( fig . because of rebleeding during the cerebral angiography , we urgently performed endovascular parent - artery occlusion without balloon test occlusion ( bto ) to save his life . cerebral angiography after the endovascular treatment showed complete disappearance of the aneurysm with a tolerable cross - flow via the anterior communicating artery ( acoa ) ( fig . he recovered fully and was discharged 3 weeks after surgery without new neurologic deficits . but 6 months after endovascular treatment , he died from an untreatable tumor relapse . a 61-year - old man was admitted to our hospital for the treatment of a left large sphenocavernous meningioma in 1999 at 48 years of age . the tumor was partially resected via the orbitozygomatic approach without removal of the cavernous mass . the left cavernous tumor had gradually grown 23 months after the initial surgery and was treated by srs using gamma knife . the tumor margin was covered by the 50% isodose line , and 12  gy were delivered to the margin . the left cavernous ica was located within the radiation field . however , the rest of the tumor continued to grow to the infratemporal fossa ( fig . two surgeries , using the infratemporal fossa approach and transsphenoidal approach , were required to remove the extracranial tumor without removal of the cavernous tumor 83 months after the first operation . the following month , the patient underwent srt using cyber knife with a dose ranging from 30.0 to 47.6  gy in five fractions that produced a complete response ( fig . ( a ) coronal t1-weighted magnetic resonance image with gadolinium ( mri - gd ) after stereotactic radiosurgery revealed tumor recurrence in the cavernous sinus and the left infratemporal fossa surrounding the left internal carotid artery ( ica ) . ( b ) mri - gd after stereotactic radiosurgery and stereotactic radiotherapy demonstrated an almost disappearance of the tumor . ( c ) left internal carotid angiogram demonstrated a small aneurysm at the left cavernous ica ( arrow ) . ( d ) right internal carotid angiogram after the endovascular treatment showed enough collateral flow via the anterior communicating artery . the patient was admitted to our hospital with complaints of massive epistaxis 77 months after the last srt . cerebral angiography showed a small aneurysm located at the cavernous portion of the left ica ( fig . 2c ) . bto of the left ica demonstrated the presence of collateral flow via the acoa without a reduced regional cerebral oxygenation state on the occluded side under the monitoring of near - infrared spectroscopy . cerebral angiography after the endovascular treatment showed complete disappearance of the aneurysm with enough collateral flow via the acoa ( fig . radiation - induced carotid artery aneurysm is a rare complication of radiation therapy for head and neck carcinoma , but it is a life - threatening situation . the pathogenesis of radiation - induced aneurysm remains speculative.1 
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 8 however the mechanism is likely to be similar to that of radiation - induced vasculopathy , due to chronic vascular damage such as obstruction of the vasa vasorum , premature atherosclerosis , adventitial fibrosis , and necrosis of the arterial wall.9 
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 12 combined with high blood pressure of the great vessel , it could result in the rupture of the arterial wall and even dissection with extravasation blood.13 
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 23 therefore , even a small radiation - induced aneurysm is more prone to rupture than other common saccular aneurysms.24 
  the clinical characteristics of radiation - induced aneurysms differ from other saccular aneurysms.13 radiation - induced aneurysms originate directly from the arterial wall , which is less likely to be influenced by the direction of the blood flow , in contrast to other saccular aneurysms . therefore , the formation of an aneurysm after irradiation might occur at any location on the vessel included within the radiation fields . in our cases , these aneurysms were not located at a branching site and were included within the radiation field . these findings suggest that the srt was responsible for the formation of the carotid artery aneurysm . several authors have reported  30 cases of radiation - induced intracranial aneurysms with subsequent rupture.1 
 2 
 5 
 8 
 13 these aneurysms were diagnosed from 10 months to 21 years after radiation therapy . however , our literature review yielded only seven cases of aneurysm induced by srs and/or srt.14 
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  among them , four cases were presented as anterior inferior cerebellar artery aneurysm induced by srs ( gamma knife ) for vestibular schwannoma.14 
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 20 the remaining three cases were reported as ica aneurysms15 
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 17 ( table 1 ) . with the inclusion of our cases , these patients were three men and two women ( mean age : 52.2 years ; range : 2962 years ) . there were two cases of nasopharyngeal carcinoma , and one each of pituitary adenoma , atypical meningioma , and ewing pnet . although the interval between the latest radiotherapy and the diagnosis of the aneurysm varied from 3 months to 13 years ( mean : 49.8 months ) , three cases developed within a year . these results indicated that repeated srt causes an aneurysm to occur earlier than conventional radiotherapy or single srt . abbreviations : 3d - crt , three - dimensional conformal radiotherapy ; ec - ic bypass , external carotid - internal carotid artery bypass ; ica , internal carotid artery ; pnet , primitive neuroectodermal tumor ; rt , radiotherapy ; sah , subarachnoid hemorrhage ; srs , stereotactic radiosurgery ; srt , stereotactic radiotherapy . srt makes it possible to deliver efficacious therapeutic doses accurately to the targeted lesion with secure preservation of adjacent normal anatomical structures . however , if these structures are located within the targeted lesion , they must be involved in the radiation field . therefore the surviving patients who have received srt should undergo sequential follow - up for possible vascular involvement . treatment for radiation - induced aneurysms includes clipping,2 
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 26 trapping,11 
 27 and wrapping the aneurysm and parent artery.2 
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 29 in addition , parent artery occlusion using an endovascular technique is effective.19 
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 30 because of the high risk of mortality , if the radiation - induced aneurysm ruptures , aggressive surgical intervention or endovascular treatment should be considered for the aneurysm . sacrifice of the carotid artery would lead to severe cerebrovascular events , and therefore a bto should be performed . if a bto is successful , trapping or parent artery occlusion becomes an option . if the patient can not tolerate the test , an extracranial - to - intracranial bypass surgery should be considered . in case 1 of our series , the patient was semicomatose and in a state of hypovolemic shock due to repeated massive epistaxis . therefore , an immediate salvage procedure was needed to save his life without performing bto . in case 2 we have presented two cases of a ruptured ica aneurysm induced by repeated srt for anterior skull base tumor . it was definitely difficult to clarify accurately the timing of aneurysm formation in our cases . in addition , although the primary factor was presumed the high dose delivered to the ica by the repeated srt , an unrecognized carotid injury at the former surgical intervention to the tumor or direct damage to the vessel wall by the tumor could also have been the probable causes . there are some reports on iatrogenic intracranial traumatic aneurysms after the resection of skull base tumors.31 
 32 
 33 it was suggested that most traumatic intracranial aneurysms have a symptomatic onset within 4 weeks after injury of the vessel wall.32 in our cases , however , the hemorrhagic presentation appeared 48 and 78 months after the final surgery , respectively . therefore , we are convinced that the aneurysms in our cases were most likely induced by the repeated srt and indicated a low probability of traumatic origin . histologic analysis , if possible , might contribute to an understanding of the entity of these lesions . we present two cases of catastrophic epistaxis due to ica aneurysm that were most likely induced by repeated srt for anterior skull base tumors . the srt may be very effective to control the residual tumor as well as tumor relapse . however , the possible development of radiation - induced aneurysm of the carotid artery should be considered in the case of repeated srt for malignant skull base tumors .
objectives  radiation - induced aneurysm is a rare complication for head and neck tumors . only seven cases of an aneurysm after stereotactic radiosurgery and/or stereotactic radiotherapy ( srt ) have been described . 
 we report two patients with a ruptured internal carotid artery ( ica ) aneurysm presenting with catastrophic epistaxis after repeated srt for an anterior skull base tumor . 
 results  two male patients received repeated srt in various combinations following surgery for an anterior skull base tumor . 
 they presented with significant epistaxis due to rupture of the aneurysm of the ica 6 and 77 months after the final srt , respectively . 
 the aneurysms were located within the radiation field . 
 preoperative angiography had revealed no aneurysms . 
 thus the aneurysms in these cases were most likely induced by the repeated srt . 
 conclusions  this is a proven report of aneurysm formation following repeated srt without conventional radiotherapy . 
 srt may be very effective to control malignant skull base tumors . 
 however , the possible development of radiation - induced aneurysm of the ica should be considered in the case of repeated srt . 
 the surviving patients who have received srt should undergo sequential follow - up for possible vascular involvement .