Radiation-Induced Cerebral Aneurysm Treated with Endovascular Coil Embolization

Summary

Radiation-induced cerebral aneurysms are rare. We describe a case of radiation-induced cerebral aneurysm successfully treated with endovascular coil embolization. A 39-year-old man received 60 Gy of radiation to a pineal germinoma at eight years old. The left internal carotid artery (ICA) aneurysm which developed within the irradiated field and stenotic change in the left ICA due to radiation-induced vasculopathy were detected incidentally. Because these aneurysms show a high risk of rupture and mortality, and even small aneurysms are prone to rupture, any such suspected aneurysm should be treated with surgical or endovascular procedures. Endovascular treatment is probably useful if the aneurysm is inaccessible to direct surgery. Special attention must be paid to treatment because of stenotic changes in cerebral vessels within the irradiated field.

Introduction

Radiation therapy (RT) is now a reliable and effective part of the standard treatment regimen for not only brain tumors, but also for cerebral vascular deformities such as arteriovenous malformations. RT is sometimes accompanied by complications and has been implicated as a risk factor for aneurysm formation ^11,17. Radiation-induced cerebral aneurysms are rare, but are difficult to treat successfully and associated with a high mortality rate ^{7,10,16,26,28}. We describe a case of radiation-induced cerebral aneurysm successfully treated with endovascular coil embolization.

Case Report

A 39-year-old man received 60 Gy of radiation to a pineal germinoma at eight years old. After RT, the tumor had diminished in size. At 28 years old, he suffered from motor aphasia and mild right hemiparesis. Magnetic resonance imaging (MRI) revealed multiple cerebral infarction and magnet resonance angiography (MRA) showed stenotic changes in the intracranial artery without aneurysm. Cerebral infarction due to radiation-induced vasculopathy was diagnosed and antiplatelet therapy was initiated. He had subsequently shown no clinical deterioration, although follow-up MRI was not performed due to claustrophobia. At 39 years old, because ten years had passed since cerebral infarction occurred, we strongly recommended follow-up MRI. MRI revealed multiple old cerebral infarctions (Figure 1A,B) and MRA showed not only bilateral stenosis of the internal carotid artery (ICA) and middle cerebral artery (MCA), but also left ICA aneurysm (Figure 1C). Angiography demonstrated the left ICA aneurysm projecting upward and measuring 5.7 mm × 3.8 mm with a 1.8-mm neck, along with bilateral stenosis of the ICA and MCA without moyamoya vessels. The aneurysm arose directly from the C2 portion of the left ICA anterior wall and was associated with stenotic changes in the neighboring artery (Figure 2A,B). We therefore diagnosed radiation-induced cerebral aneurysm and performed endovascular coil embolization.

The patient was premedicated with 75 mg clopidogrel and 100 mg aspirin for one week. Under general anesthesia and systemic heparinization (5000 units), an 8-F sheath was placed in the right femoral artery. An 8-F Optimo balloon guiding catheter (Tokai Medical Products, Kasugai, Japan) was placed in the left ICA, and a 4 mm × 7 mm HyperForm balloon (eV3 Covidien, Irvine, CA, USA) was placed in the left ICA to perform balloon-assisted maneuvers or immediate hemostasis. An “S-shaped” Excelsior SL-10 microcatheter (Stryker, Kalamazoo, MI, USA) was placed within the aneurysm using a 0.010-inch microguidewire (ASAHI CHIKAI 10; Asahi Intecc, Nagoya, Japan) (Figure 3A). We used five bare-platinum coils for obliteration of the aneurysm, with a total coil length of 23.5 cm. Angiography performed immediately after the procedure demonstrated only a small neck remnant (Figure 3B,C). The postoperative course was uneventful. Although MRI performed one day after coil embolization revealed a small asymptomatic infarction, the patient was discharged uneventfully.

Figure 1.

A,B) Magnetic resonance imaging revealed multiple old cerebral infarctions in both hemispheres on fluid-attenuated inversion recovery imaging. C) Magnetic resonance angiography revealed the left internal carotid artery aneurysm (arrowhead).

Figure 2.

Angiography demonstrated that the aneurysm arose directly from the C2 portion of the left internal carotid artery anterior wall (arrow) and was associated with stenotic changes in the neighboring artery (A: anterior-posterior view, B: 3-dimensional view).

Figure 3.

A) Intraoperative angiography demonstrated the left internal carotid artery (ICA) aneurysm projecting upward and measuring 5.7 mm × 3.8 mm with a 1.8-mm neck, along with bilateral stenosis of the ICA and middle cerebral artery. B,C) Postoperative angiography performed immediately after the procedure demonstrated only a small neck remnant (B: conventional view, C: 3-dimensional view).

However, follow-up angiography performed one year after the operation demonstrated recanalization of the aneurysm without formation of a de novo aneurysm (Figure 4A). We performed coil embolization again with the same type of equipment and used four bare-platinum coils for obliteration of the aneurysm, with a total coil length of 20 cm. Angiography performed immediately after the procedure demonstrated complete obliteration of the aneurysm (Figure 4B,C). The postoperative course was uneventful and the patient was discharged without infarctions.

Figure 4.

A) Intraoperative angiography in the second operation demonstrated recanalization of the aneurysm. B,C) Postoperative angiography performed immediately after the procedure demonstrated complete obliteration of the aneurysm (B: conventional view, C: 3-dimensional view).

Discussion

Radiation therapy (RT) for intracranial disease causes not only vasculopathy, but also cerebral aneurysm formation ^7,8,13,16,17. The pathogenesis of radiation-induced aneurysms is likely to resemble that of radiation-induced vasculopathy, in which initial endothelial injury caused by radiation results in aneurysmal change ^22,27. Radiation-induced aneurysms display different clinical characteristics to congenital saccular aneurysms. The rupture rate is high, with even small aneurysms prone to rupture, and the mortality rate for ruptured aneurysms is also high ^7,17,27. Radiation-induced aneurysms often arise directly from a segment of a major artery and are associated with stenotic changes due to radiation-induced vasculopathy in the neighboring arteries situated within the radiation field ^4,7,16,24,27.

In this case, although the possibility of congenital saccular aneurysm remains, we diagnosed radiation-induced aneurysm based on the following findings. The aneurysm developed within the irradiated field and arose directly from the anterior wall of the ICA with stenotic changes due to radiation-induced vasculopathy. These findings agree with previously reported cases.

Including the present case, 35 cases with 48 cerebral aneurysms after RT for intracranial diseases have been reported ^1-28, and Table 1 summarizes the clinical features. In our case, the aneurysm was detected incidentally 31 years after conventional RT for pineal germinoma. Although aneurysms usually occurred within roughly ten years after RT, there were six cases in which the aneurysms occurred over 20 years after RT, as in this case. Careful follow-up is therefore necessary in long-term surviving patients to investigate not only the primary intracranial lesion, but also vascular lesions within the radiation field, although the incidence of aneurysm formation is not high ²⁷.

Table 1.

Summary of radiation-induced cerebral aneurysms.

Sex (male: female) Primary intracranial disease  Brain tumors    Pituitary adenoma    Acoustic neurinoma    Optic glioma    Retinoblastoma    Chondrosarcoma    Pineal germinoma  Others    Arteriovenous malformations Mean age at RT (years) Radiation modalities  Conventional  Brachytherapy Mean interval between RT and diagnosis (years) Multiple aneurysms Location of the aneurysms  ICA  ACA  VA  AICA Rupture of the aneurysms  Yes Aneurysm treatment  Surgical treatment  Clipping  Wrapping  Endovascular treatment    Coil embolization    Balloon occlusion  ND  None Prognosis  Good  Dead	23:12 8 4 3 1 1 1 3 20 7 8 14 13 1 4 23 9 4 4 1 2 8 23 7	Medulloblastoma Craniopharyngioma Glioma Metastatic tumor Suprasellar germinoma  30.7 (range 0-75) SRS ND  11.9 (range 0.2-33) MCA BA PCA PICA No Trapping Parent artery ligation Trapping Poor ND	6 3 3 1 1 7 1 6 3 6 1 12 4 3 3 1 4
ACA: anterior cerebral artery, AICA: anterior inferior cerebellar artery, BA: basilar artery, ICA: internal carotid artery, MCA: middle cerebral artery, ND: not described, PCA: posterior cerebral artery, PICA: posterior inferior cerebral artery, SRS: stereotactic radiosurgery, RT: radiation therapy, VA: vertebral artery.

Radiation-induced cerebral aneurysms can be treated with surgical or endovascular treatment ^{1,2,5-8,10,12-14,16,18,20,22,24-28}. Radiation-induced aneurysms are divided into the following three types: saccular; fusiform; and pseudoaneurysm ¹⁷. In cases of saccular aneurysm, neck clipping or coil embolization can be performed. However, surgical or endovascular trapping with or without a bypass procedure should be performed in cases of fusiform aneurysm or pseudoaneurysm ²⁷.

In the present case, because the aneurysm was saccular and located on the anterior wall of the ICA, endovascular coil embolization was selected. Eight cases have been described in which aneurysms were treated with endovascular surgery; four with coil embolization, three with trapping, and one with balloon occlusion ^{6,8,10,16,20,24,26}. The outcome was satisfactory in all except two cases. On the other hand, several problems are associated with such treatment. First, because radiation-induced aneurysms themselves may be more fragile and prone to rupture than congenital ones ^7,10,17, the possibility of rupture during the procedure must be considered. Second, because the ICA and MCA undergo stenotic changes due to radiation-induced vasculopathy, there is a possibility of embolism when instruments such as microcatheters pass through the ICA and MCA. Third, details on the long-term outcome of endovascular treatment for radiation-induced aneurysms are unknown. We therefore used not only balloon-guiding catheters, but also balloon microcatheters to control bleeding after intraoperative rupture. To prevent infarction due to embolism, we kept gentle manipulation of the instruments in mind under rigorous dual antiplatelet therapy and systematic heparinization. However, a small asymptomatic infarction occurred. Moreover, recanalization of the aneurysm occurred one year later. Although endovascular treatment for radiation-induced aneurysm is probably a useful procedure if direct surgery is inaccessible, embolism may be likely to occur as a complication because of stenotic changes due to radiation-induced vasculopathy along the access route. Moreover, there is a possibility of higher recanalization or de novo aneurysm formation because it is not a focal arterial injury but a regional vasculopathy. Hence, close follow-up is necessary after the operation.

Conclusions

Although radiation-induced cerebral aneurysms are rare, careful follow-up is necessary in long-term surviving patients. Because these aneurysms show a high risk of rupture and mortality, and even small aneurysms are prone to rupture, any such suspected aneurysm should be treated with surgical or endovascular procedures. Endovascular treatment is probably useful if the aneurysm is inaccessible to direct surgery. Special attention must be paid to treatment because of stenotic changes in cerebral vessels within the irradiated field. Moreover, close follow-up is necessary after the operation because of the possibility of higher recanalization or de novo aneurysm formation.