Microsurgical clipping is widely used in neurosurgery. Although, the incidence of IPR is significantly reduced compared with the non-microscopy era, IPR complications cannot be prevented. IPR often leads to blurred vision, which in turn presents great obstacles to neurosurgeons. Thus, IPR remains a potentially catastrophic event that may lead to a poor outcome. However, the results of several studies regarding the risk factors for IPR are controversial. The present study sought to elucidate the risk factors and identify appropriate treatment strategies for IPR.
4.1 Risk factors:
There are very few comprehensive analyses addressing the effect of age on IRP in the literature. Kunz et al demonstrated a statistically significant correlation between age and IPR. In this study the average age of the IPR and non-IPR groups were 57 and 52 years, respectively17. In the present study the average age of IPR group was 54.94 and 56.04 years for the non-IPR group, however, no statistically significant difference in age between the two groups was observed. Moreover, age was correlated with IPR in the aneurysm sites. Thus, in OphA aneurysms, the average age was 60.5 and 53.68 years in the IPR and non-IPR groups, respectively. In addition, in MCA aneurysms the mean age of the IPR group was 52.11, whereas the mean age of the non-IPR group was 56 years. Additionally, a 0.387- and 0.267-fold decreased risk for IPR was detected in middle-aged (41 to 60 years) and elder patients (age > 60 years), respectively. Finally, the mean age in the IPR group was lower compared with the non-IPR group. The association between increased IPR risk and age is perplexing, as the results are inconsistent with previous studies possibly due to the small sample size.
The association between IPR and the size of aneurysm remains controversial. Several studies have reported increased IPR risk in large aneurysms10,19, while others have indicated that there is no significant correlation between these factors2,7. The results of the present study showed that there was no association between IPR and aneurysm size. However, the size of the aneurysm was associated with its location, particularly with AChA and supraclinoid ICA. When the diameter of the aneurysms at the AChA and supraclinoid ICA was < 5 mm, the IPR rate was significantly increased by 10.6 and 81.8%, respectively (Video 1). Although increased aneurysm diameter makes its exposure and occlusion difficult, especially in areas with atherosclerotic plaque, more attention should be paid to the smaller ones at AChA and supraclinoid ICA. During the clamping process the artery walls are usually thinner, therefore, uneven force may easy cause IPR.
Although the studies by Sundt et al.28 and Giannotta et al.24 have shown that there is no correlation between aneurysm location and IPR, the majority of studies indicate a strong association between them7,11,14,29. Thus, Schramm et al revealed that the IPR incidence rate was increased in ACoA and ACA (approximately 36.9%)14. In addition, Sandalcioglu et al. reported that the IPR incidence rate of ACOA and ICA aneurysms were 39.1 and 31.2%, respectively11. Consistent with the previous studies, Ragonovic et al. demonstrated an IPR rate for ACA and ICA aneurysms of 40 and 16.7%, respectively29. In the present study, a significant correlation between IPR incidence rate and supralinioid ICA (50%) and PICA (38.1%) aneurysms was identified. The overall rupture rate was 14.8%. The rupture rates of aneurysms at different sites were as follows: 50% for supraorbital ICA, 38.1% for PICA, 26.1% for PCA, 15% for ACOA, 14.4% for PCOA, 14.1% for ACA, 12.5% for MCA, 11.9% for OphA, 10.4% for AChA, 3.4% for ICA bifurcation and 7.7% for other sites. Supracervical ICA aneurysms are usually caused by thin artery walls. PICA is very complex and tortuous, and surgery for aneurysms in this site is challenging due to the deep location. The dome of ACOA and POCA aneurysms mainly points to various directions, thus they easily adhere to the surrounding tissues. When the aneurysm neck is exposed, the aneurysm wall is easily pulled, leading to rupture.
4.1.4 H-H grade and Fisher score:
Although, several studies have shown that the IPR incidence is not associated with H-H grade25,27, Elijovich et al. indicated that lower H-H grade was correlated with increased IPR risk15. However, the majority of studies have suggested that patients with higher H-H grade are more likely to experience IPR8,11. Thus, Sandalcioglu et al. reported that the IPR incidence rate was 19.6 and 30.8% in H-H grade I-III and IV-V patients, respectively11. The results of the present study showed that the IPR incidence rate was 4.4% in H-H grade I, 15% in II, 14.7% in III, 21% in IV and 32% in grade Ⅴ patients. Increased H-H grade is often accompanied by intracranial hematoma, brain swelling and intracranial pressure. Thus, it is difficult to separate and clip the aneurysm during surgery, while it is easy to rupture the aneurysm by pulling the hematoma. Furthermore, the IPR incidence rate was 4.4% in Fisher score I, 15% in II, 14.7% in III, 21% in IV and 32% in Fisher score Ⅴ patients. Overall, increased Fisher score was associated with more severe intracranial hemorrhage, edema and swelling symptoms. The results suggested that the successful implementation of aneurysm clipping is challenging, indicating H-H grade and Fisher score as risk factors to predict IPR occurrence.
4.1.5 Number of SAH
As expected, the ruptured aneurysms exhibited a significantly increased IPR incidence compared with that noted to the unruptured aneurysms. It has been reported that the IPR incidence rate of unruptured and ruptured aneurysms is 1.2 and 10.7%, respectively1,7,27. These findings were consistent with the results of the present study, in which the IPR incidence rate of unruptured and ruptured aneurysms was 4.4 and 15.7%, respectively. Moreover, the present results suggested that the elevated IPR risk was associated with increased SAH incidence. Following aneurysm rupture, the hematoma expands, resulting in its adhesion to the vessel wall. In addition, the aneurysm separation process may lead to its rupture. Moreover, it has been shown that in patients with multiple ruptures, the blood vessel walls are usually thinner and less elastic, further increasing risk of IPR.
4.1.6 Operation time
Several studies have suggested that early surgical treatment may minimize the risk of rebleeding7,20,29. However, the clinical data indicated that the timing of the operation was not associated with the incidence of IPR11,25,27,28. Thus, the results of the present study were consistent with previous studies, as no significant correlation was detected between the timing of operation and the occurrence of IPR. Nevertheless, in patients with OphA aneurysms, a shorter operation timing was found to increase the risk of rupture. It has been reported that in the early stages of aneurysm formation the blood clot is fragile. However, in the late stages of aneurysm formation peripheral vasospasm, hydrocephalus and adhesion with surrounding tissues may be induced, which may increase the risk of IPR.
4.1.7 Surgical approach
Only few studies have evaluated the association between surgical approach and IPR incidence. Kang et al indicated that the incidence rate of IPR in supratentorial aneurysms treated with the supraorbital keyhole approach was higher compared with those treated with the pterional approach23. The pterional approach, as a classic surgical process, is widely used for treating the majority of aneurysms. Analysis of ACOA aneurysms revealed increased risk of rupture in patients treated with the left pterional and coronal craniotomy approaches, whereas it was significantly reduced when the supraorbital approach was performed. However, further studies with a larger sample size are required to confirm these findings. When the top of the aneurysm is pointing somewhat anteriorly lower, it often spreads to the anterior fossa or optic chiasmata. In addition, when the frontal lobe is lifted, the aneurysm wall may easily rupture. Furthermore, clinical studies have shown that the supraorbital approach has several advantages in terms of small incision, small bone window, shorter operation time and less bleeding. Additionally, this approach does not affect the intracranial pressure, thus preventing the occurrence of IPR3,4,13.
In the present study, no significant correlation between IPR incidence rate and sex, aneurysm side, number, direction and morphology were observed. Although irregular morphology and complex direction of aneurysms may increase the difficulty of the surgery, the aforementioned results indicated that they were not associated with the occurrence of IPR. In addition, several studies have suggested that intraoperative controlled hypotension may reduce the incidence rate of IPR8,11,16.
4.2 Treatment strategies
According to imaging data, the aneurysm location, size, shape and its association with peripheral tissues, blood vessels and nerves should be assessed from various angles. Thus, the choice of the operative approach, the clipping of the aneurysm and lowering the occurrence rate of IPR are of great importance. There has been controversy regarding the control of blood pressure preoperatively. Thus, blood pressure should be maintained at normal levels, as lower levels may lead to adverse effects. Furthermore, temporary occlusion of the parent artery may significantly reduce the incidence of IPR5,9,27. However, the clipping could inevitably cause damage to the blood vessel wall during temporary occlusion. In addition, attention should be paid to patients with atherosclerosis. When a temporary occlusion clip is used, the atherosclerotic plaque may be easily detached, leading to cerebral infarction and vasospasm. Therefore, when the temporary occlusion approach is performed to clamp the artery, healthy or less sclerotic artery segments should be selected and the temporary occlusion time should not exceed 20 min. Additionally, the intracranial pressure should be reduced by releasing the cerebrospinal fluid during the procedure. Finally, the available operating space may facilitate the procedure, as the aneurysm is adequately exposed.
4.2.2 Treatment after IPR
First of all, we should have a strong psychology, and don't feel nervous when IPR happens. Secondly, it is necessary to compress the ICA and temporarily block the carrier artery to reduce the bleeding rate. At the same time, the double aspirator method is used to quickly clean up the blood in the surgical field. Then, we should find and clipping the aneurysm neck. If necessary, the electric coagulation break can be selected according to the situation26(Video 1).