Comparison of Surgical and Endovascular Treatments for Partially Thrombosed Intracranial Aneurysms : Insights into Recurrence and Residual Lesions

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J Korean Neurosurg Soc. 2025;68(5):568-577

Publication date (electronic) : 2025 April 1

doi : https://doi.org/10.3340/jkns.2025.0047

Yong-Jun Lee, Woong-Beom Kim, You-Sub Kim, Sung-Pil Joo

Department of Neurosurgery, Chonnam National University Medical School & Research Institute of Medical Sciences, Gwangju, Korea

Address for correspondence : Sung-Pil Joo Department of Neurosurgery, Chonnam National University Hospital, 42 Jebong-ro, Dong-gu, Gwangju 61469, Korea Tel : +82-62-220-6606, Fax : +82-62-224-9865, E-mail : nsjsp@jnu.ac.kr

Received 2025 February 17; Accepted 2025 March 27.

Abstract

Graphical Abstract

INTRODUCTION

Partially thrombosed intracranial aneurysms (PTIAs) represent a unique and challenging subgroup of aneurysms characterized by organized intraluminal thrombi. The optimal treatment strategy for PTIAs remains controversial despite the proposal of various classification systems and surgical approaches to address this condition [9,16]. Surgical clipping and endovascular coil embolization are commonly utilized treatment modalities; however, in cases where direct clipping is not feasible, parent artery occlusion with or without bypass surgery may be required [17]. Occasionally, spontaneous thrombosis may progress completely, allowing conservative management with antiplatelet or steroid therapy and close clinico-radiological follow-up, particularly when the aneurysm size is not large 2[4,28].

Currently, no standardized treatment guidelines exist for PTIAs, making the selection of an appropriate therapeutic approach particularly burdensome. Although a recent review suggested that surgical treatment might be superior to endovascular approaches in managing PTIAs [9], data remain limited, and the most effective treatment strategy continues to be debated. To address this issue, we analyzed data from our institution to evaluate treatment outcomes for PTIAs, focusing on morbidity, retreatment rates, and functional outcomes. This study aimed to provide insights into optimizing therapeutic strategies for this complex condition.

MATERIALS AND METHODS

This retrospective study was approved by the Institutional Review Board of Chonnam National University Hospital (approval No. CNUH-2024-270).

RESULTS

Patient characteristics

A total of 45 patients with PTIAs were treated at our institution. The demographic and clinical characteristics of these patients are summarized in Table 1. The cohort included 17 males and 28 females, with a mean age of 53.87 years. Treatment modalities for PTIAs included direct clipping, endovascular intervention, trapping with bypass, and wrapping, which were classified into surgical and endovascular treatments. The mean aneurysm size, measured based on the largest sac diameter, was 20.03 mm, which was larger than the size of non-thrombosed intracranial aneurysms.

Table 1.

Baseline characteristics

PTIAs were most commonly located in the middle cerebral artery (n=17, 37.8%), followed by the internal carotid artery (n=11, 24.4%), posterior cerebral artery (n=7, 15.6%), vertebral artery (n=4, 8.9%), basilar artery (n=3, 6.7%), anterior cerebral artery (n=2, 4.4%), and posterior inferior cerebellar artery (n=1, 2.2%). A total of 16 patients (35.6%) presented with ruptured aneurysms, demonstrating a higher rate of SAH compared to that of non-thrombosed aneurysms treated during the same period.

Radiological and clinical outcomes

Postoperative radiological and clinical data are presented in Table 2, and data on the correlation with the treatment method are presented in Table 3. Radiologically, remnant aneurysms were identified in six cases immediately after treatment. Among 39 cases with confirmed complete occlusion, recurrence was observed in three cases during the follow-up period. Remnant or recurrent aneurysms were significantly more common in patients treated with endovascular methods (eight of 14 cases) compared to those treated surgically (one of 31 cases) (odds ratio [OR], 0.03; 95% confidence interval [CI], 0.003–0.24; p=0.001). Additional treatment was performed in six cases, with surgical methods used in five of these cases (Table 4).

Table 2.

Postoperative characteristics and complications

Table 3.

Cross-analysis between treatment method and preoperative/postoperative characteristics and complications

Table 4.

Summary of 9 cases with remnant or recurrent aneurysms

DISCUSSION

The pathological characteristics of PTIAs differentiate them from common aneurysms [24,30]. PTIAs are rare entities, and their occurrence and growth are associated with intramural or intrathrombotic hemorrhage caused by recurrent microdissections within the vascular wall. These vascular changes often involve calcification, atherosclerosis, or inflammatory processes [9,25,30].

The intraluminal thrombosis observed in PTIAs is influenced by the aneurysm volume-to-neck diameter ratio, with larger aneurysms demonstrating a higher propensity for thrombosis [1,28]. Consequently, most PTIAs fall into the large or giant category [6], where mass effect often results in neurological symptoms [24]. The underlying pathophysiological mechanisms are depicted in the scheme (Fig. 1).

Fig. 1.

During the progressive growth of an aneurysm, calcification tends to occur primarily in areas where blood flow exerts a direct impact (yellow arrow), whereas thrombus formation is more likely to occur in regions where blood flow slows down, resulting in an indirect impact (red arrow).

Advanced imaging modalities, including CT angiography, MRI, and TFCA, are vital for diagnosing PTIAs. Among these modalities, MRI is particularly valuable for detecting inflammation and neovascularization, aiding in the initial diagnosis, surgical planning, and follow-up [19,24]. Characteristic MRI findings of PTIAs include a hyperintense peripheral rim on noncontrast T1-weighted images and low signal intensity within the thrombus on T2-weighted images, indicative of blood degradation products [19,27].

The treatment objective for PTIAs is complete aneurysm occlusion to prevent recurrence or rupture [10]. Although spontaneous thrombosis induced by anti-inflammatory treatments such as steroid therapy has been reported [14,24], this approach is limited due to the potential for progressive neurological symptoms or SAH before occlusion occurs [15]. Moreover, no significant outcome differences have been observed between PTIA patients treated with steroids and those in control groups, indicating inappropriate medical management [5,12].

Treatment strategies for PTIAs can be broadly categorized into surgical and endovascular approaches. Lawton et al. [16] proposed surgical methods such as direct clipping and thrombectomy-clip reconstruction while classifying thrombosed aneurysms. To date, studies involving endovascular treatment and trapping-bypass management have been published; however, the best treatment has not been established [9,24,30].

Surgical options often necessitate advanced techniques, such as bypass procedures, compared to standard clipping for common aneurysms. Not all PTIAs can be treated with direct clipping, and in cases of calcification or atherosclerosis of the aneurysm neck, it can be a factor that makes clipping difficult by interfering with the positioning of the clip [22]. Moreover, in cases of a complex aneurysm where it is difficult to preserve the parent artery or its branches, direct clipping may be challenging, and bypass can provide blood flow as an alternative [4,26] (Fig. 2). Additionally, bypass may be required in cases where thrombus detachment during clipping results in distal flow compromise (Fig. 3).

Fig. 2.

A 75-year-old female presented with dizziness. A T2-weighted image demonstrated a partially thrombosed giant cerebral aneurysm in the temporal lobe (A). Transfemoral cerebral angiography showed a fusiform aneurysm (around 4 cm in length) in the distal M1-proximal M2 segment of the right middle cerebral artery (B). Intraoperatively, we confirmed the presence of a thrombus inside the aneurysm (C). After clipping the proximal part of the partially thrombosed intracranial aneurysm (D), superficial temporal artery-middle cerebral artery bypass was performed (E). Postoperative brain computed tomography angiography demonstrated aneurysmal clipping and removal in the proximal M2 segment of the right superior division middle cerebral artery and right superficial temporal artery-middle cerebral artery bypass (F).

Fig. 3.

A 52-year-old female patient presented with persistent headache for 2 weeks. Brain computed tomography (CT) revealed subarachnoid hemorrhage in the left cerebral sulci (A). Brain CT angiography identified an aneurysm (approximately 1.7 cm) in the M2 segment of the left middle cerebral artery (yellow arrow) (B). Subsequent transfemoral cerebral angiography confirmed a wide-neck aneurysm (yellow arrow), approximately 15 mm in size, at the left middle cerebral artery bifurcation (C). Considering the potential need for bypass, the superficial temporal artery was prepared, and direct clipping of the aneurysm was attempted (D). However, intraoperative Doppler ultrasound and indocyanine green angiography revealed no flow in the M2 segment. It was suspected that thrombus detachment during the clipping procedure caused the occlusion of the M2 segment. To address this, superficial temporal artery-M2 bypass was performed, and subsequent indocyanine green angiography confirmed adequate flow restoration (yellow arrow) (E). Postoperative brain CT angiography showed no evidence of a remnant aneurysmal sac (F).

Endovascular treatment methods, including the Woven Endovascular Bridge and flow diversion, have been utilized as alternatives [2,7,11]. However, parent vessel occlusion, a consideration for managing mass effect, may be limited by anatomic or geometric constraints [6]. Therefore, surgical options should be prioritized when parent vessel occlusion is unfeasible. In such cases, bypass surgery can be performed first, followed by consideration of parent vessel occlusion. However, there are instances where an aneurysm undergoes spontaneous occlusion due to flow changes after the bypass procedure (Fig. 4). Spontaneous occlusion of a cerebral aneurysm is thought to occur gradually after bypass surgery due to thrombus formation within the aneurysm, with results from flow collision (Fig. 5).

Fig. 4.

A 65-year-old male presented with headache. Brain magnetic resonance angiography revealed a thrombosed aneurysm (arrow) (approximately 11 mm) in the left P2 segment (A). Transfemoral cerebral angiography demonstrated an 11.2 mm-wide neck aneurysm (arrow) in the P2 segment of the left posterior cerebral artery (B). Brain computed tomography (CT) confirmed the presence of a thrombosed aneurysm (arrow) in the left ambient cistern (C). We planned for parent artery occlusion following occipital artery-posterior cerebral artery bypass. The bypass surgery was performed accordingly (D). Postoperative transfemoral cerebral angiography showed a patent left occipital artery- posterior cerebral artery bypass with good patency at the anastomotic site. Additionally, there was no visualization of the P2 segment of the left posterior cerebral artery and known aneurysm (E). Brain CT also demonstrated marked regression of the thrombosed aneurysm (arrow) at the P2 segment of the left posterior cerebral artery (F).

Fig. 5.

In case of partially thrombosed aneurysm, the direction of blood flow can be schematically represented as follows (A). After bypass surgery, the flow behind the thrombosed aneurysm collides with the flow from the bypass site, leading to progressive in the previously partially thrombosed region, ultimately resulting in total occlusion (B).

Current evidence suggests that surgical treatment offers superior long-term stability compared to endovascular approaches [9]. According to Kim and Choi [13], midterm follow-up angiograms of PTIAs treated with an endovascular method revealed a 5-fold higher rate of recanalization than that in non-thrombosed cases. However, there are very few papers that compare surgical treatment and endovascular treatment in terms of complications and clinical outcomes. In some cases with thrombosed aneurysms, craniotomy or craniectomy may need to be performed rather than endovascular treatment for decompression purposes, and in these cases, bypass or direct clipping should be prioritized (Fig. 6).

Fig. 6.

A 29-year-old male with a partially thrombosed intracranial aneurysm located in the middle cerebral artery segment causing altered mentality and dysarthria. A T2-weighted image demonstrated a mass effect on the adjacent frontal and temporal lobeb (A). A sagittal unenhanced T1-weighted image demonstrated partial thrombosis in the inferior portion of the aneurysm (yellow arrow) (B). Brain computed tomography (CT) angiography confirmed the presence of a bi-lobulated huge aneurysm (around 4.1 cm) in the middle cerebral artery (C). Postoperative brain CT angiography presented evidence of aneurysm clipping in the M1 segment without a definitive remnant aneurysmal sac (D).

Based on our data, the rates of remnant or recurrent PTIAs were lower in the surgical treatment group than in the endovascular treatment group. Among the 14 patients who underwent endovascular treatment, there were nine cases (64.2%) of occlusion and three cases (33.3%) of recanalization during the follow-up period. According to Kim and Choi [13], the recanalization rate was 78% in the endovascular treatment group, and the midterm cumulative rate of recanalization was reported as 30% in another published study [2]. Considering that the recanalization rate of endovascular treatment performed on all intracranial aneurysms has been reported to be higher than that of surgical treatment, surgical treatment may be superior for remnant aneurysms with recanalization risk [3,23].

To the best of our knowledge, we have not found any studies comparing complication rates according to the treatment method in patients with PTIAs. Some studies suggested that coiling may yield better clinical outcomes for intracranial aneurysms [18,20,21]; however, other studies reported no significant differences between surgical and endovascular approaches [8,29]. In our study, no significant differences in complications or clinical outcomes were observed between treatment methods for PTIAs.

This study has several limitations, including its retrospective design, small sample size, and data from a single institution. Treatment methods were determined based on the neurosurgeon’s judgment without standardized protocols, and location-dependent treatment variation further limited analyses. Additionally, the data were insufficient for the location-specific analyses of thrombosed aneurysms. Future large-scale prospective studies are warranted to address these limitations and establish standardized treatment guidelines for PTIAs.

CONCLUSION

PTIAs are one of the subgroups of complex aneurysms that are challenging for neurosurgeons. In this study, surgical treatment was superior to endovascular treatment in terms of the rates of remnant and recurrent aneurysms. There were no significant differences in other complications or functional outcomes according to the treatment method. Therefore, a surgical approach must be considered first when treating PTIAs, and surgical proficiency in techniques such as bypass is necessary for successful treatment.

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