Spontaneous thrombosis in giant intracranial aneurysms

Introduction

Giant intracranial aneurysms (GIAs) are rare pathological entities, and account for approximately 5% of all aneurysm cases (1). Spontaneous thrombosis in GIAs is exceptionally rare. The natural course, characteristics, and management of this special type of aneurysm have not yet been fully clarified.

Case presentation

A 75-year-old woman was admitted to hospital with a history of intermittent dizziness persisting for over 2 months. The patient reported the removal of a meningioma or cavernous hemangioma some 20 years earlier, but could not provide any further details. Otherwise, her medical history was unremarkable. Head computed tomography (CT) at the local hospital indicated a meningioma or cavernous hemangioma.

At the time of the current presentation, the patient underwent head CT, computed tomography angiography (CTA), magnetic resonance imaging (MRI), and time-of-flight magnetic resonance angiography (TOF-MRA). CT showed a low-density lesion in the right cavernous sinus, with a clear boundary, a flocculent high-density shadow inside, and ring calcification at the edge (Figure 1A). The CT color map showed the lesion more intuitively than non-enhanced CT image (Figure 1B). CTA showed multiple nodulous protrusions in the lesions, communicating with the cavernous segment of the right internal carotid artery (ICA) (Figure 1C). In addition, two other small aneurysms were observed in the right ICA (Figure 1D).

Figure 1 CT images of a 75-year-old woman with spontaneous thrombosis in giant intracranial aneurysms. (A,B) CT showed a low-density lesion in the right cavernous sinus, with a clear boundary, a flocculent high-density shadow inside, and a ring calcification at the edge (A). CT color map showed the lesion more intuitively than Figure 1A (B). (C,D) CTA (C) showed multiple nodulous protrusions in the lesions, communicating with the cavernous segment of the right ICA. Two other small aneurysms were observed in the right ICA (D, red arrows). CT, computed tomography; CTA, computed tomography angiography; ICA, internal carotid artery.

MRI revealed a mass with a short T1 and T2 signal in the right cavernous sinus region, measuring 3.2 cm × 3.9 cm × 3.1 cm. The lesion included flocculent areas with slightly high signal intensity on T2-weighted imaging with an onion-skin appearance (Figure 2A,2B). Nodular enhancement was observed in the lesions (Figure 2C). The nodular enhancement lesions displayed hyperperfusion on the arterial spin labeling sequence (Figure 2D).

Figure 2 Magnetic resonance and DSA images of a 75-year-old woman with spontaneous thrombosis in giant intracranial aneurysms. (A,B) T1- and T2-weighted imaging revealed a mass with a hypointense signal in the right cavernous sinus region. The lesion included flocculent areas with slightly high signal intensity on T2-weighted imaging with an onion-skin appearance (B). (C,D) Nodular enhancement was observed in the lesion (C), which displayed hyperperfusion on the cerebral blood flow map (D). (E) The three-dimensional TOF-MRA revealed a giant intracranial aneurysm on the C4 segment of the right ICA. (F,G) DSA revealed three aneurysms in the C4 segment of the right ICA. The aneurysm was successfully embolized with stent assistance. After stent embolization, the blood vessels were well developed and unobstructed (G). DSA, digital subtraction angiography; ICA, internal carotid artery; TOF-MRA, time-of-flight magnetic resonance angiography.

The three-dimensional TOF-MRA revealed a GIA on the C4 segment of the right ICA (Figure 2E). Finally, digital subtraction angiography (DSA) was performed to accurately evaluate the patient’s condition. The results revealed three aneurysms in the C4 segment of the right ICA (Figure 2F,2G). The largest aneurysm measured approximately 35 mm × 32 mm, and its neck was 16 mm. Thrombosis was observed in the aneurysm. The aneurysm was successfully embolized with stent-assisted embolization, and the stent completely covered the neck of the aneurysm and adhered well to effectively block the blood flow within the aneurysm and reduce the risk of internal leakage (Figure 2G).

All the procedures in this study were performed in accordance with the ethical standards of the institutional research committee, and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this case and the accompanying images. A copy of the written consent form is available for review by the editorial office of this journal.

Discussion

GIA is a dynamically asymptotic process of natural growth, characterized by three distinct events: spontaneous thrombosis, rupture leading to subarachnoid hemorrhage, and progressive enlargement resulting in a mass effect (2,3). The mechanism of spontaneous thrombosis is very complex, and is related to the stasis of blood flow in the vessel and within the lumen (4). The dome-to-neck aspect ratio has a vital role in the spontaneous thrombosis of GIAs, as it leads to reduced shear rates and diminished pulsatile flow. These hemodynamic alterations contribute to the formation of a procoagulant and proinflammatory microenvironment along the aneurysm wall (5).

Intravascular events caused by spontaneous or iatrogenic factors, resulting in aortic recanalization or proximal vascular occlusion, are also associated with spontaneous thrombosis in unruptured GIAs (6,7). This phenomenon has been attributed to endothelial damage induced by altered hemodynamic stresses on the aneurysm wall (2,6).

Partially thrombosed aneurysms are categorized as a separate subgroup, and exhibit particular features (3,8). They often continue to grow, sometimes even following the occlusion of the parent vessel. These lesions typically present with a significant mass effect, and exhibit thrombus features such as an onion-skin pattern. The hemodynamics of thrombosed aneurysms is unstable, which not only increases the risk of rupture but also increases the risk of ischemic stroke (8,9). It has been suggested that the persistent growth of partially thrombotic aneurysms is due to the recurrence of intramural hemorrhage in the aneurysm wall.

During surgical exploration of partially thrombotic aneurysms, a huge fine vascular network covering the aneurysm and obviously developed blood vessels may also be observed (8-11). This mainly occurs at the periphery of the aneurysm, in the “thrombotic portion” of the aneurysm, away from the patent lumen, with a marked enhanced rim and edematous reaction in the adjacent brain parenchyma, but the precise pathogenesis needs to be elucidated.

Currently, there is no consensus as to the definitive therapeutic strategy for the management of partially thrombosed aneurysms (12). However, it is well established that if thrombosis in the aneurysm is suspected, direct surgery, parent artery occlusion, or endovascular treatment (for the prevention of distal thromboembolism) may be required (9,12,13). Therefore, in this case, the microneurosurgical technique with clipping of the aneurysm and decompression of the mass effect through aneurysm emptying was considered the best option. Additionally, due to the configuration of the aneurysm, revascularization through extracranial-intracranial bypass surgery may be appropriate.

Currently, no definite spontaneous dissolution mechanism for spontaneous thrombosis in GIAs is available. However, neuroimaging can be used to identify spontaneous thrombosis caused by large intracranial aneurysms. This approach aids in the selection of appropriate therapies for patients.

Acknowledgments

We sincerely thank the patient and family members who participated in this study. We thank Dawei Yin from the Department of Radiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China for providing technical support.

Footnote

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1175/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional research committee and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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