GSAs reportedly account for approximately < 0.1% of all kinds of intracranial aneurysms and approximately 17.6% of giant serpentine aneurysms which can transform into the former [2]. At present, there remain no specific studies on epidemiology and pathogenesis in this respect. GSA originating from the MCA or its branch vessels is almost common in half of the cases, the internal carotid artery in 13%, and the anterior cerebral artery in less than 3%. GSA can be associated with recurrent intramural bleeding and thrombosis in the initial fusiform aneurysm. Senbokuya et al. reported a case of a fusiform aneurysm in the anterior cerebral artery that transformed into GSA within a space of 5 months with intramural thrombus [3]. GSA usually exhibits progressive mass effects due to its 1–4-mm-thick fibrous wall and peripheral calcified thrombus (midline shift and perifocal brain tissue edema on CT scan). Nevertheless, subarachnoid hemorrhage is not regarded as a common presentation of GSAs [4]. Thus, GSA progression can be characterized by progressive mass effects, rupture bleeding, and spontaneous occlusion. Among them, the development of mass effect is identified as the most common in MCA [5].
The major clinical symptoms of GSA include headache, seizures, hemiplegia, facial paralysis, cranial nerve palsy, and visual impairment. Sari et al. described a case of GSA where acute complete thrombosis was manifested after the first diagnostic angiography, with no sign of neurological impairment spotted. Radiological revealed persistent thrombotic aneurysms with peri-wall calcification after a 3-year follow-up observation [6]. McLaughlin et al. reported a case of GSA that was spontaneously completely thrombosed, and the distal territory of the occluded MCA branch was irrigated by numerous collaterals or unnamed arteries [7]. However, Mahadevan et al. reported a case of GSA that led to a rapid process of neurologic deterioration (Hemiplegia and speech impairment) after occlusion, due to a poor collateral circulation [8].
Cerebrovascular angiography represents the most commonly used standard for the diagnosis of GSA, which is capable to clearly demonstrate the characteristic serpentine channels, offer support for normal distal circulation of the maternal artery, and provide a reference for subsequent treatment [9]. CT angiography and MRI can be performed to screen for GSA and perfusion CT can clearly indicate the ischemic changes occurring in brain tissue around aneurysms. In this patient, MRI clearly demonstrates the mass effect, perivascular enhancement, and hypointense flow void representing the patent channel within the aneurysm [10].
A rare case of both GSA and MA is described, and it is speculated that congenital vascular wall dysplasia and weakness could contribute to the formation of GSA and MA. The large snake-like channel completely fuses the opening of the anterior choroid artery and the posterior communication artery, and these fixed perforation blood flow ensures blood supply to the significant functional areas in the brain. Retrograde blood flow in the serpentine channel results in the reduction of blood supply to the distal arteries, as manifested in a noticeable decline of contrast agent filling in the ipsilateral anterior and middle cerebral arteries [11]. In addition, retrograde blood flow is suspected to increase blood pressure in the external carotid artery through the high-flow bypass, thus further promoting the growth of MA [12]. The MA between the internal maxillary artery and the facial artery is possibly more floating and changeable than any other portions of the ECA, and the regrowth of the MA with GSA has the potential to cause delayed complications [13, 14].
The placement of a double stent reconstructs the direction of blood flow in the channel. Therefore, it can be expected that the reduction of perfusion pressure in the terminal artery is less severe with the serpentine channel inlet [15]. The turbulence of blood flow resulting from the abrupt change in the arterial diameter is conducive to thrombus formation, which may result in occlusion of important perforating vessels, hemiplegia, and visual impairment that may not be apparent previously. Therefore, flow diverter (FD) slightly shorter than the longest diameter of GSA was selected and released below the expected opening of the anterior choroid artery to avoid perforating artery occlusion caused by high metal coverage. After follow-up observation, overlapping of FD we could be performed selectively based on the actual progress of GSA.
GSA therapy is designed for a complete elimination of aneurysm cavities, reduction of mass effects, and reconstruction of distal circulation. A combination of its large size, lack of aneurysmal neck, and dependence on distal vessels presents certain technical challenges to the treatment. GSA is supposed to be treated possibly soon, as there is a possibility that normal blood vessels subsequently merge into the aneurysm cavity, thus causing difficulty in revascularization and leading to progressive neurological deterioration, spontaneous thrombosis, or intracranial hemorrhage. The latest FD including Pipeline, Tubridge, and Surpass provide a better option for the treatment of GSA [16, 17]. FD can change the direction of hemodynamics by means of intracavitary reconstruction of the parent artery and dismissing the serpentine channel. It allows the indirect exclusion of the sac from the vasculature and facilitates the growth of endothelial cells and neointimal tissue across the aneurysm neck. The controlled clinical trial was designed to assess the safety and efficacy of the Tubridge flow diverter in the treatment of large or giant aneurysms compared with enterprise stent-assisted coiling, and the results of 6-month follow-up imaging included complete occlusion rates of 75.34% for the Tubridge [18]. At present, there remain no studies focusing on the complete occlusion rate of GSA following FD implantation. Therefore, a LEO stent combined with Tubridge was chosen to implant for this patient. With consideration given to the serpentine channel, uncertain anchoring site, and the stability and tolerance of the stent, a decision was taken to abandon the double-pipeline or Tubridge bridging technology. The first release of LEO stent contributed to initially establishing the release path of subsequent supports and provided sufficient radial support. Then, the Tubridge was released to overlap with LEO, thus increasing the metal coverage density of the aneurysm neck and achieving the reconstruction of the parent artery. The patient’s vision returned to normal without the occurrence of any new neurological defects. DSA revealed that abnormal serpentine channel basically disappeared, and almost complete occlusion was achieved.
