Discussion and conclusion
Peripheral aneurysms, usually originating from distal fragile arteries, which include moyamoya vessels, such as the lenticulostriate and thalamoperforating arteries and the anterior/posterior choroidal arteries, are more likely to disappear [8]. However, these aneurysms have also been disposed to re-rupture in patients with MMD and hemorrhagic manifestations [9]. Patients with IVH and multiple moyamoya collateral vessels often have periventricular collaterals responsible for the hemorrhage, especially from posterior choroidal artery (PChoA) collaterals called choroidal anastomoses. These choroidal collateral vessels have an outflow tract of the distal cortical M4 branches of the MCA, which is associated with hemodynamic burden after bypass surgery [10]. Revascularization surgery, either direct STA-MCA bypass or indirect encephaloduroarteriosynangiosis, reduces the hemodynamic burden of the aneurysm’s parent artery, the distal choroidal artery, and the lenticulostriate arteries. Previous studies have suggested that surgically increased bypass blood flow could decrease the flow in the parent artery, causing MMD-associated aneurysms to regress spontaneously [7, 11].
However, the current case showed rapid growth of the pseudoaneurysm after direct bypass surgery. There are several reasons for the growth of MMD-associated aneurysms. We hypothesized that the swollen brain tissue in the left cerebral hemisphere compresses and diminishes the blood flow of the adjacent cortical M4 branches of the left MCA, obstructing the outflow tract. Consequently, the compensatory ipsilateral distal PChoA blood flow increases, causing the preexisting pseudoaneurysm to grow rapidly. This hypothesis is supported by the reduction in choroidal collaterals after the second direct revascularization surgery, resulting in a new outflow tract via the STA-MCA bypass.
Another hypothesis was inferred from Lee’s paper [11]. Lee et al. reported the rapid growth and regression of a preexisting unruptured pseudoaneurysm in the left choroidal artery after indirect revascularization. They suggested that the reason for the fluctuation in aneurysm size was massive hydration after surgery, inducing hemodynamic instability of the aneurysm’s parent artery [11]. In our cases, massive hydration of over 3 L~6 L of normal saline per day was perfused for two days after surgery, and over 3 L of hydration persisted for three days, which might have caused hemodynamic instability of the aneurysm. Simultaneously, the patient developed pulmonary edema with bilateral pleural effusion owing to fluid overload.
There are two reasons for the selection of endovascular embolization rather than surgical options: 1) Our patient had a distal choroidal collateral artery large enough to pass through the microcatheter wire; 2) The amount of intraventricular hemorrhage increased further during rebleeding, even after revascularization surgery. With the choroidal collaterals remaining after post-embolization angiography to prevent rebleeding, we decided to conduct a second operation that removed the flow tracts and reduced choroidal anastomosis. The treatment strategy has not been standardized for posterior choroidal artery aneurysm cases and should be individualized based on the patient’s situation. Multiple treatment options are available, including surgical clipping, direct resection, revascularization, and endovascular embolization. Recently, endoscopic clipping was reported to be safe and less invasive in cases with intraventricular aneurysms [12]. Nevertheless, many studies have reported difficulty in treating PChoA pseudoaneurysms owing to the deep location, tortuosity, and fragility of the parent vessel, which makes surgical targeting and endovascular superselection of the parent vessel challenging [13].
From this case report, it is clear that the treatment of posterior choroidal pseudoaneurysms can be challenging, and multiple treatment options should be considered to prevent rebleeding. Furthermore, this case demonstrates the importance of maintaining hemodynamic control, including postsurgical cerebral perfusion and hydration, when treating MMD-associated aneurysms. Treatment of MMD-associated aneurysms should be individualized based on the characteristics of the patient’s aneurysm and their hemodynamic conditions. Further studies and case reports are needed to identify the best combination of treatment options for each type of posterior choroidal aneurysm and fluid management.