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.