Choroid plexus AVM with anomalous origin of the capsulothalamic artery: A case report

Introduction

Traditionally, the plexal segment of the anterior choroidal artery (AChoA) has been believed to exclusively feed the choroid plexus, and thus could be sacrificed safely. ¹ However, some recent reports investigating anatomical variations of the plexal segment of the AChoA have shown that neural branches could arise from the plexal segment of the AChoA. According to those reports, plexal segments of the AChoA usually bifurcate into the medial perforating branch (MPB) and lateral plexal branch (LPB), with the neural branches originating from the MPB or proximal trunk.^2,3 To the best of our knowledge, no reports have described a neural branch originating from the LPB.

On the other hand, the capsulothalamic artery is one of the neural branches that generally originate from the cisternal segment of the AChoA. ⁴ Although some recent reports have shown that the capsulothalamic artery can also arise from the proximal plexal segment of the AChoA,^3,5 no reports have referred to a capsulothalamic artery originating from the distal LPB. Here, we present a case of choroid plexus arteriovenous malformation (AVM) in which the capsulothalamic artery originated from an unusually distal LPB of the AChoA.

Case presentation

A 45-year-old right-handed man complaining of headache was referred to our outpatient clinic. Magnetic resonance imaging (MRI) showed an abnormal flow void involving the left trigon and inferior horn (Figure 1(a)). Diagnostic angiography revealed a cerebral AVM fed by the AChoA and the lateral posterior choroidal artery (LPChA), and mainly draining into the inferior ventricular and lateral atrial veins (Figure 1(b) and 1(c)). OPEN IN VIEWER

A left internal carotid angiogram showed the plexal segment of the AChoA bifurcating into the LPB and MPB just beyond the plexal point, and each branch fed the nidus (Figure 2(a)–(c)). This plexal point was clearly confirmed with a time of flight (TOF) source image (Figure 2(d)–(f)). Lateral and anterior-posterior view revealed intranidal aneurysm (Figure 2(a) and (b)). OPEN IN VIEWER

Based on these findings, we discussed treatment of the AVM. This AVM was unruptured Spetzler Martin grade 4, so we preferred stereotactic radiosurgery (SRS) to open surgery. But as the AVM had an intranidal aneurysm, drained into only a deep vein and was deep located in the nidus, we thought the bleeding risk in the latency period after radiosurgery might be relatively high. On the other hand, as the feeders of the AVM originated from the choroidal segment and the cisternal segment was large enough and not so tortuous, we thought elimination of the intranidal aneurysm could be achieved with acceptable risk and might be beneficial. Target embolization followed by SRS was therefore planned.

Transarterial embolization was performed under general anesthesia. A 6-Fr Envoy® guiding catheter (Cordis/Johnson and Johnson, Miami, FL, USA) was inserted into the right vertebral artery via the left transfemoral approach. A Baltacci® 1.8-Fr microcatheter (Balt, Montmorency, France) was navigated to the plexal segment of the LPChA. Selective angiography showed no normal branch and the LPChA exclusively fed the posterior part of the nidus (Figure 3(b) and (e)). This microcatheter was kept in this position until the third injection of NBCA. OPEN IN VIEWER

Another 6-Fr Envoy® guiding catheter was inserted to the left internal carotid artery via the right transfemoral approach. Another Baltacci® 1.8-Fr microcatheter was navigated to the AChoA. Superselective angiography via the inferior choroidal point showed an intranidal aneurysm located on the distal MPB. No neural branch was demonstrated on this angiogram (Figure 4(a) and (d)). Initially, we attempted to navigate the microcatheter to the MPB of the plexal segment in which the intranidal aneurysm was located. However, this proved too difficult and the plan had to be changed. To diminish flow to the LPB, we decided to embolize the feeder from the LPB prior to target embolization of the MPB. We navigated the microcatheter to the distal portion of the LPB of the plexal segment. Selective angiography did not demonstrate a normal branch. Injection of 33% NBCA was performed, obliterating the posterior lateral part of the nidus (Figure 4(b) and (e)). OPEN IN VIEWER

Another attempt was made to select the MPB of the plexal segment, but this was still difficult. We therefore decided to sacrifice the LPB itself. Next, a microcatheter was again navigated to the proximal portion of the LPB. Selective angiography showed a small normal branch, apparently arising solely from the bifurcation of the AChoA (Figure 5(a) and (d)). We therefore thought that the LPB would be able to be sacrificed safely. The LPB of the plexal segment was therefore obliterated using 20% NBCA (Figure 4(c) and (f)). After the second injection, control angiography showed vasospasm of the cisternal segment of the anterior choroidal artery (Figure 3(a) and (d)). We then gave up embolizing the medial branch in this session. A third injection was performed with the first microcatheter, which had initially been placed in the LPChA. This branch was obliterated using 17% NBCA (Figure 3(c) and (f)). We then finished the first procedure. OPEN IN VIEWER

Two days after the procedure, the patient complained of right homonymous hemianopsia. MRI revealed cerebral infarction of the left optic radiation (Figure 1(d)). We reviewed the angiogram obtained during the procedure and confirmed that the neural branch that we had thought originated solely from the bifurcation of the AChoA during the procedure was actually arising from the LPB of the plexal segment of the AChoA (Figure 5(b) and (e)). Two months later, a second procedure was performed. At that time, superselective arteriography was performed from the proximal AChoA and the neural branch disappeared (Figure 5(c) and (f)). In this procedure, the MPB was easily selected and the intranidal aneurysm was successfully obliterated with 33% NBCA (Figure 1(e) and (f)). The patient was then sent to SRS in accordance with the plan.

Discussion

Anatomically, the AChoA is a small branch originating from the first segment of the internal carotid artery. The AChoA divides into two segments at the inferior choroidal point. The proximal division is called the cisternal segment, and runs through the carotid and crural cisterns. This segment gives off several neural branches and is known to be one of the most dangerous arteries for surgical and interventional procedures. The distal division is called the plexal segment, and runs into the inferior horn of the lateral ventricle. Traditionally, no neural branch has been considered present in this segment, allowing safe sacrifice.^6,7 However, Fernández-Miranda et al. studied 48 hemispheres, finding the plexal segments of 18 hemispheres (38%) gave off 31 perforating neural branches (one to four per hemisphere). ³ Erdem et al. also reported that a perforating neural branch could arise from the plexal segment of the AChoA in some branching patterns of the plexal segment. ²

Marinković et al. investigated the branching pattern of the plexal segment of the AChoA. ⁵ According to that report, the plexal segment has one to three terminal trunks, with 75% of their cases showing two terminal trunks. ⁵ Edem et al. also reported finding a perforating neural branch in cases of bifurcated terminal trunk of the plexal segment. According to that report, the medial trunk, which they named the MPB, runs along with the tenia of the choroid plexus and sometimes gives off several perforating branches to the pulvinar nucleus. Conversely, the lateral trunk, which they termed the LPB, runs along with the free edge of the choroid plexus. ² To the best our knowledge, no reports have referred to neural branches originating from the LPB.

In the present case, we injected NBCA three times. The ischemic complications encountered could have been attributable to any of those injections, but were considered most likely due to the second injection of NBCA. This was because, before this second injection, a small neural branch originating from the LPB was observed on the superselective angiogram, but was obliterated in the second procedure. Retrospective review showed this artery was actually originating from the distal LPB, initially running anteromedially then making a U-turn posterolaterally across the choroid plexus on oblique view, and was running slightly superiorly along the dorsal wall of the inferior horn in the lateral view. This artery had been directed toward the infarcted area.

This small artery might have been the capsulothalamic artery. The capsulothalamic artery is one of the perforating branches of the AChoA that supplies the ventral and caudodorsal parts of the posterior limb of the internal capsule, the retrolenticular part of the capsule (which contains the optic radiations), the tail of the caudate nucleus, and the lateral thalamic nuclei.^3,4,8 In our case, postoperative MRI revealed the infarction involved this area.

The capsulothalamic artery is known to be the largest perforating branch of the AChoA, and usually originates from the cisternal segment of the AChoA.^4,8 Although some reports have described this artery as potentially arising from the proximal plexal segment of the AChoA,^3,5 none have referred to a capsulothalamic artery originating from the LPB.

This unusual origin of the capsulothalamic artery might be formed by hemodynamic compromise due to the existence of the AVM. In our case, as a persistent primitive trigeminal artery was observed, the AVM was thought to have been formed in early gestation. Generally, in this period, the brain and its demand for blood supply are rapidly growing, and the anatomy of the blood vessels is thus dynamically changing. ⁹ Under such conditions, brain tissue surrounding the AVM might be exposed to ischemia due to the steal phenomenon. This ischemic stimulation might modify the vasculogenesis and angiogenesis of the fetus, then an unusual capsulothalamic artery as in the present case might be formed.

To the best of our knowledge, this represents the first report to refer to the capsulothalamic artery originating from the distal LPB and its ischemic complications. To avoid such complications, we must not only be aware of this unusual origin of the capsulothalamic artery, but also know that an AVM can change the vascular anatomy and no universally safe point is present on the AChoA, even in an LPB of the plexal segment.