2025 Volume 12 Pages 175-179
Variations in the posterior inferior cerebellar artery are well-documented. However, bilateral posterior inferior cerebellar artery originating from the posterior meningeal artery is extremely rare, and no such cases have been previously reported. Anastomosis between the anterior inferior cerebellar artery and posterior inferior cerebellar artery is a rare arterial anomaly that may arise due to remnants of the primitive lateral basilovertebral anastomosis during embryonic development.
A 61-year-old male presented with headache, vomiting, and left lower extremity ataxia. Brain magnetic resonance imaging revealed an acute infarction in the left medulla, and magnetic resonance angiography suggested a dissection of the left vertebral artery. Digital subtraction angiography revealed the posterior meningeal artery originating from the extracranial vertebral artery, supplying the bilateral posterior inferior cerebellar artery hemispheric branches. The original posterior inferior cerebellar artery from the distal vertebral artery supplied only the cerebellar vermis. Additionally, an anterior inferior cerebellar artery-posterior inferior cerebellar artery anastomosis was observed on the left side.
This case highlights two rare arterial anomalies: bilateral posterior inferior cerebellar artery hemispheric branches originating from the posterior meningeal artery and an anterior inferior cerebellar artery-posterior inferior cerebellar artery anastomosis, offering insights into the embryologic development and unique vascular structures involved.
The posterior meningeal artery (PMA), which arises from the vertebral artery (VA), provides the primary blood supply to the paramedial and medial portions of the dura covering the cerebellar convexity.1) The posterior inferior cerebellar artery (PICA) typically originates from the distal VA. However, many variations have been reported, including hypoplasia, absence, duplication, double origin, origin from the extradural VA, and origin from arteries other than the VA.2) To the best of our knowledge, PICA originating from the PMA is extremely rare,3,4) and no reports of bilateral PICA originating from the PMA have been published.
An anastomosis between the anterior inferior cerebellar artery (AICA) and PICA is due to the remnant of the primitive lateral basilovertebral anastomosis (PLBA). During the embryonic stage, there are two longitudinal arteries on the hindbrain: longitudinal neural artery (LNA) and PLBA. The basilar artery (BA) is formed from the fusion of LNAs. The PLBA is a longitudinal anastomosis temporarily present in the lateral hindbrain, connecting the developing lateral branches of the LNAs.5) The transverse arteries between the PLBA and LNA enlarge to meet the demands of the blood flow from cerebellum and brainstem, forming the three cerebellar arteries: the superior cerebellar artery, the AICA, and the PICA (Fig. 1A). Therefore, the partial persistence of the PLBA is associated with some anatomical variations in the three cerebellar arteries.5-7)
The development of the vertebrobasilar system in normal and the current case.
A: Normal development. During the embryonic stage, there are two longitudinal arteries on the hindbrain: LNA and PLBA. The BA is formed from the fusion of LNAs, and the PLBA is a temporary longitudinal anastomosis in the lateral hindbrain. Transverse arteries between the PLBA and LNA enlarge to accommodate blood flow demands, giving rise to the SCA, AICA, and PICA.
B: In the current case, the PICA hemispheric branch originates from the PMA, and the AICA-PICA anastomosis is attributed to the persistence of the PLBA.
AICA: anterior inferior cerebellar artery; BA: basilar artery; LNA: longitudinal neural artery; PICA: posterior inferior cerebellar artery; PLBA: primitive lateral basilovertebral anastomosis; PMA: posterior meningeal artery; SCA: superior cerebellar artery
Herein, we report a case of two rare arterial anastomoses: first, bilateral PICA hemispheric branches originating from the PMA, and second, an anastomosis between the AICA and PICA. These rare anastomoses provide insights into the embryological development of the AICA, PICA, and PMA.
The abbreviations used in this article are listed in Table 1.
Abbreviations and Acronyms
| AICA | Anterior inferior cerebellar artery |
|---|---|
| BA | Basilar artery |
| LNA | Longitudinal neural artery |
| PICA | Posterior inferior cerebellar artery |
| PLBA | Primitive lateral basilovertebral anastomosis |
| PMA | Posterior meningeal artery |
| SCA | Superior cerebellar artery |
| VA | Vertebral artery |
A 61-year-old man presented with headache, vomiting, and left lower extremity ataxia. The patient had untreated hypertension and was a former smoker. Brain magnetic resonance imaging revealed an acute infarction in the left medulla. Magnetic resonance angiography (MRA) and computed tomography angiography demonstrated stenosis of the left VA with a pearl-and-string sign, suggesting dissection. Furthermore, the left PMA was well-developed, raising suspicion of arteriovenous shunt disease (Fig. 2A). Therefore, we performed digital subtraction angiography (Fig. 2B-F). The arterial phase of left vertebral angiography revealed stenosis and pearl-and-string sign in the VA proximal to the union, involving the PICA. The developed PMA originated from the extracranial VA, coursed intracranially, ascended along the inferior surface of the cerebellum, and bifurcated to the left and right, connecting to the bilateral PICA hemispheric branches. The original PICA from the distal VA supplied only the cerebellar vermis. Furthermore, an AICA-PICA anastomosis parallel to the BA was observed on the left side. Right vertebral angiography revealed the PICA vermian branch without blood flow to the right inferior cerebellar hemisphere. No evident development of leptomeningeal anastomosis was observed. The neurological symptoms improved, and conservative management was chosen without antiplatelet therapy, surgery, or endovascular treatment. The patient was treated for hypertension and underwent careful imaging follow-up. Imaging follow-up was conducted at 1, 2, and 3 weeks, as well as at 3 and 6 months after onset, revealing no new infarcts or hemorrhages. The findings on MRA at 6 months post-onset showed improvement in the dissection, while the development and visualization of the PMA remained unchanged.
Arterial anomalies in the left VA.
A: Computed tomography angiography reveals stenosis of the left VA with a pearl-and-string sign indicative of dissection (white arrowhead) and a well-developed left PMA (green arrowhead).
B, C: Left vertebral angiography shows dissection of the left VA (white arrowhead). The PMA (green arrowhead) connects to the bilateral PICA hemispheric branches (right, blue arrowhead; left, yellow arrowhead). An AICA-PICA anastomosis is visible parallel to the BA (white arrow).
D: Right VA angiography shows an avascular region, indicating the absence of vascular supply in the PICA territory.
E: Three-dimensional rotational angiography reveals the left VA dissection (white arrowhead), the bilateral PICA hemispheric branches (right, blue arrowhead; left, yellow arrowhead) originating from the PMA (green arrowhead), and the AICA-PICA anastomosis (white arrow).
F: Schematic illustration of Fig. 2E. The developed PMA bifurcates to the left and right, connecting to the bilateral PICA hemispheric branches. The original PICA branch from the distal VA supplies blood exclusively to the cerebellar vermis. The AICA has two branches: the AICA-PICA anastomosis and the hemispheric branch.
AICA: anterior inferior cerebellar artery; BA: basilar artery; PICA: posterior inferior cerebellar artery; PMA: posterior meningeal artery; VA: vertebral artery
This case report was conducted in compliance with the ethical guidelines set forth by the Declaration of Helsinki. Approval was obtained from the institutional review board of Tokyo Metropolitan Tama Medical Center (approval number: 3-3). Written informed consent, including consent for participation in this study and for the publication of images, was obtained from the patient. To safeguard patient privacy, all data were anonymized prior to analysis, and any identifying details were removed from imaging and publication materials.
This report presents a case of rare vascular anastomoses involving bilateral PICA hemispheric branches originating from the PMA and a persistent PLBA. These vascular imaging findings are crucial for suggesting the presence of PMA-PICA or AICA-PICA vascular anastomoses during the embryonic stage.
The relationship between the left VA dissection and the observed vascular anomalies (PICA from the PMA and AICA-PICA anastomosis) remains uncertain. However, these anomalies are likely of embryonic origin and are not directly associated with the dissection. Further case studies are needed to enhance understanding.
PMA-PICA anastomosisIn our literature research, only two reports of the PICA originating from the PMA were identified.3,4) At the spinal level, the radiculomedullary, radiculopial, and radiculomeningeal arteries are present at each vertebral segment, whereas at the craniocervical junction, the VA, PICA, and anterior/posterior meningeal arteries correspond to these vessels, respectively. Therefore, these vessels may branch from a common trunk or maintain connections. Segmental arteries at the craniocervical junction correspond to the primitive proatlantal artery type I (PPA1) and the primitive hypoglossal artery during embryonic development.5) As the VA develops, connections with the intradural arteries regress, leading these vessels to become the occipital artery and ascending pharyngeal artery, respectively. Thus, the PMA could branch from the PICA, occipital artery, or hypoglossal artery, and potential anastomoses may become evident due to hemodynamic changes, such as PICA occlusion. This case suggests that the substantial blood supply to the PICA via the PMA, established during embryonic development, has persisted.
In one case, the tonsillohemispheric branch of the PICA originated from the PMA, and the branch to the medulla was supplied by the distal portion of the VA, beyond the origin of the PMA.3) In another case, the left hemispheric branch of the PICA was supplied by the bilateral PMAs, while a second PICA perfused the tonsillo-medullary and televelotonsillar segments of the left PICA territory.4) In both cases, the PMA was connected to the hemispheric branch of the PICA, and the vermian branch was supplied directly from the VA, as in our present case. While two previous cases reported a unilateral anomalous origin of the PICA, instances of bilateral PICAs originating from the PMA are extremely rare.
Several reports have indicated that collateralization via the PMA-PICA anastomosis is induced by hypoperfusion of the terminal branches of the PICA after occlusion of the main trunk of the PICA.1) Tanohata et al.8) reported the anomalous origin of the PMA from the PICA and speculated about the persistence of an anastomosing channel between the primitive PMA and the PICA. According to Streeter,9) the primitive blood vessel network encompasses the embryonic encephalic vesicle, which differentiates into the cerebral arteriovenous vessels during development. In embryos measuring 12-20 mm, the primitive blood vessels differentiate into three main strata (external, dural, and cerebral), with anastomotic channels existing between these three vascular systems prior to such differentiation. It is hypothesized that during differentiation into these three layers, several anastomoses may persist, including a pre-existing connection between the primitive vessels of the PICA and PMA, potentially leading to the rare occurrence of the PMA-PICA anastomosis.1,3,8)
In most cases, the PMA can be sacrificed during surgical procedures, as it supplies blood only to the dura mater.1,3) However, as seen in the present case, the PMA may form collateral circulation with the PICA, and sacrificing the PMA during dissection of the dura mater can lead to an ischemic stroke in the posterior circulation. Therefore, blood flow in the posterior circulation, including the PMA, should be carefully evaluated before performing surgery on the posterior fossa.
AICA-PICA anastomosisThe anastomosis between the AICA and PICA results from remnants of the PLBA, which plays an important role during certain embryonic stages of hindbrain development. While numerous studies have reported anatomical variations of the PICA, only a few have discussed PLBA in detail.6) This may be because the PLBA is not widely recognized within the fields of neurosurgery and neurointervention.10)
During the embryonic stage, the BA is formed from the fusion of LNAs. The PLBA is a transient longitudinal anastomosis located in the lateral wall of the hindbrain, including the pons, medulla, and cerebellum lying parallel to the outer side of the LNA. The PLBA is supplied caudally by the proatlantal artery and cranially by the lateral branches of the LNA and the primitive trigeminal artery. There are various transverse anastomoses between the LNA and PLBA, with numerous transverse branches from the PLBA supplying the hindbrain. Three cerebellar arteries-namely, the superior cerebellar artery, the AICA, and the PICA-arise as transverse branches from the LNAs, and the PLBA expands to meet the demands of the cerebellum and brainstem.5) Early in development, only the superior cerebellar artery supplies the cerebellar rudiment; the AICA and PICA develop later, with the dominance of either artery determined by the extent of the cerebellar surface they encompass. Hence, various anatomical variations exist in the AICA and PICA. Although the PLBA typically degenerates during this process, its remnants play a crucial role in the formation of the AICA-PICA anastomosis and the double origin of the PICA.7)Fig. 1 illustrates the schema of both the normal and the present case, based on the depiction in the article by Ota et al.7) The partial persistence of the PLBA may elucidate the anastomosis in our case (Fig. 1B).
This case report details a rare occurrence of bilateral PICA originating from the PMA and an AICA-PICA anastomosis, providing insights into the embryological development and the unique vascular structures involved.
There are no conflicts of interest.
