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We incidentally observed the occipital artery (OA) arising from the cervical internal carotid artery (ICA) at the level of the C2 vertebral body on magnetic resonance (MR) angiography in three patients. In the rare case in which the OA arises from the ICA, it is generally at its origin. The OA arises from the cervical ICA when all but the distal part of the anastomosis of the primitive proatlantal artery between the ICA and vertebral artery persists. Careful review of MR angiographic images is important to detect rare arterial variations, and both partial maximum-intensity-projection images and source images aid their identification on MR angiography.

Among variations of the anterior cerebral artery (ACA), anastomosis of its A1-A2 junction with the ophthalmic segment of the internal carotid artery is rare and described as carotid-ACA anastomosis or infraoptic course of the ACA. One common variant, an azygos ACA, demonstrates no pairing of the A2 segment. To our knowledge, association of a carotid-ACA anastomosis with an azygos ACA is not reported in the English-language literature. We report a case diagnosed by magnetic resonance angiography in which right carotid-ACA anastomosis was associated with an azygos ACA and the right ophthalmic artery originated from the middle meningeal artery.

Bilateral persistent hypoglossal arteries (PHAs) are extremely rare, with only 5 cases reported in the English-language literature. Using magnetic resonance angiography, we diagnosed a case in which the left side was a typical PHA and the right side was presumed a PHA variant that supplied only the posterior inferior cerebellar artery.

Rarely, the anterior cerebral artery (ACA) arises from the ophthalmic segment of the internal carotid artery, a condition described as carotid-ACA anastomosis or infraoptic course of the ACA that generally demonstrates right-sided predominance. We diagnosed a case of bilateral anastomoses of the carotid and ACA vessels in which bilateral ophthalmic arteries arose from the origins of the anastomotic vessels using magnetic resonance (MR) angiography. Identification of rare arterial variations on MR angiography requires careful scrutiny of source images, and creation of partial volume-rendering images can aid visualization of detailed anatomic structures.

Congenital anastomosis of the external carotid (ECA) and vertebral (VA) arteries is extremely rare. We report a case of right ECA-VA anastomosis diagnosed by computed tomography (CT) angiography. The presumed dilated ascending pharyngeal artery coursed posteriorly and entered the C1 right transverse foramen. The proximal right VA was aplastic, and the C2 right transverse foramen was absent. Based on these findings, we diagnosed congenital anastomosis of the ECA and V3 segment of the VA, which we presumed to represent persistence of the second cervical intersegmental artery. Detection of rare variations of the vertebral arteries requires careful observation of CT angiography with bone images and source images, especially to identify the level of entry into the transverse foramen. Correct diagnosis of anastomosis is important when intravascular embolization or infusion chemotherapy or surgical ligation of the ECA is planned.

Anastomosis between the ophthalmic segment of the internal carotid artery and the A1-A2 junction of the anterior cerebral artery (ACA), described as carotid-ACA anastomosis or infraoptic course of the ACA, is rare and known to demonstrate right-sided predominance. We report a case of bilateral carotid-ACA anastomoses associated with bilateral ophthalmic arteries arising from the sphenoidal branch of the middle meningeal artery that were diagnosed by magnetic resonance (MR) angiography. Identification of rare arterial variations on MR angiography requires careful scrutiny of source images.

Tetralogy of Fallot (TOF) can be associated with vascular malformations or variations, especially of the aortic arch or supracardiac major venous systems. We report its association with an extremely rare combination of three such variations of the cerebral arteries-a right persistent hypoglossal artery, an extremely rare left carotid-right anterior cerebral artery (ACA) anastomosis, and a left accessory middle cerebral artery arising from the A1-A2 junction of the left ACA-which were diagnosed by magnetic resonance angiography in a 9-year-old girl during evaluation of multiple acute cerebral infarctions.

We present what we believe is the first report of a patient with an anomalous artery arising from the distal basilar artery and fusing with the mid-portion of an extremely long P1 segment of the left posterior cerebral artery that was diagnosed on magnetic resonance (MR) angiography. Careful review of MR angiographic images is important to detect rare arterial variations, and partial maximum-intensity-projection images aid their identification on MR angiography.

An anterior cerebral artery (ACA) of duplicate origin results from the fusion of two arteries that arise from the terminal segment of the internal carotid artery (ICA) to form a ring. This variation is extremely rare and differs from proximal ACA fenestration, supraclinoid fenestration of the ICA, and duplicate origin of the middle cerebral artery. We report a case diagnosed incidentally by magnetic resonance angiography.

Variations of the anterior cerebral artery-anterior communicating artery (ACoA) complex are common. Most are duplicated or partially duplicated ACoAs that are confused with fenestration of the ACoA. We report here an extremely rare case of true fenestration of the ACoA diagnosed by magnetic resonance angiography. Tiny true fenestrations of the ACoA may be overlooked easily by MR angiography. Partial maximum-intensity-projection image and volume-rendering image are useful in identifying true fenestration of the ACoA.

We report two cases in which the vertebral artery (VA) entered the spinal canal via the intervertebral foramen at the C2-C3 disc level, an extremely rare variation regarded as a C3 segmental type of VA, that we diagnosed by magnetic resonance angiography. The C2 segmental type of VA, in which the VA enters the spinal canal via the C1-C2 intervertebral space, is relatively common. It is important to identify these variations before surgery of the craniovertebral junction or interventional procedures to prevent complications.

We present an extremely rare case of an aberrant course of the petrous internal carotid artery (ICA) associated with the ipsilateral occipital artery arising from the cervical ICA, a combination not previously reported by magnetic resonance (MR) angiography. The patient was a 53-year-old woman with no symptoms related to the anomalous ICA. Source images and partial maximum-intensity-projection images of MR angiography are useful in diagnosing these variations. Source images and curved multiplanar reconstruction images of computed tomography angiography are important for the accurate evaluation of reduced arterial diameter and the relationship between the anomalous artery and petrous bone.

Extremely rarely, the ophthalmic artery (OphA) arises from the A1 segment of the anterior cerebral artery (ACA). Discovery of this anomalous OphA during angiography or surgery has been reported in several patients. We report a case in which an OphA of ACA origin was diagnosed by magnetic resonance (MR) angiography and confirmed by selective cerebral angiography. To our knowledge, this is the first report of this variation with MR angiography. Careful observation of MR angiographic images is important for detecting rare arterial variations. Partial maximum-intensity-projection images are useful in identifying tiny anomalous arteries on MR angiography.

The several types of agenesis of the internal carotid artery (ICA) are classified based on the aplastic segment of the ICA and types of collateral circulation. On magnetic resonance angiography, we incidentally found an extremely rare case in which the patient had 2 types of collateral circulation-anastomosis between the paraclinoid and supraclinoid segments of the contralateral ICA and anastomosis between the tip of the basilar artery and the posterior communicating artery. This is the first report of a case of ICA agenesis with 2 such types of collateral circulation.

Anastomosis of the carotid-anterior cerebral artery (ACA) is a rare anomalous vessel that arises from the internal carotid artery (ICA) at the level of the ophthalmic artery and takes an infraoptic and prechiasmatic path to anastomose with the ACA. It has known right-sided predominance. We report the case of an 83-year-old man with a left carotid-ACA anastomosis that was diagnosed by magnetic resonance (MR) angiography from the neck to the head during investigation of transient left hemiplegia. The right ICA was occluded at its origin. Our literature search revealed only six reported cases of left carotid-ACA anastomoses. We believe ours is the first case diagnosed by MR angiography.

Introduction: A persistent dorsal ophthalmic artery (OA) is a rare variation that originates from the cavernous segment of the internal carotid artery (ICA) and enters the orbit via the superior orbital fissure (SOF). Occasionally, the OA also arises from the middle meningeal artery (MMA) and enters the orbit via the SOF. These two major variations of the OA have not been well described by magnetic resonance (MR) angiography. We evaluated their prevalence on MR angiography at 3 T., Methods: We retrospectively reviewed our database of MR angiographic images obtained using a 3 T imager. Of images of 846 patients, we evaluated those of 826 patients (1,652 OAs) with special attention to OA origin and its course into the orbit. We excluded images of the 20 because quality was insufficient to assess., Results: We found 7 (0.42%) persistent dorsal OAs among 1,652 OAs (right/left, 6/1; male/female, 3/4). Twenty-four (1.45%) OAs arose from the MMA (right/left/bilateral, 11/5/4; male/female, 10/10), three of which also demonstrated a small normally branching OA. In one patient, we observed both right persistent dorsal OA and left OA arising from the MMA., Conclusions: Per OA, the prevalence of persistent dorsal OA was 0.42% and of OA arising from the MMA, 1.45%, with a tendency toward right-side predominance. OA arising from the MMA can be seen bilaterally; preprocedural knowledge of this variation is important because of the danger associated with endovascular procedures of the external carotid system when the OA arises from the MMA.

Introduction: The left common carotid artery (LCCA) is usually a second branch of the aortic arch that arises between the brachiocephalic trunk (BCT) and left subclavian artery; relatively frequently, it also arises from or shares a common origin with the BCT. In patients with LCCA of anomalous origin, transfemoral catheterization into the LCCA is sometimes difficult, and transbrachial or transradial approach may be recommended. We evaluated the prevalence of these variations on computed tomography (CT) angiography., Methods: We retrospectively reviewed CT angiographic images of 2,357 patients obtained using either of two 64-slice multidetector CT scanners. All patients were Japanese and underwent scanning from the aortic arch to the intracranial region; most had or were suspected of having cerebrovascular diseases., Results: We evaluated CT angiographic images of 2,352 patients after excluding four patients with LCCA occluded at its origin. The LCCA arose from the BCT in 141 patients (6.0 %) and had a common origin with the BCT in 130 patients (5.5 %). We found 11 aberrant right subclavian artery (0.47 %), and four of the 11 patients (36 %) had LCCA of common origin with the right common carotid artery, forming a bicarotid trunk (prevalence: 0.17 %)., Conclusions: The total prevalence of variations of LCCA origin diagnosed by CT angiography was 11.7 %.

Rarely, the ophthalmic artery (OA) arises from the cavernous segment of the internal carotid artery (ICA) inferolaterally and enters into the orbit via the superior orbital fissure. This anomalous OA that originates from the inferolateral trunk is regarded as a persistent dorsal OA. Extremely rarely, both normal OA and persistent dorsal OA arise from the ICA. We report the first case of such double OAs, one of which arose from the cavernous segment of the ICA superolaterally and we believe that it originated from the meningohypophyseal trunk rather than the inferolateral trunk.

Purpose: We report a case of type 1 proatlantal intersegmental artery (PIA) associated with multiple anomalies of the aortic arch, and discuss the possible embryonic mechanism and clinical importance of the multiple cerebrovascular variants in this patient., Methods: A 65-year-old woman with dizziness underwent cerebral magnetic resonance (MR) imaging and head and neck MR angiography using a 3-tesla scanner and computed tomography (CT) angiography using a 64-slice multidetector CT scanner., Results: MR and CT angiography demonstrated an aneurysm of the distal end of the azygos anterior cerebral arteries and hypoplasia of the proximal right vertebral artery (VA) with an anastomotic artery, between the right internal carotid artery (ICA) and distal right VA that passed through the foramen magnum, indicating a type 1 PIA. She also demonstrated an aberrant right subclavian artery (ARSA) with hypoplasia of the right VA, and the left VA arose directly from the aortic arch., Conclusion: To our knowledge, this is the first report of a type 1 PIA associated with multiple vascular anomalies of the aortic arch, such as ARSA and origin of the left VA from the arch. In cases of persistent anastomoses between the carotid and vertebrobasilar arteries, such as PIAs, imaging examination should include the aortic arch to identify associated vascular variations.

Purpose: The type 2 proatlantal intersegmental artery (PIA) is a rare anastomosis between the external carotid artery (ECA) and vertebral artery (VA) that passes through the foramen magnum. The persistent trigeminal artery (TA) is the most common anastomosis between the internal carotid artery (ICA) and basilar artery. The purpose of this paper is to present the first case of a type 2 PIA associated with an ipsilateral persistent TA diagnosed using magnetic resonance (MR) angiography, and we briefly discuss the embryology of this rare anomaly., Methods: An 83-year-old man with cerebral infarctions underwent cerebral MR imaging, and head and neck MR angiography using a 1.5 T imager. MR angiography was obtained using the standard non-contrast three-dimensional time-of-flight technique., Results: MR angiography showed aplasia of the proximal left VA and a large anastomotic artery between the left ECA and distal left VA that passed through the foramen magnum, indicative of a type 2 PIA. This patient also had an anastomosis between the precavernous segment of the left ICA and midbasilar artery via a lateral course, indicative of a lateral-type persistent TA., Conclusion: We present the first case of type 2 PIA associated with ipsilateral lateral-type persistent TA diagnosed by MR angiography. MR angiography should be performed including the carotid bifurcation to find more frequently extracranial arterial variations, including type 2 PIAs.

A persistent trigeminal artery (PTA) is the most common carotid-vertebrobasilar anastomosis, usually arising from the cavernous or precavernous segment of the internal carotid artery (ICA) and connecting to the distal basilar artery. There are two types of PTA, lateral and medial. We present the first case of a lateral-type PTA arising from the large arterial ring/fenestration of the cavernous segment of the left ICA with findings from both magnetic resonance angiography and selective catheter angiography.

Introduction: Duplicate origin of the middle cerebral artery (MCA) is rare and has been misdiagnosed or confused as fenestration of the proximal M1 segment of the MCA. The condition is not a true fenestration and occurs when two MCA branches arise separately from the terminal segment of the internal carotid artery, and fuse to form an arterial ring. We researched our institutional records to determine the prevalence of such cases and investigated its characteristic features on magnetic resonance (MR) angiography., Methods: To isolate these cases, we retrospectively reviewed cranial MR angiographic images of 3,491 patients obtained on either of two 1.5-tesla scanners at our institution from April 1, 2007 through December 31, 2009., Results: We found four cases of duplicate origin of the MCA, two cases each on the right and the left (3 men, one woman), representing a prevalence of 0.11%. All four arterial rings were small and mimicked fenestration of the proximal M1 segment. During the same period, we found three MCA fenestrations, two at the proximal M1 segment and one at the middle M1 segment. Total prevalence of duplicate origin and fenestration was 0.20%., Conclusions: In our institution, we observed 0.11% prevalence of duplicate origin of the MCA on MR angiography, and all were small and mimicked fenestration. Clinically, an important difference between duplicate origin and fenestration of the MCA is the potential collateral circulation available from the inferior branch in the case of saddle embolism occlusion of only the superior branch when there is duplicate origin of the MCA.

Introduction: A persistent trigeminal artery (PTA) is the most common carotid-vertebrobasilar anastomosis. A cerebellar artery that arises from the precavernous segment of the internal carotid artery (ICA) without connecting to the basilar artery is regarded as a PTA variant. Our study aimed to determine the incidence of PTA and its variants and classify them based on magnetic resonance (MR) angiography., Methods: We retrospectively reviewed cranial images of 3,626 patients who underwent MR angiography in our institution from April 1, 2007 through December 31, 2009. We ultimately reviewed and analyzed images of 3,491 patients (2,066 men, 1,425 women) after excluding 135 with unilateral or bilateral ICA occlusion or suboptimal image quality., Results: We found 12 cases of PTA (7 men, 5 women; right 4, left 8; incidence; 0.34%) and 6 of PTA variants (3 men, 3 women; right 3, left 3; incidence; 0.17%). 11 of the 12 PTAs were lateral type; 1 was medial. In two of the lateral-type cases, the superior cerebellar artery (SCA) arose from the PTA. Among the six variants, the anterior inferior cerebellar artery (AICA) arose in five and the posterior inferior cerebellar artery (PICA), in one., Conclusions: On MR angiography, the incidence of PTA was 0.34% and of PTA variants, 0.17%. Left PTA was twice as frequent as right PTA, but with no statistical significance. Medial-type PTA was extremely rare. AICA arose in most PTA variants. Rarely, a lateral-type PTA gave rise to the cerebellar artery.

Purpose: Extremely rarely, a persistent hypoglossal artery arises from the external carotid artery; only three cases have been reported in the English-language literature. The purpose of this paper is to report a case of this variation diagnosed by magnetic resonance (MR) angiography., Methods: A 75-year-old man with sudden-onset right hemiparesis and dysarthria underwent emergency cerebral MR imaging and cerebral MR angiography that included the cervical carotid bifurcation. A 1.5-T scanner was used and MR angiographic images were obtained using the standard three-dimensional time-of-flight technique., Results: On MR angiography, an anomalous artery arose from the proximal right external carotid artery, ascended just like the ascending pharyngeal artery, entered the hypoglossal canal (anterior condyloid foramen), and finally connected with the terminal segment of the right vertebral artery (VA). The proximal right VA was not visible, probably due to hypoplasia., Conclusion: We present the first case of this anomaly diagnosed using MR angiography, and we propose the term "type 2 persistent hypoglossal artery" to describe this condition.

Introduction: Persistent primitive olfactory artery (PPOA) is a relatively rare variation of the proximal anterior cerebral artery (ACA) that generally follows an extreme antero-inferior course and takes a hairpin turn. To our knowledge, incidence of PPOA has not been reported, so we researched cases in our institution records to determine incidence and investigated characteristic features of the condition on MR angiography., Methods: To isolate cases with PPOA, we retrospectively reviewed cranial magnetic resonance (MR) angiographic images of a total of 3,626 patients in our institution and collected similar images from cases with PPOA from our two affliated hospitals., Results: We found 14 cases with PPOA (six men and eight women); 5 patients in our institution, representing an incidence of 0.14%, and 9 cases from our group hospitals. The location was on the right in six cases, left in seven, and bilateral in one. An aneurysm was found at the hairpin turn in one patient, and in another patient, the PPOA connected with the accessory middle cerebral artery (MCA) and not the distal ACA., Conclusions: In our institution, incidence of PPOA on MR angiography was 0.14%. We found no laterality in frequency and rare bilaterality, aneurysm at the point of the hairpin turn, and accessory MCA arising from the PPOA.