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Fig. 23.3 A 52-year-old man was evaluated for moyamoya disease. Anteroposterior (AP) left vertebral artery angiogram revealed a single right arterial trunk supplying the paramedian thalami bilaterally, in keeping with an ar tery of Percheron. The patient showed an unusually straight course of the interpeduncular segment.

Fig. 23.4 A 16-year-old patient presented to the emergency department with acute onset of hypo- and dysesthesia. He admitted to using a “designer drug.” Drug screening was positive for amphetamines. Fluid-attenuated inversion recovery, diffusion-weighted imaging, and apparent diffusion coefficient scans (a,b,c) demonstrate a focal area of restricted infarction in the right paramedian thalamus (ventral pole of the dorsomedial thalamic nuclei). This territory is classically supplied by the thalamotuberal arteries that arise from the PcomA ar tery segment. On high-resolution time-of-flight MRA, there is a focal narrowing of this segment (arrows in d,e) that was believed to be related to either drug-induced vasculitis or drug-induced vasospasm.

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of the P1 segment. In addition, in cases of balloon remodeling, the balloon must be inflated for short periods of time, as there is no other potential supply to that thalamic territory.

23.3.4 Subependymal versus Trans-mesencephalic AVM Supply

In choroidal or third ventricular AVMs, it is important to diﬀerentiate a subependymal course of a recruited ThPA from the trans-mesencephalic supply. The former can be used for embolization if a distal position is reached, whereas the latter is considered to be dangerous. The diﬀerentiation between both can be done in the lateral angiogram, as the ThPA subependymal course will be longer and will follow the wall of the third ventricle before joining the nidus or one of the choroidal arteries. In contrast, the trans-mesencephalic arteries will be shorter and more direct, connecting directly to the nidus rather than to another vessel.

23.4 Additional Information and Cases

See ▶ Fig. 23.4, ▶ Fig. 23.5, ▶ Fig. 23.6, ▶ Fig. 23.7, ▶ Fig. 23.8, and ▶ Fig. 23.9.

Fig. 23.5 A 54-year-old woman presented with a past history of subarachnoid hemorrhage secondary to a ruptured right PcomA aneurysm that was clipped 18 years earlier, which now showed a large local recurrence. A right fetal PCA originated from the medial aspect of the aneurysm sac. After multidisciplinary discussion, we decided to treat this patient with a superior temporal artery/PCA bypass followed by endovascular coiling, sacrificing the origin of the right fetal PCA. (a) Lateral and (b) 3D angiography of the right internal carotid artery show a recurrent PcomA aneurysm with a fetal PCA arising from the medial wall of the aneurysm sac (arrow in b). (c) Postcoiling lateral ICA angiogram shows complete occlusion of the aneurysm and no filling of the fetal PCA. (d) Right external carotid arter y angiogram shows a widely patent extracranial–PCA bypass, with good opacification of the distal PCA branches but no retrograde filling of the proximal P2 segment or PcomA. After the procedure, the patient presented with left upper extremity weakness with no personality changes or memory impairment. (e,f) Nonenhanced CT 24 hours later reveals a recent thalamic infarct in the tuberothalamic artery territory (arrow in e,f).

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Pearls and Pitfalls

●

The ThPAs are divided into three groups that arise from the PcomA, P1 segment, and P2 segment.

●

The tuberothalamic group can be absent in ~30% of cases. In such patients, the paramedian group takes over that arterial territory.

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There is no consistent relationship between PcomA size and arterial supply (i.e., presence of tuberothalamic arteries), so sacrificing a hypoplastic PcomA should be avoided.

●

The artery of Percheron is a well-known but unusual variant in which a single trunk supplies both paramedian thalamic territories plus a variable extent of the midbrain.

●

In choroidal AVM treatment, it is important to diﬀerentiate the subependymal course of a recruited ThPA from transmescencephalic supply, as the former can be potentially used

Further Reading

[1] Endo H, Sato K, Kondo R, Matsumoto Y, Takahashi A, Tominaga T. Tuberotha-

lamic artery infarctions following coil embolization of ruptured posterior communicating artery aneurysms with posterior communicating artery sacrifice. AJNR Am J Neuroradiol 2012; 33: 500–506

[2] George AE, Raybaud C, Salamon G, Kricheﬀ II. Anatomy of the thalamoperfo-

rating arteries with special emphasis on arteriography of the third ventricle: Part I. Am J Roentgenol Radium Ther Nucl Med 1975; 124: 220–230

[3] Lazzaro NA, Wright B, Castillo M et al. Artery of percheron infarction: imag-

ing patterns and clinical spectrum. AJNR Am J Neuroradiol 2010; 31: 1283– 1289

[4] Rangel-Castilla L, Gasco J, Thompson B, Salinas P. Bilateral paramedian thala-

mic and mesencephalic infarcts after basilar tip aneurysm coiling: role of the artery of Percheron. Neurocirugia (Astur) 2009; 20: 288–293

[5] Schmahmann JD. Vascular syndromes of the thalamus. Stroke 2003; 34:

2264–2278

[6] Uz A. Variations in the origin of the thalamoperforating arteries. J Clin Neuro-

sci 2007; 14: 134–137

for embolization.

Fig. 23.6 A 72-year-old woman presented 6 years ago with intracranial bleeding from a large left PcomA aneurysm that was coiled at the time. She made good clinical recovery; however, follow-up imaging demonstrated aneurysm recanalization, and she was retreated with coil embolization. The aneurysm recurred again (a), despite dense packing, and flow-diverter treatment was therefore performed. Note the patency of the PcomA on the time-of-flight MRA source images (b) before retreatment (arrow). After flow-diverter treatment (c), the patient was discharged without neurological deficits on dual antiplatelet medication. After 1 year, clopidogrel was discontinued and the patient experienced right weakness and dysarthria with sudden onset 1 week later. Angiography demonstrated occlusion of the aneurysm (d). On the source images, the PcomA is no longer filling (arrow in e). The infarction is in the rostral parts of the ventrolateral nucleus, in the territory of the thalamotuberal arteries (diffusion-weighted MRI in f) that arise from the PcomA.

Fig. 23.7 Left vertebral artery injection (AP and lateral view) in a patient with a basilar tip thrombus demonstrates complete absence of the PCAs, the basilar tip, and the thalamoperforators (a,b). After successful reopening of the vessel (c, d), bilateral supply to the thalamus is seen to arise from the left P1 segment (arrows in c)

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119

Fig. 23.8 A 6-year-old boy presented with a left thalamic hematoma secondary to a small thalamic AVM. (a,b) AP and lateral left vertebral arter y angiograms show a small nidal-type AVM supplied by a large paramedian perforator arising from the contralateral P1 segment. The angiogram shows the characteristic sinuous course of the interpeduncular segment (arrow in a), followed by a straight mesencephalic segment. (c,d) Microcatheter superselective injections (AP and lateral) with the tip placed in the midinterpeduncular segment. (e,f) AP and lateral left vertebral artery angiogram postembolization, showing occlusion of the AVM nidus.

Fig. 23.9 This patient presented with intraventricular hemorrhage, the cause of which was identified to be a choroidal-type AVM that was fed by the medial choroidal artery from the distal P2 segment (arrow in a). This artery follows a recurrent course around the splenium of the corpus callosum (arrow in b) before it reaches the choroid plexus (asterisk: tip of the microcatheter). (c) Lateral view after embolization of the AVM demonstrates persistent choroidal blush from the lateral choroidal arteries (arrow in c) and complete obliteration of the AVM.

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Fig. 24.1 CTA in axial cuts (a,b) demonstrates the left medial occipital hemorrhage (arrowheads) and a focal outpouching (arrow) arising from the arteriovenous malformation nidus and pointing into the hemorrhagic cavity. Conventional angiography of the left vertebral artery (c,d anteroposterior and lateral view) demonstrates a small left inferior parietal AVM fed by the proximal calcarine artery with a focal outpouching pointing anteriorly (arrows).

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24 The Cortical Branches of the Posterior Cerebral Artery

24.1 Case Description

24.1.1 Clinical Presentation

A 12-year-old boy presented with nausea, vomiting, headaches, and a visual field deficit. An outside CT scan demonstrated a left occipital hemorrhage.

24.1.2 Radiologic Studies

See ▶ Fig. 24.1, ▶ Fig. 24.2, and ▶ Fig. 24.3.

24.1.3 Diagnosis

Ruptured arteriovenous malformation fed by a medial recurrent branch of the calcarine artery of the distal posterior cerebral artery (PCA).

24.2 Embryology and Anatomy

Four major arterial territories are fed by the cortical branches of the PCA: the inferior temporal territory with a hippocampal

and an anterior, middle, and posterior temporal subdivision; the calcarine territory; the parieto-occipital territory; and the splenial territory.

The inferior temporal arteries may arise as separate arteries or from a common trunk of the P2 segment. The first branch to arise from the inferior temporal branches is the hippocampal artery, which is in equilibrium with the anterior choroidal artery at the uncus and supplies the hippocampus; the remainder of the inferior temporal branches will be in balance with the middle cerebral artery (MCA) anteriorly and laterally and supply the undersurface of the brain.

The calcarine artery supplies the visual cortex, and its branching of the main PCA trunk is considered the termination of the PCA, with the second continuing branch being the parietooccipital artery. Accessory supply to this territory can arise from the MCA (posterior temporal branch).

The parietooccipital artery supplies the medial surface of the brain in its posterior aspect, including the cuneus and precuneus and the superior parietal lobule, but also the lateral occipital gyrus. It can supply parts of the convexity and is in equilibrium with the anterior and middle cerebral arteries at their respective border zones. An accessory calcarine supply can arise from the parietooccipital artery.

Fig. 24.2 Distal catheterization of the calcarine artery (a,b) demonstrates the distal territory supplied by this vessel and the AVM arising from a small recurrent medial branch that was subsequently catheterized (c), allowing embolization.

Fig. 24.3 Conventional angiography in AP (a) and lateral (b) view of the left vertebral artery after embolization demonstrates complete obliteration of the AVM with a preserved distal calcarine artery. Unenhanced CT after embolization (c,d) demonstrates the glue cast, including filling of the previously noted aneurysm (arrow in d).

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Fig. 24.4 Left vertebral artery injection in AP (a) and left internal carotid artery injection in lateral view (b) in two different patients. The distal cortical branches of the PCA territory are best appreciated on AP views, whereas the proximal temporal branches are best seen on the lateral view. PO, parietooccipital; Ca, calcarine; IT, inferior temporal (a, anterior; m, middle; and p, posterior).

Fig. 24.5 Axial unenhanced CT (a), axial T2-weighted MRI (b), axial CTA (c), coronal fusion image of digital subtrac tion angiography and MRI (d), coronal CTA (e), and left vertebral artery injection in AP view (f) in a child with intraventricular hemorrhage. As the P2 segment courses through the ambient cistern, it traverses the free margin of the tentorium in its P2/3 segment (white arrow in d). It is believed that because of repeated microtrauma, dissecting aneurysms can form at this level (arrows in b,c,e,f). These aneur ysms may arise from the main PCA stem or from smaller lateral branches. As this is a symptomatic distal dissecting aneurysm, treatment of choice is parent vessel occlusion.

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Fig. 24.6 Companion case to ▶ Fig. 24.5: CTA in three-dimensional reconstructions (a,b), axial fluid-attenuated inversion recovery (c), T2 (d), and T1

postcontrast (e) sequences show a fusiforme aneurysm in the distal ambient cistern in close contact with the free margin of the tentorium. Case continued in ▶ Fig. 24.7.

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The splenial artery either arises separately or from the parietooccipital branch to supply the posterior corpus callosum. It represents an important collateral pathway to the anterior cerebral artery. In this regard, it is of interest that in cases of PCA occlusion, this collateral is typically not used and, instead, the cortical branches (especially the posterior temporal branches) will supply the PCA territory (▶ Fig. 24.4).

24.3 Clinical Impact, Additional Information and Cases

See ▶ Fig. 24.5, ▶ Fig. 24.6, ▶ Fig. 24.7, and ▶ Fig. 24.8.

Pearls and Pitfalls

●

The main branches of the PCA are the inferior temporal branches and the calcarine, parietooccipital, and splenial arteries.

●

Cortical branches of the PCA are in hemodynamic equilibrium with the anterior cerebral artery and MCA, mainly via their cor tical branches and via the hippocampal artery, as well as with the anterior choroidal artery.

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If the final division of the PCA into calcarine and parietooccipital arteries is proximal on the P2 segment, it will be the parietooccipital artery that will supply the choroidal and thalamus territories.

Fig. 24.7 Angiography of the left vertebral artery in AP (a) and lateral (b) views confirms the diagnosis of a dissecting aneurysm. In the same setting, a

balloon test occlusion of the proximal P2 segment was performed (inflated balloon in c), and injection of the left internal carotid artery was done (d),

showing excellent filling of the undersurface of the brain (arrowheads in d) via leptomeningeal collaterals of a dominant posterior temporal branch

from the MCA. Subsequently, the distal PCA was sacrificed with dense coil packing (e,f), and the follow-up digital subtraction angiography

demonstrates complete filling of the PCA territory (g). T2-weighted scan after treatment demonstrates that the aneurysm is no longer visible (arrow)

and no PCA territory infarction is present.

Fig. 24.8 Eight years before the current presentation, a 47-year-old patient had presented with a single seizure, and a right posterior AVM was found

(angiography in lateral view in (a) that was fed by both the parietooccipital and the calcarine branch. The patient had refused treatment. On present

hospitalization, resulting from repeated seizures and visual disturbances, axial T2 weighted MRI (b,c) demonstrates perifocal edema surrounding a

focal outpouching in the inferior parts of the AVM. Repeat angiography (d) demonstrates a newly developed, intranidal, inferiorly pointing

outpouching (arrow) that was subsequently targeted with embolization.

The Cortical Branches of the Posterior Cerebral Artery

125