Meningohypophyseal Trunk Research Articles

Arterial supply of the trigeminal ganglion, a micromorphological study.

In this study, we explored the specific microanatomical properties of the trigeminal ganglion (TG) blood supply and its close neurovascular relationships with the surrounding vessels. Possible clinical implications have been discussed. The internal carotid and maxillary arteries of 25 adult and 4 foetal heads were injected with a 10% mixture of India ink and gelatin, and their TGs subsequently underwent microdissection, observation and morphometry under a stereoscopic microscope. The number of trigeminal arteries varied between 3 and 5 (mean 3.34), originating from 2 or 3 of the following sources: the inferolateral trunk (ILT) (100%), the meningohypophyseal trunk (MHT) (100%), and from the middle meningeal artery (MMA) (92%). In total, the mean diameter of the trigeminal branches was 0.222 mm. The trigeminal branch of the ILT supplied medial and middle parts of the TG, the branch of the MHT supplied the medial part of the TG, and the branch of the MMA supplied the lateral part of the TG. Additional arteries for the TG emerged from the dural vascular plexus and the vascular network of the plexal segment of the trigeminal nerve. Uniform and specific intraganglionicdense capillary network was observed for each sensory trigeminal neuron. The reported features of the TG vasculature could be implied in a safer setting for surgical approach to the skull base, in relation to the surrounding structures. The morphometric data on TG vasculature provide anatomical basis for better understanding the complex TG blood supply from the internal and external carotid arteries.

A rare marginal tentorial artery to ophthalmic artery anastomosis

We report a patient with a marginal tentorial artery to ophthalmic artery anastomosis. A middle-aged man presented with subarachnoid hemorrhage and underwent angiography, where selective microcatheter injection of the meningohypophyseal trunk and marginal tentorial artery revealed a collateral to the distal ophthalmic artery. The radiological findings, embryology behind ophthalmic artery anastomoses and the neurosurgical and neurovascular relevance are discussed.

Transnasal endoscopic anatomy and approaches to the cavernous sinus

The goal of the current study is to describe the transnasal endoscopic anatomy of the cavernous sinus and to provide the surgical approaches to this area. Six silicon-injected adult cadaveric heads (12 sides) were dissected through endoscopic endonasal approach. The cavernous sinus and adjacent structures were exposed; detailed anatomies were demonstrated. High-quality pictures were produced. The cavernous sinus had four walls, namely medial, lateral, posterior and superior walls. Five venous spaces within the sinus were identified by their relation to the carotid artery; those were the medial, lateral, posterosuperior, posteroinferior and anterolateral compartments. Three branches arising from the cavernous segment of internal carotid artery from proximal to distal were meningohypophyseal trunk, inferolateral trunk and McConnell capsular artery. Cavernous sinuses communicated each other by intercavernous sinuses, as well as basilar sinus in middle line, and connected with superior and inferior petrosal sinuses. The third and fourth nerves coursed in superior part of the lateral wall of the cavernous sinus; Meckel's cave located in the posteroinferior part of the lateral wall of the cavernous sinus; V1 sloped to the superior orbital fissure along the lateral wall; the sixth nerve entered the posteroinferior compartment then passed through the internal carotid artery and reached to superior orbital fissure. The approaches to the cavernous sinus included trans-sphenoid-sellar-medial cavernous sinus (medial to the internal carotid artery) and trans-ethmoid-pterygoid-sphenoid-lateral cavernous sinus (lateral to the internal carotid artery). Trans-sphenoid-sellar-medial cavernous sinus approach was able to expose medial compartment and posterosuperior compartment and part of posteroinferior compartment. Trans-ethmoid-pterygoid-sphenoid-lateral cavernous sinus approach was able to expose anteroinferior compartment, lateral cavernous sinus and cranial nerves in lateral wall. An understanding of the complex relationships of the cavernous segment of internal carotid artery and cranial nerves in cavernous sinus is paramount for surgically dealing with the disease involved cavernous sinus and adjacent region.

Facial Palsy and Nystagmus after Transvenous Embolization of a Carotid Cavernous Fistula

Facial Palsy and Nystagmus after Transvenous Embolization of a Carotid Cavernous Fistula

Double ophthalmic arteries arising from the internal carotid artery

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.

E-010 Preoperative embolization of meningioma with dural branch of internal carotid artery

PurposeOne of the most important issues in the surgical treatment of large hypervascular meningiomas is the securing and coagulation of feeding arteries. However, securing the feeding artery prior to actual...

Transcortical Venous Approach for Direct Embolization of a Cavernous Sinus Dural Arteriovenous Fistula

Dural arteriovenous fistulas (dAVFs) represent 10% to 15% of all intracranial arteriovenous malformations. Most often, embolization is accomplished with transfemoral catheter techniques. We present a case in which embolization of a cavernous sinus dAVF was made possible through transcranial cannulation of a cortical draining vein. An 82-year-old woman presented with diplopia, left sixth cranial nerve palsy, intraocular hypertension, and bilateral chemosis. Angiography revealed a complex cavernous dAVF with cortical venous reflux, supplied by both external carotid arteries and the left meningohypophyseal trunk. Percutaneous transvenous access failed, and only partial occlusion was achieved by transarterial embolization. A frontotemporal craniotomy was performed to access the superficial middle cerebral vein in the left sylvian fissure. Under fluoroscopic guidance, a microcatheter was advanced through this vein to the floor of the middle cranial fossa and into the dAVF, permitting coil occlusion. This transcranial vein technique may be a useful adjunct in dAVF therapy when percutaneous transarterial or transvenous approaches fail or are not possible.

The Artery of Bernasconi and Cassinari: A Morphometric Study for Superselective Catheterization

The artery of Bernasconi and Cassinari is an important infraclinoid branch of the internal cerebral artery. It is of neuroendovascular relevance in view of its supply to complex lesions such as meningiomas and arteriovenous malformations in the tentorial and falcotentorial regions. The present microanatomic study attempts a morphometric elucidation of this slender but important branch of the meningohypophyseal trunk. The origin, course, dimensions, and related variations of the tentorial artery were studied in 10 formalin-fixed human cadaveric sides. The tentorial artery originated from the meningohypophyseal trunk in all but 1 specimen, in which it arose directly from the intracavernous internal carotid artery. In 80% of specimens, it took origin as a single branch; as a bifurcation and trifurcation in 1 each. It was usually the terminal branch of the meningohypophyseal trunk (in 90%). In all, 5 distinct microvascular patterns were noted. The mean diameter of this artery was 0.7 mm (range, 0.3-0.8 mm; SD, ± 0.1 mm). The mean length was 15.4 mm (range, 9-23 mm; SD, ± 4.4 mm). Its mean distance from the origin of the meningohypophyseal trunk was 1.7 mm (range, 1.3-2.3 mm; SD, ± 0.4 mm). The mean distance from the free edge of the tentorium was 3.7 mm (range, 3-5 mm; SD, ± 0.7 mm). The artery of Bernasconi and Cassinari is an important vascular conduit to myriad neoplasms and vascular malformations in the vicinity of the tentorium cerebelli. In this era of advanced microneurosurgical techniques and superselective endovascular interventions, morphometric knowledge of this artery is important for precise and safe management of these lesions.

Anatomical Relationships of Intracavernous Internal Carotid Artery to Intracavernous Neural Structures

The objective is to correlate the intracavernous internal carotid artery (ICA) with the position of the intracavernous neural structures. The cavernous sinuses of nine injected cadaveric heads were dissected bilaterally. As measured on computed tomographic angiograms from 100 adults, anatomical relationships and measurements of intracavernous ICA and neural structures were studied and correlated to the intracavernous ICA curvature. Intracavernous ICAs were classified as normal and redundant. The meningohypophyseal trunk (MHT) of normal ICAs appeared to be closely related to the abducens nerve compared with redundant ICAs (5.5 ± 2.1 mm versus 10.0 ± 2.5 mm, respectively; p = 0.001). The position of the inferolateral trunk (ILT) varied along the horizontal segment of the intracavernous ICA. On imaging studies the ICA curvature correlated with the kyphotic degree of the skull and similarity of the ICA curvature between sides. The safety margin for preventing iatrogenic intracavernous nerve injury during surgical exploration or transarterial embolization of vascular lesions around the MHT is high with redundant ICAs. In contrast, a transvenous endovascular approach via the inferior petrosal sinus may be too distant to reach the MHT when ICAs are redundant. Approaching lesions of the inferolateral trunk may be the same regardless of ICA type.

Extended Endoscopic Endonasal Approach to the Clival Region

The objective of this study was to recognize the endoscopic anatomy of the clival region of the skull base and its neurovascular relations, which will make us able to perform safer and minimal invasive endoscopic approaches to this region with lower rate of complications. Six fresh cadavers were studied (n = 5). We approached the clivus by performing binostril extended endoscopic endonasal approach. After locating the sphenoid sinus as a key point, the vomer was totally removed to expose the clival region located inferiorly to the sphenoid sinus. Mucosal incision is done vertically from the sphenoidal portion the clivus caudally to the inferior portion of nasal cavity just medially to vidian nerve. The mucosal flap is then dissected and retracted. The clivus was resected until the foramen magnum inferiorly. The lateral limit of the resection is the paraclival portion of the internal carotid artery (ICA).The dura and the meningohypophyseal artery is exposed. A vertical dural incision was done and retracted laterally to expose the intradural structures. The prepontine cistern and basilar artery were visualized. The clivus was best localized by orienting the endoscope +15 degrees rostrally. After resecting the inferior wall of the sphenoid sinus and vomer and the overlying mucosa is retracted laterally until the vidian nerve, we obtained sufficient exposure of the clivus. The safe lateral limit of the surgical corridor was the vidian nerve. The clivus is resected until the foramen magnum inferiorly. The safe lateral limit of the resection in this step was the proximal cavernous and the distal petrosal portions of the ICA. This resection provided us with a wide exposure of the clival dura. The basilar plexus, the abducens nerve (sixth cranial nerve) passing through the basilar plexus, and the paraclival portion of the ICA can be injured when careful dissection is not performed. After dural incision, the prepontine cistern and the basilar artery were able to be exposed widely. Binostril extended endoscopic endonasal approach is an appropriate approach to the clival region of the skull base. With good knowledge of the endoscopic anatomic features of this region and its neurovascular relations, surgical procedures can be performed safely with more minimal invasiveness.

SURGICAL CONSIDERATIONS IN THE MANAGEMENT OF FALCOTENTORIAL MENINGIOMAS

Meningiomas arising from the falcotentorial junction are relatively rare, and the description of the surgical nuances in approaching these tumors is limited. We describe our surgical management of these lesions in detail. From 2001 to 2005, 9 patients underwent operation for meningiomas arising from the falcotentorial junction, with some extending to and/or invading the torcula. All patients were assessed preoperatively with magnetic resonance neuroimaging and cerebral angiography. Furthermore, preoperative embolization was attempted in all cases. A supratentorial/infratentorial torcular craniotomy technique was used in all but 1 of these cases. The average dimensions of the falcotentorial meningiomas were 5.1 x 4.4 x 4.2 cm. The angiograms revealed that these tumors were fed by branches of the internal carotid artery, choroidal arteries, branches of the meningohypophyseal trunk, and branches of the posterior cerebral artery. Preoperative embolization was achieved in only 2 patients. Five patients had gross total resection (Simpson grade 1), and 4 had subtotal resection (Simpson grade 4). Two of the tumors (22%) recurred during a mean follow-up period of 49 months (range, 17-88 months). The most common complication after surgery was cortical blindness, but all postoperative visual deficits had fully recovered at the last follow-up evaluation within several months. An excellent outcome can be expected with detailed preoperative neuroimaging and knowledge of the nuances of the surgical technique that we describe in detail in this article.

Surgical Treatment of the Tentorial and Falco-Tentorial Junction Meningiomas

Tentorial meningiomas account for 3-7.7% of all meningiomas in surgically treated patients. In this group, the falco-tentorial meningiomas are considered to be the rarest. The paper presents three cases of the tentorial and falco-tentorial junction meningiomas. Two of the meningiomas were of major size and with an attachment at the falco-tentorial junction, while the other was attached to the inferior notch of the tentorium. The lesions manifested as headaches and disequilibrium that persisted for many years. The Parinaud syndrome and diplopia were observed in the patient with the meningioma attachment at the inferior notch of the tentorium. One of the lesions was resected completely using an occipital bitranstentorial/falcine approach. In the second case an occipito-transtentorial approach was used. However, during the surgery problems arose with resecting the lesion on the other side. The meningioma of the inferior notch of the tentorium was vascularized through the tentorial artery stemming from the meningo-hypophyseal trunk of the intracavitary section of the internal carotid artery on the right side. This meningioma required a two-stage operation. The surgical treatment was satisfactory and depended on the patient's condition at the time of the surgery. The presented rare cases of tentorial and falco-tentorial junction meningiomas seem to suggest that their treatment should be surgical and launched promptly after making a diagnosis. The results of the treatment might then be favourable.

Anatomical study of the cavernous sinus emphasizing operative approaches

The aim of this article is to describe the microsurgical anatomy of the cavernous sinus, the triangles, and the osseous relationships in the region with special attention to the relationships important in surgical approaches on the intracavernous structures. Fifty cavernous sinuses obtained from twenty-five cadaver heads were studied in detail using magnification. Stepwise dissections of the cavernous sinuses performed to demonstrate the intradural and extradural routes, anatomy of the triangles and osseous relationships in the region. The main branches of the intracavernous portion of the carotid artery were the meningohypophyseal, the inferior cavernous sinus, and McConnell;s capsular artery . The main branches of the meningohypophyseal trunk were the tentorial, the dorsal meningeal, and the inferior hypophyseal artery. There were variations of the main branches of the meningohypophyseal trunk. The sixth cranial may splite into rootlets as it passes lateral to the carotid artery. There were size and shape variation of the triangles. Aprecise understanding of the bony relationships, the anatomy of the triangels and neurovascular content of the cavernous sinus, together with the use of cranial base and microsurgical techniques are necessary for safer surgery. Asingle approach is not capable of providing exposure of all parts of the sinus.

Transvenous embolization with a combination of detachable coils and Onyx for a complicated cavernous dural arteriovenous fistula

Treatment of cavernous dural arteriovenous fistulas (DAVF) is usually made by a transarterial approach. However, in many complicated patients, treatments via transarterial approaches can not be achieved, and only an operation via a transvenous approach is feasible. We aimed to study the feasibility of transarterial embolization of cavernous dural arteriovenous fistulas with a combination detachable coils and Onyx to embolize a complicated cavernous DAVF via a transvenous approach. From August 2006 to August 2007, six cases of complicated cavernous DAVF were embolized with a combination of detachable coils and Onyx via a transvenous approach. Three cases were male and the other three were female. Their ages ranged from 36 to 69 years old. The fistula was in the right lateral cavernous sinus in one case, in the left lateral cavernous sinus in another, and in the bilateral cavernous sinus in 4 cases. One fistula was fed by the right internal carotid artery and its meningohypophyseal trunk; one was fed by the branches of the left internal carotid artery and left external carotid artery; four were fed by the branches of the bilateral internal carotid artery and/or the bilateral external carotid artery. One case was drained via one lateral inferior petrosal sinus; three were drained via bilateral inferior petrosal sinuses; one was drained via one lateral ophthalmic and facial veins; one was drained via the inferior petrosal sinus and the ophthalmic and facial veins. Four were embolized via the inferior petrosal sinus, and two were embolized via the ophthalmic and facial veins. Among six cases of complicated cavernous DAVF, four were fully embolized with Onyx by a single operation, and two cases were fully embolized with Onyx following two operations. Transient headache was found after operation in all patients, but was cured after several days by the symptomatic treatments. In one case, the first operation via the inferior petrosal sinus was a failure; the feeding branches of the external carotid artery were embolized, and transient facial palsy was appeared after operation. The fistula was fully embolized with Onyx via the inferior petrosal sinus after two months with no complications. One bilateral cavernous sinus DAVF was embolized with Onyx via the inferior petrosal sinus by two operations, and transient abducens nerve palsy occurred after embolization. Because Onyx may be injected via a transvenous approach and the microcatheter is easily withdrawn, cavernous sinus via transvenous catheterization and embolization is a safe and efficient way to treat complicated cavernous dural arteriovenous fistulas, especially those for which operations via transarterial approaches have failed, or spontaneous cavernous dural arteriovenous fistulas.

The antero-medial triangle: The risk for cranial nerves ischemia at the cavernous sinus lateral wall: Anatomic cadaveric study

Objective Vascular damage in the cavernous sinus can cause ischemic injury to the cranial nerves. An appropriate anatomical knowledge of the blood supply to the cranial nerves can help to reduce the morbidity associated with cavernous sinus surgery. Material and methods Three formalin-fixed and six adult cadaveric fresh heads, with common carotid arteries injected, were used for anatomical dissection in this study. A fronto-temporal craniotomy was performed and the cavernous sinus was explored according to the Dolenc technique. With microsurgical dissection and photographic documentation, we demonstrate the anatomy of the superior orbital fissure artery in the antero-medial triangle. Results The 12 explored cavernous sinuses demonstrated the presence of two principal branches directly from the intracavernous internal carotid artery that supply the cranial nerves: the infero-lateral trunk and the meningohypophyseal trunk. The artery of the Superior Orbital Fissure (SOF), originated more often from the infero-lateral trunk, and vascularized the III, IV, VI, and VI, and ophtalmic division of the trigeminal nerve (TGN VI) at their entry in the fissure. Conclusion In this study we demonstrate that the superior orbital fissure artery is a branch from the infero-lateral trunk which runs immediately under the reticularis layer at the level of the anteromedial triangle in the lateral wall of the cavernous sinus. The blood supply to all cranial nerves in the SOF is at risk to injury when the lateral wall of the cavernous sinus is transgressed at the anteromedial triangle since the SOF-artery runs superficially at this level.

The retrosigmoid intradural suprameatal approach to posterior cavernous sinus – Microsurgical anatomy

Objective The retrosigmoid intradural suprameatal approach includes the standard retrosigmoid suboccipital route with drilling of the petrous bone above and anterior of the internal auditory meatus, allowing for exposure of the trigeminal nerve within the Meckel's cave and of the middle fossa. In this study, the authors analyzed the potential use of an extended variation of the suprameatal route to approach the posterior cavernous sinus for microsurgery of, e.g., petroclival meningiomas and trigeminal schwannomas. Methods The microsurgical anatomy of the retrosigmoid suprameatal approach was examined by using 10 adult cadaveric specimens (20 sides), using 3–40× magnification. The exposure to the posterior cavernous sinus provided by this approach was focused. Results After drilling the suprameatal tubercle toward the petrous apex, the Meckel's cave was exposed. The trochlear nerve was the landmark for opening the cavernous sinus by this approach. The dura located medially to the entry point of the trochlear nerve into the tentorium was resected, allowing exposure of the intracavernous carotid artery with its meningohypophyseal trunk. Conclusion The extended retrosigmoid intradural suprameatal approach allows exposure of the posterior cavernous sinus and may be used to remove lesions of the posterior fossa extending into the Meckel's cave and into the cavernous sinus.

EXTRADURAL TRANSCAVERNOUS APPROACH TO CAVERNOUS SINUS HEMANGIOMAS

Cavernous sinus hemangiomas (CSHs) are uncommon lesions and comprise fewer than 1% of all parasellar masses. Because of their location, propensity for profuse bleeding during surgery, and relationship to complex neurovascular structures, they are notoriously difficult to excise. The authors describe their experience with seven cases of CSHs. Headache and visual impairment were the most common presenting complaints, followed by facial hypesthesia and diplopia. Computed tomographic scans revealed iso- to hyperdense expansile lesions in the region of the cavernous sinus and middle cranial fossa. Magnetic resonance imaging scans revealed hypo- to isointense lesions on T1-weighted images and markedly hyperintense lesions on T2-weighted images, with marked homogeneous enhancement after contrast administration. All CSHs were treated by a purely extradural transcavernous approach. This involved reduction of sphenoid ridge, exposure of the superior orbital fissure, drilling of the anterior clinoid process, coagulation and division of the middle meningeal artery, and peeling of the meningeal layer of the lateral wall of the cavernous sinus from the inner membranous layer. The cranial nerves in the lateral wall of the cavernous sinus were exposed (Cranial Nerves III and IV, as well as V1, V2, and V3). The tumor was accessed through its maximum bulge through either the lateral or anterolateral triangle. The tumor was removed via rapid decompression, coagulation of the feeder from the meningohypophyseal trunk, and dissection along the cranial nerves. All but one patient had complete tumor excision. Transient ophthalmoparesis (complete resolution in 6-8 wk) was the most common surgical complication. To our knowledge, we describe one of the largest series of pure extradural transcavernous approaches to CSHs. CSHs are uncommon but challenging cranial base lesions. The extradural transcavernous approach allows complete excision with minimal mortality or long-term morbidity.

Combined Use of TruFill DCS Detachable Coil System and Guglielmi Detachable Coil for Embolization of Meningioma Fed by Branches of the Cavernous Internal Carotid Artery-Technical Case Report-

A 57-year-old female presented with a left petroclival meningioma fed by the meningohypophyseal trunk of the internal carotid artery (ICA). The enlarged tentorial marginal artery and inferior hypophyseal artery were successfully embolized with the TruFill DCS Detachable Coil System through a 0.019-inch inner diameter microcatheter. Superselective catheterization into the dorsal meningeal artery could not be achieved with the same microcatheter, because the catheter tip was too large to pass into the vessel. Subsequently the feeding artery was successfully embolized with a Guglielmi detachable coil (GDC) through a 0.016-inch inner diameter microcatheter. The patient underwent surgery without blood loss on the day after embolization. Our subjective impression was that the TruFill DCS was softer and had less resistance during insertion, whereas the GDC could be delivered through a smaller caliber system for smaller vessels. Appropriate use of the TruFill DCS and GDCs can allow efficient embolization of the feeding branches of the ICA.

Solitary Fibrous Tumor Arising from Cranial Nerve VI in the Prepontine Cistern: Case Report and Review of a Tumor Subpopulation Mimicking Schwannoma

The authors present a report of a solitary fibrous tumor (SFT) arising from the intradural component of the VIth cranial nerve as it travels through the prepontine cistern. SFTs of the central nervous system are extremely rare entities that clinically masquerade as dural-based lesions, such as meningiomas or hemangiopericytomas. Because of their infrequency and clinical similarity to other central nervous system (CNS) lesions, diagnosis is largely dependent on pathological features. In this study, the authors define a subpopulation of SFTs that seem to arise directly from nerve, rather than meninges, and clinically mimic the appearance of a schwannoma. The patient was a 29-year-old woman with a several-month history of progressive right arm and leg numbness and mild hemiparesis, with the development of diplopia 2 weeks before admission. Outside imaging revealed a 3.9-cm mass in the prepontine cistern with extension into Meckel's cave and the cavernous sinus, resulting in significant brainstem compression. The patient underwent preoperative angiography with embolization of feeding vessels off of the left meningohypophyseal trunk. The patient was then taken to the operating room by a combined neurosurgical and ear, nose, and throat team, where the patient underwent a retrolabyrinthine/subtemporal craniotomy for tumor resection. During resection of the prepontine component, the tumor was identified as originating from the left Cranial Nerve VI as it traversed through the prepontine cistern. Resection of the tumor component involving the cavernous sinus and Meckel's cave was deferred for follow-up treatment with intensity-modulated radiation therapy. Pathological examination revealed tissue consistent with the diagnosis of SFT. SFTs involving the CNS are rare entities that are almost always diagnosed after tissue is obtained because of their clinical and radiographic similarity to meningiomas. This patient had an SFT masquerading as a VIth cranial nerve schwannoma. Although the natural history of SFTs in the CNS is not completely understood, correct diagnosis is important, given the rate of recurrence found in the more common pleural-based SFT and examples of CNS SFTs with malignant features.

A Case of Posterior Ischemic Optic Neuropathy in a Posterior-draining Dural Cavernous Sinus Fistula

A 79-year-old woman presented with sudden unilateral visual loss after an ocular motor disturbance and pulsatile tinnitus. Neuro-ophthalmologic examination showed a presumed right posterior ischemic optic neuropathy (PION), oculosympathetic, and third, sensory fifth, and sixth cranial nerve pareses. Selective angiography of the right internal and external carotid arteries confirmed a posterior-draining dural carotid cavernous sinus fistula (CCF) fed by the right meningohypophyseal trunk and right middle meningeal artery. Angiography also showed an ophthalmic-middle meningeal arterial anastomosis. We postulate that the PION was caused by an arterial steal, because blood was drawn into the fistula and away from the intraorbital optic nerve.