Endovascular Management of Intracranial Pial Arteriovenous Fistulas: Experience of Largest Series at a Single Center Over Six Years

INTRODUCTION

Pial arteriovenous fistulas (AVFs) are extremely uncommon intracranial vascular lesions. The pial AVFs represent only 1.6%–4.7% of all neurovascular malformations.[1] In the past, pial AVF was once regarded as a type of arteriovenous malformation (AVM). However, current evidence suggests that pathological characteristics and clinical presentations and therapeutic options are different from those of AVM. These were previously categorized as AVFs; however, available evidences suggest that these are special entity which require different therapeutic approach for management. Authors present a case series, who were managed in the Instituto Nacional de Neurología y Neurocirugía “Manuel Velasco Suárez” of México constituting the largest case series reported to date. Pial AVF may have single or multiple arterial connections to single venous drainage channel without any intervening nidus. Pial AVF differs from dural AVF in that the arterial supply is derived from pial or cortical arterial vessel and the location is not within the dural leaflets.[2] Due to high-flow dynamics, pial AVF is often associated with a venous varix.[2]

METHODS

A review of the clinical files of the National Institute of Neurology and Neurosurgery was the year 2007 until 2012 with a diagnosis of pial AVF. Medical records were carefully evaluated to determine the functional prognosis of the patients before treatment and in the late follow-up [Table 1].

Table 1 Clinical review of pial arteriovenous fistula managed with endovascular technique

CASE SERIES (CASE 5)

A 6-year-old male patient presented with a history of sudden loss of consciousness. The general examination and neurological examination were within normal limit at admission. A cranial computed scan was carried out to evaluate the causes of unconsciousness which revealed the presence of parietal hematoma; a cerebral angiography revealed evidence of an arteriovenous communication between posterior cerebral artery and distal anterior cerebral artery that drained to the sagittal sinus [Figure 1]. Based on angiography findings, the plan was decided to perform embolization with Onyx™ under general anesthesia, the posterior cerebral angiography showed the complete occlusion of the fistula [Figure 2a and b], and the postoperatory was satisfactory. At 12-month follow-up, the patient was asymptomatic.

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Figure 1

A cerebral angiography revealed evidence of an arteriovenous communication between posterior cerebral artery and distal anterior cerebral artery that drained to the sagittal sinus

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Figure 2

(a and b) A control cerebral angiography showed the complete occlusion of the fistula

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DISCUSSION

The pial AVF is considered as rare cerebrovascular lesion and considered as variant of AVM for decades. However, newer studies showed that pial AVF is a distinct especial entity different from cerebral AVM, dural intracranial AVF, or other cerebral vascular lesions due to the different angiographic architecture, clinical course, and management options for pial AVF.[34]

The pathophysiological abnormality in pial AVF is related to high-flow nature of fistula. The communication between arterial feeder drains directly into a solitary draining vein without an intervening tangle of vessels called nidus and associated venous varices are related to the high turbulent flow from arteriovenous shunting.[56]

Due to lack of nidus, the existing higher pressure gradient, which can make such lesions more prone for rupture, leading to relatively worse prognosis.[7] It has been reported the case of a pial AVM with dural substitution associated with dural venous sinus thrombosis. The pial fistulas that occur in the 1^st years of life may be associated with disease syndromes such Rendu-Osler-Weber and Klippel-Trenaunay-Weber syndromes. To our knowledge, this is the largest pial fistulas cases series reported.

Due to their rarity, the natural history of intracranial pial AVF is still not well understood. In case of untreated pial fistula, the conservatively managed pial AVF and associated high mortality: five (63%) of eight patients died due to acute or subsequent fatal bleeding, so pial AVF requires surgical or endovascular treatment.[8]

The pial fistulas may present as bleeding, seizures, neurological deficits, cardiac failure in neonates and infants, headache and symptoms of increased intracranial pressure in children and may also present as palpable masses, erosion in the skull, and macrocephaly. The pial fistulas can also present with hemorrhage, headache, high-output cardiac failure in neonates and infants, macrocephaly, and features of raised intracranial pressure.[19]

Management of pial AVF differs from that of AVM and disconnection of the arteriovenous communication could eliminate the abnormality eliminating the need of resection. Fistulas in pediatric patients are associated with varicose veins in a high percentage; in these cases, the patient may experience mass effect symptoms; in adult patients, the symptoms are more frequently associated with hemorrhages. Regard therapeutic strategies, the endovascular management studies had showed obliteration rates of 86.5% and the surgical treatment offers similar rates, 86.8%.

In contrast, in AVM, resection of the entire lesion is necessary because of the multiplicity of the communicating shunts and occluding only the feeding arteries leaves behind the nidus, which can cause further recruitment of newer arterial feeders and the draining veins must also need to be obliterated because they persist after resection and may recruit recommunication with collaterals. The pathological features of a congenital pial AVF arise principally from its high-flow nature. Treatment of pial AVF by simply cutting off the shunt connection through surgery or endovascular intervention is sufficient, with removal of the entire vascular malformation was unnecessary.[1011]

Disconnection of the high-flow system leads to elimination of the abnormality and also the venous varices.

Management including the disconnection of the AVF was traditionally accomplished surgically by either clip application or cauterization of the vessel with proven effective. However, some lesions may be in deeply located or surgically inaccessible locations and as such surgery was associated with high risk. Recently, endovascular applications have been reported as successful means of disconnecting AVF with a variety of different agents such as balloons, coils, glue, silk sutures, or polyvinyl alcohol.[912]

Accessing the lesion through an endovascular technique eliminates the risks associated with surgical craniotomy and surgical-dissection approach. However, endovascular methods are not always successful or safe and many times may be unsuitable or develop postprocedural complications are well known. High-flow fistula makes it difficult to deliver the desired embolic agent precisely to the fistulous point. Delivery of embolic material into the draining vein can compromise venous outflow of the fistula or cause pulmonary embolism-like complications. Similarly, compromised venous outflow in the setting of an incompletely obliterated fistula can have disastrous consequences.[891314] As endovascular technologies continue to rapidly advance, we expect higher pial AVF detection rates, as well as higher success rates with endovascular flow disconnection of arteriovenous shunting.[314151617]

CONCLUSION

Pial AVFs are rare intracranial vascular malformations, and due to poorly understood natural course and associated significant morbidity, early prompt diagnosis and appropriate management are very important and highly desired. Early decision of endovascular therapy can lead to good neurological outcome and avoid or eliminate the risk of pial diurnal AVF-related complications. The goal of treatment is to remove the pial fistulas of high flow, to be disposed parallel disappear aneurysms and varicose veins. The aim is to close the fistula with obliteration of the vessels that feed the lesion and preserving venous drainage. Total resection of the lesion is unnecessary.