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INTRODUCTION
Intracranial pial arteriovenous fistulas (pAVF) are rare vascular lesions accounting for only 1.6% of all vascular malformations of the brain.9)28) These lesions have a single or multiple arterial connections to a single venous channel without any intervening nidus of vessel or capillaries. pAVF differs from dural AVF in that the arterial supply is derived from pial or cortical arterial vessels and the location is not within the dural leaflets.11) Natural course of pAVFs is not favorable and most require an intervention.18) Due to their rarity, there is no consensus regarding an optimal method of treatment. Most authors have reported simple disconnection of an arteriovenous shunt by either microsurgery or endovascular embolization without surgical resection, however, in large ones, pressure effect cannot be eliminated by use of these methods. In this report, we describe two cases of pAVF associated with giant varices that underwent surgical resection.
CASE REPORTS
Case 1
A 65-year-old woman with a complaint of headache and paresthesia in the left upper extremity was transferred to our hospital. The onset of symptoms dated back to one month ago. She had a history of hypertension and diabetes mellitus but had no history of head injury. Neurological examination showed normal motor function of extremities. Brain computed tomography (CT) and magnetic resonance imaging (MRI) showed a large saccular lesion in the posterior part of the right sylvian fissure with signal void and small calcifications in its wall (Fig. 1A and 1B). CT angiography and catheter angiography showed a giant venous aneurysm fed by one branch of the middle cerebral artery (MCA) and draining into the vein of Trolard, which was consistent with single-channel pAVF (Fig. 1C).
We attributed the patient's symptoms mainly to the mass effect of the aneurysm and decided to perform resection of the lesion. After right frontotemporoparietal craniotomy, the sylvian fissure was opened widely. Venous aneurysm and its feeding artery and draining vein were detected; one clip was placed on a feeding artery and another on the draining vein just close to the aneurysm. Blood in the lesion was aspirated and the aneurysm collapsed. It was dissected from surrounding tissues through the arachnoidal plane and en bloc removal was finally achieved (Fig. 1D). Microscopic examination of the resected specimen revealed fragments of hyalinized and calcified vessles with myxoid changes (Fig. 1E).
Her postoperative course was uncomplicated. At a follow-up visit three months after surgery, she had no headache and neurological examination was normal.
Case 2
A 12-year-old right-handed boy was transferred to our hospital after two weeks of admission in a local hospital due to sudden loss of consciousness and hemiplegia. On arrival, the patient was drowsy with left-sided severe hemiparesis (motor power = 2/5). Brain CT scan showed a huge heterogeneous hemorrhagic mass in the right hemisphere as well as peripheral edema (Fig. 2A). Cerebral digital subtraction angiography (DSA, Fig. 2B) showed a pAVF with a large aneurysmal varix, which was fed by multiple branches of the right MCA and draining to the superior sagittal sinus. Twenty eight days after the onset of symptoms and with remarkable recovery in neurologic status (motor power = 4/5), he underwent right temporoparietal craniotomy. After dural opening and obtaining proximal control, the varix was carefully dissected. We detected three large and four small arteries entering the lesion. Arterial feeders were obliterated, just proximal to the varix and the solitary draining vein was tied and cut. The varix was finally removed in one piece (Fig 2C and 2D). During the 48 hour post operative period, he was under mild sedation and hypotension was induced with intravenous infusion of midazolam and labetalol. Postoperative course was uneventful, and brain CT scan and CT angiography were convincing. He was dischared one week after surgery with full motor power.
DISCUSSION
pAVFs consist of one or more arterial connections to a single venous channel without any intervening nidus of vessels or capillaries. Intracranial pAVFs differ from arteriovenous malformations (AVMs) owing to the lack of nidus and from dural arteriovenous fistulas in that they derive their arterial supply from pial or cortical arterial vessels. They are rare vascular lesions. In the surgical series of 419 brain AVMs reported by Yasargil, pAVF accounted for 2.4% of the total.29) Little is known regarding the pathophysiological mechanisms giving rise to these lesions. It is possible that a misstep in embryological development of the cerebrovasculature produces these lesions. Alternatively, abnormal angiogenesis and associated vascular growth factors and cytokines may play a role.11)
The abnormality from an AVF arises from its high-flow nature. A communication between an arterial feeder directly into a solitary draining vein without an intervening tangle of vessels creates conditions for rapid high flow. Associated venous varices are produced by the high, turbulent flow from AV shunting.1)2)3)5)8) pAVFs can cause seizures, hemorrhage, headache, neurological deficit, cardiac failure in neonates and infants, symptoms of increased intracranial pressure, and intracranial bruit.6)14)15)25)26)
pAVFs may result from trauma or may be congenital.9)22) Congenital AVFs are usually diagnosed during infancy or early childhood, although many patients reported in the literature are adult. None of our patients had a history of significant head injury.
Natural history of these lesions is unfavorable. Conservative management of pAVFs fistulas has been associated with mortality in 63% of patients.18) Therefore, treatment of these lesions appears to be necessary. Treatment of pial fistulas differs from that of AVMs owing to the lack of a nidus. There are several strategies for treatment of pAVF. Most authors advocated simple disconnection of arteriovenous shunting, either by microsurgery or endovascular embolization.7)10)12)13)17)19)20)21)24)27) This strategy is based on the characteristics of pAVFs, which are high-flow communications between an arterial feeder and a single draining vein without an intervening tangle of vessels. Surgical disconnection of AV shunting offers a higher rate of complete obliteration of fistula than endovascular methods, however, it poses the risks of craniotomy and surgical dissection.11) Endovascular applications have been reported as successful means of disconnecting AV fistulae, particularly in deep and eloquent areas. Some angiogeometric configurations, such as multiple arterial connections or drainage of a normal cortical vein into the venous channel of a pAVF, are unfavorable for endovascular flow disconnection.
Some authors reported treatment of pAVF by surgical ligation of both arterial feeders and draining veins and then removal of the varix.4)16)23) This could be an appropriate option, particularly in lesions with large varices and significant mass effect because it reduces the volume of the lesion better and faster than other methods.
Both of our patients had very large surgically accessible varices that convinced us to perform resection of the lesion. Careful evaluation of angiography was helpful to us in finding vascular connections intraoperatively. In Case 2, there were small feeding arteries that were not obvious on DSA and we think that only surgical microdissection could detect all of them. In both patients, varix had thick walls and was surrounded by arachnoid, which made its dissection from other tissues possible. There was no new neurological deficit and the postoperative course was uneventful. Therefore, surgical ligation and resection of giant varix resulted in successful treatment in our patients.
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