Introduction

   An abnormal configuration of the cerebral arteries that has a bypass artery extending into an extracranial or intracranial segment is in general referred to as a duplication or fenestration.²⁾⁵⁾ This condition has been diagnosed more frequently with the advent of cerebral angiographic investigation. This anomaly is frequently associated with other congenital intracranial and extracranial vascular abnormalities including saccular or dissecting aneurysms.^{1)6)7)10)12)15)} However, a fenestration in association with an arteriovenous malformation (AVM) is much less common.^10)13)14) In this report, we describe a rare case of an AVM supplied by the right anterior inferior cerebellar artery(AICA) and posterior inferior cerebellar artery (PICA) in conjunction with a fenestration of the left vertebral artery.

Case Report

   An 18-year-old girl had a sudden onset of severe headache and recurrent vomiting while studying at night. Neurological examination on admission disclosed that she was drowsy, with a positive cerebellar sign on right side. A computed tomographic scan (CT scan) revealed cerebellar hemorrhage, particularly dense at the right cerebellopontine angle (CP angle) and cerebellar hemisphere, but did not reveal obstructive hydrocephalus (Fig. 1A). Magnetic resonance imaging revealed an acute hemorrhage on the right cerebellum with edematous changes (Fig. 2A). An AVM nidus in the hematoma was suspected near the right CP angle. The coronal T2-weighted image revealed two dilated vessels feeding the nidus (Fig. 2B). A subsequent fourvessel angiograms showed an arteriovenous malformation(AVM) fed from the right anterior inferior cerebellar artery (AICA) and posterior inferior cerebellar artery (PICA)(Fig. 3A and B). It drained medially into the right inferior vermian vein and laterally into the inferior hemispheric vein, then subsequently into the transverse sinus. The AVM was approximately 2×2×3 cm in size. The right PICA was originated in an unusual manner from the basilar trunk. Coincidentally the left vertebral artery (VA) was anomalously fenestrated. Both branches of the fenestration arose from the level of C1, extended to the intracranial segment, and reached the confluence of the vertebral arteries. The right PICA was originated from the larger limb of the fenestration. Surgery was planned for the day following admission but clinical changes forced a reevaluation. A second CT scan of the brain disclosed the hemorrhage to be slightly enlarged and obstructive hydrocephalus(Fig. 1B). She urgently was treated with extraventricular drainage (EVD) for obstructive hydrocephalus the day after her admission.
   The AVM was approached via a right retromatoid suboccipital craniotomy with the patient in the park-bench position. Two reddish dilated veins were found on the cerebellar cortex, medial and lateral side respectively. These were felt to be draining veins. After removal of bloody cerebrospinal fluid (CSF) from the cisterna magna and proper evacuation of cerebellar hemorrhage, two dilated arteries were found between the ninth cranial nerve and the largest bundle of the tenth cranial nerve. The cerebellar AVM nidus was supplied by the main branch of AICA and PICA itself. Ligation of two feeding arteries at the AVM margin with two small straight clips(Sugita clip, No. 81) was successfully accomplished. This was then followed by meticulous microsurgical dissection of the uncertain AVM periphery, sparing the two venous drainages. The AVM nidus was intermingled with the intracerebellar hemorrhage. After exposure of the entire nidus, the feeding arteries were cauterized. Then the draining veins were separated from the nidus. After complete resection of the AVM nidus, we attempted to visualize the opposite vertebral artery, but a large limb of the fenestration was partially observed. The postoperative course was uneventful. Intracranial pressure was monitored continuously. There was no drainage of CSF. The EVD tube was removed 5 days after her operation. Complete removal of AVM nidus was confirmed with angiogram taken 14 days after the operation (Fig. 4). At the time of discharge, there was a mild neurological deficit manifest by the right cerebellar dysfunction and the right hearing difficulty. One year later, the patient returns to nearly full activity and a normal life.

Discussion

   Fenestration or partial duplication of the vertebral artery seldom demonstrated at time of autopsy. The angiographic demonstration of these anomalies is even rarer. More than 72 cases have been reported in the world literature.^{1)6-10)12-15)} Most of them have been reported in Japan.
   Fenestration of the vertebral artery is considered to be a developmental anomaly occurring in the embryological processes. According to Padget's description,¹¹⁾ the vertebral artery forms in the embryo between the thirtysecond and fortieth days of the fetal age. Anastomoses developing between successive cervical segmental arteries lead to the formation of a primitive vertebral artery on each side in the neck. Primitive lateral basilovertebral anastomoses appear transiently, while the basilar artery is formed by a pair of longitudinal neural arteries. When a portion of the primitive accessory basilovertebral artery remains, this later forms an intracranial fenestration of the vertebral artery.³⁾⁷⁾ Extracranial duplications or fenestrations are most likely caused by persistence of cervical segmental arteries.
   Some authors have stated that a fenestration of the vertebral artery itself was an incidental, asymptomatic finding and has no clinical significance.⁸⁾¹²⁾ Other reports find that this anomaly is frequently associated with other congenital intracranial and extracranial vascular abnormalities including saccular or dissecting aneurysms.^{1)6)7)10)12)15)} Although the occurrence of aneurysms in the fenestration is a subject of controversy, there is evidence to suggest that existence of defects in the tunica media of the vessel at each end of the fenestration and local hemodynamic forces at the proximal site may precipitate aneurysm formation.²⁾ A fenestration of the vertebral artery associated with an arteriovenous malformation (AVM) is much less common.^10)13)14) The association of intracranial arterial fenestration and AVMs is not well understood. Yoshimoto, et al.,¹⁴⁾ proposed that hemodynamic stress resulting from fenestration of the feeding system of AVM might be an important factor in the enlargement of the small cerebellar AVM. Even if the commonest presentation of cerebellar AVM in children is intracranial hemorrhage,⁴⁾ hemodynamic stress resulting from a fenestration of the left vertebral artery may play a major role in the AVM rupture as in this patient. An AVM associated with fenestration of the cranial arteries may more likely to bleed than AVM without this anomaly.
   There are not enough case reports available to draw firm conclusions about the possible association of vertebral artery fenestration and AVM. Further studies of this possible association are needed.

Conclusions

   We experienced a case of the ruptured arteriovenous malformation at cerebellopontine angle with a fenestration of the vertebral artery. The hemodynamic stress resulting from fenestration of the feeding system of AVM might be an important factor in the enlargement of the small cerebellar AVM.

REFERENCES

1. Arai K, Endo S, Hirashima Y, Takaku A. Posterior inferior cerebellar aneurysm associated with fenestration of the vertebral arterycase report. Neurol Med Chir(Tokyo) 29:29-31, 1989

2. Black SPW, Ansbachen LE. Saccular aneurysm associated with segmental duplication of the basilar artery. A morphological study. J Neurosurg 61:1005-8, 1984

3. De Caro R, Parenti A, Munari F. Fenestration of the vertebrobasilar junction. Acta Neurochir(Wien) 108:85-7, 1991

4. Griffiths PD, Blaser S, Armstrong D, Chuang S, Humphreys RP, Harwood-Nash D. Cerebellar arteriovenous malformations in children. Neuroradiology 40:324-31, 1998

5. Hasegawa T, Kubota T, Ito H, Yamamoto S. Symptomatic duplication of the vertebral artery. Surg Neurol 20:244-8, 1983

6. Kowada M, Takahashi M, Gito Y, Kishikawa T. Fenestration of the vertebral artery: report of 2 cases demonstrated by angiography. Neuroradiology 6:110-2, 1973

7. Kowada M, Yamaguchi K, Takahashi H. Fenestration of the vertebral artery with a review of 23 cases in Japan. Radiology 103:343-6, 1972

8. Maki Y, Watanabe M, Nakada Y, Ono Y, Shirai S. Angiographic demonstration of the vertebral artery fenestration. Clin Neurol 9:199-204, 1969

9. Miyazaki S, Kamata K, Yamaura A. Multiple aneurysms of the vertebrobasilar system associated with fenestration of the vertebral artery. Surg Neurol 15:192-5, 1981

10. Mizukami M, Tomica T, Mine T, Mihara H. Bypass anomaly of the vertebral artery associated with cerebral aneurysm and arteriovenous malformation. J Neurosurg 37:204-9, 1972

11. Padget DH. The development of cranial arteries in the human embryo. Contrib Embryol 212:205-62, 1948

12. Sanders WP, Sorek PA, Mehta BA. Fenestration of intracranial arteries with special attention to assoicated aneurysms and other anomalies. AJNR 14:675-80, 1993

13. Teal JS, Rumbaugh CL, Bergeron RT, Segall HD. Angiographic demonstration of fenestrations of the intradural intracranial arteries. Radiology 106:123-6, 1973

14. Yoshimoto H, Maeda H, Aoyama H, Kanazawa J, Kitaoka T, Uozumi T. Enlargement of cerebellar arteriovenous malformation associated with fenestration of the vertebral arterycase report. Neurol Med Chir(Tokyo) 32:585-8, 1992

15. Zhang QJ, Kobayashi S, Gibo H, Hongo K. Vertebrobasilar junction fenestration associated with dissecting aneurysm of intracranial vertebral artery. Stroke 25:1273-5, 1994