Vermian Arteriovenous Malformation
Arteriovenous Malformation of the Vermis lies in the midline and may be on the tentorial surface or on the suboccipital surface.
Superior and inferior, divided by the horizontal fissure.
Clinical features
Intracranial hemorrhage was the presenting symptom in 73% of the cases and recurrent bleeding episodes occurred in 60% 1).
Diagnosis
Computed tomographic scans demonstrated the site of the malformation in 80% and documented the presence of intracerebral bleeding in all posthemorrhage patients.
Angiography revealed two consistent patterns of arterial supply depending on the involvement by the malformation of the superior inferior cerebellar vermis 2).
Treatment
Vermian AVMs were typically resected through torcular craniotomies (89%), improving access to the superior vermian surface, relative to the standard subocciptial craniotomy, by removing the ledge of overhanging bone and lift the transverse sinuses with tacking sutures on the dural flap.
Vermian Arteriovenous Malformations are located in the midline and exposed with a torcular craniotomy to gain access to both the suboccipital and tentorial surfaces. The suboccipital part of the - vermis (tuber, pyramid, uvula, and nodule) is superficial and easily accessed, but the tentorial part (culmen, declive and folium) is deep and requires subarachnoid dissection to open the supracerebellar-infratentorial plane. The ascending slope of the tentorial part of the vermis requires significant neck flexion when positioning the head, tucking the chin two finger breadths from the manubrium in the prone position to align the tentorium vertically. Alternatively, small AVMs at the apex of the vermis or anteriorly in the quadrigeminal cistern can be approached with the patient in the sitting position, which allows gravity to retract the cerebellum and open the supracerebellar-infratentorial plane. Vermian AVMs attract bilateral feeding arteries, with superior vermian AVMs supplied by superior cerebellar artery SCAs and inferior vermian AVMs supplied by PICAs.
Case series
Fifteen cerebellar vermian arteriovenous malformations were surgically treated over a 7-year period. Intracranial hemorrhage was the presenting symptom in 73% of the cases and recurrent bleeding episodes occurred in 60%. Computed tomographic scans demonstrated the site of the malformation in 80% and documented the presence of intracerebral bleeding in all posthemorrhage patients. Angiography revealed two consistent patterns of arterial supply depending on the involvement by the malformation of the superior inferior cerebellar vermis. All lesions were surgically removed via a midline suboccipital posterior fossa microsurgical approach. Intraventricular extension of arteriovenous malformation was common, often in association with the choroid plexus of the fourth ventricle. Immediate postoperative angiography was used to document arteriovenous malformation removal. Three instances of unsuspected residual malformation were documented and required reexploration. The total operative mortality was 7%, and the neurological morbidity was 21% 3).