Intracranial Vertebral Artery Dissection Dr Mat Bateman, Dr Danus Ravidran, Dr Ayton Hope, Dr Maurice Moriarty, Dr Stefan Brew, Dr Ben McGuinness Auckland City Hospital, Auckland, New Zealand

Introduction Intracranial vertebral artery dissection (iVAD) is a rare condition but one which is increasingly recognised as a cause of morbidity and mortality in younger patients. (1,2,3) It can occur spontaneously or be related to trauma (4) Vertebral artery dissecting aneurysm (iVAD) can result in rupture and subarachanoid haemorrhage (SAH) (3) Due to the risk of haemorrhage, management of iVAD can be challenging (5)

Epidemiology Initially thought to be rare however iVAD is being increasing described as a cause of SAH (6). The exact incidence of iVAD is unclear (2) iVAD represents approximately 2% of intracranial aneurysms (7) A slight male predominance is described with the most common age group being 30 - 50 year olds (3) Hypertension is thought to be the most common modifiable risk factor. Other risk factors include minor trauma, oral contraceptive pill, migraine, or intrinsic disorders of the vessel wall (2,7)

Pathophysiology The vertebral artery consists of 3 layers; the intima, media and adventitia. (2,7) The intradural vertebral artery has much thinner media and adventitial layers with little or no elastic fibers compared to the extradural artery. (8) Intracranial dissection usually disrupts both the intima and media. False aneurysms can occur when the subadventitia is disrupted. (2,7) Rate of re-rupture in ruptured aneurysms is as high as 70%. Re- rupture is most likely to occur early in the clinical setting (2,7,9)

Clinical Presentation The most common presenting symptom of vertebral artery dissection is severe occipital headache (5,10). TIA or ischemia can either from occlusion of local perforators resulting in lateral medullary dysfunction or from distal embolism (9) Aneurysmal dilatation can lead to rupture and subsequent SAH It is important to recognise that the same pathology may present with either haemorrhage or ischemia. If iVAD is diagnosed within hours to days after onset it is difficult to know which of these two clinical scenarios will potentially unfold

65 year old male presents with sudden occipital headache after exercise. CT and LP was negative for subarachnoid haemorrhage. No abnormal vascular density is seen about the intradural vertebral arteries in retrospect 65M. Sudden thunderclap HA after exercise. CT and LP negative. Presented with 2-3hrs.

3 days later he collapses 3 days later he collapses. CT on admission showed large extensive subarachnoid haemorrhage. CTA demonstrated an irregular sidewall aneurysm of the intradural right vertebral artery (red arrow) thought most likely to be a dissecting aneurysm. Patient died as a result of the hemorrhage. Collapsed 3 days later.

Late Presentation Delayed presentation of iVAD may be as an incidental fusiform aneurysm There are other possible causes of fusiform vertebral artery aneurysms and it is often not possible to determine the cause: atherosclerosis, disorders of collagen or elastin (e.g. FMD), rarely invasion of vessel wall by infection or tumour (e.g. left atrial myxoma)

Incidental Finding Small fusiform aneurysm of the intradural right vertebral artery (red arrows) in a 50 year old female who underwent MRI for two episodes of hemisensory disturbance. The presumed dissecting aneurysm was thought incidental and was stable in size on 3 years of follow up. 50 year old female underwent MRI for two episodes of left hemisensory disturbance. Small fusiform aneurysm of the intradural right vertebral artery was identified but thought unlikely to have caused clinical symptoms. This was followed and remained static over 3 years.

Imaging Findings Sequalae of iVAD such as SAH or ischemic changes are the most common imaging findings on CT imaging. MRI – Cresenteric shaped intramural haematoma (especially when T1 hyperintense). This may be difficult to identify in the setting of coexistant subarachnoid hemorrhage. (5) Angiographic appearances – CTA and MRA can be used but catheter angiography is often required (5,9) - Occlusion with vessel expansion - Focal stenosis (nonspecific without MRI findings) - Fusiform aneurysm often with stenotic change proximal or distal to the aneurysm It is important to note that imaging diagnosis is challenging and potentially subjective.

Angiographic Findings Two different cases showing typical fusiform aneurysmal change (red arrow) with proximal stenosis (yellow arrow) of iVAD. Similar findings can be seen on CT angiography although they are often more subtle

CTA showed no clear source of the hemorrhage Challenging Case CTA showed no clear source of the hemorrhage 55 year old male presents with collapse GCS 6. CT shows posterior fossa predominant SAH MRI showed focal hematoma (red arrow) about the intradural left vertebral artery (yellow arrows) associated with an acute left PICA infarct Cerebral angiography shows subtle irregularity of the intradural left vertebral artery with associated contrast stasis (red arrows). The left PICA is absent and likely occluded (hypoplastic left AICA). This was treated with coil occlusion

Management - Unruptured Unruptured iVAD represent a diagnostic challenge due to the potential risk of haemorrhage however studies have shown that aneurysms that are unruptured at the time of presentation have a low chance of subsequent rupture (9) In these patients, the prevention of ischemia is paramount, therefore anticoagulation or antiplatelet medication is warranted (5) Unruptured iVAD aneurysm should be treated if they enlarge on follow-up or if the patient develops recurrent symptoms on medical management (5)

Unruptured iVAD 44M acute onset slurred speech, headache and nausea. Anticoagulated 6 months and vertebral artery remained occluded on follow-up 44 year old male presents with acute onset slurred speech, nausea and headache. Non contrast CT shows expanded and hyperdense left intradural vertebral artery and a small infarct in the left cerebellum MRI comfirmed expanded vertebral artery compatible with dissection. Acute cerebellar infarct was present on diffusion. Both MRA and CTA showed the vertebral artery was occluded. The patient was anticoagulated for 3 months and follow up imaging showed that the vessel remained occluded

Management - Ruptured Ruptured iVAD are most commonly treated with endovascular treatment (2) Early treatment is important due to the risk of re-rupture – thought to be approximately (~50% @ 24hrs, ~80% @ 1wk (2,9,11) Therefore immediate treatment should be performed secure the diseased segment

Endovascular Treatment Options Trapping of diseased segment – usually coils Reconstructive – stent or flow diverter with or without coils

Coil trapping Endovascular historical standard Major advantage is immediate prevention of re-bleed and technically straight forward Most patients not suitable for test occlusion due to the acute hemorrhage Unlike carotid blisters – loss of access for endovascular treatment of vasospasm is usually not a consideration Reported low rate of morbidity even when involving PICA origin in small series. However there is a known risk of severe ischemic complications due to occlusion of brainstem perforators and spinal cord supply (7) Peluso – Series of 14 patients, 13 trapped and 1 stented. 2 trapped cases involved PICA. No medulla or PICA infarcts.

Coil Trapping - Complication 50yr old, drowsy but intact, 50 year old male presents with acute SAH, drowsy but otherwise intact. Angiography demonstrates fusiform dissecting aneurysm of the intradural right vertebral artery involving the origin of right PICA. The left vetebral artery is co-dominant and anterior spinal artery supply is not seen The aneurysm and dissected segment was coil occluded. The patient awoke from anesthesia but would not breath or protect his airway. An MRI performed showed a large right PICA territory infarct and also extensive infarction of his cervical cord.

Reconstructive techniques Recent developments in stent technology have enabled vessel preserving treatment of fusiform and dissecting aneurysms Theoretical advantage is less risk of ischemic complications Disadvantages are that antiplatelet medication is required, often more technically demanding, securing the aneurysm from re- bleed may not be achieved immediately i.e. higher risk of early re-bleed than with coil trapping. Anatomical considerations – PICA involved (size of AICA), anterior spinal origin, PICA origin and medullary perforators Lots of technical considerations: timing of antiplatelets, regular stent or flow diverter, jail and coil or not Yeung – series of 4 cases of PED, all had excellent outcome

52 year old male prsents with neck pain and headache 52 year old male prsents with neck pain and headache. CT shows posterior fossa SAH. Neurologicaly intact. Angiography shows a fusiform aneurysm of the intradural right vertebral artery beyond PICA. The left vertebral artery had a severe origin stenosis and was non-dominant.

Reconstructive Two overlapping flow diverting stents were deployed and the aneurysm lumen coiled via a jailed microcatheter. Complete occlusion of the aneurysm was achieved immediately with preservation of the right PICA.

Summary iVAD are a rare but important cause of both SAH and acute ischemia Imaging diagnosis can be challenging and may require more than one modality For those presenting with ischemia the primary focus should be prevention of further emboli For those presenting with SAH the primary focus should be treatment of the diseased segment (usually endovascular) to prevent a re-bleed Coil trapping or stent assisted vessel preserving techniques can be used

References 1) Ro A, Kageyama N, Abe N, Takatsu A, Fukunaga T; Intracranial vertebral artery dissecting resulting in fatal subarachnoid hemorrhage: clinical and histopathological investigations from a medicolegal perspective; Journal of Neurosurgery; 2009, 110: 948-954, 2) Su W, Gou S, Ni S, Li G, Liu Y, Zhu S, Li X; Management of ruptured and unruptured intracranial vertebral artery dissecting aneurysms; Journal of Clinical Neuroscience; 2011, 18: 1639–1644 3) Lee JM, Kim TS, Joo SP, Yoon W, Choi HY; Endovascular treatment of ruptured dissecting vertebral artery aneurysms - long term follow-up results, benefits of early embolisation, and predictors of outcome; Acta Neurochirurgica; 2010, 152:1455-1465 4) Arnold et al; Vertebral Artery Dissection, Presenting findings and predictors of outcomes; Stroke; 2006; 37:2499-2503 5) Kim BM et al; Outcomes and prognostic factors intracranial unruptured vertebrobasilar artery dissection; Neurology 2011, 76: 1735 - 1741

References 6) Lee JW et al: Spontaneous dissecting aneurysm of the intracranial vertebral artery: Management strategies; Yonsei Medical Journal; 2007, 48: 425-432 7) Peluso JPP et al; Endovascular treatment of symptomatic intradural vertebral dissecting aneurysms; AJNR 2008, 29: 102-106 8) Wilkinson I; The Vertebral Artery: Extracranial and Intracranial Structure; Archives of Neurology; 1972, 27(5):392-396. 9) Yutaka K et al; Dissecting aneurysms of the vertebral artery—angiographic patterns at the dissecting site on balloon test occlusion; Neuroradiology (2012) 54:857–862 10) Yutaka K et al; Strategy for Treating Unruptured Vertebral Artery Dissecting Aneurysms; Neurosurgery 2011, 69:1085-1091 11) Mizutani T et al; Recurrent subarachnoid hemorrhage from untreated ruptured vertebrobasilar dissecting aneurysms; Neurosurgery 1995, 36:905-913