Vertebrobasal Dolichoectesia.pptx

Vertebrobasal Dolichoectesia: Clinical & Imaging

1. Vertebrobasilar Dolichoectasia: Clinical & Imaging Spectrum Dr. Shahnawaz Alam MCh -Neurosurgery Moderated by: Dr. V. C. Jha HOD, Dept. of Neurosurgery

2. INTRODUCTION Dolichoectasia is derived from the Greek words dolichos , meaning “ abnormally long,” and ectasis, meaning “ to extend or dilate .” Vertebrobasilar dolichoectasia (VBD), characterized by clinically significant ectasia, elongation, and tortuosity of the vertebrobasilar arteries . The posterior circulation arteries appear to be particularly susceptible to dolichoectasia when compared with the anterior circulation. Because of less sympathetic innervation ; resulting in less trophic support on the vessel wall; More prone to deformity when exposed to increases in blood flow and pressure. Prevalence rates : 0.05% to 18%; 2% in a first-ever-stroke population. Clinical presentations, common imaging appearances and pitfalls, and the role of radiology in diagnosis and management of VBD are discussed.

3. REVIEW OF ANATOMY V4 pierces the dura b/w CN12 & the anterior root of C1 and ascends anterior to MO. At the lower border of the pons , it unites with the vessel of the opposite side to form BA. BA is formed by the junction of the two VA and extends from the lower border of the pons to the upper border within its median groove. It terminates by dividing into the two PCA in the interpeduncular or suprasellar cistern. There are close anatomic relationships b/w VA and CN12 at its entry to the hypoglossal canal, as well as b/w BA and CN-9/10/11/7/8/6/5/4/3 at their entry points to the skull and dural foramina. This close relationship predisposes the cranial nerves to compression in the event of a change in the diameter or course of the vertebrobasilar arteries. BA approx. 30 mm in length and 1.5–4.0 mm in width ; A diameter larger than 4.5 mm measured at the mid-pons level is considered ectatic by most authors.

4. Anatomy of the relevant CNs BS basal view Coronal T2WI at the level of the BA tip; CN3 (arrowheads) coursing b/w SCA (white arrows) and P1 (black arrows). Axial T2WI; CN6 leaving BS at the junction of the pons and the medulla (black arrows) and CN7/8 emerging from the pontomedullary junction (white arrows). Axial T2WI at the level of CN5 root entry zone at the anterior pons (arrows); right CN6 (arrowhead). Axial T2WI shows that CN9 (arrows) exit the BS from the sides of the upper medulla just rostral to CN10. Axial T2WI shows that CN12 (arrows) emerge from the ventromedial medulla oblongata and exit the skull base through the hypoglossal canal.

5. DISEASE ORIGIN Hypertension induced atherosclerosis early concept ; major risk factors for VBD development; In atherosclerosis, the intima and endothelia of arteries are primarily involved. Study suggest that in VBD, the media is the main layer affected with multiple gaps in the internal elastic lamina and thinning of the media secondary to smooth muscle atrophy and degeneration of the reticular fibers . In addition, the rare occurrence of VBD in children and adolescents without clinically significant atherosclerosis and the low incidence of VBD despite the markedly higher incidence of atherosclerosis and hypertension.

6. Primary pathophysiologic mechanism of dolichoectasia is now believed to be aberrant vascular remodelling and abnormal connective tissue within the arterial wall due to an imbalance between matrix metalloproteinases and antiprotease activity in the connective tissue. Hereditary predisposition for VBD: polycystic kidney disease, Ehlers Danlos and Marfan syndromes, neurofibromatosis type 1, Fabry disease, Pompe disease, and sickle cell disease. Other reported associations include infection, such as syphilis and varicella-zoster virus.

7. IMAGING FEATURES First imaging diagnostic criteria for VBD were established by Smoker et al on the basis of CTA findings. Include 3 quantitative measures of BA morphology: Laterality score and the height of bifurcation as surrogate measures for tortuosity and elongation, respectively, and the BA diameter . The laterality and height of the BA are graded from 0 to 3 on the basis of severity. By using the Smoker criteria, the transverse diameter is measured on axial images at the mid-pons level as a landmark. The location of the BA bifurcation as a surrogate for the length is evaluated on axial images and is most commonly within the interpeduncular cistern, at the level of the dorsum sellae, or within the suprasellar cistern just below the floor of the third ventricle. Termination above this level is considered abnormal.

8. Axial CEMRI T1WI at the midpons shows measurement of BA diameter. The severity of laterality is described according to the location of the BA (0, midline; 1, medial to the lateral margin of the clivus or DS; 2, lateral to the lateral margin of the clivus or DS; 3, in the CPA cistern). Sagittal CEMRI T1WI shows assessment of the height of bifurcation of the BA and its severity scores as a surrogate for length of the BA (0, at or below DS; 1, within the suprasellar cistern; 2, at the level of 3 rd V floor; 3, indenting and elevating floor). “Smoker criteria” for diagnosis of VBD Smoker, W. R. et al. High-resolution computed tomography of the basilar artery: 2. Vertebrobasilar dolichoectasia: clinicalpathologic correlation and review. AJNR Am. J. Neuroradiol . 7, 61 (1986). Basilar artery diameter Score of 1 is abnormal : 0: 1.9–4.5 mm 1: >4.5 mm Laterality Score ≥2 is abnormal Height of bifurcation Score ≥2 is abnormal The above criteria were defined on 5 mm thick slices .

9. Sites of measurement of the BA via MRA AB is basilar artery length (BAL), and CD is bending length (BL) BADE was diagnosed on the basis of the criteria established by Ubogu et al. According to the criteria, BA ectasia was defined as an arterial diameter >4.5mm at any location along its course. BA curve length >29.5mm or BL >10mm was considered as BA dolichosis . BL criteria : for the C-shaped or inverted C-shaped BA , BL was defined as the vertical distance from the bending point of the BA to the standard line, namely, the BAL. For the S-shaped BA, BL was defined as the length difference between the two lateral deviations on both sides. Ubogu , E. E. & Zaidat , O. O. Vertebrobasilar dolichoectasia diagnosed by magnetic resonance angiography and risk of stroke and death: a cohort study. J. Neurol. Neurosurg . Psychiatry 75, 22 (2004).

10. Correlation with sagittal and coronal images can result in more accurate scoring of the BA bifurcation. The height of the BA is particularly important in patients with VBD who have hydrocephalus , which most commonly is the result of an elongated BA indenting the floor of 3 rd V. Regarding the laterality of the BA, its location is considered normal on axial images if it lies medial to the margin of the clivus or dorsum sellae throughout its course. Positioning of any part of the artery lateral to the clivus or dorsum is considered abnormal. The MR imaging criteria for laterality of the BA have been modified from the CT criteria because of the inherent absence of bone landmarks, although there is good correlation between the two .

11. Several imaging modalities can be used to diagnose VBD. NCCT has been shown to depict dolichoectasia in 50% of cases , while CT angiography is a more sensitive option, providing greater definition of vessel morphology. Use of MRI and time-of-flight (TOF) MR angiography with the diagnostic criteria developed by Smoker et al results in excellent delineation of VBD and neural structures and has been validated despite the lack of definite osseous landmarks for grading BA laterality. Other diagnostic tools: transcranial Doppler ultrasonography- Slow arterial blood flow velocity ; DSA: Gold standard.

12. The degree of dolichoectasia according to the established criteria for VBD, including the maximum transverse diameters of the BA and the presence of a dominant vertebral artery, should be determined on axial images reconstructed perpendicular to the BA. The length of the BA can be assessed more accurately on reconstructed images in the coronal plane parallel to the BA by using the maximum intensity projection function. Both CT angiographic and MR angiographic images of the dolichoectatic vertebrobasilar system should be evaluated for an intraluminal thrombus, which manifests as filling defects.

13. An intraluminal thrombus may manifest as the hyperintense vessel sign on T1WI or FLAIR. On T1WI crescent-shaped hyperintensities in the lateral vessel wall s/o acute intramural hemorrhage ; it correlate with successive growth and rupture of intracranial arterial aneurysms and development and growth of VBD. T2IW and FLAIR should also be evaluated for edema within the brainstem related to VBD compression. Considering the different diagnostic value of (a) CT and CT angiography and (b) MR imaging and MR angiography, it may be beneficial to perform both imaging procedures to attain the most comprehensive characterization of VBD, especially in symptomatic patients .

14. Axial CT angiograms at the level of the clivus (a) and sphenoid sinus (b) show marked dolichoectasia of the BA (white arrow) and an intraluminal nonocclusive thrombus (arrowhead). Axial FLAIR MR image shows the hyperintense vessel sign (arrow), which is more intense adjacent to the vessel wall.

15. (a) Axial NCCT shows a hyperattenuating crescent-shaped intramural hematoma (arrowheads). (b) Axial maximum intensity projection CT angiogram shows a dissection (arrow) involving the dolichoectatic BA. (c) Axial DWI at the cerebellum shows multiple cerebellar infarcts (arrows) that are likely embolic.

16. 65/M with episodes of dizziness, unsteadiness, and anisocoria with a smaller left pupil . (a, b) Axial coned-down NCCT at the level of the pons (a) and maximum intensity projection CT angiogram (b) show dolichoectasia of the BA ( white arrow), which extends to the origin of SCA (black arrows in b). (c) Axial DWI obtained at the level of the pons shows a left pontine infarction (arrowhead). (d) Axial ADC map obtained at the level of the pons shows the left pontine infarction (arrowhead). (e) Axial FLAIR shows the hyperintense vessel sign (arrowhead) owing to decreased blood flow velocity in the VBD and laminar flow.

17. CLINICAL MANIFESTATIONS Most patients with VBD are asymptomatic and detected incidentally . Patients with VBD are more likely to be asymptomatic than are patients with anterior circulation dolichoectasia, possibly because more space exists around the vessels in the posterior fossa to accommodate enlargement. Clinical manifestations can be divided into compressive symptoms and vascular events, including TIA, ischemic stroke, and ICH or SAH. Vascular Events Ischemic Stroke Ischemic stroke is the most common clinical manifestation and the most common cause of VBD-related death. The most frequently described ischemic lesion is in the brainstem , accounting for 41% of cases, and is most often in the pons, followed by the posterior cerebral artery territory (29%), thalamus (22%), cerebellum (2%).

18. Mechanisms for the pathogenesis of ischemic stroke in VBD: Reduced antegrade flow in the VBD system, as well as decreased mean systolic velocity, because of bidirectional antegrade and retrograde flow within dolichoectatic arteries ; Further increases the risk for thrombus formation, obstruction of penetrating branches by the thrombus, and embolization of the perforators. Reduced perfusion and blood flow in penetrating branches because of distortion of the orifices of arterial branches due to elongation and angulation of the VBD. Endothelial injury related to hemodynamic alterations in the VBD system can lead to secondary atherosclerotic plaques.

19. Compressive Symptoms Caused by the enlarged vessels exerting pressure against surrounding structures , including BS & CNs; Most commonly involved CNs roots are 5/7/8 th . MC symptoms are trigeminal neuralgia and hemifacial spasm caused by pulsatile compression of the trigeminal nerve root and facial nerve root. Other symptoms : nystagmus, tinnitus, and hearing loss from compression of CN8 or nerve root entry; visual loss and homonymous hemianopia from compression of CN2 ; diplopia and Horner syndrome. It has been reported that patients with compressive symptoms tend to be spared from vascular events and vice versa.

20. 55/M with left trigeminal neuralgia (a, b) Axial T2WI (a) and T1WI (b) show mass effect on the cisternal segment of the left CN5 (black arrow) from the dolichoectatic left VA (white arrow). The left CN5 has been stretched compared to the right (arrowhead). (c, d) Oblique sagittal T2WI of the left (c) and right (d) CN5 are used to compare the course of the two nerves. In c, note the mass effect of VBD (red) on the left CN5 (yellow), which causes superior displacement of the nerve before it enters the Meckel cave . In d, note the normal course of the right CN5 (yellow).

21. 54/F with left facial spasm (a) Axial T2WI shows mass effect on the root exit zone of the left 7/8 CN complex (arrow). (b, c) Coronal reformatted TOF MR angiograms show a dolichoectatic left vertebral artery (black arrow in b and red shading in c) causing superior displacement of the left 7/8 CN complex (white arrows in b and yellow shading in c). Note the widened angle between the left seventh and eighth nerve roots and the lateral pons compared with the right side.

22. Symptoms from brainstem compression are the least common manifestations among symptomatic patients, accounting for 25% of cases. Compression from VBD typically has slow progression, and the brainstem can gradually tolerate compression without showing overt clinical manifestations. Compression typically occurs along the a nterolateral surface . BS basal view shows the location of CST . The lateral segments of the medulla contain it (blue). Below the pyramids of the medulla, most axons of CST cross over to the opposite side (arrow) from which they originated. Damage to CST can cause either C/L or I/L findings, depending on the level of the compression (above or below the decussation, respectively).

23. In addition to pyramidal tract signs , symptoms of vertigo, dysphagia, imbalance, and tinnitus can be caused by compression of lower parts of the brainstem or nucleus ambiguous. A rare complication of VBD is obstructive hydrocephalus , which is mainly due to cerebrospinal fluid circulation disruption caused by direct or indirect compression of the floor of 3 rd V or midbrain aqueduct. Hydrocephalus in a 62/M with worsening chronic headache (a) Sagittal reformatted CTA shows a dolichoectatic BA (arrow; large area of light green shading) causing mass effect on and posterior displacement of the pons and midbrain, as well as compression and displacement of the floor of 3rd V , resulting in hydrocephalus. (b) Axial CTA shows the BA bifurcation (arrow) at the level of FOM (Smoker grade 3).

24. PROGNOSIS The long-term prognosis of patients with VBD depends largely on the severity of the dolichoectasia at diagnosis, the diameter of the BA and the height of bifurcation, and its evolutionary characteristics. As the deformity progresses, the morbidity and mortality also increase. The survival rate in VBD after 3 years of follow-up was found to be 60% in a small case series. A mortality rate of 36% has been shown in a retrospective study, with half of the deaths occurring within 34 months of the initial diagnosis. Patients with VBD are more prone to experience recurrent stroke . The cumulative 10-year risk for a first recurrent stroke is 56% in patients with VBD, compared with a 43% cumulative risk in the general population.

25. TREATMENT There currently is no effective treatment for VBD itself because of the location and usually long length of the dolichoectatic vertebrobasilar artery and the important major arterial and perforating branches that supply critical structures. A variety of surgical techniques with inconsistent outcomes and morbidities have been attempted to repair the VBD itself, such as changing flow hemodynamic by reducing blood flow to the posterior circulation or other direct surgical intervention, including resection, proximal occlusion, and arterial bypass grafts. Endovascular interventional treatments, such as flow diversion by using stents with or without coils , have shown more promising outcomes compared with open surgical procedures. However, most of the current literature is based on small case series. In addition, brainstem infarction as the most common complication of these procedures has been reported in up to 22% of cases. Therefore, treatment is usually reserved for symptomatic cases of VBD.

26. Antiplatelet or anticoagulant agents for patients with more severe forms of dolichoectasia should be prescribed with caution b/c of risk for bleeding. Several treatment options are available to control VBD induced drug-refractory nerve compression symptoms specifically for trigeminal neuralgia and hemifacial spasm, including radiofrequency ablation, g-knife radiosurgery, percutaneous balloon compression of the trigeminal nerve, and botulinum toxin injection . The most effective treatment is reported to be microvascular decompression , which has now become a safe and highly effective surgical technique to relieve simple neurovascular compression syndromes. It is usually performed by interposing polytetrafluoroethylene felt or padding or other synthetic implants between the culprit vessel and the nerves.

27. CONCLUSION VBD is a progressive arterial disease characterized by clinically significant ectasia, elongation, and tortuosity of the vertebrobasilar arteries . The main clinical manifestations include stroke , which is the most common cause of death, and compressive symptoms. In the presence of VBD, the available nonsurgical, endovascular, and surgical management options for compressive and vascular manifestations may differ from standard treatment options.

28. References: Youmans and Winn neurological surgery 7th edition Ramamurthi & Tandon's textbook of neurosurgery 3 rd edition Internet THANK YOU