Vertebrobasilar Dolichoectasia - An Overview

What Is VBD?

Vertebrobasilar dolichoectasia is also known as dilatative arteriopathy, mega-dolichoectasia, and fusiform aneurysm of the vertebral and basilar arteries. It is a condition characterized by dilation, elongation, and tortuosity of the vertebrobasilar arteries. The vertebrobasilar arteries are part of the vertebrobasilar system that serves as crucial blood supply to the various parts of the brain responsible for vision, coordination, consciousness, etc.

The exact cause of VBD is not yet determined, but it is known to be associated with conditions like atherosclerosis, hypertension, collagen vascular disease, etc. The primary mechanism of VBD is believed to be due to an imbalance in the activity of proteolytic enzymes (like matrix metalloproteinases) and antiproteases resulting in vascular remodeling and abnormal connective tissue within the arterial wall.

In patients with associated risk factors, the elongation and dilation in VBD will reduce blood flow velocity, leading to vascular symptoms similar to transient ischemic attack, ischemic stroke, cranial nerve compression, etc. In some cases, VBD can result in aneurysm formation.

Patients with symptomatic VSD will need treatment, and it is usually a combination of surgery and medication to strengthen the arterial wall and maintain hemodynamics, respectively.

What Causes VBD?

The exact cause of VBD is unclear; some of the acceptable mechanisms are mentioned below-

• Hypertension-Induced Atherosclerosis- Atherosclerosis is caused due to the gradual deposition of cholesterol and fats in the walls of the arteries leading to the narrowing of the blood vessels.

Atherosclerosis, when combined with hypertension, increases the chances of VBD in patients over 40 years of age. In fact, atherosclerotic degeneration of the vascular wall, with or without hypertension, is the initial pathogenic factor in the development of VBD.

• Congenital Factors- Patients with the following conditions have higher chances of developing VBD.
  • Autosomal Recessive Polycystic Kidney Disease- It is a congenital condition caused due to abnormalities in the development of the kidney and liver.
  • Pompe Disease- It is a rare inherited condition that disables the heart and muscular system.
  • Sickle Cell Anemia- An inherited condition that causes the red blood cells to be misshapen (to the form of a sickle) and breaks down.
  • Marfan’s Syndrome- It is a genetic condition that affects the connective tissue.
  • Ehlers-Danlos Syndrome- A group of inherited genetic conditions that affect the connective tissue in the skin, joints, and blood vessels.
  • PHACES Syndrome- It is an uncommon disorder of unknown etiology characterized by large segmental hemangiomas of the face and various developmental defects.
  • Moyamoya Disease- It is a cerebrovascular disorder caused due to the blockage of the carotid artery, thereby reducing blood flow to the brain.
  • Patent Ductus Arteriosus- It is a condition caused due to the abnormal opening of a fetal vessel (ductus arteriosus) even after birth.
  • Pupillary Function Disorder- These are abnormalities that affect the function of the pupil; some of them are RAPD (relative afferent pupillary defect), deafferented pupil, defective pupillary light reaction unassociated with vision loss, etc.

• Other Factors- Infections like syphilis and HIV (human immunodeficiency virus) have also been known to increase the chances of developing VBD.

What Are the Symptoms of VBD?

Most cases of VBD do not have any symptoms; however, the clinical manifestations vary widely in cases with obvious symptoms. The most common symptom is stroke (caused due to insufficient blood supply), followed by compression of the brain and cranial nerves. If left untreated, this will lead to bleeding (cerebral hemorrhage) and accumulation of fluid in the brain cavities (hydrocephalus).

• Ischemic Stroke- It is the most common symptom of VBD and also the most common cause of VBD-related death. The events leading to an ischemic stroke in VBD are as follows-
  • The forward flow in vertebrobasilar blood flow (which is actually a two-way flow) is reduced in patients with VBD. This causes hypoperfusion (decreased blood flow) to the concerned area, leading to symptoms typically seen during an ischemic stroke.
  • This reduced blood flow can also cause intraluminal thrombosis (blood clot), which tends to obstruct the opening of the perforating arteries leading to infarction.
  • Along with the above changes, the hemodynamic changes in the vertebrobasilar arteries can cause endothelial injury leading to atherosclerosis, and the resultant plaques can block the blood vessels.
  • Dolichoectasia (elongation and distension) of the vertebrobasilar arteries also causes pulling and twisting of the branching vessels, particularly those of the basilar arteries leading to a cerebral stroke.
• Brainstem And Peripheral Nerve Compression- VBD will also compress the nearby brain structures, leading to symptoms such as weakness and dizziness. Occasionally, patients will also choke on water if the compression involves the cranial nerves.
  • Brainstem Compression- The most common subclinical symptoms of brainstem compression are the extension of the blink-reflex latency (delay) and changes in the limb's motor-evoked potentials.
  • Cranial (or Peripheral) Nerve Compression- VBD can compress any of the twelve cranial nerves, the most commonly affected ones are the trigeminal nerves and the facial nerve resulting in trigeminal neuralgia and hemifacial spasm, respectively.
  • Neurogenic Hypertension- This is caused due to the compression of the ventrolateral medulla, which is the center for sympathetic activities and cardiovascular events.
• Obstructive Hydrocephalus- It is a rare complication of VBD and is caused due to compression of the midbrain aqueduct (which is the bottom of the third ventricle of the brain), which in turn leads to an abnormal buildup (hydrocephalus) of cerebrospinal fluid.

Along with the symptoms mentioned above, patients with VBD also suffer from non-specific symptoms like hemorrhage and headache.

How Is VBD Diagnosed?

Diagnosis of VBD usually relies on assessing the radiological images performed by experienced radiologists, along with the clinical symptoms. Various imaging techniques that can help in the diagnosis are-

1. CT (Computed Tomographic) Scan- This technique provides relatively limited information regarding peripheral nerve structures and hemodynamics. Still, it can be used in diagnosing VBD if the diameter of the enlarged basilar artery is more than 4.5mm.

2. MRI (Magnetic Resonance Imaging)- It is useful in the cases of hydrocephalus because it can show the VBD impingement upon the third ventricle, thereby eliminating the possibility of concurrent abnormalities.

3. Other Methods- Accessory tools like ultrasound and distal subtraction angiography (DSA) can assist in diagnosing VBA.

How Is VBA Treated?

VBA occurs predominantly in the brain's deep parts, making it extremely difficult to treat it. There is no standard treatment for VBD; the available treatments mainly target symptoms and complications of VBD.

Some of the frequently used treatment modalities are-

• Surgery- The frequently used surgical techniques to combat the symptoms and complications of VBD are microsurgeries and endovascular interventional treatment (EVT). Microsurgeries include surgical techniques like craniotomy, anastomosis, aneurysm suture, thrombectomy, etc. the type of surgical approach depends on the underlying complication.

EVT, on the other hand, uses stents to divert the flow, which in turn reduces the blood flow to the aneurysm. This is the most frequently used technique to tackle complications of VBD due to its high success rate.

• Medication- This includes anticoagulants and antiplatelet drugs, often combined with surgery to maintain the hemodynamic flow in the elongated vertebrobasilar arteries. However, they can be used independently in cases of recurrent ischemic stroke.

Conclusion:

VBD is a progressive vascular condition that needs further investigation; it is a life-threatening condition that can cause death from insufficient blood supply. It can be resolved with the help of advanced stent technology. The effect is more prominent when combined with anticoagulant and antiplatelet therapy and thus deserves further clinical validation.