Central Nervous System Vascular Malformations

Central nervous system vascular malformations are rare abnormalities of blood vessels in the brain or spinal cord and their membranes. AVMs are tangled anastomoses of blood vessels of varying caliber in which arteriovenous shunting occurs in a central nidus.

There are several types of central nervous system vascular malformations. They are −

• Capillary telangiectasias − These are usually small (0.3 to 1.0 cm) lesions composed of tiny blood vessels similar to the tiny capillaries in the brain. These vessels are separated from one another by more or less normal-appearing brain tissue. These lesions are rarely symptomatic during life. These are most commonly found at autopsy as incidental findings.

• Cavernous malformations − Cavernous malformations are also called cavernous angiomas, cavernomas, or sometimes simply angiomas. Cavernous malformations are abnormally formed blood vessels in the brain or spinal cord, which have the appearance of a mulberry. These are well-defined lesions, which may reach a significant size and at times can be confused with a brain tumor. These vessels are not separated from one another by brain tissue. These are more common lesions.

• Dural arteriovenous fistulas − Dural arteriovenous fistulas are abnormal connections between arteries and the dura covering the brain or spinal cord and a draining vein.

• Venous malformations − Venous malformations, also known as developmental venous anomalies/angiomas, are abnormally enlarged brain or spinal cord veins. These have no definite arterial input. The veins in these malformations are separated from one another by normal-appearing brain tissue. These lesions are best left alone.

• True arteriovenous malformations (AVMs) − AVMs are the most significant lesions from the clinical point of view. These are composed of masses of arteries and arterialized veins. There is brain tissue that separates the vessels, but it is usually abnormal and often scarred from previous tiny hemorrhages (which the patient may not have been aware of/ represented as a bad headache).

• Vein of Galen Malformation (Aneurysm of the Vein of Galen) − a congenital lesion that develops when multiple arteriovenous shunts form between the choroidal/limbic circulation and a persistent embryologic vein.

CNS vascular malformations are frequently diagnosed in the setting of systemic diseases and syndromes with multiorgan presentations.

• Hereditary hemorrhagic telangiectasia (HHT)

• Capillary malformation–arteriovenous malformation (CM‐AVM) syndrome

• PHACES

• Vascular metameric syndrome

• Sturge weber syndrome

The most common brain vascular lesions in adults are arteriovenous shunts and cavernous malformations with estimated detection rates of 1.0 and 0.5 / 100 000 adults per year. Spinal cord vascular lesions are rare.

CNS Vascular Malformations: Symptoms

Not all people have symptoms. Symptoms depend on the size and location of the malformation.

Headaches, seizures, cranial nerve deficits, backaches, neck aches, and eventual nausea. Other common symptoms are pulsing noise in the head, progressive weakness and numbness, vision changes, and debilitating, excruciating pain.

In serious cases, the blood vessels rupture and there is bleeding within the brain (intracranial hemorrhage). Symptoms due to bleeding include loss of consciousness, sudden and severe headache, nausea, vomiting, incontinence, and blurred vision. Impairments caused by local brain tissue damage depends also on the bleed site, including seizure, one-sided weakness (hemiparesis), a loss of touch sensation on one side of the body, and aphasia. Ruptured AVMs are responsible for considerable mortality and morbidity.

CNS Vascular Malformations: Causes

The cause is yet unknown, however, it is possibly multifactorial. Both genetic mutation and angiogenic stimulation play roles in development.

Some other believed reasons for malformations are development in utero, exposure to alcohol, drugs, medications, toxins, or an angiopathic reaction following a cerebral ischemic/hemorrhagic event (subtypes of stroke).

CNS Vascular Malformations: Risk Factors

Things that may raise the risk of malformations are −

• A family history of malformations.

• Prior head injury

• Prior surgery or radiation therapy

CNS Vascular Malformations: Diagnosis

After a thorough medical history and physical and neurological examination, patients are subjected to neuroimaging studies.

The three main techniques used to visualize the brain and search for malformations are CT, MRI, and cerebral angiography.

• CT scan − It can suggest the approximate site of the bleeding.

• MRI provides better information about the exact location of the malformation.

• Cerebral angiography − It provides the best images. A ⦁ catheter passes through an artery up to the head, to deliver a ⦁ contrast agent into the malformation site. As the contrast agent flows through the malformation, a sequence of ⦁ x-ray images is taken.

More detailed pictures of the tangles of blood vessels that form malformations can be obtained by injecting radioactive agents into the bloodstream. If a CT/MRI is used in conjunction with an angiogram, it is called CT/MRI angiogram respectively.

CNS Vascular Malformations: Treatment

The goal of treatment is to prevent bleeding and to remove the malformation. Treatment depends on the location and size of the malformation and whether there is bleeding or not. Sometimes, more than one method is used.

Medical Management

Medicines can be given to manage a malformation that has not ruptured. They are also given to ease: Pain, High blood pressure, Blood clots, Seizures, and Pressure inside the skull.

• Anticonvulsant medications (phenytoin) − Control seizure.

• Medications/procedures − To relieve intracranial pressure.

• Eventually, curative treatment may be required to prevent recurrent hemorrhage. However, any type of intervention can also carry a risk of neurological damage and deficit.

Preventive treatment of as-yet unruptured brain malformation has been controversial.

Surgical Management

Surgical elimination of the blood vessels involved is the preferred curative treatment for many types of malformation.

If the malformation has ruptured, surgery may be delayed for 2 to 6 weeks. The type of surgery depends on the size and site of the vascular malformation. Options are −

Microsurgery

Surgery is performed by a neurosurgeon who temporarily removes part of the skull (craniotomy), separates the malformation from surrounding brain tissue, and resects the abnormal vessels. A special microscope helps the surgeon see the area.

While surgery can result in immediate, complete removal of the malformation, risks exist depending on the size and the location of the malformation. The malformation must be resected en bloc (partial resection will likely cause severe hemorrhage).

The preferred treatment of AVMs in young, healthy patients is surgical resection due to the relatively small risk of neurological damage compared to the high lifetime risk of hemorrhage.

Radiosurgery

The gamma knife is an apparatus used to precisely apply a controlled radiation dosage to the volume of the brain occupied by the malformation. While this treatment does not require an incision and craniotomy. Complete obliteration may or may not occur after several years, and a repeat treatment may be needed.

Neuroendovascular Therapy (Embolization)

A tube is inserted through the skin. It is passed through arteries until it reaches the malformation. An ethylene-vinyl alcohol copolymer(onyx) or n-butyl cyanoacrylate(nbca), is passed to the area, which will block off blood flow to the malformation. Embolization is frequently used as an adjunct to either surgery or radiation treatment. Embolization reduces the size of the malformation, and during surgery, it reduces the risk of bleeding.

CNS Vascular Malformations: Prevention

There is no way to prevent malformation. The cause is not known.

Conclusion

Central nervous system vascular malformations are rare abnormalities of blood vessels in the brain or spinal cord and their membranes. There are several types of central nervous system vascular malformations. The most common brain vascular lesions in adults are arteriovenous shunts and cavernous malformations.

Patients with CNS vascular lesions can present with a variety of presentations from headache and seizure to isolated cranial nerve deficits and progressive motor and sensory alterations.

After a thorough medical history and physical and neurological examination, patients are subjected to neuroimaging studies. The goal of treatment is to prevent bleeding and to remove the malformation.