straight sinus

Vein of Galen Malformations: A Misnomer of Sorts

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The vein of Galen is located deep within the brain. The internal cerebral veins, basal veins of Rosenthal, atrial veins, and precentral cerebellar veins join together to form the vein of Galen.

As expected, the vein of Galen drains blood from deeply located brain structures. The vein of Galen then connects with the inferior sagittal sinus to form the straight sinus; blood then drains from the straight sinus into the transverse and sigmoid sinuses, where it eventually finds its way into the internal jugular veins and back to the heart.

Interestingly, a "vein of Galen" malformation is not actually a malformation of the true vein of Galen; the term is a misnomer. It is actually a malformation of primitive fetal anatomical structures that normally regress during development. These primitive structures include a dilated venous structure, as well as "feeding" arteries. Therefore, vein of Galen malformations represent true arteriovenous fistulas; in other words, blood moves directly from an artery to a vein without an intermediary capillary bed.

Between the 3rd and 11th weeks of fetal development a large primitive vein known as the median prosencephalic vein of Markowitz drains the deepest parts of the brain. As the brain develops, the internal cerebral veins annex the territory normally drained by the anterior portion of this vein. As a result, this portion of the median prosencephalic vein regresses. The internal cerebral veins then plug in to the posterior portion of the median prosencephalic vein, which becomes the "true", or "normal", vein of Galen.

The most common arterial "feeders" of the malformation can also be explained by aberrant embryology. During early fetal brain development the distal branches of the anterior cerebral arteries (ie: the pericallosal branches) make connections with the posterior cerebral arteries. These connections usually regress to form the anterior and posterior circulations, which are connected to one another via the posterior communicating arteries.

So how does a vein of Galen malformation form? In some infants the median prosencephalic vein of Markowitz does not regress like it should. As a result, a large abnormal venous midline pouch remains. It also retains its primitive arterial blood supply from the distal branches of the anterior cerebral artery (ie: pericallosal branches), anterior choroidal arteries, posterior communicating arteries, and branches of the posterior cerebral arteries (ie: posterior choroidal arteries).

Vein of Galen malformations are also associated with other abnormalities in the venous structure of the brain. Not uncommonly, the straight sinus is absent or severely narrowed. As a result venous blood drains into a persistent falcine sinus, which is a structure that normally regresses in-utero.

To summarize, vein of Galen malformations are primitive direct arteriovenous fistulas. They are composed of a dilated venous pouch (ie: the median prosencephalic vein of Markowitz) with any combination of anterior and posterior circulation feeding arteries.

Signs and Symptoms

Signs and symptoms depend on the severity of the malformation. Severe malformations present in new borns with high output cardiac failure. This is because so much blood is being shunted into the malformation that the heart cannot keep pace!

Less significant malformations present later in infancy with a rapidly enlarging head circumference secondary to hydrocephalus, developmental delay, and seizures. The increase in venous blood pressure within the head can cause a "melting brain" syndrome in which the white matter of the brain fails to develop properly. This can lead to severe mental retardation later in life if left untreated.

Diagnosis

Vein of Galen Malformations
Diagnosis is made with a combination of MRI, CT, and diagnostic angiograms. MR venograms can show the dilated venous pouch, as well as associated venous anomalies.

CT angiograms can show associated arterial feeding vessels. Formal diagnostic angiograms are the gold standard test; they delineate both the spatial and temporal relationship of the arterial feeding vessels to the venous pouch.

Formal catheter angiograms are also necessary to distinguish true vein of Galen malformations from arteriovenous malformations of the adjacent brain tissue.

Treatment

Treatment is dependent on the age of the child as well as the severity of the malformation. The most commonly used grading system developed by Dr. Lasjaunias is known as the Bicetre score. It takes into account the child’s cardiac, pulmonary, hepatic (liver), and renal (kidney) function. Lower scores indicate more severe disease with poorer outcomes.

The Bicetre score also dictates the optimal time for treatment. If the score is very low then aggressive treatment, even in the neo-natal period, may be indicated to try and prevent death and severe disability. Higher scores are typically treated later in life; however, worse outcomes, in terms of mental retardation, have been illustrated if treatment is delayed.

Most of these lesions are treated endovascularly (ie: from inside the blood vessels). The arterial feeders are embolized with a glue like material, which ultimately shuts down the fistula in an attempt to restore normal venous pressures. The vein itself may also be filled with tiny metal coils to help reduce flow through the fistula; this is known as trans-venous endovascular therapy.

Surgical ligation of the arterial feeders has mostly become a treatment of the past. Radiation therapy with Gamma Knife has also been used in some cases; it is showing some promise as an alternative treatment modality in select cases.

Overview

Vein of Galen malformations are fetal abnormalities in the brain’s normal venous drainage. They represent true arteriovenous fistulas. They are composed of a dilated median prosencephalic vein of Markowitz and numerous arterial feeding vessels. Feeders may come from the anterior cerebral arteries, posterior cerebral arteries, or posterior communicating arteries. Symptoms are usually from high output heart failure in the neonatal period; older infants and children suffer from increasing head circumference, seizures, and developmental delay. Treatment is usually with endovascular techniques.

References and Resources

When Brain Veins Go Bad: Cerebral Sinus Thrombosis

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In order to understand cerebral sinus thrombosis, we need a quick overview of blood vessel anatomy and the normal direction of blood flow in the body. In the most general terms, blood flows from the heart to large arteries (ie: aorta) then smaller arteries (branches off the aorta) then even smaller vessels called capillaries. It is at this point where the different body tissues extract nutrients and oxygen from the blood. The blood then drains into progressively larger veins until it empties back into the heart where it is re-oxygenated.

The largest veins of the brain are referred to as cerebral venous sinuses. They include the superior sagittal sinus, inferior sagittal sinus, a pair of transverse sinuses, a pair of sigmoid sinuses, straight sinus, cavernous sinus, a pair of superior petrosal sinuses, a pair of inferior petrosal sinuses, and the occipital sinus. The role of these sinuses is to collect all the “used” blood from the brain and deliver it back to the heart.

Like other veins in the body, the cerebral sinuses can form blood clots in them (the technical term for a blood clot is actually a "thrombosis", hence the name “sinus thrombosis”). When this happens a back up of blood in the brain occurs leading to increased pressure and sometimes hemorrhage within the brain tissue itself.

The exact cause of a dural venous thrombosis is not always clear. However, there are numerous risk factors associated with their development. They include inherited defects in proteins responsible for blood clot formation. These defects are collectively known as “thrombophilias”, which in Latin means “thrombus loving”. People with these inherited issues are more prone to forming blood clots.

In addition, patients with a kidney condition known as nephrotic syndrome are at increased risk. In this condition patients urinate out proteins responsible for keeping the blood clotting system at bay. The resulting imbalance can cause blood clots to form where they normally would not.

Infections such as mastoiditis and meningitis can cause inflammation of the sinuses, which can result in blood clot formation. Trauma to the head can also cause clot formation. In addition, that beautiful parasitic infection known as pregnancy (a joke of course!) also increases the risk of developing blood clots. Many commonly used birth control pills, especially those containing estrogen, can also increase a person’s risk.

Signs and Symptoms

Depending on the severity of the clot, everything from a mild headache (the most common presenting symptom) to death is possible. Patients with severe headaches may also have associated nausea and vomiting secondary to elevated intracranial pressures. Decreased mental status is also sometimes observed.

It is also important to remember that not all sinuses are created equal. For example, thrombosis in the superior sagittal sinus can present with leg weakness secondary to edema (ie: swelling) of the adjacent motor cortex.

If a clot forms in the cavernous sinus it may cause dysfunction of the third, fourth, fifth, and/or sixth cranial nerves. In addition, when blood pools in the brain behind the clot it can result in a type of stroke known as venous infarction.

Diagnosis

With todays modern imaging studies, MRI, and more specifically, MR venography has become a crucial diagnostic aid.

An example of an MR venogram is shown in the picture below. Other commonly used tests include traditional angiograms, in which radio-opaque dye is injected directly into the sinuses through catheters inserted in the groin. Finally, CT scans are also commonly obtained, especially to evaluate for possible co-existent hemorrhage into the brain.

MRV of Cerebral Sinus Thrombosis

Treatment

Treatment is usually with a blood thinning medication known as heparin. It is delivered through an IV and helps prevent further clot formation. If a venous stroke is present the use of blood thinning medications must be weighed against the possibility of causing bleeding into the stroked brain tissue. Aggressive hydration with normal saline is also often advocated.

Treating other underlying co-problems such as seizures and increased intracranial pressure is also an important part of managing patients with cerebral sinus thrombosis. Patients with substantial increases in intracranial pressure may require removal of the skull (craniectomy).

Overview

Cerebral sinus thrombosis is a abnormal blood clot in one of the large venous draining systems of the brain. They are uncommon and can present with everything from a mild headache to coma and death. Diagnosis is made most commonly with MRI. Treatment is based on preventing further clot formation with heparin and aggressive hydration.

References and Resources

  • Xu H, Chen K, Lin D, et al. Cerebral venous sinus thrombosis in adult nephrotic syndrome. Clin Nephrol. 2010 Aug;74(2):144-9. Review.
  • Dlamini N, Billinghurst L, Kirkham FJ. Cerebral venous sinus (sinovenous) thrombosis in children. Neurosurg Clin N Am. 2010 Jul;21(3):511-27.
  • Ju YE, Schwedt TJ. Abrupt-onset severe headaches. Semin Neurol. 2010 Apr;30(2):192-200. Epub 2010 Mar 29.
  • Kamal AK. Thrombolytic therapy in cerebral venous sinus thrombosis. J Pak Med Assoc. 2006 Nov;56(11):538-40.
  • Greenberg MS. Handbook of Neurosurgery. Sixth Edition. New York: Thieme, 2006.