Intracranial vascular malformations

Intracranial vascular malformations are congenital lesions due to alterations in the development of the arteriolocapillary network. Traditionally, they are divided into four types according to their histological characteristics:

1. Cavernous angiomas or cavernomas
2. Arteriovenous malformations
3. Venous angiomas
4. Telangectasias.

Cavernomas are a type of vascular malformation with specific histological features. Cavernoma can arise de novo, or with an associated family history. They are generally supratentorial but can occur anywhere in the neural axis. They have been reported in the brain stem, spinal cord, lateral ventricle and the cavernous sinus

Risk factors for cavernomas

• Cranial radiation
• Coexistent vascular malformation
• Genetic and hormonal factors
• Previous surgery for intracranial lesions,
• Other apparently unrelated intracranial lesions have been reported as risk factors.

Cavernomas are purple or dark red lesions macroscopically, with a honey-comb appearance due to unequal blood-filled spaces of varying sizes. The cavernomas are multilobulated lesions which are clearly delimited and contain blood at different stages of evolution. Histologically they are composed of sinusoidal spaces lined by endothelium and closely interlinked, without intervening nervous tissue. They are usually found at a supratentorial level, and less frequently in the posterior fossa. Usually there are no feeding vessels demonstrable in relation to these anomalies on angiography.

Diagnosis

The usual clinical features are convulsions and parenchymatous bleeding for the supratentorial cavernomas. CT, MRI and digital angiography are utilized in the diagnosis.

• On CT, the lesion is isodense to hyperdense precontrast, with frequent heavy calcification. After contrast injection, enhancement is variable and range from minimal to intense.
• MRI has been most useful in the diagnosis and shows evidence of previous haemorrhage. The nodule itself shows up as a multisignal lesion with associated haemorrhage appearing as a low or high signal intensity around the lesion depending on the stage of maturity of the hemosiderin deposits. Gradient-echo sequences are essential to reveal multiple lesions which occur in 50% of cases (80% are familial with a dominant inheritance).
  

The MRI image is characteristic.

• The appearance of MR has permitted diagnosis of asymptomatic cavernomas and is currently considered to be the technique of choice for diagnosis.
• Differential diagnosis such as meningioma and metastasis or cystic glioma should be considered. On the MRI of cavernoma as compared to these other lesions, there is usually little oedema.
• Angiography is usually normal due to the slow flow of blood in these lesions.

Although the prevalence of brain cavernomas is high (0.50%), for unknown reasons, only a few of them display aggressive clinical behavior. Calcifications are mostly observed in patients presenting with chronic epilepsy. The dynamism of cavernomas is determined by extrinsic factors, mainly hemorrhage (with its own consequences); and by intrinsic factors: the pseudotumoral growth of the cavernous matrix.

When symptomatic, cavernomas should be totally removed. See image of cavernoma removed.

Cavernous angiomas of the brain stem

• Cavernomas are frequently located supratentorially.
• Approximately 18-35% are in the brain stem or infratentorial compartment.

Direct treatment of brain stem cavernomas

represent a considerable challenge due to the close proximity of the vital structures in the skull base. However, more recently the surgical treatment has been achieved with acceptable morbidity and mortality and excellent results have been reported by several groups. Certain developments have aided the operations notably, high resolution magnetic resonance imaging (MRI) allowing a clearer understanding of the precise nature of the lesion, location and relationships to other structures preoperatively (see axial image of a cavernoma). It also allows surgical approaches to be planned in better detail. Imaging developments aided by microsurgical techniques have therefore improved the ability to deal with these lesions.

Indications for surgery
The natural history of brain stem cavernomas indicate a high risk of rupture, bleeding and significant morbidity. There is also a slight propensity to rebleeding. This was assessed by Kupersmith et al. 2001, and they found in a series of 37 patients, that age less than 35 years and cavernomas less than 10mm were associated with reduced risk of rebleeding. The bleeding rate was 2.4% per year in that report. It is however considerably higher in other reports and closer to 5%.

The clinical status in symptomatic patients is very important. Patients in good condition with little morbidity should probably be offered surgery. Surgery is recommended for symptomatic patients, for cavernomas which have bled at least once, or are noted on serial MRI scan to be enlarging, and lesions that are easily approached and close to a pial surface. Surgery appears best performed subacutely unless it is necessary to save life from a significant haematoma.

Note: several authors have now established that RADIOSURGERY is not recommended for cavernomas.

Surgical approaches
There are several useful skull base approaches but the key factors are experience, location of the lesion and use of additional intraoperative topographic mapping and monitoring. The parenchymal window provided by the cavernoma and its dissecting hematoma is the most important parameter for the surgical approach, however, some safe entry zones exist in the brain stem.
A significant number of brain stem cavernomas have associated venous anomalies. Venous angiomas, or developmental venous anomalies, represent the most often occurring cerebral vascular malformation associated with cavernomas. Venous angiomas do not seem to be associated with a specific clinical presentation. In many cases these are the main draining veins for basal arteries and MUST NOT be removed. The cavernoma should be selectively dissected out protecting these veins at all cost to avoid venous infarction of the cerebellum/brain stem.

Cavernomas of the spinal cord
Patients with spinal intramedullary cavernomas present with either an acute onset of neurological compromise or a slowly progressive neurological decline. Acute neurological decline occurs secondary to hemorrhage within the spinal cord. Chronic progressive myelopathy occurs due to microhemorrhages and the resulting gliotic reaction to hemorrhagic products. Magnetic resonance imaging is virtually diagnostic for spinal cavernoma lesions. There is no evidence that cavernomas increase in size. The rate of rebleeding is unknown, but spinal cavernomas appear to be clinically more aggressive than cranial cavernomas, probably because the spinal cord is less tolerant of mass lesions (Deutsch, 2000).

Arteriovenous Malformation

Arteriovenous malformation of the posterior fossa
AVM of the posterior fossa present with haematoma and often previously recognised during the removal of a blood clot. Nowadays, they may be demonstrated preoperatively by cerebral angiography of the vertebral circulation. AVM in the brain stem, cerebellum, fourth ventricle and the Cerebello-pontine angle are uncommon lesions. The reported incidence range from 7-17% and occur predominantly in the cerebellum or the vermis. Next are the AVM of the brain stem with those in the fourth ventricle and the flocculonodular nodes bringing up the rear.

Presentation

• Subarachnoid haemorrhage,
• Intracerebellar haematoma and or intraventricular haemorrhage are the commonest presentations in 67-92% of cases (Peerless, Neurosurgery update).
• Other patients present with headaches, trigeminal neuralgia, and hydrocephalus.

Diagnosis is initially by CT scan in patients with coma or sudden focal neurological deficit located to the posterior fossa. The suspected cause often due to haematoma or ventricular haemorrhage from an aneurysm.

• On CT scan, calcifications may be seen and serve as clues to the presence of an AVM. If contrast is injected, the feeding vessels and draining veins may be highlighted as high signal serpentine, linear or tubular abnormalities in the brain.
• MRI provides quite impressive detail. The nidus of the AVM is seen as an area of signal void and may have a honey-comb appearance. Aneurysms may be demonstrated as cavernous areas in the or related to the lesion.
• Angiography is the definitive mode of diagnosis.

Telangiectasia

These lesions are sometimes recognised as the cause of a bleed. Magnetic resonance (MR) image showed a subacute or chronic localized hematoma with a low intensity rim caused by telangiectasia that could not be completely removed in two reported cases (Fukui, 1998). Postoperative rebleeding in the hematoma cavity continued insidiously in a case of telangiectasia. The abnormal vessels of telangiectasia in the brainstem were preoperatively not visualized by cerebral angiography or MR imaging, but became visualized by enhanced MR imaging after evacuation of hematoma in two cases. It is stressed that an angioma with a hematoma intensity core surrounded by a low intensity rim on MR images is not always a cavernoma, but possibly is a telangiectasia.

Moya Moya Disease (syndrome)

Moya-moya is an extremely rare disorder in most parts of the world except in Japan. The pathogenesis of Moya-moya syndrome is unknown. Moya Moya disease is characterized by progressive intracranial vascular stenoses of the circle of Willis, resulting in successive ischemic events. The condition leads to irreversible blockage of the main blood vessels to the brain as they enter into the skull. This is a lesion that tends to affect children and adults in the third to fourth decades of life. In children it tends to cause strokes or seizures. In adults it tends to cause bleeding or strokes. The clinical features are cerebral ischaemia, recurrent transient ischaemic attacks, sensorimotor paralysis, convulsions and migraine-like headaches.

The process of blockage (vascular occlusion) once it begins tends to continue despite any known medical management unless treated with surgery. The repeated strokes can lead to severe functional impairment or even death so that it is important to recognize these lesions and treat them early on. Without treatment, there is progressive deterioration of neurologic function and re-hemorrhage.

The diagnosis is initially suggested by CT or MRI. Contrast-enhanced T1-weighted images are better than FLAIR images for depicting the leptomeningeal ivy sign in moyamoya disease. MRI and MRA should be performed for the diagnosis and follow-up of moyamoya disease. Diffusion-weighted imaging can also be used for following the clinical course of children with moyamoya disease, in whom new focal deficits are highly suspicious of new infarcts.

Often nuclear medicine studies such as SPECT (single photon emission computerized tomography) are used to demonstrate the decreased blood and oxygen supply to areas of the brain involved with the Moya-moya disease. Conventional angiography provided the conclusive diagnosis of moyamoya disease in most cases and should be performed before any surgical considerations.

Angiographic scan	CT scan	MRI Scan

There are many operations that have been developed for the condition, but currently the most favored are: EDAS, EMS, STA-MCA and multiple burr holes. Direct superficial temporal artery to middle cerebral artery bypass is considered the treatment of choice, although it's efficacy, particularly for hemorrhagic disease, remains uncertain.

The EDAS (encephaloduroarteriosynangiosis) procedure requires dissecting a scalp artery over a course of several inches and then making a small temporary opening in the skull directly beneath the artery. The artery is then sutured to the surface of the brain and the bone replaced.

In the EMS (encephalomyosynangiosis) operation, the temporalis muscle, which is in the temple region of the forehead, is dissected and through an opening in the skull placed onto the surface of the brain.

Other operations include: the STA-MCA (superficial temporal artery-middle cerebral artery) in which a scalp artery is directly sutured to a brain surface artery; and a procedure in which multiple small holes (burr holes) are placed in the skull to allow for growth of new vessels into the brain from the scalp.

All of these operations have in common the concept of a blood and oxygen "starved" brain reaching out to grasp and develop new and more efficient means of bringing blood to the brain and bypassing the areas of blockage. The modified direct anastomosis and encephalo-myo-arterio-synagiosis play a role in this improvement by increasing CBF after the operation. A significant correlation is found between the postoperative effect and the stages of preoperative angiograms. It is crucial for surgery that the anesthesiologist have experience in managing these children as the type of anesthesia they require is very different from the standard anesthetic children get for almost any other type of neurosurgical procedure.

The long term outlook for children with treated Moyamoya seems to be good. While symptoms may seem to improve almost immediately after surgery, it will take probably 6-12 months before new vessels can develop sufficiently. Once major strokes or bleeding take place, even with treatment the child may be left with permanent loss of function so it is very important to treat this condition promptly.

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Created by B I Ogungbo in September 2002. Modified January 2008. ©