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Yoshihiro Katsuura1

Author affiliations
1RCSI medical student

Royal College of Surgeons in Ireland Student Medical Journal 2012;5: 50-3.


Introduction
Arteriovenous malformations (AVMs), first described by Steinhal in 1895, are rare but increasingly recognised foci for neurological dysfunction characterised by direct arterial-to-venous connections that form a conglomeration of vessels devoid of normal vascular architecture and branching capillary beds.1 The result of this union is the creation of a high-pressure vascular shunt, which allows blood to pass from the arterial to the venous system without perfusing tissue or undergoing the pressure reductions produced by passage through arterioles.2 AVMs have an incidence of one in 100,000, and are diagnosed mainly between ages 10 and 40 in unselected populations.3,4 They are generally considered to be sporadic developmental abnormalities, although familial occurrences have been described, such as in Osler-Weber-Rendu and Sturge-Weber syndromes.5

AVMs vary in intracranial location, with the majority occurring in the supratentorial region of the right parietal lobe (90%), investing deep structures of the brain.3 Size varies from small (<2cm) to large (>6cm), with small, deep AVMs predisposing to haemorrhage and large, superficial lesions to epilepsy.3

Diagnosis is generally made by advanced imaging techniques, including CT, CT-angiography (CTA), MRI, MR-angiography (MRA) and angiography. CTA is known to provide good vascular detail, while MRI and MRA permit visualisation of any ischaemic
changes, as well as surrounding eloquent structures (brain regions with readily identifiable function and resulting neurological deficit if disrupted, e.g., sensorimotor, language and visual cortices; hypothalamus; thalamus; internal capsule; brainstem and cerebellar peduncles).1 Nonetheless, angiography remains the gold standard as it allows for the evaluation of possible aneurysms and patterns of venous drainage, and can be used for planning clinical intervention.1 Clinically, AVMs most commonly present with intracerebral haemorrhage, and account for 2% of all CVAs.1,4 Other signs include seizures and focal neurological signs caused by either mass effect, due to pressure from the malformation on adjacent structures, or ischaemic change/gliosis due to steal phenomenon – that is, preferential low resistance blood flow through the AVM, diverting blood from adjacent vessels and possibly away from vital centres.1,4

Case
A 60-year-old Hispanic female suffered from a witnessed tonic-clonic seizure at her nursing home lasting approximately 45 minutes that began in the right upper and lower extremities and progressed to involve the head. The emergency medical service workers who arrived on the scene were able to control the seizure with 5mg diazepam, and subsequently brought the patient to the emergency room at Montefiore Medical Center in the Bronx, NY.

The medical history of the patient was significant for similar episodes of seizure, the most recent of which occurred one month previously. On that occasion, the patient also suffered from altered mental status and incontinence, for which she was admitted to the neurology service at Montefiore. A previously diagnosed non-resectable left parietal AVM was determined to be the focus of the seizure. Patient history was also significant for type II diabetes mellitus, hypertension, schizophrenia, depression and obstructive sleep apnoea. The patient’s baseline medications are listed in Table 1.


Table 1. (Click to enlarge.)

Social history was significant for mounting long-term care needs with respect to the management of the patient’s schizophrenia and general inability to care for herself. She had a 35 pack-year history of smoking, but quit 10 years ago, and has no other toxic habits.

On examination, the patient was confused and lethargic but awake. She was oriented to person and was able to follow commands, but could not name objects or repeat phrases and had negligible recall. She often repeated the phrase “don’t know, don’t know”, and other incoherent sounds. Peripheral neurological examination was significant for a left upper extremity resting tremor and decreased power (4/5) in the right upper and lower limbs. Babinski’s sign was elicited in the right lower limb. Cranial nerve examination was normal.

MRI of the brain showed a left hemispheric AVM involving the parasagittal regions of the frontal and parietal lobes (Figures 1 and 2). No evidence of haemorrhage was demonstrated, but there was high signal in the surrounding area due to sclerosis secondary to steal phenomenon (Figure 1). Deep draining vessels could be indentified on coronal sections (Figure 2). Internal carotid and vertebral angiography showed multiple draining vessels, both superficial (cortical venous system) and deep (internal cerebral veins, basal veins) (Figures 3, 4 and 5).

FIGURE 1: Axial T1-weighted MRI at the level of the superior frontal gyrus, showing the arteriovenous fistula (blue arrow) as well as secondary ischaemic changes (red arrow) due to steal phenomenon.


FIGURE 2: Coronal T2-weighted MRI at the level of the posterior commissure, showing deep venous drainage into the left lateral ventricle (blue arrow).


FIGURE 3: Angiogram of the left internal carotid artery showing the arteriovenous malformation in the arterial phase (red arrows) with collateral serpiginous draining vessels (blue arrow).


FIGURE 4: Angiogram of the internal carotid artery in venous phase exhibiting multiple large superficial draining vessels (blue arrow).


FIGURE 5: Angiogram of the vertebral artery in the arterial phase showing the midline arteriovenous fistula (red arrows).

Seizure work-up suggested an ongoing urinary tract infection (UTI) as the exacerbating factor for the seizure. The patient’s UTI was treated with ceftriaxone and her baseline dose of valproic acid was increased from 500mg to 1g. Levetiracetam was added on the third day of admission after the patient suffered another breakthrough seizure, and was titrated to 750mg from 500mg. The patient’s paralysis, believed to be a Todd’s paresis, resolved over the course of her admission. As she suffered no further seizures, the patient was eventually discharged back to her subacute rehabilitation facility.

Discussion
Staging is an important component of the management strategy for AVMs, as surgical treatment primarily intends to eliminate the possibility of future haemorrhage.6 Speizler and Martin proposed a simplified grading scheme for staging AVMs in the clinical setting that evaluates three critical variables: size (also used to estimate number of feeding arteries, amount of flow and degree of steal); pattern of venous drainage; and, neurological eloquence of adjacent brain regions.7

The size of an AVM is evaluated by measuring the largest diameter of the malformation. Venous drainage is evaluated on angiogram and determined to be either superficial or deep, the latter being more difficult to access surgically. Based on these parameters, a grade is calculated from the sum of the scored variables, ranging from I-V (Table 2), where grade I corresponds to a size 1, location 0, venous drainage 0 score, and grade V corresponds to a size 3, location 1, venous drainage 1 score. Lower grades correlate with a lower risk of mortality and neurological deficit following surgery.7


Table 2. (Click to enlarge.)

The risks of surgical resection of an AVM – that is, intracranial haemorrhage, focal neurological deficits, hydrocephalus, intracranial infections, ischemic stroke and death – must be weighed against the risk of subsequent intracranial haemorrhage, which increases with age.2,8 Crawford et al. report a 42% gross haemorrhage rate, 29% risk of death, 18% risk of epilepsy and 27% risk of neurological handicap in all patients 20 years after diagnosis that do not undergo surgical resection.2 In addition, the authors report that only 25% of patients with AVMs who do not undergo resection become socially disabled in the long term. Thus, conservative management may be optimal for individuals with surgically inoperable AVM, considering that the risk of disability with surgical intervention in these patients exceeds 25%.6 A meta-analysis of the efficacy and safety of AVM interventions reported considerable risks associated with microsurgical treatment, including an overall case fatality rate of 1.1 per 100 person years, compared to 0.68 overall.8

If intervention is warranted, several approaches may be employed, such as surgical resection, radiosurgery and embolisation.1 The aim of treatment should be the complete obliteration of the AVM, as partial obliteration can increase the risk of subsequent haemorrhage.1

Typically, grade I-III AVMs are amenable to treatment.1,7 Resection of grade IV and V AVMs carries significantly higher rates of surgical complication and these AVMs are thus treated conservatively.7 Conservative treatment typically consists of symptomatic management of neurological sequelae (such as seizures and headaches) and expectant monitoring of the lesion with the knowledge that the patient will have some risk of intracerebral haemorrhage or focal neurological deficit.1,9

Recently, studies have shown promising results for stereotactic radiosurgical treatment of grade IV and V AVMs, but these findings have not yet been corroborated.1,9,10 The ongoing ARUBA study compares the risks and benefits of conservative management of unruptured AVMs to surgical intervention (www.aruba.org), but a more encompassing analysis of different treatment interventions is needed.8

In the case described above, the patient is suffering from a grade IV AVM – a 6cm malformation (3 points) in the presence of deep draining vessels (1 point) that is not in the proximity of eloquent structures (0 points). Thus, surgical intervention is not indicated, and the patient should be treated conservatively instead.

Conclusion
This case exhibits a relatively uncommon grade IV AVM and demonstrates some aspects of the history, diagnosis, grading and considerations for surgical intervention. Although AVMs pose a lifelong risk of haemorrhage, surgical resection itself is not without significant danger, and should not be undertaken unless complete obliteration of the lesion is feasible.1 While each patient must be evaluated on an individual basis, simplified schema for aiding in this decision have been proposed based on characteristics of the lesion.

Acknowledgements
A special thanks to Dr Steve Sparr, a true friend of the Irish.

References

  1. Friedlander R. Arteriovenous malformations of the brain. New Engl J Med. 2007;356(26):2704-12.
  2. Crawford P, West D, Chadwick, Shaw M. Arteriovenous malformations of the brain: natural history in unoperated patients. J Neurol Neurosurg Psychiatry. 1986;49:1-10.
  3. Al-Shahi R, Warlow C. A systematic review of the frequency and prognosis of arteriovenous malformations of the brain in adults. Brain. 2001;124(10):1900-26.
  4. Parkinson G. Arteriovenous malformations, summary of 100 consecutive supratentorial cases. J Neurosurg. 1980;53(3):285-99.
  5. Van Beijnum J, Van der Worp HB. Familial occurrence of brain arteriovenous malformations: a systematic review. J Neurol Neurosurg Psychiatry. 2007;78(11):1213.
  6. Andersen E, Petersen J et al. Conservatively treated patients with cerebral arteriovenous malformation: mental and physical outcome. J Neurol Neurosurg Psychiatry. 1988;51:1208-12.
  7. Speizler R, Martin N. A proposed grading system for arteriovenous malformations. J Neurosurg. 2009;108(1):186-93.
  8. Van Beijnum J, Van der Worp HB. Treatment of brain arteriovenous malformations. JAMA. 2011;306(18):2011-9.
  9. Ogilvy CS, Stieg PE, Awad I, Brown RD Jr, Kondziolka D, Rosenwasser R et al. Recommendations for the management of intracranial arteriovenous malformations: a statement for healthcare professionals from a special writing group of the Stroke Council, American Stroke Association. Stroke. 2001;32:1458-71.
  10. Friedman WA, Bova FJ, Mendenhall WM. Linear accelerator radiosurgery for arteriovenous malformations: the relationship of size to outcome. J Neurosurg. 1995;82:180-9.

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