CHAPTER 11 CENTRAL NERVOUS SYSTEM

10.1055/b-0037-145012

CHAPTER 11 CENTRAL NERVOUS SYSTEM

Edward R. Smith

KEY POINTS

Surgical principles include preparation of relevant equipment, including frameless stereotaxy, ultrasonography, an operating microscope, and bipolar electrocautery. In surgeries on both arteriovenous and cavernous malformations, the surgeon should work circumferentially around the lesions while avoiding the limitations of a single, narrow corridor (“working in a hole”) whenever possible.
For arteriovenous malformations, the surgeon should consider preoperative embolization, consultation with anesthesia to anticipate risk of blood loss, and careful obliteration of feeding vessels before draining veins.
For cavernous malformations, preservation of any associated developmental venous anomalies may help to reduce the risk of complications, and resection of surrounding hemosiderinstained tissue should be done only after the surgeon considers the potential function of adjacent anatomy.
At the conclusion of the resection of both the cavernous and arteriovenous malformation, meticulous inspection of the surgical cavity, preferably with the operating microscope, is critical to reduce the risk of bleeding and recurrence from an inadvertent residual lesion.

Vascular malformations of the CNS are a heterogenous group of lesions that occur in both the brain and spinal cord. As in other anatomic sites, vascular anomalies of the CNS can be classified according to rheologic characteristics (fast flow and slow flow) and by the predominant types of vessels comprising the malformation. These include arteriovenous malformation (AVM), cavernous malformation (CM), and venous malformation (VM) and may occur either independently or in association with syndromic conditions. This chapter reviews the management of two of the most common lesions requiring surgical treatment, AVMs and CMs.

The significant morbidity and mortality associated with intracranial hemorrhage typically favor treatment of AVMs or CMs when possible, but the calculus of management can be complex. Risk of iatrogenic injury, variable natural history, and a variety of treatment options (for example, radiation, surgery, and in AVMs, embolization) contribute to an active, constantly evolving debate centered on providing the best evidence-based plan of care for patients with these lesions. This chapter focuses solely on the surgical management of AVMs and CMs (more detailed papers on multimodality care are found in the Suggested Readings section at the end of this chapter).

ARTERIOVENOUS MALFORMATIONS

AVMs consist of direct arterial-to-venous connections without intervening capillaries; they occur in the cerebral hemispheres, brainstem, and spinal cord. Functional neural tissue does not reside within the lesion. Anomalies range from simple arteriovenous fistulas to complex tangled channels connecting enlarged feeding arteries to draining veins. AVMs are arguably the most important vascular anomaly in the nervous system in children. They are relatively common and usually require treatment, given the risk of hemorrhage (associated with a 25% risk of death with each bleeding event; they can also cause other symptoms, including seizure, focal neurologic deficits (ischemic “steal” phenomenon), and headache.

SURGICAL INDICATIONS

The treatment goal is complete removal/obliteration of the lesion. The decision to operate on an AVM is based on several factors:

Eloquence of cortical location (speech, motor function, and sensation)
Pattern of venous drainage
Size
Associated aneurysms
Recent hemorrhage
Clinical deterioration
Risk of complication from other modalities of therapy (for example, radiation injury to the developing brain)

Several of these factors are combined in the Spetzler-Martin AVM grading scale that incorporates eloquence of location, pattern of venous drainage, and size and is considered predictive of outcome from surgical management. The Spetzler-Martin grade helps to predict surgical risk. If a low-grade lesion (grades 1 to 3) is present, surgery should be considered. This includes incidental, asymptomatic lesions in select cases; recent data support this more proactive approach in younger patients. Higher-grade lesions (grades 4 and 5) often benefit from a multidisciplinary approach and may be considered for radiotherapy.

**Table 11-1** **Spetzler-Martin Arteriovenous Malformation Grading Scale**
Size	0-3 cm >3-6 cm >6 cm	1 2 3
Location	Noneloquent Eloquent	0 1
Deep venous drainage	Not present Present	0 1

SURGICAL MANAGEMENT

Initial therapeutic maneuvers are dependent on the presentation of the child. For the healthy child or the child who presents with chronic symptoms (for example, seizure or developmental delay), no immediate interventions are often necessary (with the exception of antiepileptic medication if seizures are present). The following steps are warranted for the child who presents with an intracranial hemorrhage. The severity of presentation can vary greatly, and thus treatment must be individually tailored.

STABILIZATION

Vascular access: A large-bore (at least 2) intravenous arterial line, bladder catheter (airway intubation if unable to protect airway), and nasogastric tube if intubated can be used.
Blood pressure control: Antihypertensives such as labetalol or nitroprusside (Nipride) can be used to control blood pressure, with a goal of normotension for the child’s age.
Intracranial pressure control: An external ventricular drain can be placed if hydrocephalus is present (NB: The surgeon should avoid overdrainage of CSF to prevent rerupture, often no more than 5 ml at a time) and the head of the bed is elevated.
Avoidance of seizures: Antiepileptic medication can be given if concern exists regarding seizure.

PREOPERATIVE PREPARATION

Prepare the operating room: In addition to the steps noted in the “Stabilization” section, the operating room should be notified to prepare for surgery. Equipment should include the operating microscope, multiple suctions, bipolar electrocautery, an array of AVM/aneurysm clips, a craniotome (drill), and a retraction system.
Consider preoperative embolization: The surgeon should consider this in select cases to reduce the risk of bleeding.
Consult with the anesthesiologist: Anesthesia should be consulted, and the appropriate measures should be taken to ensure that multiple, large-bore intravenous access is present and adequate blood products are in the operating room.
Prepare the equipment for microsurgery: If possible, the microscope should be draped and the clips prepared before starting the case, so that quick access can be obtained if unexpected bleeding occurs during opening.