Awake Craniotomy for an Arterio-venous Malformation in the Eloquent Area - Clinical Decision Making and Dilemmas
Kevin Piepsney, MD
Rabia Gill, MD
Shobana Rajan, MD
Cerebral cavernous malformations (CMs), also known as cavernous angiomas, cavernomas or cavernous hemangioma, constitute the most common type of angiographically occult arteriovenous malformations (AVMs) representing 10-15% of all the symptomatic vascular malformations1 with a prevalence of roughly 0.1-0.5%.2 They can be found in several locations in the brain, but 70–80% of them are supratentorial. The supratentorial lesions frequently present with new-onset seizures and headache while infratentorial usually lead to progressive neurological deficits.3
Management of arteriovenous malformations (AVM) in the eloquent areas of the brain can be a challenge. Surgery with awake brain mapping can potentially facilitate resection with preservation of neurological functions. Awake brain mapping along with microsurgical excision of AVM with craniotomy therefore is the standard of care in these patients.4 An alternative treatment option is stereotactic radiosurgery depending on the lesion characteristics. Surgery is usually indicated for the symptomatic lesion presenting with intracranial hemorrhage, the most feared complication of cavernous malformation and the primary reason for treating them.5
Originally used for epilepsy surgery, the indication for awake craniotomy has expanded to brain tumor resection when eloquent areas are at risk and for insertion of deep brain stimulators. Awake craniotomy for an AV malformation excision is not standard and somewhat infrequent. Hence, we describe our experience with the anesthetic management of an awake craniotomy along with awake brain mapping in excision of a cavernous angioma which had bled.
A young patient presented with seizures and associated confusion. After the seizure she experienced pain in her arm and became non-verbal. A CT was done after she experienced her second episode of seizure and she was found to have intracranial haemorrhage from a cavernous malformation. With a past medical history of cavernous malformation complicated by multiple episodes of intracranial hemorrhage and seizures presented for left sided awake craniotomy. Brain functional MRI at the time showed a left parietal cavernoma with expected activation during finger and facial motor tasks. The primary sensorimotor cortex was located slightly anterior to the cavernoma. It was decided between the patient and the surgical team to perform an awake craniotomy for resection due to the location of the cavernous malformation. Her other past medical history included hyperthyroidism. Lab work showed CBC, BMP, PT/INR and aPTT all within normal limits. A type and screen and confirmation of blood type was performed and two units of packed red blood cells were made available for perioperative administration.
The patient arrived to the OR with an 18G peripheral IV in the left forearm. A second 18G peripheral IV was placed in her right hand. She was given 1 mg of midazolam along with 25 mcg of fentanyl and a pre-induction arterial line was placed in the right radial artery. Upon induction, infusions of propofol at 75 mcg/kg/min and dexmedetomidine at 0.7 mcg/kg/min were started. She received dexamethasone 10 mg upon induction along with cefazolin 2 g for antibiotics. Adequate respirations and ventilation were monitored with a MAC safe nasal cannula. Local anesthetic infiltration was performed by the surgeon before placement of the Mayfield frame. After frame placement, the dexmedetomidine infusion was decreased to 0.5 mcg/kg/min. Incision was made, followed by creation of two burr holes and subsequent craniotomy flap. The patient maintained spontaneous respirations throughout. At this time, the infusions were discontinued and the patient regained consciousness. The lesion was removed while continuous awake neurological monitoring (Picture 1) was performed and showed no language or motor deficits throughout the procedure. Upon completion of resection, the propofol and dexmedetomidine infusions were restarted at their previous settings with a bolus of propofol for closure of craniotomy flap and skin suturing. After skin closure, the infusions were discontinued, and the patient regained consciousness and neurological exam revealed no deficits. She was taken to the PACU for recovery. The patient was discharged home uneventfully.
What are the indications for awake craniotomy? How frequently do we do AVMs as an awake craniotomy?
How do we identify AVMs near the eloquent cortex? Should these patients undergo surgery with awake mapping or undergo conservative management?
What is the benefit/risk analysis of awake craniotomy in AVM surgery and how is it different from awake craniotomy for other brain lesions?
Awake craniotomy was introduced for surgical treatment of epilepsy and has subsequently been used for excision of brain tumor in the eloquent areas, deep brain stimulation, interventional pain procedures like pallidotomy, thalamotomy.6
The benefits of awake craniotomy is that it allows neurocognitive testing during intra-operative period and maximizes resection of the brain lesion with minimal harm to functional brain tissue which helps to minimize the risk of post-operative neurological dysfunction. It also aids in shorter hospital stay and cost-effectiveness. The anesthesiologist should be well acquainted with the principles underlying neuroanesthesia, the technique of scalp blockade, sedation protocols, and advanced airway management. Patients with lesions in proximity to the eloquent cortex had better neurological outcome and maximum tumor removal with awake craniotomy than surgery under general anesthesia.7
It is important to emphasize that awake craniotomy for AVM surgery is an uncommon procedure usually indicated for patients with high-grade AVMs with hemorrhage, an existing significant permanent deficit, progressive neurological deficit related to vascular steal, or an associated arterial or intranidal aneurysm.8
The widespread adoption of MRI followed by fMRI (functional MRI) allows the clinician to locate the eloquent areas. fMRI maps used in surgical planning are generated from signals which are dependent on blood oxygen level - the difference between oxyhemoglobin and deoxyhemoglobin levels of blood. However, there could be false negatives with resultant risk of a speech deficit in the postoperative period. Using this in conjunction with patient comprehension and speech mapping intra-operatively may be more useful for preservation of function.9 Cerebral angiography and magnetic resonance angiogram are other techniques used for localization of AVM.
The main concerns during awake craniotomy include loss of airway control due to excessive sedation or inadequate sedation leading to patient movement during surgery that can lead to hazardous complications. Bleeding can occur during resection of an AVM and is a potential hazard especially during awake craniotomy requiring tight control over hemodynamic parameters as well as degree of sedation. If bleeding occurs patient can suddenly appear excessively sedated and stop breathing and emergent control of the airway along with resuscitation may be necessary. Sometimes closure of the arteriovenous shunt can lead to hyperemia of the adjacent part of the brain and patient can suddenly stop speaking leading to a false positive. Intra-operative seizures are another issue and may need proactive steps like pre-treatment with anti-epileptic drugs or iced saline application on the surface of the brain if seizures occur. Thus, while an awake craniotomy for an AV malformation is being planned, a thorough preoperative discussion between the surgeon and neuroanesthesiologist is mandatory to be proactive about these potential decisions that may need to be made intraoperatively.
Propofol often used as target-controlled infusion is most frequently used because it provides titratable sedation, decreases incidence of seizures & postoperative nausea, vomiting. However, additional analgesia may need to be provided with local anesthetic scalp infiltration, supplemental narcotics, or dexmedetomidine. Remifentanil also has favorable pharmacokinetics with easy titrability and rapid dissipation of the effects, at low-dose infusion.10
Dexmedetomidine (Dex) seems to be an attractive alternative or adjunct to the currently used anesthesia techniques. It has sedative, analgesic and anesthesia sparing effects. Moreover, it does not suppress ventilation. It can be used as a sole agent or as an adjunct to other medications.
Conservative treatment with observation have shown to have lower morbidity and mortality for unruptured AVM in short term.(4) However, it was not applicable to a patient who had a ruptured AVM with hemorrhage.
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