Chapter 116. Burr Holes

Burr holes in the Emergency Department setting are uncommonly performed for diagnostic and therapeutic purposes. Diagnosis and treatment of increased intracranial pressure (ICP) in a timely fashion can be a lifesaving measure. Increased ICP can be the result of congenital anomalies, hemorrhage, infection, trauma, and tumors. There has been less need to make exploratory burr holes in head-injured patients since CT scanning has become widely available.

Burr holes can be lifesaving on rare occasions when the patient is worsening neurologically or has blown a pupil and CT scan is unavailable. Suspect a space-occupying lesion when there is clinical evidence of tentorial herniation or upper brain stem dysfunction. This includes pupillary dilation with a decreased or absent light reflex, progressive deterioration in the patient's level of consciousness, and/or hemiparesis including posturing (decerebrate/decorticate) or flaccidity. The placement of a temporal burr hole on the side of the mydriatic pupil to decompress an epidural or subdural hematoma can be lifesaving. Up to 70% of patients with evidence of brain stem dysfunction soon after head trauma have significant intracranial mass lesions, most of which are extra-axial blood collections.1

A significant proportion of patients with fatal head injuries die before reaching the hospital. The cause of death is usually a result of an expanding intracranial hemorrhage, extensive basilar skull fractures with associated injury to the venous sinuses, intracranial carotid artery lacerations, and/or major cortical blood vessel lacerations. Skull fractures are present in up to 90% of adults who develop a traumatic intracranial hematoma. Children are less likely to suffer a skull fracture after head trauma than adults.

The middle meningeal artery is a branch of the maxillary artery and enters the cranium via the foramen spinosum. It is usually located between the periosteal and meningeal layers of the dura mater. Shortly after entering the skull, it divides into anterior and posterior branches. The larger branches of the middle meningeal artery lie within the dura and are accompanied by veins. Their superficial location in the dura produces grooves on the interior of the cranium. This location makes them vulnerable to injury, especially from fractures of the temporal bone. The bony vault of the skull is fairly thick, approximately 5 mm in thickness, and shows considerable individual and regional variation. The temporal bone, in particular the squamous temporal bone, is much thinner than other areas of the skull. This makes it more vulnerable to a fracture with an associated injury to the underlying middle meningeal vessels.

Posttraumatic epidural hematomas usually develop in the temporal or temporoparietal location as a result of an injury to the middle meningeal vessels (Figures 116-1A & B). More than 50% of all epidural hematomas result from an injury to the middle meningeal artery itself. Epidural hematomas occur laterally over the cerebral hemispheres with the epicenter at the pterion in approximately 70% of patients (Figure 116-2). The remaining epidural hematomas are distributed in the frontal area, occipitoparietal area, and the posterior fossa. Other sources of epidural hematomas include a torn venous sinus or an injury to the carotid artery before it enters the intracranial dural mater.

Subdural hematomas are collections of blood between the dura mater and the brain (Figures 116-1C & D). They usually are the result of blunt head trauma.1 These result from the tearing of a bridging vein as the brain forcefully moves within the skull. The patient will present with an abnormal neurological examination minutes to hours after the acute injury.

Pupillary changes are not an early sign of an intracranial hematoma. However, when they do occur, they signify cerebral compression and transtentorial herniation. Other causes of acute pupillary changes need to be ruled out. Hematomas are usually found ipsilateral to the pupillary change in up to 85% of cases.

There are a few indications to emergently place a burr hole in the Emergency Department. These include monitoring of intracranial pressure, the emergent drainage of an intracranial hematoma, and the emergent cannulation of the ventricular system (Chapter 118). This procedure may be performed by trained Emergency Physicians if a Neurosurgeon has been consulted and is not immediately available.

The only absolute contraindication is a patient who is coagulopathic. Otherwise, the available Emergency Physician with the most skill and experience in performing this technique should be the one to place the burr hole. Other contraindications include localized infections of the scalp and patients who are thrombocytopenic. This procedure should not be performed by those unfamiliar with the technique and its complications.

A coagulopathy or thrombocytopenia makes a burr hole dangerous to perform. The use of anticoagulants and antiplatelet agents by the patient increases their risk of hemorrhagic complications. Consider reversing these conditions by the administration of fresh frozen plasma and/or platelets prior to performing a burr hole. A mild elevation in the international normalized ratio (INR) up to 1.6 may be acceptable to place a burr hole.3

• Sterile prep kit
• Sterile gloves and gown
• Face mask with an eye shield or goggles
• Cap
• Povidone iodine or chlorhexidine solution
• Sterile drapes
• 1% or 2% lidocaine containing epinephrine
• 22 gauge needles
• 5 mL syringe
• #10 scalpel blades
• #11 scalpel blades
• #3 scalpel handle
• Bipolar cautery, optional
• Self-retaining mastoid retractors
• Hudson brace drill
• Skull perforator bits
• Conical burr bits
• Small hook
• Bone wax
• Thrombin-soaked Gelfoam
• Periosteal elevator
• Suction catheter kit
• Head covers, masks, and sterile gowns
• Ventriculostomy catheter (optional)
• Bone rongeur
• Mayo scissors
• 4-0 nylon suture
• Potts scissors

The required equipment is all contained within a prepared sterile tray that can be obtained from the Operating Room or hospital central supply (Figure 116-3). A completely disposable, sterile, and single patient use instrument set is also available (Spectrum Surgical Instruments Corp., Stow, Ohio). The Hudson brace drill is a handheld device (Figure 116-4). It has a stabilizing handle in series with a handle that rotates in circles. The distal end has a snap lock chuck that slides to allow easy insertion and removal of the bits. The bits come in a variety of shapes and sizes (Figure 116-5). The perforator bits have a sharp point. The tip of the perforator bit is designed to penetrate the inner table of the skull and lock without allowing it to puncture the dura or the brain (Figure 116-6). However, exercise extreme caution as the bit may occasionally not lock when it penetrates the inner table of the skull. The burr bits are rounded. They are used to enlarge the hole in the skull made by the perforator bit (Figure 116-6).

The patient should be fully monitored with a noninvasive blood pressure cuff, pulse oximetry, cardiac monitor, and end-tidal carbon dioxide monitor (if available). Obtain a CT scan of the head to determine the presence of an acute subdural or epidural hematoma, the location and extent of the hematoma, to rule out the presence of a mass, and to determine if there is any herniation. Obtain a complete blood count (hemoglobin, hematocrit, and platelet count) and a coagulation profile (PT, PTT, and INR) to ensure that the patient is not thrombocytopenic or coagulopathic. These may require reversal with the administration of fresh frozen plasma and/or platelets.

Explain the risks, benefits, and complications of the procedure to the patient and/or their representative. Obtain an informed consent. However, in the patient who is deteriorating neurologically with tentorial herniation, consciousness is usually lost and time is of the essence.

Determine the site for the skin incision and the burr hole (Figure 116-7). A frontal or anterior burr hole is made just anterior to the coronal suture and 3 cm lateral to the midline, approximately along the midpupillary line (Figure 116-7A). The coronal suture is often palpable. If not, draw a perpendicular line midway between the lateral canthus of the orbit and the external auditory meatus. The frontal burr hole can be used to drain an intracranial hematoma or to perform a ventriculostomy. The temporal burr hole is made two finger breadths above the zygomatic arch and two finger breadths anterior to the external auditory meatus (Figure 116-7B). The parietal or posterior burr hole is made two finger breadths behind the external auditory meatus and three finger breadths above the mastoid process (Figure 116-7B).

Prepare the patient. Orotracheally intubate the patient to protect and secure the airway. Insert a nasogastric tube to decompress the stomach. Shave the scalp at least 5 cm in all directions from the proposed skin incision. This procedure requires strict aseptic technique. Clean the skin of any dirt or debris. Cleanse the skin first using 70% alcohol followed by povidone iodine or chlorhexidine solution. Allow the povidone iodine or chlorhexidine solution to dry. The Emergency Physician should don full sterile and personal protective equipment at this point. This should include sterile gloves, a sterile gown, a face mask with an eye shield or goggles, and a cap. Isolate the surgical field by using sterile drapes. Prophylactic intravenous antibiotic coverage is recommended if time permits. Administer a broad-spectrum antibiotic that covers gram-positive skin flora. Position the patient so that the proposed incision site is visible and easily accessible. Place the patient supine with a folded blanket or towel under the ipsilateral shoulder. Turn the head to the contralateral side if the cervical spine has been cleared. Instruct an assistant to hold and steady the patient's head.

Burr Holes

Identify the site to make the burr hole. Infiltrate 5 mL of lidocaine containing epinephrine along the proposed incision site and down to the level of the periosteum on the skull. This will result in analgesia and vasoconstriction that may aid in hemostasis. Make a 2 cm long skin incision centered about the site to make the burr hole. Carry the incision down to the bone of the skull. The incision must traverse all layers of the scalp including the skin, the subcutaneous tissue, the temporalis muscle (if present), and the periosteum. Remove the periosteum overlying the skull by scraping it away with a periosteal elevator. The periosteum will otherwise get caught in the perforator bit and make it difficult to turn. Insert a small self-retaining retractor into the wound (Figure 116-8A). Hemostasis can often be obtained with the use of the retractor. However, having cautery available can be helpful. Small bleeding vessels may be tied off with absorbable suture (Figure 116-8A).

Fit the Hudson brace drill with a perforator bit. Grasp the stabilizing handle of the Hudson brace with the nondominant hand. Grasp the rotating handle with the dominant hand. Place the tip of the perforator bit against the skull (Figure 116-8B). Turn the rotating handle clockwise with the dominant hand using a smooth and slow motion. Always maintain the drill perpendicular to the skull. Maintain controlled pressure on the Hudson brace drill. Watch as the perforator bit cuts through the skull. Frequently remove the perforator bit to examine the hole. Irrigate the area. Use suction to remove the bone fragments and the irrigation fluid. Gently probe the hole to determine if the inner table has been penetrated. Continue to drill until the inner table has been penetrated or the perforator bit locks (Figure 116-8C). Do not apply too much downward pressure on the brace to prevent it from plunging into the brain. Exercise extreme caution as the bit does not always lock when the inner table is perforated.

Remove the perforator bit from the Hudson brace drill. Place the burr bit on the Hudson brace drill. Place the burr bit into the hole in the skull. Hold the Hudson brace drill as described above. Rotate the handle clockwise to enlarge the hole in the skull (Figure 116-8D). Frequently remove the burr bit to examine the hole. Irrigate the area. Use suction to remove the bone fragments and the irrigation fluid. Continue to drill until the hole in the inner table is enlarged enough to accept the tip of the bone rongeur. Do not apply too much downward pressure on the Hudson brace drill to prevent it from plunging into the brain.

Control bleeding from the bone with bone wax and from the epidural space with Gelfoam. The clot of an epidural hematoma will be obvious as it separates the inner table of the skull from the dura. This clot will be gelatinous in consistency and drainage through a single burr hole can be difficult. Free the underlying dura from the bone edge with a Penfield elevator. Gently insert the elevator between the inner table of the skull and the dura. Gently separate the dura from the skull. Enlarge the burr hole in order to facilitate aspiration of the blood clot. Insert a bone rongeur into the hole. Take small bites of the skull to enlarge the hole (Figure 116-8E). Do not concern yourself with making the hole smooth or symmetric. The Neurosurgeon will later trim and repair the bony defect.

Hematoma Drainage

An epidural hematoma is aspirated by gentle suction and irrigation with normal saline through an adequate bone opening (Figure 116-8E). Pay close attention to the temperature of the irrigation solution. It should ideally be body temperature. Use wall suction with a #9 or #11 French aspirator.

Epidural and subdural hemorrhages are usually clotted in the acute stages. In the event that an epidural hematoma is not identified after placement of the burr hole, inspect the underlying dura for a possible subdural hematoma. The presence of a subdural hematoma causes the dura to have a bluish hue or tinge (Figure 116-9A). Carefully place a traction suture in the middle of the exposed dura using 4-0 nylon (Figure 116-9B). Apply traction on the suture to elevate the dura. Incise the dura with a fine Mayo scissors or a #11 scalpel blade (Figure 116-9B). Exercising extreme caution during the maneuver is mandatory to prevent lacerating the brain. Open the dura in a cruciate fashion. Drain the subdural clot using suction and gentle irrigation. At no time should any pressure be placed on the brain. Care should be taken not to irrigate with any force directly against the brain surface.

Ventriculostomy

The burr hole can be made in order to place a ventriculostomy catheter. Make a nick in the dural with an 18 gauge needle or a #11 scalpel blade. Perform a ventriculostomy using an appropriate ventricular catheter. Anatomical landmarks suggestive for placement of the catheter within the ventricular system are to insert the catheter perpendicular to the skull and directed toward the ipsilateral inner canthus.2 Advance the catheter to a depth of approximately 5 to 6 cm. If unsuccessful after three attempts, place the parenchymal monitor or a subarachnoid bolt. Refer to Chapter 118 for the complete details of performing a ventriculostomy.

Assessment and stabilization of the head injury victim prior to placement of the burr hole, during the procedure, and postprocedurally requires attention to securing the patient's airway, adequate and aggressive treatment of hemodynamic instability and shock, stabilization of the cervical and thoracolumbar spine, and concomitant treatment of any extracranial injuries. Aggressive management of hypoxia and hypotension cannot be overemphasized. Hyperventilation in the first 24 hours after severe head injury should be avoided as it can reduce cerebral blood flow. The assessment should include hemodynamic parameters, Glasgow Coma Score, and frequent neurological examinations. The neurological examination should include pupillary size and reaction, extraocular muscle function, and motor movements of the extremities. Intubation utilizing the rapid sequence technique often precedes burr hole placement in the patient with severe head injury. This precludes a detailed neurological examination as most patients will have received neuromuscular blockade.

Reduction in pupillary size can be appreciated postevacuation of the hematoma in patients who have had pupillary changes preceding the burr hole placement. Repeat the hemodynamic and neurological assessments often, every 5 minutes, and document these in the patient's record. Obtain a postprocedural CT scan of the head as early as possible to check the status of the hematoma. CT scanning also verifies catheter location and reduction in ventricular size in patients in which trephination has been completed for ventricular catheter placement.

Patients who have had burr hole placement because of neurological deterioration require further definitive management by a Neurosurgeon. A craniotomy is indicated for a more thorough evaluation, irrigation of the epidural or subdural space, and for hemostasis. Postprocedural CT scanning should not be performed if definitive management by a Neurosurgeon is available. It is an unnecessary waste of time and the patient should proceed directly to the Operating Room. Cranioplasty is often not completed initially after burr hole placement in order to minimize the infectious risk. Postprocedural treatment often requires airway protection with continued endotracheal intubation, adequate fluid resuscitation, management of hypoxia, management of hypotension, management of seizures, and management of any coagulopathy. Secondary injuries can evolve, even after adequate hematoma evacuation. They need to be anticipated, recognized, and treated aggressively.

A two-layer closure is recommended in the event a craniotomy is not to follow or will be delayed. The dura is usually not closed. Cover the dura with a small piece of thrombin-soaked Gelfoam. Close the galea with 3-0 absorbable suture. Close the scalp/skin with 3-0 nylon suture. Apply a dry dressing to the scalp wound. Alternatively, apply sterile saline-soaked gauze over the wound and cover this with a dry dressing.

Wound infections, abscesses, hemorrhage, and postoperative hematomas are major complications.3 These can be avoided by using sterile precautions, antibiotic prophylaxis, and fine surgical technique. Other complications include plunging with the perforator bit or the burr bit resulting in a penetrating injury to the brain, cortical lacerations, cortical contusions, and seizures. Blunt or penetrating brain injuries can result in delayed stroke and hemorrhage. At times, this can be produced by a post-traumatic aneurysm or arteriovenous fistula. In the severely head-injured patient, a multitude of coagulopathic abnormalities can occur including hypercoagulable and fibrinolytic states as well as disseminated intravascular coagulation (DIC).

Significant bleeding complications can occur from this procedure.3 Penetration of the sagittal sinus can result in significant hemorrhage and possible exsanguination. Prevent this by staying at least 2 cm from the midline and properly identifying the landmarks before drilling into the skull. Avoid lacerating the middle meningeal artery or its branches. Prevent injuries to these arteries by not drilling beyond the inner table and carefully separating the dura from the skull before using the bone rongeur. Another option is to obtain a lateral plain radiograph of the skull. Note the position of the grooves in relation to the external auditory meatus. Avoid these grooves, and thus the branches of the middle meningeal artery, when determining the exact site to place the burr hole.

The prognosis for the severely head-injured patient with clinical evidence of tentorial herniation and brainstem compression is poor. Rapid evacuation of an intracranial hematoma may help to improve the outcome. Ideally, these patients are resuscitated and a CT scan of the head is completed in order to determine the presence of an intracranial hematoma. Patients may at times undergo rapid neurological deterioration prior to CT scanning or CT scanning may not be readily available. Diagnostic burr hole exploration and evacuation of an extra-axial hematoma can be a lifesaving measure. The author does not wish to suggest that exploratory surgery should replace CT scanning in the management of patients with a severe head injury. The CT scan is invaluable in assessing and identifying accurately the location of any mass lesion intracranially. Burr hole evacuation in a trauma setting should be considered only in the presence of rapid neurological deterioration with evidence of herniation and brainstem compression and the unavailability of a Neurosurgeon to perform the procedure.