Cranial Burr Holes and Emergency Craniotomy: Review of Indications and Technique

Daniel J Donovan and Ross R Moquin and James M Ecklund
Military Medicine

Dec 31, 2005 19:00 EST

Introduction

Traumatic head injury causes primary injury to the brain itself, but may also result in intracranial hematoma (ICH) formation. ICH can cause compression of the brain, resulting in a shift of intracranial structures, cerebral herniation, coma, and death. It can be located in either the intra-axial compartment (within the brain itself) or extra-axial, as either an epidural hematoma (EDH) or subdural hematoma (SDH). EDH occurs in 0.5 to 12.3% of patients with moderate to severe head injury1-6 and SDH in 12 to 18%.6-8 The incidence of both is even higher in those with brainstem dysfunction or a skull fracture,1,9-11 and ICH occurs frequently in patients with penetrating injuries.12-15 The clinical outcome depends on many factors, including the type, location, and size of ICH, as well as the severity of the associated primary brain injury.1,3,5 Some authors have proposed that a shorter duration of time between injury and hematoma evacuation improves ultimate outcome,1,15,16 but other series have not confirmed this result.3,7,17,18 The overall morbidity and mortality ranges from 12 to 41% with EDH1,2,17,19 to 57 to 90% with SDH.1,6,7,20 SDH is associated with worse outcome because it generally is caused by high-velocity injuries, resulting in more primary brain injury. Since EDH is usually associated with low-velocity injury, it results in little primary injury to the brain and causes poor outcome only if the expanding hematoma is allowed to compress the brain. Combinations of EDH and SDH in the same patient may occur. It is evident although that the patient's preoperative neurological function correlates highly with outcome,1,3,4,7,19,21 and that early recognition and prompt surgical evacuation of ICH avoids preventable death and dysfunction, especially in those patients who "talk and deteriorate."22

Burr hole craniotomy, or trephination, may be the earliest form of surgical procedure ever performed.23,24 Archeological studies of ancient skulls show it was performed in various ways on several different continents before the dawn of written history and confirm that many patients survived the procedure.25-27 It has been practiced extensively throughout the history of medicine, particularly in military conflicts, and the fascinating history of this procedure has been reviewed in detail elsewhere.27-32 The procedure was expanded, refined, and standardized throughout World Wars I and II and in civilian practice thereafter.33-43 With the arrival of computerized tomography (CT) in the 1970s, the indications for burr holes quickly dwindled. CT is rapid, noninvasive, and provides much more information about the location and nature of the brain injury than burr holes.

Since the development of trauma management and evacuation systems in the United States, the situation is rarely encountered where a patient with acute neurological deterioration is unable to undergo CT. In certain rare circumstances, burr hole craniotomy remains a relatively rapid and frequently effective treatment for patients who otherwise will likely die. These situations are much more common in combat health support operations, particularly at echelons II and III. For example, a patient injured in a remote area may require burr holes if there is no access to immediate evacuation or CT, or a multitrauma patient who develops a unilaterally dilated pupil while under anesthesia for non-neurological surgery may not be stable for immediate transport to CT. Because many general surgeons or other nonneurosurgeons in the military are deployed to remote areas of the world without the availability of CT or a neurosurgeon, the authors have occasionally advised such surgeons (via telephone or radio link) to perform burr holes as a lifesaving measure. Successful cases have also been reported in the literature.44-46 Such experiences from Operations Enduring Freedom and Iraqi Freedom have especially spurred renewed interest in reviewing the anatomy, technique, and indications for this procedure. However, it must be strongly emphasized that this procedure should not be performed randomly for all comatose patients, nor should it be undertaken without contacting a neurosurgeon first, except in the most dire circumstances.

Methods

Initial Assessment and Stabilization

The injured patient must undergo general resuscitative measures first, in accordance with a standard trauma protocol such as that taught by the American College of Surgeons in the Advanced Trauma Life Support course.47 It must be ensured that the patient has a patent airway and is breathing, the blood pressure and pulse are stabilized, and at least a primary survey is conducted before any consideration of burr holes. A critically important factor in the outcome for patients with ICH is avoidance of hypoxemia and hypotension.48,49 Improved oxygenation and blood pressure often improve a patient's altered mental status and may even normalize dilated or asymmetric pupils. A rapid neurological assessment is performed and the Glasgow Coma Scale score is determined. A detailed secondary survey is then performed to identify other possible causes of deterioration and to look for any secondary complications of head injury.50,51 Of paramount importance is maintenance of spinal immobilization precautions and assessment with a lateral cervical spine X-ray if available, since 5 to 10% of head-injured patients also have an associated cervical spine fracture.

If the patient exhibits signs of increased intracranial pressure, nonsurgical treatment is first delivered. This includes endotracheal intubation, assisted ventilation, elevation of the head, and administration of osmotic agents such as 0.5 to 1.0 g/kg of a 25% intravenous mannitol solution or a bolus of hypertonic saline. The patient is then reassessed, since these measures alone may adequately reduce intracranial pressure48,52 and potentially mitigate the need for surgery. An intravenous anticonvulsant agent such as fosphenytoin (18 mg/kg) is given to reduce the incidence of early seizures.53 Assessment of coagulation function is extremely helpful if available, since brain injury may cause coagulopathy,54 and administration of clotting factors may be required before surgery. Burr holes should only be considered when all other supportive measures have been taken, and yet the patient continues to decline. Every reasonable attempt should be made to contact a neurosurgeon for consultation.

Any patient who has sustained a traumatic injury and presents with the classic clinical triad of altered mental status, asymmetric or poorly reactive pupils, and hemiparesis must be deemed to have ICH until proven otherwise. These findings can be mimicked by brain contusion, which will not benefit from burr holes, but ICH must be ruled out. The "classic" clinical presentation of EDH is an immediate alteration of sensorium punctuated by a lucid interval, which is then followed by progressive neurological decline. A lucid interval can also occur with either SDH or cerebral contusion although, and less than one-third of patients with EDH demonstrate such a pattern.2 Most simply decline continuously from the time of injury.

Localization

Penetrating injuries and open, depressed skull fractures are often readily apparent and may guide the surgeon rapidly to the location of ICH. Not all fractures have associated ICH however,55 and ICH may also be located opposite to the point of impact, especially where penetrating fragments have exited or come to rest near the brain surface.36,37,40,42 Lateralizing findings such as pupillary abnormalities and hemiparesis are useful indicators, found in more than one-half of the patients with ICH, and 85% are located ipsilateral to the larger pupil and contralateral to the hemiparesis.2 These occur when ICH shifts the brain medially and downward, forcing the temporal lobe against the cerebral peduncle and the third cranial nerve (Fig. 1, A and B). Since the third nerve remains ipsilateral and the corticospinal tract crosses over to the contralateral side of the body, the dilated pupil and hemiparesis occur on opposite sides of the body. The remaining 15% of patients have "false" localizing signs, such as hemiparesis ipsilateral to the dilated pupil. These findings are caused when the brainstem is shifted over with the temporal lobe and the contralateral peduncle is compressed against the rigid edge of the dural partition called the tentorium cerebelli, creating "Kernohan's notch"56 (Fig. 1, C and D). It must be emphasized that the presence of these physical findings does not mean that ICH is always present, since they can also occur with direct injury to the brainstem or cranial nerves.

Adjuncts

The best and most rapid method of establishing the diagnosis of ICH is CT. The wealth of information collected by CT includes not only the presence of ICH, but also its location, size, presence of multiple ICH, cerebral contusion, skull fracture, etc. In the absence of CT however, a simple X-ray of the skull may provide important clues to the diagnosis.55 It should always be used for deteriorating patients when CT is unavailable, especially to visualize foreign bodies in penetrating injuries . If patients with the appropriate clinical findings have a skull fracture, especially near the middle meningeal artery or the durai venous sinuses, ICH is likely present. In >85% of the patients who have both a skull fracture and EDH, the clot is located immediately beneath the fracture site.57 Although a skull fracture may indicate a possible EDH, it does not confirm it, nor does it mitigate the possibility of coexisting injuries such as brain contusion or SDH. The injury causing SDH is more likely to be diffuse, involving a larger area than that causing EDH; therefore, the hematoma in SDH may not be located directly underneath the fracture as in EDH. In addition, an expanding blood clot in the subdural space is not restricted by any barriers and can extend from one end of the hemisphere to the other. The expansion of EDH may be limited by the cranial sutures, where the dura mater is particularly adherent to the inner table of the skull.

Technique

Burr holes are ideally performed in the operating room to minimize infectious risks and to provide proper lighting and equipment. Electrocautery, suction, irrigation, headlamp illumination, and loupe magnification are helpful (see Fig. 2 for complete list of surgical instruments). Since the patient has already been intubated, anesthesia and antibiotics are now administered. General anesthesia is preferred, but hypotension must be avoided. Local anesthesia may be used alone, but coughing or other movement during the procedure can be troublesome. The patient should be placed in the supine position with a shoulder roll ipsilateral to the suspected side of ICH and the head turned so that the surgical side is facing upward. The head should be supported with a padded gel roll or horseshoeshaped head holder, if available (Fig. 3A). A rapid shave of the involved scalp will facilitate surgical prep and visualization. A more extensive shave (i.e., the entire head) is recommended for patients with penetrating injuries or scalp lacerations, but a prolonged period of time should not be wasted on this task.

In the absence of CT or other localization as described above, burr holes are initially placed on the side ipsilateral to the larger pupil. If the pupils are equal or there is no hemiparesis, the side of obvious external trauma should be chosen and the burr hole should be placed next to, not within, a skull fracture. This allows exposure of uninjured dura so that bone fragments can be removed from the area of normal anatomy toward the injured area with a rongeur. Except in cases with obvious localization, the temporal burr hole should be performed first, since temporal lobe decompression is usually the most urgent priority in acute cerebral herniation. This site is also the most common location of EDH and allows access to the area of the middle meningeal vessels. The skin incision should begin just above the root of the zygoma, coursing 1 cm anterior to the tragus and about 5 cm in length, continuing just over the top of the ear. This avoids injuring the superficial temporal artery posteriorly and the temporal branch of the facial nerve anteriorly (Fig. 3B). If present, a scalp laceration overlying the injured skull may be used to create an incision. The temporalis fascia is sharply incised and monopolar cautery is used to divide the temporalis muscle. Significant bleeding may occur here, but can often be controlled by distracting the tissue with a self-retaining retractor. Persistent bleeding can be controlled with electrocautery or hemostats, and even severe bleeding can be tamponaded temporarily with digital pressure and a sponge until controlled. The periosteum is then dissected away using a periosteal elevator or the handle of the scalpel. The self-retaining retractor should be left in place, but should not interfere with making the burr hole.

A high-speed pneumatic drill will rapidly create a burr hole if available and even a dental drill has been improvised to perform this procedure.44 A handheld drill such as a Hudson brace was used extensively before the invention of motorized drills and remains extremely useful. It is attached to a perforating bit (Fig. 2B), which is held perpendicular to the skull and turned rapidly (Fig. 4). Initially it may be difficult to turn the drill until the outer cortex is penetrated, but the cancellous bone is softer and more easily penetrated, producing more bleeding. As the inner cortex is engaged, there is initially a feeling of cogwheel-type resistance, and then the drill feels almost as if it is being pulled into the skull with every turn. The burr hole should be visually inspected frequently to assess whether the inner cortex has been breached, otherwise the drill may penetrate all the way through the inner cortex and plunge into the brain. When 5 to 10 mm of dura are seen, the drill is removed and a sharp bone curette is used to remove the remaining lip of bone. If the Hudson brace is used, the perforating bit can be exchanged for a rounded burr at this point, which will more safely enlarge the hole without penetrating as deeply toward the brain (Fig. 2B). There may be bleeding from the bone which obscures the dura, and bone wax is applied to the edges of the burr hole. It is important to differentiate this normal liquid bleeding from the coagulum of an epidural hematoma.

If there is EDH present, it will be encountered now, and the hole should be enlarged with a rongeur to allow removal of additional clot, but great care should be taken not to tear the dura. As the clot is removed with irrigation and suction, vigorous bleeding from the middle meningeal artery can occur, which may be very difficult to control and requires persistent effort with bipolar cautery or suture ligation through the dura. The hemorrhage may be especially difficult if it arises in the proximal portion of the artery near the foramen spinosum of the skull, and cautery may be useless if the artery retracts into the foramen. Placing the wooden end of a cotton tip applicator into the foramen and breaking it off is a desperate measure that may staunch the bleeding.

If there is no EDH encountered, the blue-white dura is seen. Since the temporal area is the most likely area to contain ICH, the burr hole can be widened when exploration is initially negative. ICH may be located anywhere, including immediately adjacent to a burr hole that appears to be negative for ICH; therefore, enlarging the hole improves diagnostic accuracy. If durai pulsations are not visualized after EDH evacuation, consideration should be given to opening the dura to look for coexisting SDH, and the decision to proceed should be weighed against the risk of causing brain injury. The surface of the dura should be cauterized first under low power with bipolar cautery. The dura is then grasped with small-toothed forceps and opened with two perpendicular incisions, using a no. 11 blade. Great care is required because the incision may cause injury to the cortical brain vessels. The edges of the dura are carefully cauterized and will shrink to expose the underlying brain. SDH can now be removed if present using saline irrigation to lift the clot and gentle suction to aspirate it.

If the temporal burr hole is negative, a sponge soaked in antibacterial solution should be placed in the wound and then a frontal burr hole placed. The incision should be placed immediately anterior to the coronal suture. This suture is palpable in most patients and should lie approximately 13 cm posterior to the root of the nose in the average adult. It is imperative that the incision be at least 3 cm lateral to the midline of the skull, at approximately the mid-pupillary line (Fig. 3C). If the skull is penetrated near the midline, there is risk of injury to the underlying superior sagittal sinus, which may result in exsanguination of the patient. If the burr hole is made more posterior than the coronal suture, there is risk of injury to the motor cortex of the brain and resulting paralysis. The technique for the skull and durai opening are the same as that described for the temporal approach. If the frontal burr hole is also negative for ICH, then a parietal one should be performed in the same fashion. The incision is 3 cm posterior to the external auditory meatus and 5 cm lateral to the midline, made in a vertical fashion (Fig. 3, B and C).

Removal of a small amount of acute blood clot through a burr hole may provide enough temporary decompression to allow evacuation of the patient to a neurosurgeon. Acute clot is thick and tenacious however and usually extends beyond the exposed area, such that <10% of acute ICH can be adequately removed through burr holes alone.57 The options would then include either enlarging the craniectomy with bone rongeurs or removing a free bone flap (formal craniotomy). The latter is a more extensive procedure and the risk of complications is higher. If a large ICH is encountered and a formal craniotomy is performed, the skin incisions described will allow a smooth connecting incision in the shape of a question mark to be made, preserving vascularization of the scalp flap based anteriorly and inferiorly (Fig. 3). In this case, hemostats or hemostatic clips are applied to the scalp, the temporalis muscle is divided with monopolar cautery and detached from the skull with a periosteal elevator (Fig. 5A). A dissector is used to separate the dura from the overlying bone for SDH (Fig. 5B), but not for EDH, since the bleeding has already dissected the dura away from the bone. Connecting cuts through the skull are made between each bunhole using a specialized power drill with a foot plate attachment, a Gigli saw with a durai guide device to introduce the wire safely under the bone, or a bone punch such as a Kerrison rongeur.

If all three burr holes are negative, then the same procedure is performed on the contralateral side, proceeding in order from temporal to frontal to parietal burr holes. This sequence provides the most efficient method of finding and treating ICH, and a complete exploration on both sides reduces the chance of a falsely negative exploration. Even if ICH was present on the initial side, the surgeon must decide whether the clinical situation warrants exploring the contralateral side, depending on the patient's response to initial decompression as well as clinical and radiographie indicators that bilateral hemorrhage may be present.

If all six burr holes are negative despite strong suspicion of ICH, a posterior cranial fossa burr hole may be considered. ICH is rare here, comprising only 4 to 13% of acute EDH58,59,60 and <1% of acute SDH.60,61 The risk of surgical complications is even higher in this area; therefore, it should be pursued only as a last resort or if there is obvious injury only to this area. The patient is placed in the prone position with the head supported by a headrest, and the skin incision is vertical, 3 cm medial to the easily palpated mastoid eminence (Fig. 6). Posterior fossa EDH usually results from a laceration of the transverse venous sinus and decompression will then result in vigorous bleeding from the sinus. Pressure applied to hemostatic agents may be sufficient to control it, but a wider craniectomy and definitive repair of the dura may become necessary. Removing bone on top of the sinus risks tearing it further, so the surgeon should persevere with simple application of local pressure unless it is clearly failing to provide hemostasis. A piece of muscle is placed over the sinus, reinforced with pressure, and sutured to the dura on either side of the sinus. Simultaneously, the head of the operating table is raised to reduce venous pressure. This maneuver risks air embolism through the venous sinus, which may manifest itself as an increase in end tidal CO^sub 2^ or systemic hypotension, in which case the head must be lowered again. Copious saline irrigation and liberal application of bone wax will also reduce the amount of air entrained.

At wound closure, a drain should be left in the epidural space if EDH was evacuated. A 10-mm Jackson-Pratt drain is ideal, since it was originally designed for use in the subdural space.62 However, if SDH is encountered, the inexperienced surgeon placing a drain into the subdural space may disrupt the cerebral cortical vessels and cause further bleeding.63 It should be emphasized that meticulous hemostasis, especially of scalp bleeding, is essential before drain placement and closure, or else ICH can recur postoperatively.64 When decompression is complete, all scalp incisions should be closed in two layers, with absorbable suture in the galeal layer and staples or monofilament suture for the skin, unless the patient has a penetrating injury with gross contamination or regions of poorly vascularized scalp. For these patients, closure of the temporalis muscle or galea should be performed to cover the exposed brain and the wound is dressed with the skin open. Scalp flaps will be rotated to provide appropriate coverage later.

Postoperatively, the patient should remain intubated to ensure proper ventilation and careful attention to the vital signs and to supportive care should continue. Worsening brain edema may occur for several days after the injury and may cause increased ICP, but recurrent hemorrhage is always possible and should be considered when increasing ICP or clinical deterioration occurs. Transfer to a neurosurgical facility should be accomplished as rapidly as possible to provide the best possible care for these and other complications of head injury.

Results

In the most modern series, Andrews et al.65 in 1986 investigated 100 consecutive patients with acute cerebral herniation after blunt trauma. They were taken immediately to the operating room for burr holes without prior CT, and if ICH was found a craniotomy flap was turned to allow complete evacuation. All patients underwent postoperative CT. ICH was found in 56 patients and 86% of ICH was detected on the initial side of exploration. The need for bilateral exploration was apparent, since 14% required bilateral burr holes to find the clot. ICH was missed in six patients because an incomplete procedure was performed, including four who had ICH located very close to a single negative burr hole. No extra-axial hematoma was missed in any patient who underwent a complete bilateral procedure. No posterior fossa burr holes were performed, and no ICH for any patient was visualized there on CT.

All patients who presented with bilaterally enlarged, unreactive pupils and flaccid extremities died, whether or not ICH was present. The poor outcome for these most severely injured patients has been corroborated by numerous other clinical series.66-69 Patients with a Glasgow Coma Scale of 3, 4, or 5 and/or bilaterally dilated pupils after resuscitation are thus unlikely to benefit from burr holes, especially if they have been dilated for several hours or if the patient has sustained a through and through gunshot wound.

The results cited above show the outcomes for patients treated by experienced neurosurgeons under the best of conditions. Procedures performed by inexperienced surgeons may be expected to have worse outcomes and, in some cases, only delay transfer to an appropriate neurosurgical facility.70 It should also be noted that some authors have reported excellent success with a simple twist drill rather than using burr holes.71-73 The supposed advantage over burr holes is speed and simplicity of use. However, the twist drill hole is quite small and therefore less likely to allow sufficient evacuation of an acute clot.74

Discussion

Posttraumatic ICH is associated with great morbidity and mortality. It is best treated by experienced neurosurgeons in a medical facility equipped with a CT scanner. In the rare instance that CT is not available, burr holes may be performed to diagnose and treat this condition. If CT is available and confirms the diagnosis, even the non-neurosurgeon may be required to perform decompressive burr holes or craniotomy in dire circumstances. It cannot be condoned as a routine practice by inexperienced surgeons however, since even in the hands of an experienced neurosurgeon burr holes are a substantially suboptimal method of diagnosis compared with CT imaging. The decision itself whether to perform this procedure or not is at least as important as the technique, since nonsurgical interventions alone may mitigate the need for burr holes, and burr holes placed by the inexperienced surgeon may exacerbate the injury. Consultation with a neurosurgeon is recommended in all cases, if possible, to determine whether the patient may be transferred to a neurosurgeon for the procedure. If the patient is rapidly deteriorating and cannot await transfer, careful attention to detail by the non-neurosurgeon is required to prevent a difficult situation from becoming even worse. The patient must be transferred rapidly to the neurosurgeon when stabilized after the procedure, since worsening brain edema and/or recurrent hemorrhage will exacerbate the clinical condition and require longterm follow-up care at an appropriate facility.

Acknowledgment

We thank Ms. Ten Thomson for technical assistance in preparing the photographs and illustrations and Mr. Dalton Nouchi for his original illustrations.

© 2006 Association of Military Surgeons of the United States Provided by ProQuest LLC. All Rights Reserved.

Source: Military Medicine