Brain Biopsy Technique

 

Background

Tissue-based pathological diagnosis is the criterion standard in the diagnosis of brain tumors. In situations in which surgical resection is not necessarily indicated but diagnosis of a brain lesion is needed to determine optimal treatment, a stereotactic brain biopsy offers a relatively safe and reliable method of obtaining diagnostic tissue. For over half a century, frame-based stereotactic methods have proven their use, and, more recently, frameless stereotaxy has emerged as a valuable alternative to this. Both framed and frameless stereotactic biopsy are discussed in this topic.

Indications

Brain biopsy should be considered when a tissue diagnosis from a suspicious brain lesion is needed to guide treatment and less-invasive methods of diagnosis are exhausted or inappropriate. Generally, brain biopsy is performed in 2 different scenarios. First, and most commonly, it is performed to confirm a suspected brain tumor. A typical situation occurs when diagnostic imaging demonstrates the classic appearance of a primary brain tumor and resection is not felt appropriate, as when the treating team suspects a high-grade glial tumor on the basis of imaging characteristics and does not feel that an aggressive resection is achievable. [1Tissue diagnosis can confirm the suspected pathology and guide further non-operative treatments.

The second and fortunately less-common scenario occurs when a wide-ranging differential diagnosis has been cast, and a diagnosis remains elusive despite less invasive work-up.

Contraindications

Practically speaking, absolute contraindications to brain biopsy are limited to those lesions felt to be too small to accurately and safely target and to those patients who are coagulopathic or otherwise unable to safely tolerate intravenous sedation or general anesthesia. In patients whose mental status would not permit stereotactic frame placement while under local anesthetic, a general anesthetic could be considered.

In any patient considered for stereotactic brain biopsy, weighing the relative merits of biopsy, namely the ability to obtain a tissue diagnosis, against the potential risks is important. In making this decision, all less-invasive opportunities to obtain a diagnosis should be considered. These could potentially include imaging adjuncts such as MR spectroscopy, sampling of spinal fluid by lumbar puncture, or identification of alternative systemic lesions to biopsy, such as an accessible lung lesion in the setting of multiple intracranial metastases. Exercising caution is important when considering biopsy of lesions that are suspicious for vascular malformations or with highly vascular tumors such as metastatic melanoma. With intraventricular tumors, an endoscopic biopsy can be entertained in favor of a stereotactic biopsy.



Equipment

Several different stereotactic frames are widely used and available to surgeons. The 2 most commonly used are the Leksell frame (Elekta Instrument, Stockholm, Sweden) illustrated in the first image below and the Cosman-Roberts-Wells, or CRW frame (Radionics Inc, Burlington, MA), illustrated in the second image below. Commonly used surgical planning and navigation software is available from both proprietors, as well as from BrainLAB (BrainLAB, Heimstetten, Germany) and StealthStation (Medtronic, Fridley, MN).

The Leksell head ring. The Leksell head ring.
Upper left: The Cosman-Roberts-Wells (CRW) unit isUpper left: The Cosman-Roberts-Wells (CRW) unit is affixed to the skull using 4-point fixation of the base ring. The CRW frame is attached to the base ring by way of 3 ball-in-socket joints. Upper right: With adequate low placement of the base ring, direct posterior fossa trajectories are practicable. Lower left: Demonstration of a direct lateral entry point approach is possible with the frame. Lower right: Lateral placement of the base ring is feasible with the use of specially designed partial arcs.

Brain Biopsy Periprocedural Care


Patient Preparation

Anesthesia

Framed stereotactic biopsy is generally performed under local anesthetic with intravenous sedation, whereas frameless stereotactic biopsy is more commonly performed under general anesthetic. Stereotactic frame placement typically occurs in the preoperative holding area or on the inpatient ward. During frame placement, a combination of intravenous narcotic (such as fentanyl) and anxiolytic (such as midazolam) are both given as a single dose. Additionally, local anesthetic is injected at the 4 pin sites. The authors prefer to use 0.5% bupivacaine with epinephrine. Consideration can also be given to performing nerve blocks as well. [2The injection of local anesthetic is better tolerated when buffered with sodium bicarbonate.

Once the frame is placed, the patient is taken to CT or MRI without additional sedation, which facilitates patient transfers onto the CT or MRI gurney and subsequently onto the operative table. When satisfactorily positioned on the operative table, additional intravenous sedation can resume and continue through the procedure. At this point, a continuous infusion, such as propofol, is frequently used as needed for patient comfort. Additional local anesthetic is injected at the planned surgical incision. Intravenous sedation, should be performed under monitored anesthesia care from the time of frame placement until frame removal. Maximum tolerated doses of local anesthetics should be borne in mind. With 0.5% bupivacaine and 1:1000 epinephrine, the maximum dose is 3 mg/kg. [3]

In those patients unable to tolerate frame placement under local anesthetic and sedation alone, general anesthesia can be performed. This generally requires frame placement in the operating room and requires more support staff to facilitate with patient positioning and transfers.

Positioning

For most lesions being biopsied, the patient can be positioned on the operating table in the supine position. This allows comfortable entry to most frontal, temporal, parietal, and subcortical structures. Lateral position can be used for a horizontal trajectory to approach temporal lesions, and prone position can be used for access to the posterior fossa. For patient comfort and access, the back of the table is raised to 30-45º, and the legs dropped. The frame is rigidly secured to the operating table with a Mayfield head holder. The patient can be firmly secured to the table with a padded safety belt. Arm boards can remain attached to the table for patient comfort. For a more detailed description of frame placement, see the Technique section.

Monitoring & Follow-up

Routine postoperative imaging

In a survey of 629 practicing neurosurgeons, the slight majority (59%) routinely perform an automatic noncontrast head CT scan following biopsy, regardless of patient clinical condition. [4Several advantages to obtaining a postoperative CT scan exist. First, the location of the biopsy can usually be appreciated by a scant amount of hemorrhage or air at the site. This can prove useful in the event that the pathology does not corroborate precisely, either nondiagnostically or with a discrepancy in tumor grading. Second, a CT scan that shows no appreciable or clinically relevant hemorrhage can help more appropriately select a postoperative setting for the patient.

Overnight observation

Among patients who are admitted for an elective biopsy, the postoperative care can range from discharge home to intensive care unit observation. In a recent survey, 6% of surgeons routinely discharge patients home following biopsy, and 47% admit them to a routine surgical ward. [4Some data suggest that patients can be safely discharged home without risk of deterioration or readmission in the appropriately selected patients who undergo a routine postoperative head CT scan and 4 hours of observation without risk of deterioration or readmission.


Brain Biopsy Technique


Framed Stereotactic Brain Biopsy

Frame placement

The patient should have adequate intravenous sedation but remain alert enough to participate and maintain an upright seated posture, which greatly facilitates frame placement. If sedation is performed without monitored anesthesia care, then pulse oximetry and oxygen delivered by nasal cannula should be used. The authors do not routinely perform any head shave for frame placement, although this is preferred by some surgeons. An approximate entry point should be anticipated to avoid placement of a pin-site or frame post too close to the desired incision.

The frame should be assembled without pins in place, and placed on the patients head in the approximate position. The posts can be rotated into a position that optimizes fixation by avoiding excessively medial or lateral location. The pins should be located at or below the greatest circumference of the calvaria. This aids with fixation and places the localizing carbon fiber rods appropriately. Ensuring that the frame is not positioned too close to the bridge of the nose is also important.

The anticipated pin sites can then be wiped with an alcohol or Betadine wipe and injected with local anesthetic. The pins are then placed in the frame posts, with attention to use the appropriate length pins. With the CRW frame, generally the shorter pair of pins are placed in the posterior posts, while the longer pair of pins are placed in the anterior posts. Antibiotic ointment is applied to the pins, and the pins are advanced through the posts to each be flush with the skin surface.

The authors generally prefer to secure one anterior pin and a contralateral posterior pin first, which then allows the frame to be balanced relative to the horizon as desired. Once in satisfactory position, the remaining 2 pins are advanced until each is rigidly secured. As the pins are advanced, giving more local anesthetic as needed may be necessary. Ensuring that the posts exert no pressure on the scalp is important while advancing the pins. Placing 1 or 2 radio-opaque fiducial markers on the scalp near the planned incision can be useful. This can help tailor the incision, and, before the sterile stereotactic frame is attached to the base, it can help with approximating the skin incision and a smaller area of hair can be shaved if desired.

Trajectory planning

With the frame satisfactorily placed, the patient can then be taken for a localizing CT scan or MRI. Generally, a contrast-enhanced head CT scan is sufficient for identifying a target. With high-grade intrinsic brain tumors, the area of thickest enhancement is conventionally targeted. [7A target can also be selected such that slightly deeper or shallower samples could be obtained along the same trajectory. With low-grade gliomas, a T2-weighted MRI may allow for better targeting. The localizing CT scan is fused with the preoperative MRI, which provides adequate accuracy. Advanced planning of an MRI-based trajectory with subsequent fusion to a localizing CT scan reduces overall operative time. [8]

The entry point should be planned to avoid entry into a dural blood vessel, cortical blood vessel, or sulcus. Depending on whether or not future attempts are resection are anticipated, the entry point could be planned to be incorporated into the craniotomy incision. The trajectory should then be reviewed to ensure that the biopsy cannula will avoid unnecessarily traversing pial or ependymal surfaces. Generally, the shortest distance that takes these structures into consideration and avoids eloquent cortex is preferred.

Separate specimens can be obtained from a single trajectory by altering the depth of the biopsy cannula and also by rotating the aperture of the side-cutting biopsy cannula. Although even further sampling heterogeneity may be afforded by planning multiple trajectories, this is reported to increase the risk of postoperative deficits in deeper lesions. [9]

Biopsy

Once a trajectory is planned, the stereotactic coordinates should be confirmed and transferred from the planning station into the operating room. Once the patient arrives in the operating room, he or she can be positioned on the operating table and intravenous sedation resumed. The stereotactic frame should be assembled by a skilled operating room nurse or the surgeon. The stereotactic coordinates should be registered onto the frame and verified.

With the planned scalp entry site, a small area of hair can be shaved if desired. The patient can be prepped with caution to avoid the eyes. A custom drape, the Apuzzo Stereotactic Drape (Integra LifeSciences, Plainsboro, NJ) can be useful when using the CRW frame because it has 3 perforations in the drape that exist where the sterile stereotactic ring attaches to the nonsterile patient frame. Once the ring is placed, the trajectory should be verified, and any minor adjustments to the scalp incision can be made. Local anesthetic is injected into the scalp for patient comfort and hemostasis.

The 2 methods of trephination are twist-drill or bur hole. Twist-drill offers the advantage of a small punctate skin incision that can be made with a #11 or #15 scalpel and need measure no larger than a standard 2.7-mm diameter twist-drill. This allows for less scalp bleeding, quicker closure, improved cosmesis, and can also facilitate incorporation into a craniotomy if staged tumor resection is anticipated.

In contrast, a bur hole can be made with a high-speed cranial perforator or fluted matchstick bur. The theoretical advantage of making a bur hole is that any dural or cortical blood vessels can be directly cauterized with bipolar cautery. A bur hole requires a larger linear or curvilinear incision. If a twist-drill is made, the drill bit should be guided through the guide tube and reducer in the exact planned trajectory of the biopsy needle. If a bur hole is made, the ring of the stereotactic arc can be temporarily rotated out of the way to improve access.

Once the bur hole is made, the biopsy needle should be advanced down the guide tube to confirm that no bony edges deflect its trajectory. Once the dura is sharply opened, this should again be confirmed. The biopsy needle should be measured to the appropriate depth. The standard distance to the target should be borne in mind depending on the exact configuration of reducers and guide tubes. The authors use a disposable Nashold Biopsy Needle (Integra Radionics, Burlington, MA) and measure the distance from the mid position of the side-cutting port to the depth stop. The biopsy needle has a Luer lock attachment in which a saline-filled syringe can be attached in order to apply slight negative pressure.

The system is flushed with saline, and the side-cutting port is closed. When the hub of the inner cannula of the needle is rotated 180º, the side-cutting port is opened. The port should be flushed and closed and then gradually advanced to the planned depth, with attention to notice any change in resistance as the needle is advanced, which can be an indication that tumor is entered. Once at the planned depth, the side-cutting port is opened by rotating the inner hub 180º, and slight negative pressure is applied by withdrawing on the saline-filled syringe to pull tissue into the needle. The side-cutting port is then closed and the needle withdrawn.

The specimen can be retrieved in a similar manner, by opening the port and flushing saline through to eject the specimen. Additional specimens can be obtained by rotating the aperture in different directions, or alternatively by varying the depth slightly. The authors generally avoid taking more than 4 specimens. Once specimens are obtained, they can be sent to pathology, where frozen sections are obtained at the discretion of the surgeon. The scalp can be closed with a single figure-of-8 absorbable suture in the case of twist drill. With a bur hole, the scalp is closed in layers with buried suture in the galea and a running suture or staples in the skin. The frame is removed, and any bleeding encountered from the pin sites can generally be controlled with tamponade or antibiotic ointment.

Frameless Stereotactic Brain Biopsy

The stereotactic accuracy of frameless stereotactic brain biopsy has been reported to be comparable to that of frame-based systems. [1011Frameless biopsy occurs without a stereotactic frame but typically is performed with the patient in pin-fixation. Generally, pin-fixation is better tolerated under general anesthesia, which is more common for frameless procedures. Because a stereotactic frame is not used, a coregistration process must be performed. Several methods for this include fiducial markers, anatomic landmarks, and surface matching.

Fiducial marks can be placed on the patient’s scalp prior to acquisition of CT scan or MR imaging. When placing fiducial markers on the scalp, shaving a patch of hair so the adhesive backing can adhere to the scalp may be necessary. The authors outline the fiducial with a marker in the event that it is removed. A minimum of 4 fiducial marks are typically necessary to accurately register the patient to an image set. The fiducial markers should be placed a sufficient distance from each other so that they can be easily distinguishable from one another. Effort should also be made to avoid placing them in a single plane. Confirming that the appropriately compatible fiducials are used depending on whether CT scan or MRI is performed is also important.

After the CT scan or MRI is obtained and the target is planned, the patient is brought to the operating room and placed under anesthetic. Generally, pin-fixation is performed such that a rigid reference probe can be attached to the frame. An optical imaging system is used to register the patient, and a reference probe to the preoperative images using one of the registration methods mentioned above is used to match image space with physical space. If surface matching registration is used with a laser, avoiding significant distortion of the scalp when performing pin-fixation is important. Among the 3 registration methods, no significant advantage exists regarding one method over another in regards to accuracy. [12]

Once the patient is registered to the preoperative image with the planned target, the patient is prepped and draped. A sterile reference star is applied within the sterile field. Although a free-hand method can be performed by registering the biopsy needle within the navigation system, a guide tube may provide a more accurate method for smaller lesions. A guide-tube can be registered to the navigation system and then oriented in the desired trajectory and held rigidly in place with a retractor system. Once this is satisfactorily done, a small incision is made in the same manner as described above. A twist-drill is passed through the guide tube when it is replaced in the desired trajectory. Once the biopsy needle is measured to the appropriate depth, specimens can be obtained in the same manner as described above for frame-based biopsy.

Pearls

Having a clear conceptualization of framed stereotactic biopsy makes surgery safer and simpler. In essence, the target is defined as a single point within 3 axes, x,y, and z. The frame can translate in these 3 axes to position the center of a sphere over that target. Termed the center-of-arc principle, this can be conceived as a sphere in space that is centered at the target. Following a trajectory from any point along the surface of that sphere still leads to the center of the sphere when the trajectory remains perpendicular.

Thus, as long as the x, y, and z coordinates define the target, the arc and ring angles can be used to vary the entry point. Although this will alter the skin incision, the bur hole, the exact trajectory, and the structures traversed, it will lead to the same target. Thus, modification of the arc and ring angles can be used intraoperatively without recalculating a target. Drastic alterations in these angles should be reviewed on the planning station to confirm that no unexpected structures are encountered by the trajectory of the probe.

Along the same lines, the distance to the target remains constant for a given configuration of the biopsy set-up. With the Leksell system, the radius measures 190 mm. With the CRW system, the radius measures 160 mm. As guide tubes and reducing cannulas are introduced, the clinician needs to account for the distance to the target possibly increasing. It should be emphasized that once the distance to target is calculated it should always be measured with a ruler, and all guide-tubes and cannulae should be measured as well. 

The distance to the target can be calculated, but The distance to the target can be calculated, but direct measurement with a phantom base should be considered to confirm the calculation.

With both frame systems, the trunnion rings can be flipped from the standard left-right position to an anterior-posterior position in order to access lower temporal lesions. When rotating the trunnion rings, remember that the coordinates generated are no longer referenced to the frame-space but to the patient-space and that the arc and ring angles will differ. Also bear in mind that when coordinate-space is rotated because the frame is rotated, the anterior-posterior markings on the frame system, for example, will no longer correspond to the A-P coordinate system relative to the patient. 

Complications

Hemorrhage

In a consecutive series of 500 patients at a single institution undergoing framed stereotactic brain biopsy between 1990 and 1999, the reported rate of hemorrhage identified on routine postoperative CT scan was 8%, whereas the rate of neurologically symptomatic hemorrhage was 1.2% and the rate of fatal hemorrhage was 0.2%. [7The authors identified a platelet count below 150,000/mm3 and pineal region lesions as predictors of hemorrhage. The method of biopsy described by the authors is a small 4-mm twist-drill craniotomy as opposed to a standard bur hole, which is also worth emphasizing. This small trephination does not appear to confer any increased risk of extra-axial hemorrhage. Another series reports no additional risk of an even smaller trephination using a 2-mm twist-drill. [13]

Some have argued that the number of specimens obtained may confer increased risk of hemorrhage, [14although this was not borne out in a large series, where the median number of specimens was 3, and over 10% of patients had more than 5 specimens sent. [7]

Nondiagnostic sample

The goal of performing a stereotactic brain biopsy is to obtain tissue diagnosis. Thus, a nondiagnostic sample enables no therapeutic decision-making and potentially commits the patient to an additional procedure. Technical reasons for nondiagnostic tissue are minimized with the use of stereotaxy, and diagnostic yields are consistently reported to approach 100% in many series. [71516]

Visual inspection of the specimens can help determine whether or not diagnostic tissue is obtained. One consideration is to send a sample for immediate frozen section pathology, while the patient remains on the operating table such that further specimens can be obtained if necessary. Some have argued that diagnostic tissue can be consistently obtained without intraoperative pathology. [15In a single series of 134 patients treated between 2005 and 2007, a diagnostic yield of 99.3% was reported without the guidance of frozen section pathology to determine the number of specimens to obtain. [15]

Increasing the number of specimens obtained has not been shown to increase the diagnostic yield. [7Use of frameless stereotactic technique has not been shown to negatively affect diagnostic yield. 

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