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Operation
Burr holes
Craniectomy
Craniotomy
Special
Risks
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Introduction
Craniotomy
"Craniotomies" are procedures where scalp and bone flaps are made as opposed to "exposures" named after the surface regions of the brain. A single craniotomy may, with minimal extension or modification, enable exposure of different extents of the brain surface.
Size-wise, craniectomies uncover several square cm of dura contiguous with or around a calvarial perforation as compared to 25 - 100cm square cm for a small (25cm) to large (100cm) craniotomy bone flap.
Standard craniotomies useful for head trauma operations are named after their skin incision and include the coronal, pterional, temporal trauma, convexity straight line, occipital, and suboccipital.
Coronal craniotomy
A bicoronal flap exposes the frontal lobe on the same side as its longer segment adequate to perform a frontal lobectomy or evacuate a unilateral subdural or epidural hematoma. Two long segments, spanning from both temporal regions, will be required for cases where a bifrontal bone flap must be elevated (rarely required for head trauma surgery except for frontal fossa reconstruction with ophthalmology and/or plastic surgery and/or otolaryngology).
Position
Supine-forward or supine-rotated. A good third of the bicoronal skin incision is across the midline contralateral to the pathology, therefore the head should be turned enough to give full exposure of the ipsilateral frontal and temporal lobes but to at least half of the contralateral frontal region as well.
Landmarks
The surface landmarks for the bicoronal flap are the tragus of the ear, the zygoma, the coronal sutures, the widow's peak (intersection of hairline and sagittal midline), the keyhole, the orbital ridge, the sagittal suture, and the glabella
Incision
The bicoronal scalp flap skin incision is a combination of a short and long segment. The origin of the bicoronal scalp flap skin incision is one centimeter anterior to the tragus of the ear just superior to the zygoma. The initial segment is straight for approximately 4 cm.
Since temporal access is not sought with this exposure the origin of the bicoronal incision can be a few centimeters above the level of the zygoma (floor of temporal fossa). But not too much above as the bulk of underlying temporalis muscle already makes the ipsilateral portion of the scalp flap unwieldy.
The next segment is an arc centered at the lateral canthus of the eye. This segment goes as far posteriorly as the coronal suture before swinging forward to end at the temporal line and is followed by a segment arc centered on the zygomatic process, terminating at the widow's peak. From the widow's peak the contralateral incision is the mirror image of the longer lesion-ipsilateral segment except that it ends at the contralateral temporal line.
Burr holes
Although the bicoronal scalp flap crosses the midline, the burr holes for anteromedial frontal lobe exposure are both ipsilateral: frontal and keyhole.
When the burr holes are connected, a trapezoid bone flap results.
Hazards
Structures encountered in fashioning the bicoronal scalp and bone flap include the vascular, nervous, muscular, and bony structures that must be anticipated and avoided if possible include: the superficial temporal artery, the frontalis branch of the facial nerve, the temporalis muscle, and the squamosal portion of the temporal bone.
Pterional craniotomy
The pterional craniotomy incision is shorter, the trauma to the temporalis muscle less, the bone flap smaller (in the event that it has to be left out at the end of the case less likely a cranioplasty will be needed for coverage of the defect.) The pterional is a versatile craniotomy that gives good exposure of the inferolateral portion of the frontal as well as the anterior temporal, lobe. Pterional is the craniotomy for choice for a lateral frontal lobe exposure.
The lateral frontal and anterior lobes of the brain lie within the perimeter of the craniotomy bone flap. By insertion of self-retaining retractors and with opening of the Sylvian fissure by splitting the arachnoid spanning from the surface of the temporal to frontal lobes these lobes can be more easily mobilized giving the surgeon access to the inferolateral aspect of the frontal lobe. The exposure includes the frontal lobe caudally from the coronal suture to the anterior-most frontal fossa rostrally. Laterally the exposure extends from the midline sagittal sinus to the frontal operculum.
Position
For a pterional scalp and bone flap the patient is positioned supine with the head rotated toward the side where the craniotomy will be done. The patient can be supine with a bolster under the ipsilateral shoulder and the head on a donut, or three-point pin fixation can be used to hold the patient's head rotated.
Landmarks
The surface skin landmarks for the pterional craniotomy are the tragus and the widow's peak. Those for the burr holes are the keyhole, the temporal squamosa just above and midway along the zygoma. A unilateral pterional craniotomy is for lesions on the lateral aspect of the frontal lobe and anterior temporal. The external landmarks for the skin incision are: glabella anteriorly, anterior tragus of ear posteriorly.
Incision
The incision starts posterior to the frontalis branch just anterior to the tragus of the ear, swings forward with a large radius arc, and terminate at the midline, posterior to the hairline high on the forehead.
b.4) Burr holes
Bur holes in a pterional craniotomy are placed at the keyhole and just superior to the zygoma one centimeter anterior to the tragus of the ear.
The two craniotome cut segments when jointed together create a relatively circular pterional craniotomy bone flap.
b.5) Hazards
The superficial temporal artery, the frontalis branch of the facial nerve, the temporalis muscle, and the squamosal portion of the temporal bone are the hazards that can be injured in fashioning a pterional craniotomy scalp and bone flap. The burr hole near the keyhole should be placed with the perforator directed superiorly so as to avoid entry into the orbit.
c) Temporal trauma craniotomies
A family of temporally based craniotomies related by the origin of their scalp flap incision one centimeter anterior to the tragus just above the zygoma, are used for exposing hematomas that involve the temporal lobe exclusively or in combination with one or more other lobes of the convexities.
FIGURE: Temporally-based craniotomies
c.1) Temporal (with bone flap)
The most limited temporally based craniotomy uncovers the temporal lobe from the inferior to the superior gyrus up to and including the Sylvian fissure. (In practice it provides no better exposure to do a temporal craniotomy with elevation and replacement of a bone flap that to do a technically simpler and faster extended temporal craniectomy).
c.1.1) Position
The position for a temporal craniotomy is supine-rotated or lateral. A bolster under the shoulder contralateral to the surgical lesion helps turn the face away from the lesion side with less demand on the rotational capacity of the cervical spine.
The degree of rotation depends on which portion of the brain surface must be exposed. A lateral position is also possible but requires pins and OR table attachments and is time-consuming to set up. The advantage of the lateral position is that with it exposure of the operative field is better when the lateral temporal lobe is parallel to the floor. Another important advantage of the lateral position is that in it the patient whose neck has not been "cleared" can be kept in a rigid collar.
c.1.2) Landmarks
Surface and skull structures important for the temporal craniotomy (and in fact for all temporally-based exposures) are: the tragus of the ear, the zygoma, the superficial temporal artery (located visually or by palpation), as well as the superficial temporal line (extent of temporalis muscle).
The origin of the simple temporal variant of the temporally-based trauma flap is one centimeter anterior to the tragus of the ear just superior to the zygoma.
c.1.3) Incision
The initial incision segment (identical for all temporal trauma craniotomies) measures a few centimeters and runs parallel to the pinna of the ear. This initial segment must be located just anterior to the tragus of the ear to avoid injury to the frontalis branch of the facial nerve.
In its next segment the incision curves back to form a posterior loop 1 centimeter above the pinna. The origin and radius of curvature of the posterior loop determine the side of the scalp flap raised, of the bone flap elevated, and of the dura exposed. For exposure limited to the temporal region, the radius of curvature need not exceed 10 cm..
The anterior, parasagittal segment of the temporal trauma incision extends forward two to three centimeters lateral but parallel to the midline, stopping at the coronal suture.
c.1.4) Burr holes
A single burr hole just above and midway along the zygomatic arch is the origin of a circular bone flap with its center 4 to 5 centimeters superior (diameter of temporal craniotomy bone flap: 10 cm).
c.1.5) Bone flap
Instead of cutting with a craniotome, a rongeur can be used to make a temporal craniectomy with multiple bites around a circle whose circumference originates at the temporal bur hole.
c.1.6) Dural opening
The dura is most conveniently opening with an inferiorly-based dural flap. Although it will take longer to close, a cruciate dural opening is possible.
c.1.7) Hazards
Frontalis branch (incision too far anterior to the tragus).
Hairline (incision too far anterior to coronal suture).
Just above the zygoma, at the floor of the temporal fossa not only is the bone thin but there is a thick temporalis muscle layer that provides cosmetic and protective effects so that bone can be left out without jeopardizing either patient safety or cosmetic result. The temporal squamosa is so thin that inadvertent placement of pins at this site can fracture the bone and lead to epidural hematoma formation.
c.2) Frontotemporal (FT) craniotomy
An epidural or subdural hematoma overlying more than half the temporal and frontal lobes may require an exposure larger than that possible with the skin and bone openings used for the temporal craniotomy. By swinging the incision back farther, along a larger arc, and putting an additional posterior and anterior burr hole a larger dural exposure will result.
c.2.1) Position
The position for the temporally-based frontotemporal flap is supine-rotated. To allow for frontal exposure, the rotation from the midline is less for the FT than for the temporal (FT nose at 2 or 10 o'clock versus temporal: nose at 3 or 9 o'clock).
c.2.2) Landmarks
As for other temporal based craniotomies, the landmarks of paramount importance for the FT are the zygoma and the tragus of the ear. The upper tip of the ear pinna will be the landmark for the posterior extent of the skin incision and scalp flap. As trauma flaps get larger from the limited temporal to the frontotemporoparietooccipital (FTPO) their upper most extent approaches the midline and the sagittal suture is increasing important as a planning landmark
c.2.3) Incision
The posterior loop of the FT craniotomy skin incision extends back to the midpoint between the inion and the vertex. Its radius is approximately 10-15cm.
The anterior limb of the FT craniotomy extends forward five to seven centimeters lateral but parallel to the midline, stopping at the coronal suture.
c.2.4) Burr holes
A temporal burr hole is drilled first. A second hole can be placed 1cm anterior to the edge of the posterior-most point of the scalp incision. A third hole can be placed frontally just posterior to the coronal suture.
c.2.5) Bone flap
An elliptical bone flap is cut joining the three bur holes. The bone mass of the sphenoid wing can hold up the craniotome and it may be necessary to break the bone across this thick ridge.
c.2.6) Dural opening
The dura is most conveniently opened with an inferior (temporal) base to the flap.
c.2.7) Hazards
No hazards of the FT variant are not common to all of the temporally-based craniotomies.
c.3) Frontotemporoparietal (FTP) craniotomy
The frontotemporoparietal craniotomy is the temporal craniotomy variant that gives the exposure most useful for evacuation of large acute subdural hematomas.
c.3.1) Position
The position for the temporally-based frontotemporoparietal flap is supine-rotated or lateral. The latter is preferable because the exposure of the operative field is better when the lateral temporal lobe is parallel to the floor.
With the patient supine with a towel roll or other bolster under the shoulder ipsilateral to the craniotomy, the head is turned away from the propped shoulder and placed on a donut support. The need in this craniotomy for access to the frontal lobe as well as to the temporal precludes the lateral-forward position, rather the supine-rotated is the only viable one in this case. The difference between the head position in the frontotemporal and frontotemporoparietal craniotomies is that the head is rotated further from face- forward in the former (FTP) than the latter (FT).
c.3.2) Landmarks
The landmarks for the FTP scalp and bone flap are the same as for other temporally-based craniotomy exposures with the addition of the parietal boss which is useful for locating the posterior extent of the skin incision.
c.3.3) Incision
The origin of the initial segment is one centimeter anterior to the tragus of the ear just superior to the zygoma. The initial straight segment measures a few centimeters and hruns parallel to the pinna of the ear. This segment ends and the incision curves back to form the posterior loop 1 centimeter above the pinna. (illustration of straight lines drawn just anterior to tragus, parallel to pinna, intersection with line 1 cm above pinna).
The posterior loop of the FTP incision begins with an "S"-shaped segment which travels above the pinna of the ear for three to four centimeters before beginning a semicircular loop. The radius of the loop is 15-20 cm. The posterior-most extent of the frontotemporoparietal incision is the parietal boss. The anterior limb of the FTP incision.
c.3.4) Burr holes
The burr holes for the FTP craniotomy are temporal, frontal and parietal, drilled just above the zygoma approximately halfway between the pinna of the ear and the lateral orbital rim.
c.3.5) Bone flap
On connecting the three FTP burr holes the craniotome is to curve outward along each segment such that a relatively circular bone flap results.
c.3.6) Hazards
No hazards are particular to the FTP variant of the temporally-based craniotomies.
Temporal based trauma craniotomies
A family of temporally based craniotomies related by the origin of their scalp flap incision one centimeter anterior to the tragus just above the zygoma, are used for exposing hematomas that involve the temporal lobe exclusively or in combination with one or more other lobes of the convexities.
FIGURE: Temporally-based craniotomies
Temporal based trauma craniotomies
Frontotemporoparietooccipital (FTPO)
The frontotemporoparietooccipital (FTPO) craniotomy is the largest temporal trauma craniotomy seldom necessary for evacuation of traumatic hematomas. The flap seems huge: The volume of tissue reflected forward contains, in addition to that in the FTP flap, a sizeable portion of the occipital muscle. Bringing the craniotome from the front to the back of the head makes it seem more of hemicraniotomy than an extension of a limited temporal craniotomy.
c.4.1) Position
The position for the temporally-based FTPO flap is supine-rotated or lateral. The latter is preferable because the exposure of the operative field is better when the lateral temporal lobe is parallel to the floor.
The patient is placed supine with a shoulder roll under the shoulder ipsilateral to the lesion. The head is turned away from the propped shoulder and placed on a donut support. The difference between the head position in the FTP and FTPO craniotomies is that the head is rotated further from face- forward in the former (FTPO) than the latter.
A body lateral-face forward position is also possible and may be preferable in terms of providing simultaneous access to both far frontal and occipital hematoma.
c.4.2) Landmarks
The landmarks for the FTPO scalp and bone flap are the same as for other temporally-based craniotomy exposures with the addition of the lambdoid suture midway between the vertex and the asterion which is the posterior extent of the skin incision and location of the posterior-most burr hole.
c.4.3) Incision
The origin of the initial segment of the FTPO skin incision is one centimeter anterior to the tragus of the ear just superior to the zygoma.
The straight segment measures a few centimeters and runs parallel to the pinna of the ear. This segment ends and the incision curves back to form the posterior loop 1 centimeter above the pinna.
The radius of the posterior loop is 20-25cm. The posterior-most extent of the frontotemporoparietal incision is the parietal boss. The parasagittal segment lies three to four centimeters off the midline and extends to the coronal suture.
c.4.4) Burr holes
The burr holes for the FTPO craniotomy are: 1. Temporal, 2. Frontal, 3. Parietal, and, if necessary, 4. Occipital
c.4.5) Bone flap
The FTPO bone flap shape is trapezoidal as dictated by the four burr holes used to create it.
c.4.6) Hazards
No hazards are particular to the FT variant of the temporally-based craniotomies.
c.5) Combined frontal-temporal
When it is necessary to simultaneously do a temporal and a frontal lobectomy or when an expanding frontal contusion accompanies a subdural hematoma, a combined fontal and temporal craniotomy may be necessary to provide adequate exposure.
c.5.1) Position
The patient is positioned supine with the face forward or rotated slightly (20 to 30 degrees) with the head on a donut). In order to optimize visualization and access, anesthesia and nursing should be alerted to the fact that the patient's head may need to be rotated to the side for the temporal intracranial portion of the operation.
c.5.2) Landmarks
The landmarks for a combined frontal-temporal craniotomy incision are those for the initial segment of the temporal incision (namely the zygoma and tragus) and those for a bicoronal skin incision (coronal and sagittal sutures).
c.5.3) Incision
The incision has two segments: temporal and coronal. The temporal portion of the incision begins just anterior to the tragus just above the zygoma. The incision curves slightly posterior then swings forward to the coronal suture. Then, for its coronal segment, the combined incision curves posteriorly and then forward to the widow's peak in the midline. From the midline the incision curves back and then forward for 7-10 cm from the midline. The coronal segment of incision for a combined frontal-temporal craniotomy is more limited on the side contralateral to the lesion, extending only as far as is necessary to get the scalp flap reflected far enough forward to put burr holes and cut a bone flap adequate for frontal lobe exposure.
c.5.4) Burr holes
At least three burr holes should be placed for a combined frontal-temporal craniotomy: 1. temporal - above the zygoma over the temporal squamous bone, 2. key hole, 3. 1-2cm lateral to midline at coronal suture.
c.5.5) Bone flap
The piece of bone that will be elevated following connection of the burr holes will look like a large comma: ",".
c.5.6) Dural opening
The easiest to open and close is a trap door, but a cruciate dural opening may be necessary depending on proximity to dural sinuses and other vulnerable structures.
c.5.7) Hazards
The hazards encountered in a combined frontal-temporal craniotomy include those of the temporal and coronal craniotomies described above: namely, the frontalis branch anterior to the ear, the frontal sinuses, the orbit, and the sagittal sinus.
c.6) Straight line convexity craniotomy
A "straight line convexity" craniotomy is one centered over a lesion lying on the convex aspect of the cerebral hemispheres, characterized by: a straight line skin incision, placement of self-retaining retractors, a single burr hole, and a more or less circular bone flap of diameter approximately one half the length of the skin incision.
The straight line convexity is the most versatile craniotomy in many ways. The orientation of the skin incision can be in any direction and the skin incision can vary in length from 5 or 6 to 20-25 centimeters depending on the orientation and diameter of the convexity lesion. The opened self retaining retractors provide excellent hemostasis, obviating the need for scalp clips whose application wastes surgery time and surgeon patience.
c.6.1) Position
Patient position for a straight line convexity craniotomy depends on the lobar location of the surgical lesion.
c.6.2) Landmarks
The midline sagittal sinus and the vertex are the most important landmarks for orientation of a straight line incision. The terminal branches of the major arteries supplying the scalp become increasing perpendicular to the midline as they approach it.
c.6.3) Incision
Cranitomies that are more or less elliptical with a skin incision straight or gently "S"-shaped oriented orthogonal to sagittal.
c.6.4) Bur holes
Burr holes are placed above the inferior and superior poles of the underlying lesion.
c.6.5) Bone flap
An elliptical or more circular bone flap is cut with two curved limbs joining the polar burr holes.
c.6.6) Dural opening
The easiest to open and close is a trap door, but a cruciate dural opening may be necessary depending on proximity to dural sinuses and other vulnerable structures.
c.6.7) Hazards
The hazards of a straight line convexity craniotomy depend on where the incision is made and the burr holes placed.
c.7) Occipital craniotomy
An occipital craniotomy gives exposure to the parietal and occipital regions. It is probably the least common craniotomy for head trauma because none of the hematomas - epidural, subdural, intracerebral - for which head trauma craniotomies are done are primarily or even secondarily, occpital.
c.7.1) Position
Lateral is preferred although prone is an alternative position for an occipital craniotomy.
c.7.2) Landmarks
Landmarks for the occipital scalp and bone flap are the vertex, the pinna of the ear, and the inion.
c.7.3) Incision
The occipital craniotomy scalp flap is an isoceles triangle, vertex up. The points along the incision are: 1. Vertex, 2. Occipital just above transverse sinus, and 3. Inion. The flap is an inverted "V" with the cranial vertex the point of limb convergence. The posterior limb of the scalp incision is a straight line that extends from the inion to the apex of the inverted "V". The anterior limb is a straight line orthogonal to the posterior at its point of origin at the vertex extending downward to 1-2 centimeters above the superior most portion of the pinna of the ear.
In order to help ensure that the two limb of the incision converge at the exact point of the vertex it is best to start both limbs from the same point of origin or else to start just above the ear, go to the vertex, then do the posterior limb from vertex to inion.
The origin of the mitre flap anterior segment is 4 cm off the midline at the vertex. The end of the anterior segment ends just above the pinna of the ear. The anterior segment should be cut from the vertex down towards the pinna which is the end of the anterior segment. The end of the posterior segment ends just above the inion.
c.7.4) Burr holes
Burr hole placement is easier for occipital than for most craniotomies.
The first hole is a modification of the temporal, placed above the ear in the low parietal region. Next is a standard parietal hole a centimeter or so off the midline (avoiding the sagittal sinus) just above the inion. The third hole is off the midline at the level of the vertex. This hole is placed last to avoid injuring the sagittal sinus.
c.7.5) Bone flap
A bone flap in the configuration of an isosceles triangle results from connecting the three burr holes.
c.7.6) Hazards
No significant nervous, vascular, or bony hazards are encountered in fashioning the occipital scalp and occipital bone flaps.
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