There are four basic categories of supratentorial and infratentorial craniotomy:
Convexity craniotomies may be performed anywhere according to the surgical target and goal of the operation. They range from burr holes and mini-craniotomy to decompressive hemicraniectomy, which is the most extensive variant.
Midline craniotomies are used for midline approaches that take advantage of subdural anatomical corridors to reach superficial, deep, or contralateral targets. The supratentorial suboccipital craniotomy with an intradural approach along the falx and the tentorium or an infratentorial suboccipital craniotomy with a supracerebellar approach are possible variants.
Skull base craniotomies range from the frontal midline to the foramen magnum, covering the entire skull base. ▶Fig. 1.1 and ▶Fig. 1.2 demonstrate the continuum of approaches which are often overlapping and are named according to their location at the skull base.
Skull base extensions are added to standard skull base craniotomies. They allow access with angles of approach or to structures that cannot be easily reached with standard skull base craniotomies. Typical skull base extensions are anterior clinoidectomy, removal of the orbital rim or zygoma (orbitozygomatic), transpetrosal approaches, the suprameatal extension after retrosigmoid craniotomy or the far-(enough) lateral extension to the foramen magnum (see Chapter 6, Skull Base Extensions).
Fig. 1.1 Systematics of skull base craniotomies—supratentorial. Supratentorial frontotemporal skull base craniotomies, 45° view (a) and lateral view (b). 1, frontolateral; 2, supraorbital; 3, standard pterional; 4, mini-pterional; 5, frontotemporal; 6, anterior temporal; 7a–c anterior, middle, posterior temporobasal; 8, sylvian fissure/sphenoid wing.Fig. 1.2 Systematics of skull base craniotomies—infratentorial. Craniotomies of the posterior fossa. 9, suboccipital median infra-transverse-sinus; 10, suboccipital lateral infra-transverse-sinus; 11, suboccipital far-lateral infra-transverse-sinus; 12, retrosigmoid; 13, suboccipital median periforaminal (with opening of the foramen magnum); 14, mini-suboccipital median periforaminal (with opening of the foramen magnum); 15, suboccipital lateral periforaminal (with opening of the foramen magnum); 16, far-lateral extension.
Supratentorial skull base craniotomies can be divided according to their location, their frontal and temporal extension (size), and their relation to the sylvian fissure. There is no uniform classification, but the following general rules may serve as a guide to the terminology (see ▶Table 1.1).
Table 1.1 Systematics of skull base craniotomies—supratentorial
Extends 1–3 cm lateral to the midline to approximately the sphenoid wing, but does not cross it. The proximal sylvian fissure is exposed intradurally, and targets within the sylvian fissure, the anterior skull base, and the temporal lobe can be reached. There are mini- and standard sizes. “Frontolateral” is the term that was historically first used for this approach.
Supraorbital
Usually a smaller variant of the frontolateral approach; typically by eyebrow (transciliary) incision, which limits the size of the craniotomy. Extends 2.5–3 cm lateral to the midline to approximately the sphenoid wing, but does not cross it. The proximal sylvian fissure is exposed intradurally, and targets in the sylvian fissure, skull base, and temporal lobe can be reached. Some surgeons use the term supraorbital as synonymous with frontolateral.
Pterional
Extends 1–3 cm lateral to the midline to the anterior temporal region: centered around the “H” of the sutures that form the pterion (see Chapter 2.2, Craniocerebral Topography). The sphenoid wing is always crossed. Typically defined as two-thirds of the craniotomy frontal and one-third temporal exposure of variable sizes (2:1). There is also a mini-pterional variant.
Frontotemporal
Usually a large exposure (1:1 to 2:1 frontal:temporal) centered above the sphenoid wing = sylvian fissure.
Anterior temporal
Sphenoid wing is crossed.
Temporobasal
The exact position varies according to the surgical target: does not cross the sphenoid wing. Typically used for subtemporal intradural approaches. There may be a more anterior and a more posterior variant.
Infratentorial skull base craniotomies are performed along the sigmoid sinus or the foramen magnum (see ▶Table 1.2 for further details).
Table 1.2 Systematics of skull base craniotomies—infratentorial
Location
Description
Suboccipital median infra-transverse-sinus
Midline craniotomy for supracerebellar median or paramedian approaches, e.g., for access to the pineal region or tentorial dural fistulas.
Suboccipital lateral infra-transverse-sinus
These are craniotomies based on the same principle as the midline craniotomies for an intradural approach along the subdural space parallel to the tentorium. Typically, they are used for supracerebellar lateral approaches to the midbrain or other regions. They are horizontally oriented compared to the retrosigmoid craniotomy, with more exposure along the transverse sinus and less along the sigmoid sinus. A modification is the suboccipital far-lateral infra-transverse-sinus craniotomy.
Retrosigmoid
Typically ranges from the transverse sinus to the base of the posterior fossa along the sigmoid sinus to gain access to the cerebellopontine angle. May vary in size and be centered more superiorly or inferiorly: vertically oriented.
Suboccipital median periforaminal craniotomy with opening of the foramen magnum
Typically bilateral, there is a mini-version, for example, in Chiari-decompression surgery.
Suboccipital lateral periforaminal craniotomy with opening of the foramen magnum
The lateral suboccipital craniotomy with opening of the foramen magnum is the basic craniotomy for the far lateral approach which can be regarded as a skull base extension of the basal suboccipital craniotomy.
1.2 Difference between Approach and Craniotomy
Andreas Raabe
Although often used synonymously, there is a difference between a craniotomy and an approach. Approach is the broader term and is often used for craniotomy and intradural preparation. In this book, we discuss only the steps of the craniotomy, i.e., to reach bony exposure. With a few exceptions, we stay outside the dura. We will therefore mostly use the term craniotomy instead of approach, and generally reserve the latter to describe the dissection and exposure after opening the dura mater. Craniotomy and approach may be different as in the examples given below. However, as already mentioned, the term “approach” often overlaps with craniotomy and intradural preparation.
Examples:
Supraorbital craniotomy and subfrontal approach.
Pterional craniotomy and transsylvian approach.
Temporobasal craniotomy and subtemporal approach.
Suboccipital lateral craniotomy and supracerebellar lateral approach.
Median suboccipital craniotomy and telovelar approach.
1.3 Craniotomies We Have Omitted from This Book and Why
Andreas Raabe, Bernhard Meyer, Peter Vajkoczy, and Karl Schaller
This book is intended primarily for young residents, to serve as a guide to understanding the various craniotomies. It describes the most often used craniotomies, but we decided not to include those that are used only very rarely. Therefore, it does not cover highly specialized skull base craniotomies and their extension, such as posterior transpetrosal, translabyrinthine, transcochlear, or combined approaches, nor is it our aim to provide a complete atlas of approaches and extensions.
We acknowledge that these specialized skull base approaches had their place in the heyday of skull base surgery. However, nowadays they are often replaced by a staged procedure or a combination of simpler craniotomies that provide a less invasive strategy with lower morbidity than a technically demanding and more invasive approach. Moreover, radiosurgery and endovascular treatment often complete a less invasive treatment for many patients.
We are also aware that the nomenclature for the craniotomies varies around the world and that experienced surgeons use their own tricks and modifications when performing craniotomies.
1.4 Positioning
1.4.1 Basic Rules
Andreas Raabe and Janine Abu-Isa
Time spent on careful positioning is time well spent. Mistakes in positioning may render any surgical plan, even if it is conceptually perfectly elaborated, impossible. Positioning is the first strategic step for the operation; it is the first digit of the code number to unlock the door to the target of brain surgery. Correct positioning can open the surgical field, achieve gravity retraction, reduce bleeding, and provide the most relaxing position for the surgeon.
Positioning should be highly standardized in each department to improve communication, to save time, and to achieve the goal of the surgery. Use of photographs, step-by-step instructions, and a checklist is recommended.
Fig. 1.3 Craniotomy-to-lesion trajectory. This is the first and most important factor determining the position of the head.Fig. 1.4 Combining positioning of the head and the body of the patient. Head rotation (a) combined with five body positions (b) allows the surgeon to gain access to every trajectory. Special positions are also possible (e.g., semisitting).Fig. 1.5 Positioning of the patient’s body. Typical positioning for different locations of craniotomies.Fig. 1.6 Position of the surgeon. There are two basic positions for the surgeon: the first is more upright, closer to the surgical field and short instruments, and the hands or fingers are supported (a). The second is a somewhat more oblique position with slightly longer instruments, and forearms or elbows supported (b). Both can achieve the goals of a relaxed surgeon, excellent stability, minimized trembling, and soft instrument movements with maximum haptic feedback about resistance of structures and tactile information. Normally, the positioning of the microscope and the patient’s head follows the position of the surgeon. Make yourself comfortable and then adjust the microscope and the patient, unless otherwise required by the planned surgical trajectory and the specific goals. (▶Fig. 1.6a is reproduced courtesy of Volker Seifert and ▶Fig. 1.6b courtesy of Robert F. Spetzler.)
1. Planned Surgical Trajectory
The surgical trajectory is the line between the craniotomy and the surgical target, i.e., the midline craniotomy and the tumor in the third ventricle, or the subtemporal craniotomy and the midbrain cavernoma, or the convexity craniotomy and the underlying meningioma (▶Fig. 1.3).
2. Position of the Surgeon
The same surgical trajectory can vary according to the preferred position of the surgeon (see below).
3. Gravity Retraction or Drainage
When gravity retraction is a major part of the surgery, it may become the dominant principle, for instance, in contralateral or midline approaches via the dependent hemisphere or when the semisitting position is preferred in some cases for posterior fossa surgery for pineal or cerebellopontine targets.
4. Measures for Avoiding Potential Position-Related Complications
Such measures include positioning to minimize intracranial pressure, venous congestion, and air embolism, as well as improved orientation if only standardized head positions are allowed.
Every head position can be achieved by combining head rotation (▶Fig. 1.4a) with patient’s body positioning (▶Fig. 1.4b):
Rotation of the head from 0° to 60° (this can be tested in the awake patient before surgery: in younger patients a rotation up to 90° may be possible, whereas in elderly patients head rotation may be limited to 30°), with the desired degree of head flexion and tilting.
Selection of one of five supplemental positions of the patient’s body to achieve the final desired head position. These five body positions should be standardized.
Except for special positions (e.g., semisitting), one of the following five basic positions are applied (▶Fig. 1.4b):
Supine: quick and easy.
Supine oblique (45°) upper body rotation with the pelvis and legs supine: still quick.
Lateral recumbent: more complicated, takes more time.
Lateral oblique or park bench (135°): more complicated, takes more time.
Prone: more complicated, takes more time and should be avoided if possible because of increased venous congestion.
For instance, a horizontal head position can be achieved by combining:
Fig. 1.7 Body position. View from the top (a) and the side (b). The supine position is the simplest position. The body and the legs lie straight and the right arm lies parallel to the body. The left arm lies at an angle on a separate armrest to allow insertion of arterial and venous lines and should be loosely fixed.Attention should be paid to making sure that the body is well cushioned and that the sheets beneath the patient have no wrinkles. In particular in long procedures, incorrect patient positioning may result in decubiti.Rotating the patient during surgery may give you a better angle of view. For rotating during surgery, prop the patient with additional side pads.Fig. 1.8 (a, b) Head position. The shoulders should reach the edge of the table. The head is elevated by approximately 5–10 cm in order to facilitate venous drainage
Checklist
Use side pads to prop the patient if you consider rotating the patient during surgery.
Cushion the patient well and avoid wrinkles in the sheets to prevent decubiti.
Elevate the head by approximately 5 to 10 cm to facilitate venous drainage.
1.4.3 Supine Lateral
Christian F. Freyschlag and Claudius Thomé
Supine lateral positioning (45°) of the patient’s upper body is used to enable access to the posterior fossa and the cerebellopontine angle, but may also be used for other approaches where the head is placed with the midline horizontally. In our experience, a sitting or semisitting position offers no advantage over lateral positioning. Although this has long been debated, we do not consider that gravitation-facilitated dissection outweighs disadvantages such as the complexity of positioning, need for exclusion of a persistent foramen ovale, and the risk of venous air embolism.1,2Furthermore, operating on a patient in the sitting or semisitting position is less ergonomic and more exhausting for most surgeons. Refer to ▶Fig. 1.9, ▶Fig. 1.10, ▶Fig. 1.11, and ▶Fig. 1.12.
Fig. 1.9 Equipment. The devices needed for supine lateral positioning are found in the basic neurosurgical OR: a three-pin Mayfield clamp, two wedge-shaped cushions, and a support for the pelvis that can be attached to the table.Fig. 1.10 Positioning of the patient. Supporting the pelvis helps maintain the position during rotation of the table.Fig. 1.11 Body positioning. It is possible to place the patient flat on the operating table.3However, the positioning is easier and rotation of the cervical spine and vascular structures is minimized if the shoulder is elevated by a wedge-shaped cushion. In older patients, this support is mandatory due to the patients’ limited neck movement.Fig. 1.12 Positioning. To obtain optimal conditions and exposure for a retrosigmoid approach, it is necessary to rotate the head (without creating excessive tension on the neck) away from the surgical site. The head is moved in three directions4: (1) contralateral rotation toward a position parallel to the floor, (2) bending of the vertex toward the floor (retroflexion), and (3) inclination of the head to open the cervical-suboccipital angle. This maneuver raises the mastoid process so that it becomes the highest point, while creating space between shoulder and head, which can be increased by retracting the upper shoulder caudally and securing it with adhesive tape.If the patient has limited neck mobility, the table can be easily rotated to compensate for this limitation. The use of a support prevents the patient from sliding.Finally, pressure points of the upper and lower extremities are meticulously padded to avoid any injury during surgery.
Checklist
Make sure the patient’s body is moved sufficiently toward the top end of the operating table (when operating on a patient in a supine lateral position, you tend to sit at 90° to the patient’s longitudinal axis).
Always support the patient’s position—you might want to rotate the table for better exposure.
Positioning needs three crucial head movements: rotation, inclination, and lateral flexion.
References
[1] Nozaki K. Selection of semisitting position in neurosurgery: essential or preference? World Neurosurg 2014;81(1):62–63[2] Feigl GC, Decker K, Wurms M, et al. Neurosurgical procedures in the semisitting position: evaluation of the risk of paradoxical venous air embolism in patients with a patent foramen ovale. World Neurosurg 2014;81(1):159–164[3] Wait SD, Gazzeri R, Galarza M, Teo C. Simple, effective, supine positioning for the retrosigmoid approach. Minim Invasive Neurosurg 2011;54(4):196–198[4] Elhammady MS, Telischi FF, Morcos JJ. Retrosigmoid approach: indications, techniques, and results. Otolaryngol Clin North Am 2012;45(2):375–397, ix
Fig. 1.13 View of the lateral position from above. Both arms lie secured and tension-free on separate armrests. The legs are slightly flexed and fixed. The position of the arms and legs, as well as the side pad just below the abdomen, increases the body’s stability and allows rotation of the patient to the surgeon’s right side if necessary during surgery.Fig. 1.14 Side view of the lateral position. The head lies aligned with the body’s axis and can be tilted and flexed as required. The ventral supporting side pad is positioned below the abdomen to avoid an increase of the abdominal pressure. The lower arm lies aligned with the top edge of the table at a 90° angle to the body. A cushion is placed between the legs to prevent pressure sores on the knees and ankles. Both arms and legs are secured by belts.Fig. 1.15 Lateral position from posterior. Two posteriorly supporting side pads, positioned just beneath the scapulae and over the buttocks, provide lateral stability and allow the patient to be rotated to the left if necessary during surgery. The patient’s back is aligned with the left edge of the table at an angle of 90°.Fig. 1.16 Relieving pressure from the shoulder by a supporting cushion below the axilla. It is important to prevent putting pressure on the lower shoulder. The arm and shoulder are both positioned exactly in line with the upper edge of the table, but still on the table. To relieve pressure on the shoulder, a special supporting cushion should be placed beneath the thorax and immediately below the lower arm. We use a pneumatic cushion (yellow arrows), which lifts the thorax slightly while relieving the pressure from the shoulder (blue double arrow).Fig. 1.17 Lateral position from above. The shoulder should reach the edge of the table but still entirely lie on it. Special care should be taken to cushion the shoulder and the hips well in order to avoid decubiti. The head can now be adjusted to the surgical position. Maximal flexion of the head should be limited to a chin–manubrium distance of two fingers.
Checklist
Use separate armrests for both arms; use a cushion between the legs.
Flexing the legs, correct positioning of the arms, and using a subabdominal side pad stabilize the patient ventrally.
Propping with pads on the patient’s buttock and scapulae stabilizes the patient dorsally.
Cushion the shoulder and the hips well to avoid decubiti.
1.4.5 Lateral Oblique or Park Bench
Daniel Hänggi
The lateral oblique (135°) or park bench position with the arm on the table is suitable for posterior fossa or occipital midline and lateral craniotomies as well as for subtemporal and temporal approaches. It allows rapid positioning of the patient and is less often associated with serious complications—including venous air embolism, hypotension, pneumocephalus, and laryngeal trauma—than the sitting position. In addition, in comparison to the prone position, it offers considerable advantages to the neurosurgeon in terms of gravity-assisted drainage and reduced cerebellar retraction.
Fig. 1.18 Body positioning and support. The patient is placed in a lateral recumbent position with the contralateral (lower) arm stretched out on top of the table. A support is mounted at the lumbar spine and opposite at the pelvis to make sure that the patient can be rotated up to 30° during surgery. Cushions or soft padding of the lower arm, below and between the knees, and below and between the ankles is important to avoid pressure marks and neural or vascular complications.Fig. 1.19 Ipsilateral shoulder and arm. The shoulders should be rotated about 45° away from the surgeon so that they are out of the line of access. An additional option is to tape the ipsilateral shoulder inferiorly to provide more room for the surgeon to work. Traction during taping should be applied carefully to avoid neural injury. The ipsilateral (upper arm) is positioned and fixed on a cushion positioned anteriorly at the level of the patient’s abdomen.Fig. 1.20 Head flexion. The head should be inclined as much as possible, but two fingers’ distance should be left between the chin and the jugulum.Fig. 1.21 Head rotation. Head rotation varies depending on the point of access required for posterior fossa midline or lateral craniotomies as well as for subtemporal and temporal approaches. The Mayfield pins must be placed in a plane perpendicular to the planned line of access, and the paired pins should be placed on the underside of the head. This is important for later positioning of the retraction system.Fig. 1.22 Body tilt. Finally, the operating table is turned into reverse Trendelenburg position to achieve maximal gravity-assisted drainage and to minimize venous congestion.Fig. 1.23 Final head position. The craniotomy site is at or near the highest point. In summary, this position with the shoulder rotated anteriorly and the head flexed and tilted toward the floor provides an excellent position for the surgeon with ample space for both hands.
Checklist
The patient is placed in a lateral recumbent position with the contralateral (lower) arm stretched out on top of the table.
The shoulders should be rotated about 45° away from the surgeon.
The head should be inclined as much as possible.
Head rotation depending on the point of access required for posterior fossa midline or lateral craniotomies.
Finally, the operating table is turned into reverse Trendelenburg position.
1.4.6 Park Bench
David Bervini and Janine Abu-Isa
The park bench position is suitable for approaches to the posterior fossa, including retrosigmoid and occipital midline, and for lateral infratentorial craniotomies in general. Unlike in the lateral recumbent position, the patient’s shoulder and lower arm hang over the edge of the table. This may allow greater contralateral head flexion and tilt, and hence a wider opening of the lateral craniocervical corridor. See ▶Fig. 1.24, ▶Fig. 1.25, ▶Fig. 1.26, ▶Fig. 1.27, ▶Fig. 1.28, ▶Fig. 1.29, and ▶Fig. 1.30.
Fig. 1.24 Attachment of the Mayfield clamp. Ideally, the base of the Mayfield clamp is attached to the operating table with a special connection piece, which moves the vertical main base of the clamp underneath the edge of the table and away from the down-hanging arm.Fig. 1.25 Positioning of the patient’s body. The intubated patient is turned into a lateral recumbent position to rest on his/her lateral chest. The axilla is positioned 5 cm beyond the edge of the table. The axilla and the upper arm are carefully padded.Fig. 1.26 Support of the lower body. The patient’s lower body is secured by a support at the level of the lumbosacral spine and pelvis (see also ▶Fig. 1.25).Fig. 1.27 Positioning of the patient’s head. The head is secured in the Mayfield pin holder, one pin anteriorly and two pins posteriorly. Alternatively, the Mayfield clamp can be placed vertically with two pins pointing down and one pin up. The head is rotated as far as needed, depending on the laterality of the surgical approach. After rotation, the head is flexed and slightly tilted downward, making sure to preserve a distance of two finger widths between the chin and the manubrium. This helps to prevent venous congestion and/or kinking of the tracheal tube. The craniotomy site should be at or near the highest point. Finally, the operating table is tilted in the reverse Trendelenburg position to minimize venous congestion. If needed, additional lateral tilting can be performed after verifying that the body is properly supported.Fig. 1.28 Positioning of the lower arm. The lower arm rests on a soft arm board or a sling inserted above the flexible attachment arm of the Mayfield clamp, between the operating table and the clamp itself. Special care should be taken to avoid compression of the ulnar nerve, the axilla, and elbow.Fig. 1.29 Fixation of the upper arm and shoulder. The superior shoulder falls at an angle of 30–45° anteriorly, away from the surgical approach and from the line of sight of the surgeon. If the surgeon needs more room, the shoulder can be taped and pulls inferiorly toward the feet. Traction during taping has to be applied carefully to avoid neural injury. The superior arm rests on a jelly board, slightly elevated to avoid venous congestion.Fig. 1.30 Padding the knee and ankles. Jelly cushions between and under the knees and the ankles are important to reduce the risk of pressure sores and neural compression.
Potential Complications of Park Bench Position
Potential complications of the park bench position include pressure palsies of the shoulder or arm, brachial plexus injuries, and stretch injuries. Excessive head flexion can cause jugular vein compression and venous outflow congestion.
Checklist
Lateral position, upper body tilted 15 to 30° in anti-Trendelenburg position to minimize venous pressure in the head.
Body secured at the level of the lumbosacral spine and pelvis with two supports.
Pay special attention to possible pressure points (elbow, axilla, knee, ankle).
Lower arm on arm board between the table and the Mayfield clamp; support the arm so that it does not hang from the shoulder.
Upper shoulder rotated by gravity about 30 to 45° away from the surgeon.
Further gentle downward draping of the shoulder may be needed; avoid excessive traction.
Head is rotated and tilted as far as needed.
Maximum head flexion limited to two finger widths between the chin and clavicle/sternum.
Final adjustment of the table position is made to suit the surgeon.
Further Reading
Rozet I, Vavilala MS. Risks and benefits of patient positioning during neurosurgical care. Anesthesiol Clin 2007;25(3):631–653
1.4.7 Prone/Concorde
Christian Fung
The prone position is used to access lesions in the occipital or superior parietal lobe and the posterior cervical spine. Putting the patient into the prone position increases abdominal pressure and decreases venous reflux. Special tables or frames (e.g., Wilson frame, Jackson table) enable free movement of the abdominal wall and increase venous backflow, therefore decreasing surgical bleeding due to venous congestion. Higher head positions improve venous reflux but increase the risk of air embolism.
The Concorde position is a modification of the prone position and enables access to the suboccipital region. It is a position often used for craniotomies of the posterior fossa for cerebellar approaches, approaches to the infratentorial supracerebellar region, and the foramen magnum. See ▶Fig. 1.31, ▶Fig. 1.32, ▶Fig. 1.33, and ▶Fig. 1.34.
Fig. 1.31 (a, b) Supine position. It is easier for the surgeon to place the Mayfield clamp when the patient is still in the supine position. Care has to be taken to place the pins of the Mayfield clamp anteriorly (about 2–3 cm above the helix of the auricular), to achieve secure head fixation after the patient is turned into the prone position. For a patient in the prone position, a horseshoe headrest can be used instead, depending on the surgical target and the preferences of the surgeon. All lines and tubes need to be fixed securely, since after turning and draping, access to the patient is very limited. Especially for the Concorde position, the patient needs to overhang the cranial end of the operating table. Therefore, the operating table should be put in the right position before the patient is turned (b).Fig. 1.32 Prone position. For a simple prone position, the Mayfield clamp can be fixed in the required position. This depends on the planned surgical target and the preference of the surgeon. Depending on the flexion of the head, also in prone position the operating table can be positioned in a slight reversed Trendelenburg position to increase venous reflux and align the operating field horizontally (e.g., cervical spine). If necessary, the shoulders can be taped caudally to provide better exposure of the surgical field. For patients in prone position, female breasts and nipples should be mobilized medially and male genitalia should hang freely. For a simple prone position, the patient requires less cranial overlap. Some surgeons use a head support system or specific cushions for positioning of the head instead of a Mayfield clamp or a horseshoe headrest. When such devices are used, the patient does not overhang the operating table.Fig. 1.33 Progress to Concorde position. When progressing to a Concorde position, further steps have to be taken before bringing the head into its final position. Note that the patient overhangs the cranial end of the operating table. This is necessary to enable sufficient flexion of the head in the Concorde position. For the Concorde position, the patient has to be placed in a reversed Trendelenburg position. The knees are properly cushioned and the lower legs are supported with padding in a slightly flexed position. Flexion of the knees and securing the patient with a strap around the buttocks or thighs will prevent the patient from slipping downward while in the reversed Trendelenburg position. This position can be achieved gently by alternately flexing the knees and increasing the reversed Trendelenburg position.Fig. 1.34 (a, b) Head position. The Mayfield clamp should be screwed to the base unit after the patient has been put into the right position. To achieve sufficient exposure of the posterior fossa, the head has to be maximally flexed with just two fingers of space between the chin and the manubrium. The head should be positioned at the level of the heart to achieve a sufficient venous reflux while not increasing the risk of air embolism. To achieve better exposure of the cervical spine and suboccipital region, it is advisable to tape the shoulders toward the feet. The surgeon has to check that the whole face, eyes and especially the chin, is free of any compression by either the Mayfield clamp or the table. The arms are padded and wrapped to the sides of the patient.
Potential Complications of Prone/Concorde Position
Potential complications of the prone/Concorde position include cervical strains with postoperative pain. Patients can develop skin necrosis due to compression and insufficient padding. Excessive downward taping of the shoulders can lead to brachial plexus injury. If the patient is in the prone or Concorde position, the risk of air embolism is lower than in a sitting position but may still occur. In addition, an obstruction of the cerebral lymphatic and venous outflow can cause swelling of the face, tongue, and neck, leading to macroglossia and airway obstruction. The same mechanism can also cause intraoperative brain swelling with increased intracranial pressure. Occasionally, blindness or corneal abrasion after a patient has been in the prone position has been described.
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