Neurosurgical procedures involve various patient positions such as supine, prone,
lateral, and sitting position. Prone positioning is routinely used in neurosurgical
practice to obtain access to posterior neuroanatomical structures like the posterior
fossa or suboccipital region.[1] Sphinx and Concorde positions are modifications of the conventional prone position
that are practiced less commonly in neurosurgery, probably because it requires neuroanesthesiologists
and neurosurgeons, who are familiar with these positions, and more manpower, skills,
and expertise to achieve the final positioning. Since these two positions are less
commonly encountered in neuroanesthesiology practice, reports about these two positions
in neuroanesthesiology literature are scarce. So, we have tried to review the indications,
positioning method in the operating room, advantages, and disadvantages of these modified
prone positions, with further modifications added to the classical methods described
earlier to further facilitate the surgical practice and perioperative care.
Sphinx Position
The “sphinx” or “sea-lion” position was first devised by Suzuki et al in 1983 for
total removal of a falcotentorial region meningioma by biparieto-occipital craniotomy,
wherein they positioned the patient prone with hyperextended neck with 20°elevation
of upper and lower halves of the body.[2] Since then, this position has undergone evolution and has been used in a multitude
of surgeries requiring exposure to vertex and posterior skull regions, in order to
achieve access to the anterior and posterior aspects of the cranial vault for reconstruction
in cases of craniosynostosis.[3] Nonetheless, the advent of new positioning techniques like the gel-filled collar
technique, which focused on anterior portion of the cranial vault, and the angled
horseshoe technique, which focused on the posterior portion, have decreased sphinx
positioning usage, except in cases where superior access to the anterior and posterior
aspects of the cranial vault is desired in a single setting.[4]
Indications[2]
[5]
[6]
Sphinx position is indicated in total or complex calvarial reconstruction, strip craniectomy,
and for lesions in the falcotentorial region.
Positioning[7]
The patient is positioned in a prone position with the head supported at the malar
area. In general, a horseshoe headrest is utilized. Reverse Trendelenburg position
(at 30 to 45 degrees) is employed to prevent cervical hyperextension. Anterior and
posterior parts of the skull can be accessed by tilting of the table. Arms are padded
and the torso is stabilized by applying harnesses or strapping at the thighs or gluteal
region (
[Fig. 1]
). Careful securing of the tracheal tube prevents inadvertent displacement during
the surgery. After the final positioning is achieved, the breath sounds must be checked
bilaterally. Periodic reassessment of the positioning is important, and it must be
done intermittently throughout the surgery.
Fig. 1 Sphinx position
Advantages[7]
This position provides maximum accessibility to the cranial vault, especially in patients
with scaphocephaly in terms of both anterior and posterior approaches. It bestows
neurosurgeons with adequate access to posterior cerebral structures and also facilitates
venous return resulting in a better surgical field. The tilting of table during the
procedure to further maximize the access is possible with minimal effect on the initial
positioning, which is important for neuroanesthesiologists. It also provides adequate
depth and wide visualization of the operative field in lesions pertaining to the falcotentorial
region with minimal retraction of brain parenchyma.[2]
Disadvantages[3]
[8]
This position entails a high-risk of venous air embolism due to a multitude of risk
factors, including a surgical site above the right atrium, a large head of neonates
and infants relative to adults, and increased blood loss in these surgeries, leading
to a decrease in central venous pressure. There is also a possibility of inadvertent
extubation during positioning and neck extension, which leads to a significant cephalad
movement of the endotracheal tube tip. Since this position involves hyperextension,
it is contraindicated in cases of cervical spine abnormality.[2]
Concorde Position
It was first described by Kobayashi et al for the infratentorial supracerebellar approach,
and since then, it is being used for operating in midline posterior fossa region for
pineal and cerebellar lesions.[9] Concorde position is still preferred over sitting position by some neurosurgeons
because of several complications associated with the latter like venous air embolism,
airway edema, central cord syndrome, macroglossia, spinal cord myelopathy, and postoperative
tension pneumocephalus.[10] Moreover, positioning of the patient is relatively easier in the Concorde position
than in the sitting position.[10] The proponents of sitting position cite the surgical advantages like superior visualization
of the intended area and improved preservation of lower cranial nerves.[11]
[12]
Indications[1]
[9]
This position is used for a surgical approach to the occipital transtentorial and
supracerebellar infratentorial regions of posterior fossa.
Positioning[1]
[9]
[13]
[14]
Concorde positioning is achieved by placing the patient in a reversed Trendelenburg
position and as far as possible towards the left edge of the table. The patients head
is fixed with a 15°right-side tilting. The arms are tucked and wrapped along the sides
of the patient with adequate cushioning, and the trunk is stabilized by putting chest
rolls underneath. Lower limbs are flexed at the knees with adequate padding. The patient
is secured with a strap around the thighs or buttocks to prevent slippage toward the
caudal end of the table. If the surgical site involves the cervical spine or suboccipital
area, strapping from the shoulders toward the feet is desirable. Final positioning
is achieved by alternately flexing the knees and progressively increasing the reversed
Trendelenburg position. The patient overhangs at the cranial end of the table to achieve
the required flexion of the head. The head is flexed maximally to achieve desired
exposure of the posterior fossa, ensuring at least two finger breadth space between
the chin and manubrium (
[Fig. 2]
). Positioning the head at the level of the heart minimizes the risk of venous air
embolism. The surgeon is usually seated on the patient’s left side if the lesion is
on the right side and on the right side for a left-sided lesion, which ensures natural
position to operate. In this position, there is a possibility for interference during
surgery by patient’s shoulder which is nearest to the surgeon during visualization
and instrumentation. This may not be completely avoided with the taping of shoulders
and pulling it away from the cephalad region, especially in a muscular, short necked,
or obese patients. Kyoshima et al proposed a modified arm down Concorde position to
obviate the above issue by allowing the patient’s arm to hang down by the surgeon’s
side.[14] Other techniques proposed to tackle the shoulder issue were prone oblique position
and asymmetrical fixation of the head by skew head rotation in the Sugita head holder.[13]
[15] Once the final position is achieved, it is essential to check the endotracheal tube
position by performing bilateral auscultation and ensure there is no compression of
pressure points on the face and eyes.
Fig. 2 Concorde position.
Advantages
Concorde positioning facilitates the descent of the cerebellum due to its weight,
which ensures minimal retraction on the cerebellum, adequate exposure of the desired
region, and a greater degree of surgical maneuverability for the surgeon.[9] Placing the patient to the maximum possible far edge of the table and tilting the
head toward right keeps the midline of the patient’s head axis straight in the surgical
field for comfortable and accurate surgical manipulation.[13]
Possible Complications/Disadvantages[10]
[13]
[16]
This position can cause various postoperative problems like neck pain, pressure sore/necrosis,
and brachial plexus injury secondary to excessive shoulder stretching. Besides this,
probable cerebral venous outflow/lymphatic drainage obstruction may lead to swelling
of the face, tongue, and neck and potential airway obstruction in the postoperative
phase. Moreover, various authors have reported difficulty in obtaining adequate neck
flexion, as the patient’s shoulders exceeded the operating table edge and pin site
misplacement due to part loading of the body weight on the three pin holders. Gulsen
et al proposed a technique to overcome this issue, wherein they first placed the three
pin holders in the supine position at an obtuse angle and then turned the patient
prone, finally achieving the Concorde position.[10] Rare but serious complications may include posterior circulation insufficiency (vertebrobasilar
dissection/thrombosis) due to compression/kinking of the vertebral arteries between
occipital condyles and C1 arch on account of hyperflexion. Excessive flexion may rarely
lead to bilateral carotid compression.
Conclusion
The positioning of the patient for accessing the posterior fossa midline structures
may require modified prone positions to maximize access to the desired surgical regions
with satisfactory exposure and minimal retraction on the brain. Technical expertise,
thorough planning, and adequate padding of dependent structures are of paramount importance
for modified prone positioning. Knowledge regarding these positions will enable the
neuroanesthesiologist to foresee and manage any inadvertent complications and take
better care of the patient perioperatively. Constant vigilance of the neuroanesthesiologist
and communication with the neurosurgeon is of vital importance throughout the procedure.
