23 Supracerebellar Infratentorial Approach

23.1 Introduction

The supracerebellar infratentorial approach is suitable for the bilateral exposure of the pineal region as well as the posterior surface of the midbrain, and it allows access to the posterior part of the third ventricle.

The surgical route corresponds to the anatomical corridor seated between the tentorial surface of both cerebellar hemispheres and the inferior surface of the tentorial fold.

The approach can be varied according to the pathology, in a midline and a paramedian variant. The complex venous vascular anatomy of the pineal region must be taken into consideration in the surgical planning.

The approach is indicated for lesions of the pineal gland, tectal part of the mesencephalon as well as of the posterior aspect of the third ventricle.

○Head: The head is fexed as much as possible, to get the tentorium parallel to the foor.

○Body: The body must be elevated about 60° from the horizontal. Care should be taken not to fex the head too much in order not to compromise the venous backfow.

○Legs: The legs are fexed about 20-30° and the knees elevated.

•Prone (Concorde) position

○Position: The patient is positioned in prone position with the head fxed with a Mayfeld head holder.

○Head: Patient’s head is elevated at a higher level as compared to the heart to facilitate venous backfow. The head has to be fexed as much as possible to get the tentorium perpendicular to the foor.

○Body: The chest is elevated about 30° from the horizontal.

○Legs: The legs are fexed 15° by using pillows.

23.2 Indications

•Pineal gland tumors.

•Superior and inferior colliculi tumors and cavernous malformations.

•Tumors of the third ventricle.

•Midbrain and cerebellar peduncles tumors and cavernous malformations.

23.3 Patient Positioning (Fig. 23.1)

•Sitting position

○Position: The patient is positioned in a sitting position with the head fxed with a Mayfeld head holder.

23.4 Skin Incision (Fig. 23.2)

•Linear incision (midline approach)

○Starting point: The incision starts 2 cm above the inion on the midline.

○Course: It runs inferiorly on the midline toward the cervical spinous processes.

○Ending point: It ends at the spinous process of C3 on the posterior cervical midline.

•Linear incision (paramedian approach)

○Starting point: The incision starts 4 cm above the ideal line connecting the inion and the posterior root of zygoma.

○Course: The incision line runs inferiorly in a vertical direction, perpendicular to the course of the transverse sinus.

○Ending point: It ends 8 cm below the ideal line connecting the inion and the posterior root of zygoma.

Fig. 23.1 Patient positioning. Prone (Concorde) position and sitting position. The sitting position is generally preferred for the supracerebellar approach because it facilitates cerebellar retraction, reduces venous bleeding and pooling in the operative ld. The main disadvantage is related to

the risk of air embolism. Alternatively, the supracerebellar approach can be performed in “Concorde” position, as shown by the

.

23.4.1 Critical Structures

•Greater occipital nerve.

•Occipital artery.

Fig. 23.2 Skin incision. Midline and paramedian approach. Midline approach (black dotted line). Linear incision starts 2 cm above the external occipital protuberance and runs downward to C3 spinous process.

Paramedian approach (red dotted line). Linear incision runs perpendicular to the line (blue line) connecting the inion and the posterior root of the zygoma.

Abbreviations: A = asterion; C3 SP = C3 spinous process; IN = inion.

23.5 Soft Tissues Dissection (Fig. 23.3)

•Myofascial level

○The myofascial level is incised according to the course of the skin incision.

•Muscles (Figs. 23.3, 23.4, 23.5)

○Superfcial muscle layer

The fascia covering the trapezius, splenius and semispinalis capitis is exposed.

The muscles of the superfcial layers are divided at the tendinous midline, or ‘linea alba’, reaching the periosteal layer.

In the paramedian approach, all suboccipital muscles are divided following the course of the skin incision.

○Deep muscle layer

The rectus capitis posterior minor and major, the inferior oblique as well as the semispinalis cervicis are exposed at the level of the atlas (C1) and axis (C2).

The vertebral artery and its venous plexus are not necessarily exposed.

•Bone exposure

○Midline approach: A subperiosteal dissection is carried out. Soft tissues are bilaterally detached from the posterior arch of C1, as well as from the occipital bone, starting from the midline toward the asterion. The foramen magnum might be exposed.

○Paramedian approach: The subperiosteal dissection is unilaterally performed from the inion to the asterion. The foramen magnum region is not necessarily exposed.

23.5.1 Critical Structures

•Vertebral artery and surrounding venous plexus.

•First cervical (C1) nerve rootlet.

Fig. 23.3 Muscles dissection. After dissecting t al fascia, the underlying

al suboccipital muscles are exposed. Abbreviations: IN = inion; OB = occipital bone; SEMC = semispinalis capitis; SPLC = splenius capitis; TRA = trapezius.

23.6 Craniotomy/Craniectomy (Fig. 23.6)

23.6.1 Bilateral Suboccipital Craniotomy, Landmarks

•Burr holes

○I: The frst burr hole is made on the midline, just above the inion.

Fig. 23.4 Muscles dissection. The trapezius and splenius capitis are detached and transposed laterally exposing the semispinalis capitis, which is divided on the midline from the linea alba.

Abbreviations: IN = inion; LA = linea alba; OB = occipital bone; SEMC = semispinalis capitis; SPLC = splenius capitis; TRA = trapezius.

Fig. 23.5 Muscles dissection. The suboccipital bone is largely exposed above the deep muscular layer, exposing the rectus capitis posterior minor and major. The inferior oblique as well as the semispinalis cervicis are exposed at the level of C1 and C2. Abbreviations: C2 = C2 spinous process;

IN = inion; IO = inferior oblique; OB = occipital bone; RPm = rectus capitis posterior minor; RPM = rectus capitis posterior major; SMC = semispinalis cervicis; SNL = superior nuchal line.

○II and III: Following burr holes have to be made on both sides, 4 cm laterally from the inion.

•Craniotomy landmarks

○Laterally: The lateral limits correspond to the asterion.

○Superiorly: The superior margin of the craniotomy is located 2 cm above the superior nuchal line.

○Inferiorly: The inferior limit of the craniotomy is the foramen magnum.

23.6.2 Paramedian Suboccipital

Craniotomy, Landmarks

•Burr holes

○I: The frst burr hole is placed 2 cm above the superior nuchal line, at the midpoint of the line connecting the asterion to the inion.

○II: The second burr hole is made just lateral to the external occipital crest, below the inion.

○III: The third burr hole is placed at the asterion.

•Craniotomy landmarks

○Medially: The medial margin of the craniotomy corresponds to the external occipital crest (inion).

○Laterally: The craniotomy extends laterally toward the asterion.

○Superiorly: The superior bone cut is made 2 cm above the superior nuchal line.

○Inferiorly: The inferior limit of the craniotomy is the foramen magnum.

23.6.3 Critical Structures

•Vertebral artery.

•Torcula.

•Transverse-sigmoid sinus junction.

23.7 Dural Opening (Figs. 23.7, 23.8)

23.7.1 Midline Approach

•Dura is opened in a U-shaped fashion. The fap is based on both the transverse sinuses and the torcula and refected antero-superiorly.

•Occipital sinus has to be ligated in order to avoid venous bleeding.

23.7.2 Paramedian Approach

•Dura is opened in a U-shaped fashion. The fap is based on the ipsilateral transverse sinus and refected anterosuperiorly.

23.7.3 Critical Structures

•Sigmoid and transverse venous sinuses junction.

•Occipital sinus.

•Torcula.

23.8 Intradural Exposure (Figs. 23.9–23.15)

•Parenchymal structures: Cerebellar suboccipital and tentorial surfaces, corpora quadrigemina, pineal gland, pulvinar thalami, posterolateral mesencephalic tegmental aspect and the splenium of the corpus callosum.

Fig. 23.7 Dural opening. Midline exposure showing the U-shaped durotomy. Abbreviations: OS = occipital sinus;

SSS = superior sagittal sinus; TO = torcular; TS = transverse sinus.

Fig. 23.8 Dural opening. Intradural view. Abbreviations: CH = cerebellar hemisphere; D = dura; HEV = hemispheric vein; OS = occipital sinus.

•Arachnoidal layer: Quadrigeminal and ambient cisterns.

•Cranial nerves: Fourth cranial nerve.

•Arteries: Posterior inferior cerebellar artery (PICA), superior cerebellar artery (SCA), and posterior cerebral artery (PCA).

•Veins: Superior hemispheric and vermian veins, internal occipital veins, basal veins of Rosenthal, vein of the cerebel- lo-mesencephalic fssure or precentral cerebellar veins, and great Galen veins.

References

1.Kawashima M, Rhoton AL Jr, Matsushima T. Comparison of posterior approaches to the posterior incisural space: microsurgical anatomy and proposal of a new method, the occipital bi-transtentorial/falcine approach. Neurosurgery

2002;51(5):1208–1220, discussion 1220–1221

2.Rey-Dios R, Cohen-Gadol AA. A surgical technique to expand the operative corridor for supracerebellar infraten-

Fig. 23.15 Supracerebellar infratentorial route to the pineal region.

torial approaches: technical note. Acta Neurochir (Wien)

2013;155(10):1895–1900

3.Sekhar LN, Goel A. Combined supratentorial and infratentorial approach to large pineal-region meningioma. Surg

Neurol 1992;37(3):197–201

4.Türe U, Harput MV, Kaya AH, et al. The paramedian supracere- bellar-transtentorial approach to the entire length of the mediobasal temporal region: an anatomical and clinical study.

Laboratory investigation. J Neurosurg 2012; 116(4):773–791