23 Supracerebellar Infratentorial Approach 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. • Pineal gland tumors. • Superior and inferior colliculi tumors and cavernous malformations. • Tumors of the third ventricle. • Midbrain and cerebellar peduncles tumors and cavernous malformations. • Sitting position ◦ Position: The patient is positioned in a sitting position with the head fixed with a Mayfield head holder. ◦ Head: The head is flexed as much as possible, to get the tentorium parallel to the floor. ◦ Body: The body must be elevated about 60° from the horizontal. Care should be taken not to flex the head too much in order not to compromise the venous backflow. ◦ Legs: The legs are flexed about 20-30° and the knees elevated. • Prone (Concorde) position ◦ Position: The patient is positioned in prone position with the head fixed with a Mayfield head holder. ◦ Head: Patient’s head is elevated at a higher level as compared to the heart to facilitate venous backflow. The head has to be flexed as much as possible to get the tentorium perpendicular to the floor. ◦ Body: The chest is elevated about 30° from the horizontal. ◦ Legs: The legs are flexed 15° by using pillows. • 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 field. 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 figure. • 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. • Myofascial level ◦ The myofascial level is incised according to the course of the skin incision. • Muscles (Figs. 23.3, 23.4, 23.5) ◦ Superficial muscle layer ◦ Deep muscle layer • 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. • Vertebral artery and surrounding venous plexus. • First cervical (C1) nerve rootlet.
23.1 Introduction
23.2 Indications
23.3 Patient Positioning (Fig. 23.1)
23.4 Skin Incision (Fig. 23.2)
23.4.1 Critical Structures
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)
The fascia covering the trapezius, splenius and semispinalis capitis is exposed.
The muscles of the superficial 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.
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.
23.5.1 Critical Structures
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