24 Endoscopic Approach to Pineal Region

24.1 Introduction

The endoscope-controlled supracerebellar infratentorial approach for pineal region pathology is a potentially powerful approach that can minimize surgical approach-related morbidity.

Patients are positioned in a sitting position, with the secondary surgeon holding the endoscope while the primary surgeon, who maintains bimanual dexterity, visualizes the screen. This is an ergonomic position that can facilitate surgery.

A small vertical incision is made in the scalp with a small craniotomy, which is large enough to accommodate the endoscope and microsurgical instruments.

24.2 Indications

•Pineal tumors of any size or pathology, though germinoma could be considered for biopsy and radiation instead.

•Large, symptomatic pineal cysts.

•Tectal or anterosuperior vermian tumors.

•Tentorial incisura tumors.

•Many supratentorial tumors can also be approached trans-tentorially.

•Pineal tumors that are predominantly in the anterior or mid-part of the third ventricle or the aqueduct should not be approached in this way.

24.3 Patient Positioning (Fig. 24.1)

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

•Body: Body lies sitting 45° from the horizontal.

•Head: The head is fexed an additional 45°, rotated 10° to the contralateral side, not tilted.

•Shoulder position: Shoulders are adequately padded in the sitting slouch position.

•Anti-decubitus device: Backrest should be at the level of the mid-scapula or lower.

•The inion should be facing straight back toward the surgeon, who is standing behind.

•Image guidance is very helpful; the midline tentorium should be as close to level with the foor as possible.

24.4 Skin Incision (Fig. 24.2)

•Linear vertical unilateral incision

○Starting point: Incision starts 1 cm above the line between the inion and the top of the zygoma, 25 mm from midline.

○Course: Incision line runs inferiorly from this point for 2.5 cm.

○Ending point: It ends 3.5 mm from the top of the incision, ending in the muscles.

Fig. 24.2 Alternative skin incisions are outlined; paramedian incision and extreme lateral excision. (Used with permission from Barrow Neurological Institute, Phoenix, AZ.)

Abbreviations: A = asterion; IL = incision line; IN = inion; M = midline; TS = transverse sinus.

24.4.1 Critical Structures

•Occipital artery

•Greater and lesser occipital nerves

24.5 Soft Tissues Dissection (Fig. 24.3)

•Myofascial level

○Incised according to skin incision.

•Muscles

○Layers of the splenius capitis muscle and semispinalis capitis muscle are visualized at the inferior aspect of the incision.

○These are incised along the length of the incision and retracted medially and laterally.

•Bone exposure

○Subperiosteal dissection of occipital bone overlying the lower part of the transverse sinus and the upper cerebellum, lateral to the torcular, is performed.

24.5.1 Critical Structures

• Transverse sinus.

Fig. 24.3 Soft tissue dissection.

Abbreviations: EOC = external occipital crest; OB = occipital bone; TRA = trapezius.

Fig. 24.4 Craniotomy is performed 1.5 cm lateral to inion, at the inferior edge of transverse sinus.

Abbreviations: DM = dura mater; EOC = external occipital crest; OB = occipital bone; TRA = trapezius.

24.6 Craniotomy/Craniectomy (Fig. 24.4)

24.6.1 Paramedian suboccipital craniotomy landmarks

•Burr holes

○Option 1: A single oval burr hole is made at the level of the inferior edge of the transverse sinus.

○Option 2: One medial upper corner burr hole is placed over bottom edge of transverse sinus and one 2.5 cm lateral to this at the same height.

•Craniotomy landmarks

○Medially: 1.5 cm lateral to inion.

○Laterally: 2.5 cm lateral to medial side.

○Superiorly: Inferior edge of transverse sinus, at level of the line from the inion to the upper edge of the zygoma.

○Inferiorly: 1.5 to 2.0 cm below top edge, over the cerebellar hemisphere.

24.6.2 Variants

•Extreme lateral supracerebellar infratentorial (SCIT) approach (Fig. 24.5)

○Exposure of the transverse sinus-sigmoid sinus junction.

○Longer reach for lesions located in the pineal region.

24.6.3 Critical Structures

•Transverse sinus.

•Sigmoid sinus.

24.7 Dural Opening (Fig. 24.6)

•Trap-door incision is ideal.

•Edges are based on dural venous sinuses.

•Flaps are refected toward the sinus, stich is placed close to the sinus and tied to the bone itself to maximize visualization.

24.7.1 Critical Structures

•Sigmoid and transverse venous sinuses.

•Bridging veins from the cerebellum to dura.

Fig. 24.5 Paramedian (purple arrow) and extreme lateral (green arrow) SCIT approaches to the pineal region. (Used with permission from Barrow Neurological Institute, Phoenix, AZ.) Abbreviations: CH = cerebellar hemisphere; ELA = extreme lateral approach; JV = jugular vein; PMA = paramedian approach; SS = sigmoid sinus; SSS = superior sagittal sinus; TS = transverse sinus.

24.8 Intradural Exposure

(Figs. 24.6–24.8) (See Chapter 23)

•Parenchymal structures: Superior aspect of the cerebellar cortex, vermis, pineal gland, pulvinar, superior and inferior colliculi.

•Arachnoidal layer: Cerebellopontine cistern.

•Cranial nerves: Fourth cranial nerve.

•Arteries: Superior cerebellar artery, posterior cerebral artery.

•Veins: Bridging cerebellar veins, great vein of Galen, basal vein of Rosenthal, internal cerebral vein.

24.9 Pearls

•Bridging veins are more commonly encountered with the midline approach, and we typically avoid this approach and minimize sacrifce of bridging veins.

Fig. 24.6 Dural opening, shown here in a trapdoor fashion with the pedicle at the transverse sinus.

Abbreviations: CH = cerebellar hemisphere; D = dura; OS = occipital squama.

Fig. 24.7 After dural opening, the superior surface of cerebellar hemisphere comes into view. (Used with permission from Barrow Neurological Institute, Phoenix, AZ.)

Abbreviations: CH = cerebellar hemisphere; CU = culmen; R = retractor; TEN = tentorium.

Fig. 24.8 Arachnoid dissection of the cisterna magna relaxes the cerebellum and allows for visualization of pineal region structures. The gland is covered by the venous structures.

Abbreviations: BVR = basal vein of Rosenthal; CH = cerebellar hemisphere; GVG = great vein of Galen; ICV = internal cerebral vein; IOV = internal occipital vein; OL = occipital lobule; PCV = precentral cerebellar vein; VB = vermian branches of the superior cerebellar artery; TEN = tentorium.

•The endoscope should help follow the instruments in and out of the intracranial cavity. This requires dynamic visualization, similar to endoscopic pituitary surgery.

•Three-dimensional endoscopes are typically much easier to use for the microsurgical surgeon, and helps to ease the transition to the endoscopic supracerebellar infratentorial approach.

References

1.Ammirati M, Bernardo A, Musumeci A, Bricolo A. Comparison of diferent infratentorial-supracerebellar approaches to the posterior and middle incisural space: a cadaveric study. J Neurosurg 2002;97(4):922–928

2.Cardia A, Caroli M, Pluderi M, et al. Endoscope-assisted infra- tentorial-supracerebellar approach to the third ventricle: an anatomical study. J Neurosurg 2006;104(6, Suppl):409–414

3.Zaidi HA, Elhadi AM, Lei T, Preul MC, Little AS, Nakaji P. Minimally invasive endoscopic supracerebellar-infratentorial surgery of the pineal region: anatomical comparison of four variant approaches. World Neurosurg 2015;84(2):257–266