枕后入路 CNS 01

手术入路
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Suboccipital Approach

Peter Nakaji, MD
Ben Hendricks, MD

Overview

The suboccipital approach provides access to:
    Posterior fossa
    Cerebellar hemisphere
    Pineal region
    Fourth ventricle
    Lower cranial nerves
    Posterior surface of the brainstem
    VA and PICA

通过枕下入路,可达以下位置:

Ø 后颅窝

Ø 小脑半球

Ø 松果体区

Ø 第四脑室

Ø 尾组颅神经

Ø 脑干后表面

Ø 椎动脉及小脑后下动脉

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Anatomy

Telovelar Junction

  • Telovelar junction is an attachment point of the tela to velum
  • Inferior medullary velum and tela choroidea form the lower part of the 4th ventricle
  • Vein of the cerebellomedullary fissure and branch of the PICA are positioned at the junction of the tela and velum

解剖
Ø 膜帆交界

n 膜帆交界是脉络膜与髓帆的连接处。

n 下髓帆与脉络组织形成第四脑室的下半部。

n 小脑延髓裂中的静脉及小脑后下动脉的分支位于膜帆交界处。

Surgical Technique

Position

Prone position
Operating table rotated 20°- 30° in a reverse-Trendelenburg position
Head should be above the heart level
Head is 45° flexed forward in Concorde position

体位
Ø 俯卧位。

Ø 手术床以反特伦德论伯格体位(垂头仰卧位)旋转20°-30°。

Ø 头部以“协和式飞机姿势”向前屈曲45°。

Skin Incision

Incision midline from inion to C2-3 (modify depending on location of pathology)
For a typical 4th ventricular tumor, a straight midline incision extending from just above the inion to C2 spinous process

头皮切口
Ø 沿中线自枕外粗隆至寰枢椎水平(可根据病变位置进行改良)。

Ø 对于典型的第四脑室肿瘤,可于中线做直切口,自枕外隆突至枢椎棘突。

Ø 牵开切缘头皮后,于中线处脂肪层内切开项韧带向下直至枢椎棘突。

Ø 剥离上项线处枕下肌肉,并向侧方牵开。

Ø 以电刀自寰椎后弓松解椎旁肌肉,而后于骨膜下向侧方游离。

Dissect Neck Muscles

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After retracting the skin, the ligamentum nuchae is incised within the midline fat plane, down to the C2 posterior spinous process
Suboccipital muscles are stripped off the superior nuchal line and retracted laterally
Paraspinal muscles are released from the C1 posterior arch using electrocautery followed by subperiostal dissection laterally

Craniotomy

Two burr holes are placed adjacent to midline
Posterior margin of the foramen magnum serves as the inferior border of the craniotomy or craniectomy
The bone flap is elevated from burr hole side because the atlantooccipital membrane is attached the edge of the foramen magnum

Ø 中线旁钻两孔。

Ø 将枕骨大孔后缘做为开颅或骨窗的下界。

Ø 因寰枕筋膜附于枕骨大孔边缘,应于颅骨钻孔处将骨瓣抬起。

Dural Incision

  • Dural incision is performed in a reverse ‘Y’ fashion starting at the level of the foramen magnum and ascending up the superolateral margins of the bone flap

    Ø 自枕骨大孔水平向上至骨瓣的上外侧边缘,做”Y”形硬膜切口。
    Ø 打开枕大池。
    Ø 将硬膜瓣游离缘悬吊后,即可显露枕大池(小脑延髓池)。

Opening the Cisterna Magna

  • After tacking up the free edge of the dural flap, the cisterna magna (cerebellomedullary cistern) is exposed

    Ø 打开枕大池。

Ø 将硬膜瓣游离缘悬吊后,即可显露枕大池(小脑延髓池)。

Intradural Dissection

Opening the cisterna magna and releasing CSF provides excellent relaxation of the cerebellum
If more caudal exposure is required, the C1 posterior arch is removed
Exposure of the C1 nerve rootlet, CN XI spinal root, cerebellar tonsils, VA, posterior medulla, and spinal cord


Ø 打开枕大池,释放脑脊液,使小脑充分松弛。

Ø 如果需要更多地偏向尾侧显露,可以切除寰椎后弓。

Ø 显露颈1神经束,副神经脊髓根,小脑扁桃体,椎动脉,延髓后方及脊髓。

Complication Avoidance

Adequate flexion is crucial to sufficient exposure
Using gel rolls for the chest, so the abdomen can hang, will lower venous pressure and bleeding
Keep rigorously to the midline during the dissection of cervical musculature
Injury to the occipital sinus, especially in children, may cause copious venous bleeding
Inadequate CSF release from the cistern may generate cerebellar swelling
Splitting the cerebellar vermis can be associated with akinetic mutism on rare occasion
Major bleeding and posterior fossa vein or venous sinus thrombosis may cause postoperative hydrocephalus
Inadequate dural closure or loose fascial closure may generate postoperative CSF leakage and pseudomeningocele (in case of craniectomy), respectively
Placement of a surgical site drain may increase the risk for postoperative CSF leakage

避免并发症
Ø 脑组织的充分松弛对有效的显露至关重要。

Ø 胸部下垫凝胶卷,使腹部悬空,可降低静脉压力及减少出血。

Ø 严格循中线分离颈部肌肉组织。

Ø 枕窦损伤时特别是于儿童,将导致大量静脉性出血。

Ø 若脑池中脑脊液释放不充分,将导致小脑的肿胀。

Ø 小脑蚓部的切开偶尔可能与无动性缄默相关。

Ø 大量失血、后颅窝静脉或静脉窦血栓将导致术后脑积水。

Ø 硬膜闭合不充分或以筋膜缝合疏松,将分别导致术后脑脊液漏及假性脑膜膨出(在颅骨减压时)。

Ø 术区放置引流可能会增加术后脑脊液漏的风险。

Operative Pearls

Inappropriate positioning may generate cerebellar swelling during the dural opening, which can be combatted with hyperventilation and intravenous mannitol
An occipital burr hole and ventriculostomy for supratentorial cerebrospinal fluid drainage may relax the surgical field in cases where there is fourth ventricular obstruction
In the postoperative period, the patient should undergo close ICU observation with head elevated to minimize the venous bleeding and pseudomeningocele formation

手术精要
Ø 不恰当的体位可能在硬膜开放时造成小脑的肿胀,可予过度换气及静脉输注甘露醇进行调整。

Ø 当第四脑室梗阻时,枕部钻孔并行脑室穿刺引流幕上脑脊液可降低术区脑组织张力。

Ø 病人术后应用ICU密切观察,头部抬高以降低静脉性出血及假性脑膜膨出的发生。

Discussion

The suboccipital craniotomy provides excellent midline access to the cerebellar tonsils, fourth ventricle, and dorsal brainstem
Careful anatomical orientation with bony landmarks such as inion, C2 spinous process and foramen magnum facilitate an accurate surgical approach
Meticulous hemostasis decreases the risk for postoperative hydrocephalus
Dural and fascial closure should be performed meticulously

讨论
Ø 枕下开颅为抵小脑扁桃体,第四脑室及脑干背侧提供了极好的经中线通道。

Ø 借助枕外隆突、枢椎棘突及枕骨大孔等骨性标志进行仔细的解剖定位,利于达成一个正确的手术入路。

Ø 精确止血将降低术后脑积水发生的风险。

Ø 应该认真完成硬膜及筋膜的闭合。

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