改良乙状窦后入路

neurobistoury 2019-05-05

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改良乙状窦后入路

The modified retrosigmoid approach: a how I do it

手术相关解剖学

Relevant surgical anatomy

手术治疗后颅窝及脑干血管或组织病变极具挑战性。传统乙状窦后入路显露有限，而根治性颅底入路（经岩骨入路、远外侧入路）技术难度大，并发症发生率高。改良乙状窦后入路在于改良的乙状窦后开颅和有限的乙状窦暴露。

The surgical management of posterior fossa and brainstem vascular or tissular lesions is challenging. The traditional retrosigmoid (RS) approach provides limited exposure, while radical skull base approaches (transpetrosal approaches, farlateral approach) are demanding and associated with a high morbidity rate. The modified retrosigmoid (MRS) approach consists in a modified RS craniotomy and a limited exposure of the sigmoid sinus (SS).

改良乙状窦后入路可以自延髓腹外侧面（齿状韧带水平）至双侧椎动脉汇合成基底动脉处显露同侧椎动脉第四段（硬膜内段），能够自小脑后下动脉起点至后组颅神经根部显露小脑后下动脉第一段和第二段（延髓前段和延髓外段）。颅神经的显露起自三叉神经直至舌下神经（图1a）。

The MRS exposes the fourth segment of the ipsilateral vertebral artery (VA) (intra-dural segment), from the lower lateral surface of the medulla, at the level of the dentate ligament, to the vertebrobasilar junction where it joins the contralateral VA. The MRS gives access to the first and second segments (anterior and lateral medullary segments) of the PICA, from its origin to the rootlets of the lower CNs. The CNs are exposed from the trigeminal to the hypoglossal nerve (Fig. 1a).

就改良乙状窦后入路而言，Lawton所描述的手术解剖三角是自然而然的工作窗口，大多数椎动脉远端、椎基底动脉移行部及小脑后下动脉近端的血管病变都可以经其显露。迷走神经副神经三角被精确地定义为外侧的迷走神经、副神经与内侧的延髓之间的区域，进而又借助舌下神经被细分为两个更小的三角：舌下神经上三角（迷走神经、副神经与舌下神经之间的区域）和舌下神经下三角（副神经、舌下神经与延髓之间的区域）（图1b）。

Most of the distal VA, vertebrobasilar junction, and proximal PICA vascular lesions are accessed through surgical anatomical triangles as described by Lawton, which are the natural working window for the MRS. The vagoaccessory triangle is defined superiorly by the vagus nerve, the accessory nerve laterally, and the medulla medially. It is sub-divided into two smaller triangles by the hypoglossal nerve: the supra- (the area between CNs X, XI, and XII) and infra- (between CNs XI, XII and the medulla) hypoglossal triangles (Fig. 1b).

技术说明

Description of the technique

患者体位和准备：（图2a）

Patient positioning and preparation: (Fig. 2a)

患者取健侧卧位，胸部下方垫枕。头部置于马蹄形头枕中，呈中立位，略屈曲，使患侧乳突尖位于手术野的最高点。患侧肩部肩带固定，以增加工作空间。术者站立于其头部和耳廓后方。

The patient is installed in a lateral position toward the opposite side; a bolster is placed under the thorax. The head is placed in a horseshoe headrest, in a neutral position and slightly flexed such as that the ipsilateral mastoid tip is the highest point in the operative field. The ipsilateral shoulder is taped down to increase the working space. The surgeon stands behind the head and the pinna.

软组织游离：（图2b）

Soft tissues dissection: (Fig. 2b)

行皮肤直切口，起自耳廓上1cm，止于乳突尖下缘水平，长约8cm。皮肤切开直达帽状腱膜及其下的颅骨骨膜，使用单极电刀自颅骨上游离肌肉和深筋膜，并将其牵向前方。自乳突上游离胸锁乳突肌，并将其牵向下方。彻底显露前部的乳突外表面，以及自上方的星点至下方的二腹肌沟和枕骨大孔之间的枕骨鳞部。

A straight 8-cm skin incision is carried out, starting 1 cm above the pinna and ending up at the level of the mastoid tip inferiorly. This skin incision spans the galea and the underlying pericranium. The muscles and deep fascia are elevated from the bone with a monopolar section and retracted anteriorly. The sternocleidomastoid muscle is detached from the mastoid and mobilized downward. The outer surface of the mastoid process anteriorly and the squamous part of the occipital bone, from the asterion superiorly to the digastric groove and foramen magnum inferiorly, are fully exposed.

开颅术——骨瓣：（图2d）

Craniotomy—bone flap: (Fig. 2d)

星点上下钻孔，于骨孔处显露乙状窦硬膜。自乙状窦边缘开始朝向中央部，沿枕下颅骨内板分离硬膜，以避免撕裂乙状窦。切除骨瓣，大小约3.5-4cm。肌皮瓣外侧部呈直线行，中央部呈弧形。

One burr hole is performed under and below the asterion. This burr hole exposes the dura of the SS. The dura is detached from the inner table of the suboccipital bone, starting from the sinus side toward the center in order to avoid tearing of the sinus. A 3.5- to 4-cm bone flap is cut. The shape of the flap is straight laterally and curved medially.

然后，术者使用6mm切割钻头，在大量冲水的前提下，逐渐磨除遮挡在乙状窦后1/3的乳突气房，长度达3cm以上。像握笔一样握住钻头，并且与需磨除的结构呈切线位。强烈推荐在乙状窦上方保留薄层致密骨质，以避免可能发生的乙状窦撕裂。随后，使用锋利的解剖器将其移除。

The surgeon is then equipped with a 6-mm cutting burr and gradually shaves the mastoid air cells covering the posterior third over a 3-cm length of the SS, under copious irrigation. The drill is held like a pen and oriented tangentially to the structures that must be shaved. It is strongly recommended to leave a thin shell of compact bone over the sinuses to avoid any tear. This shell will be subsequently elevated with a sharp dissector.

硬膜内操作

Intra-dural step

沿乙状窦后缘“C”字形切开硬膜。临近乙状窦悬吊硬膜，并借助夹钳将硬膜瓣翻向前方，以实现手术野的动态调整。小脑表面覆盖棉片，开放小脑延髓池释放脑脊液，在满足充分显露的前提下最大限度地降低回缩程度。手术野聚焦于后组颅神经。

A C-shaped dural opening based on the posterior edge of the SS is performed. Dural tenting sutures are placed adjacent to the SS, and the dural flap is reflected anteriorly using a clamp to provide dynamic improvement of the surgical window. Cottonoid paddles are placed over the surface of the cerebellum, and the cerebellomedullary cistern is opened to obtain CSF depletion, minimizing the amount of retraction necessary for adequate exposure. The operative window is focused on the lower CNs.

关颅

Closure

使用5/0 Prolen线缝合硬膜切口进行关颅。该处硬膜多难以水密缝合，因此常用的方法是使用脂肪充填缺损和乳突腔，但是这一步骤需要另行皮肤切口。我们通常于枕下取一条肌肉，以纤维蛋白胶粘合固定。乳突气房使用骨蜡封闭，以防脑脊液漏。骨瓣回置，并使用钛条固定，骨缺损使用骨粉覆盖。

The closure is done by reapproaching the dura using a 5/0 prolen thread. At this point, the dura cannot be easily closed watertightly. Thus, the usual way is to plug the defect and the mastoid cavity using fat. This step requires an additional skin incision. We routinely use stripes of sub-occipital muscle with fibrin glue. The mastoid air cells are waxed to prevent CSF leak. The bone flap is repositioned and fixed with titanium plates. The bony defects are covered by application of bone powder.

病例示例：（参见视频和图3, 4和5）

Illustrative case: (see video and Figs. 3, 4, and 5)

适应症：

Indications:

椎动脉远端、椎基底动脉移行部和小脑后下动脉近端（第1段和第2段）的动脉瘤

– Distal VA, vertebrobasilar junction, and proximal PICA aneurysms (1st and 2nd segments)

桥脑小脑角起源于后组颅神经的脑外病变（图5）

– Extra-axial CPA lesions of the lower CNs (Fig. 5)

表面暴露于蛛网膜下腔的，发自脑干、小脑脚和小脑半球的脑内病变

– Intra-axial lesions of the brainstem, cerebellar peduncle, and cerebellar hemisphere that present a surface to the subarachnoid space

局限性

Limitations

小脑后下动脉远端（第3段至第5段）的动脉瘤

– Distal PICA aneurysms (3rd to 5th segments)

病变上方或内侧临近三叉神经的，颈静脉孔区颅内外沟通肿瘤

– Lesions located upper or medially to CN V. Jugular foramen tumors extending intra- and extracranially

硬膜切除的潜力受限（难以实现Simpson I级切除的宽基底脑膜瘤）

– Limited potential of dura resection (difficult to achieve a Simpson I resection of broad-based meningiomas)

如何避免并发症

How to avoid complications

术者仔细阅读MRA，评估乙状窦和颈静脉球的走行，排除潜在性健侧静脉窦阻塞（禁忌症）。经岩骨CT骨窗相证实乳突气房的气化程度。

– The surgeon carefully checks the angioMR to assess the course of the SS and jugular bulb and to exclude a potential contralateral sinus occlusion (contraindication). The CT bone window of the petrous bone confirms the amount of pneumatisation of the mastoid air cells.

处理静脉窦可能导致术中静脉充血，在这种情况下，有必要暂时放松硬膜悬吊。

– Intra-operative venous congestion may occur because of sinus manipulation, in which case, it is necessary to temporarily relax the dural tenting sutures.

乙状窦或横窦的出血性损伤罕见。乙状窦垂直段较为脆弱，损伤可发生于开颅、乳突钻孔或硬膜切开时，存在的风险包括失血、空气栓塞和静脉窦血栓形成。通常很难进行直接缝合，而且需要避免永久性静脉窦闭塞。我们建议使用肌肉块和纤维蛋白胶覆盖破口。另一种方法翻转硬膜瓣，缝合修补乙状窦，并将其悬吊在乳突上。

– Hemorrhagic injuries of the SS or TS are rare. The vertical portion of the sinus is fragile. The injury may happen during craniotomy, while drilling the mastoid process or during dura opening. Dangers are blood loss, air embolism, and sinus thrombosis. Direct suture is generally difficult to achieve. There is a need to avoid permanent occlusion of the sinus. We propose to cover the hole with a patch of muscle and fibrin glue. Another technique is to rotate the flap of dura that will be stitched and maintained against the sinus with tack-up sutures on the mastoid.

围手术期特别注意事项

Specific perioperative considerations

最初24小时，患者常规送入重症监护室管理。在仔细检查后组颅神经功能后，逐渐开始经口进食水和食物。如果可疑潜在性后组颅神经功能障碍，需要在患者恢复进食之前，请耳鼻喉科医生借助内镜检查声带和吞咽功能。24小时内常规平扫CT复查。

– The patient is routinely managed in the ICU during the first 24 h. The oral administration of water and food will be started gradually after careful checking of the lower cranial nerve function. If any doubt about potential dysfunction of lower CNs, an endoscopic examination of the vocal cords and swallowing is asked to the ENT surgeon before feeding the patient back. A systematic nonenhanced CT is performed within 24 h.

术后早期严禁瓦式动作，以防范脑脊液漏的风险。

– Early postoperative Valsalva maneuvers are prohibited to limit the risk of CSF leak.

需要向患者提供有关手术和潜在风险的详尽信息

Specific information to give to the patient about surgery and potential risks

后组颅神经受累症状（发音困难、吞咽困难）

– Disorders affecting the lower CNs (dysphonia, dysphagia)

外展神经（复视）、面听神经复合体（面部无力、听力丧失）

– CN VI (diplopia), acoustic-facial bundle (facial weakness, hearing loss)

脑脊液漏：预防和处理

– CSF leaks: prevention and treatment

术后血肿及其后果

– Postoperative hematoma and consequences