Blevins N H, Jackler R K
Department of Otolaryngology/Head and Neck Surgery, University of California-San Francisco.
Otolaryngol Head Neck Surg. 1994 Jul;111(1):81-90. doi: 10.1177/019459989411100116.
The recent trend toward earlier diagnosis of acoustic neuroma has substantially increased the number of candidates suitable for surgery with an attempt at hearing preservation. Although the retrosigmoid approach affords the possibility of saving hearing in selected cases, it is associated with a somewhat greater morbidity that other approaches, in terms of persistent headache, cerebrospinal fluid leakage, and cerebellar dysfunction. For this reason, it is best used selectively, when the probability of success in hearing conservation is high. Only a portion of the internal auditory canal can be exposed through the retrosigmoid approach without violating the inner ear, a maneuver that greatly reduces the chance of preserving residual hearing. Substantial variability exists between individuals as to just how far laterally the internal auditory canal may be opened without compromising labyrinthine integrity. To assess the magnitude of this variability, measurements were obtained from 60 high-resolution temporal bone computed tomography scans with a schema intended to model the surgical angle of view used during the retrosigmoid procedure. Intraoperative measurements in a series of cases established that the actual surgical point of view is situated along a line that passes approximately 1.5 cm behind the sigmoid sinus. In this typical surgical position, these data predict that an average of 3.0 mm (32% of the internal auditory canal length) must be left unexposed to avoid labyrinthine injury, with a range between 1.1 mm and 5.3 mm (9% to 58% of the internal auditory canal). Each additional 1-cm retraction on the cerebellum beyond that customarily used affords approximately 1 mm (10% of the internal auditory canal) further exposure of the canal. When considering the retrosigmoid approach to an acoustic neuroma, the clinician is urged to evaluate each patient individually to estimate the amount of internal auditory canal accessible without the removal of a portion of the inner ear. This can be ascertained from an axially oriented, gadolinium-enhanced magnetic resonance imaging scan in the internal auditory canal plane by drawing a line that originates 1.5 cm behind the posterior margin of the sigmoid sinus and passes tangential to the most medial extent of the labyrinth. If this line intersects the posterior margin of the internal auditory canal at least 2 mm lateral to the deepest point of tumor penetration, then adequate exposure with preservation of the labyrinth is likely an achievable goal.
近期听神经瘤早期诊断的趋势显著增加了适合手术并尝试保留听力的患者数量。尽管乙状窦后入路在某些特定病例中提供了保留听力的可能性，但与其他入路相比，它在持续性头痛、脑脊液漏和小脑功能障碍方面的发病率略高。因此，当听力保留成功的可能性较高时，最好选择性地使用该入路。通过乙状窦后入路在不侵犯内耳的情况下只能暴露部分内耳道，这一操作大大降低了保留残余听力的机会。个体之间在内耳道在不损害迷路完整性的情况下可向外打开的程度存在很大差异。为了评估这种差异的程度，我们从60例高分辨率颞骨计算机断层扫描中获取了测量数据，并采用一种模式来模拟乙状窦后手术过程中使用的手术视角。一系列病例中的术中测量结果表明，实际手术视角位于一条大致经过乙状窦后方1.5厘米的线上。在这个典型的手术位置，这些数据预测，平均必须留出3.0毫米（内耳道长度的32%）不暴露，以避免迷路损伤，范围在1.1毫米至5.3毫米之间（内耳道的9%至58%）。小脑每额外向后牵拉1厘米，超出通常使用的范围，可使内耳道进一步暴露约1毫米（内耳道的10%）。在考虑采用乙状窦后入路治疗听神经瘤时，强烈建议临床医生对每位患者进行个体评估，以估计在不切除部分内耳的情况下可暴露的内耳道长度。这可以通过在内耳道平面进行轴向钆增强磁共振成像扫描来确定，方法是画一条线，该线起始于乙状窦后缘后方1.5厘米处，并与迷路最内侧范围相切。如果这条线在内耳道后缘与肿瘤最深穿透点至少外侧2毫米处相交，那么在保留迷路的情况下实现充分暴露很可能是一个可以达到的目标。
