Background: 

The modern scalp block consists of local anesthesia injections that target the supraorbital, supratrochlear, zygomaticotemporal, auriculotemporal, and greater and lesser occipital nerves. Limited data exist on the local anesthetic spread that occurs with this technique. This study examines the extent of the spread of a scalp block using methylene blue in a cadaveric model.

Methods: 

A traditional landmark-based scalp block was performed on 6 unembalmed human cadavers using 25-G, 1.5-inch needles to inject 1 to 2 mL of methylene blue 0.1% at each nerve bilaterally; a total volume of 20 mL was injected. The cadavers were then dissected, and the spread of injectate was measured and recorded.

Results: 

All the nerves required for analgesic coverage were appropriately stained by the injections, except for in 2 specimens where the lesser occipital nerve could not be identified. The zygomatic (stained in 2 of 8 specimens) and temporal (stained in 5 of 8 specimens) branches of the facial nerve were stained as a result of the zygomaticotemporal and/or auriculotemporal injections. Tracking from the zygomatic injection site was noted as far inferior as the temporalis muscle attachments on the mandible.

Conclusions: 

This cadaveric study confirms that the landmark-based technique for scalp blocks consistently stained all 6 nerves involved in scalp innervation. There was significant unintentional spread to the branches of the facial nerve when using the landmark technique.

中文翻译：

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使用亚甲蓝评估选择性神经头皮阻滞的解剖学扩散：尸体分析

背景： 

现代头皮阻滞包括针对眶上、滑车上、颧颞、耳颞以及枕大神经和枕小神经的局部麻醉注射。关于这种技术所发生的局部麻醉剂扩散的数据有限。本研究使用亚甲蓝在尸体模型中检查头皮块的扩散程度。

方法： 

对 6 具未防腐的人类尸体进行传统的基于标志的头皮阻滞，使用 25-G、1.5 英寸的针在双侧每根神经处注射 1 至 2 mL 0.1% 的亚甲蓝；注射总体积为20mL。然后解剖尸体，测量并记录注射液的扩散。

结果： 

镇痛覆盖所需的所有神经均通过注射进行适当染色，但 2 个标本中的枕小神经无法识别。由于颧颞和/或耳颞注射，面神经的颧支（8 个标本中的 2 个染色）和颞支（8 个标本中的 5 个染色）被染色。注意到从颧骨注射部位的跟踪远不如下颌骨上的颞肌附件。

结论： 

这项尸体研究证实，基于标志的头皮块技术对参与头皮神经支配的所有 6 根神经进行了一致的染色。使用界标技术时，会出现明显的无意扩散到面神经分支的情况。