Innervation of the Face Studied Using Modifications to Sihler's Technique in a Primate Model

There has been no reliable technique with which to display the innervation within whole-tissue specimens of the face. Such a technique preserves the architecture of the facial muscles and provides new data on intramuscular and sensory neural networks. Sihler's technique preferentially stains myelinated nerves within whole tissue, which is rendered transparent. On transillumination, entire neural networks can be studied in situ without the need for dissection and histologic examination. The purpose of this study was to apply Sihler's technique to study innervation patterns of the face, define end points, and improve specimen transillumination.

Eight macaque fascicularis monkeys were studied. The mimetic muscles of the face with intact facial nerve and sensory nerves were harvested as whole tissue composites. Sihler's technique was modified with formalin fixation before dissection to minimize autolysis of the myelin sheath. Prolonged immersion in glycerin improved tissue transparency. A replica of the skull was made with silicone and a light source embedded to restore three-dimensional configuration and provide transillumination.

The facial nerve and sensory nerves were clearly seen up to their terminations in the transparent muscle and soft tissue. Observations were made with regard to the extramuscular and intramuscular innervation patterns of the facial nerve and sensory nerve patterns.

Sihler's technique is a simple and reliable method with which to study the innervation of the face. This process may be applied to the human face to provide a much-needed roadmap to surgery, and the primate model may be developed for the study of facial reinnervation, facial reanimation, and dynamic facial transplantation.