Incus Necrosis and Blood Supply: A Micro-CT and Synchrotron Imaging Study.

BACKGROUND: Incus necrosis is a common complication following stapes surgery and is associated with impaired microcirculation. The objective of this study was to investigate the vascular anatomy of the human incus by using light microscopy, micro-computed tomography (micro-CT), and synchrotron phase-contrast imaging (SR-PCI) for a novel three-dimensional (3D) analysis of the middle ear, mucosal folds, major vascular pathways, and intraosseous vascular bone channels. METHODS: One-hundred-and-fifty temporal bones from the Uppsala collection were analyzed under light microscopy. Twenty temporal bones underwent high-resolution micro-CT scanning, and an additional seven specimens underwent SR-PCI at the Canadian Lightsource in Saskatoon, Canada. One of these specimens was from an individual who had undergone stapes surgery. Data were processed with volume-rendering software to create 3D reconstructions using scalar opacity mapping for bone transparency, cropping, and soft tissue analyses. RESULTS: Micro-CT and SR-PCI with 3D rendering revealed the extensive vascular plexus within the un-decalcified incus bone communicating with the exterior surface. The relationship between the vessels, lenticular process, and incudostapedial joint were clearly observed. SR-PCI allowed for histologic-level detail while preserving the specimen and its 3D relationships. CONCLUSION: SR-PCI with 3D reconstructions confirmed the main vascular supply to the lenticular process along the intraosseous lenticular vessels. This is the first synchrotron analysis of a patient having undergone stapes surgery, and it suggests that incus necrosis associated with stapes surgery may be caused by a disruption of the lenticular blood flow induced by the prosthesis loop, and not by strangulation of mucosal vessels as has been previously described.

Cranial Nerve Coactivation and Implication for Nerve Transfers to the Facial Nerve.

In reanimation surgery, effortless smile can be achieved by a nonfacial donor nerve. The underlying mechanisms for this smile development, and which is the best nonfacial neurotizer, need further clarification. The aim of the present study was therefore to further explore the natural coactivation between facial mimic muscles and muscles innervated by the most common donor nerves used in smile reanimation. The study was conducted in 10 healthy adults. Correlation between voluntary facial muscle movements and simultaneous electromyographic activity in muscles innervated by the masseter, hypoglossal, and spinal accessory nerves was assessed. The association between voluntary movements in the latter muscles and simultaneous electromyographic activity in facial muscles was also studied. Smile coactivated the masseter and tongue muscles equally. During the seven mimic movements, the masseter muscle had fewer electromyographically measured coactivations compared with the tongue (two of seven versus five of seven). The trapezius muscle demonstrated no coactivation during mimic movements. Movements of the masseter, tongue, and trapezius muscles induced electromyographically recorded coactivation in the facial muscles. Bite resulted in the strongest coactivation of the zygomaticus major muscle. The authors demonstrated coactivation between voluntary smile and the masseter and tongue muscles. During voluntary bite, strong coactivation of the zygomaticus major muscle was noted. The narrower coactivation pattern in the masseter muscle may be advantageous for central relearning and the development of a spontaneous smile. The strong coactivation between the masseter muscle and the zygomaticus major indicates that the masseter nerve may be preferred in smile reanimation.