Anatomical Comparative Study of the External Nasal Nerve in Caucasian and Asian: Application for Minimizing Nerve Damage in Rhinoplasty.

BACKGROUND: The numbness of the nasal tip is the main symptom of the external nasal nerve injury, especially after rhinoplasty. This postoperative syndrome can reduce the patient's satisfaction with the operation. Having a better understanding of the anatomical structure and intraoperative protection can effectively avoid nerve injury. At present, the anatomical research on this nerve is all from Asia. This study aims to fill the gap in the anatomical study of this nerve in Caucasians and provides comparative results with Asians. MATERIAL AND METHODS: A total of 20 Caucasian cadavers were embalmed using the Thiel method. On dissection, after complete exposure of the external nasal nerves, the distance between the exit point of the external nasal nerve and the nasal midline was measured, and the morphology of the nerves was compared with the Asian data. The nerves were classified into types based on their branching pattern. RESULTS: The nerve plane was the same as the Asian record. The distance ranged from 5.08 to 11.94 mm (mean, 8.31 ± 1.85 mm). This distance has statistical significant difference compared with the Asian population (P < 0.01). The average distance is larger, and the distribution range of the exit point is wider. On classification, 35 of 40 cases had the same type results as those previously reported, with the primary types I, II and III. Five new varieties were found which are classified as subtypes of the primary types and a new type IV. Furthermore, the bifurcation position in two-thirds of the type II cases and variations is proximal to that seen in the Asian population. CONCLUSIONS: The anatomical structure of the external nasal nerve in Caucasians and Asians has obvious differences. This nerve in Caucasians is more likely to be damaged during rhinoplasty than Asians. Except the primary types, the classification of the external nasal nerve also includes subtypes and type IV. LEVEL OF EVIDENCE III: This journal requires that authors assign a level of evidence to each article. For a full description of these evidence-based medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Pax6 exerts regional control of cortical progenitor proliferation via direct repression of Cdk6 and hypophosphorylation of pRb.

The mechanisms by which early spatiotemporal expression patterns of transcription factors such as Pax6 regulate cortical progenitors in a region-specific manner are poorly understood. Pax6 is expressed in a gradient across the developing cortex and is essential for normal corticogenesis. We found that constitutive or conditional loss of Pax6 increases cortical progenitor proliferation by amounts that vary regionally with normal Pax6 levels. We compared the gene expression profiles of equivalent Pax6-expressing progenitors isolated from Pax6⁺/⁺ and Pax6⁻/⁻ cortices and identified many negatively regulated cell-cycle genes, including Cyclins and Cdks. Biochemical assays indicated that Pax6 directly represses Cdk6 expression. Cyclin/Cdk repression inhibits retinoblastoma protein (pRb) phosphorylation, thereby limiting the transcription of genes that directly promote the mechanics of the cell cycle, and we found that Pax6 inhibits pRb phosphorylation and represses genes involved in DNA replication. Our results indicate that Pax6's modulation of cortical progenitor cell cycles is regional and direct.