The great auricular nerve in fetuses / El nervio auricular mayor en fetos

The great auricular nerve (GAN) is the largest branch of the superficial cervical plexus that winds around the posterior border of the sternocleidomastoid muscle, accompanied by the external jugular vein. Forty fetuses (right side: 40/80; left: 40/80) with gestational ages between 15 to 28 weeks were microdissected to document the anatomy of the GAN. The results obtained were classified as: i) Incidence and morphometry: GAN was present in 100 percent of the fetal specimens with average length on the right and left sides recorded as 12.65 +/- 2.14 mm and 12.55 +/- 2.82 mm respectively. ii) Course: GAN was located parallel to the transverse cervical nerve and the external jugular vein. Duplicate external jugular veins were observed in 5 percent (4/80) with GAN located anterior to one of the tributaries; iii) Branching Pattern: 16 percent (13/80) of specimens depicted a single branch. Duplicate branches in 67 percent (54/80) (referred to as Type I: anterior and posterior branches and 33 percent (26/80) referred to as Type II: anterior and posterior branches; iv) Variation: the transverse cervical nerve formed a communication with GAN, inferior to the parotid gland in 1 percent. The anatomical knowledge of the course, bifurcation pattern and variations of GAN may prevent complications during surgical procedures such as parotidectomies.

El nervio auricular mayor (NAM) es el ramo más grande del plexo cervical superficial que gira alrededor del margen posterior del músculo esternocleidomastoideo, acompañado de la vena yugular externa. Cuarenta fetos (lado derecho: 40/80; izquierdo: 40/80), con edades gestacionales de 15 a 28 semanas fueron microdisecados para describir la anatomía del NAM. Los resultados obtenidos se clasificaron en: i) Incidencia y morfometría: NAM estaba presente en el 100 por ciento de las muestras fetales con una longitud media de los lados derecho e izquierdo de 12,65+/-2,14mm y 12,55+/-2,82mm, respectivamente. ii) Curso: NAM se encuentra paralelo al nervio cervical transverso y la vena yugular externa. Duplicación de las venas yugulares externas se observaron en el 5 por ciento (4/80) con el NAM situado por delante de uno de los afluentes, iii) Patrón de ramificación: 16 por ciento (13/80) de las muestras presentaba una solo ramo. Ramos duplicados en el 67 por ciento (54/80) de Tipo I, ramos anterior y posterior y, el 33 por ciento (26/80) Tipo II, ramos anterior y posterior, y iv) Variación: el nervio cervical transverso formando una comunicación con NAM, inferior a la glándula parótida en el 1 por ciento. El conocimiento anatómico del curso, patrón de bifurcación y variaciones del NAM pueden prevenir las complicaciones durante los procedimientos quirúrgicos como la parotidectomía.

Central projection of the peripheral cochlear nerve from each turn to the cochlear nuclei in the Mongolian gerbil

The central projections of the peripheral cochlear nerve fiber from each turn to the cochlear nuclei (CN) in the mongolian gerbil were investigated using retrograde transportation of horseradish peroxidase (HRP). The organ of Corti and the osseous spiral lamina were scratched with an electrolytically-sharpened fine needle via a small hole at each turn of the cochlea. The cochlea was filled with a 30% horseradish peroxidase (HRP) solution. After 48 hours, 50 microns transverse serial sections of the brainstem were made with a vibratome. The tissue was processed with the diaminobenzidine procedure of the cobalt-glucose method. Our experiment revealed that the fibers from the basal turn terminated at the dorsomedial portion of anteroventral cochlear nuclei (AVCN), but those from the apical turn were distributed among the ventrolateral portion of the AVCN. In the posteroventral cochlear nuclei (PVCN) and dorsal cochlear nuclei (DCN), the fibers from basal to apical turns extend from the dorsal to the ventral portion of each nuclei. A distinct tonotopic arrangement could be found between the origin of cochlear fibers of each turn and their termination in the regions of the cochlear nuclei (CN). Also, the results suggested that the scratch method combined with retrograde transportation of horseradish peroxidase was useful in investigating the tonotopic arrangement of the peripheral auditory nerve in the CN.