Morphometric characteristics and intradural connections of the spinal root of accessory nerve in human fetuses

Intradural connections between the spinal root of accessory nerve (SRAN) and the posterior roots of spinal nerves in the cervical region are clinically significant for torticollis, occipital neuralgia and surgeries of the craniocervical region. However, information on these connections during the fetal period is limited. This study aimed to examine the morphology and morphometry of the SRAN in fetuses and its intradural connections with the posterior roots of spinal nerves in the cervical region. Twenty-nine fetuses (58 sides; 18 to 35 gestational weeks) fixed in 10% formalin, were bilaterally dissected under a surgical microscope. The most caudal level of origin, width and intradural connections of the SRAN with the posterior roots of spinal nerves were evaluated and classified. The SRAN most frequently receives rootlets from the C2, C3, C1, C4, C5, and C6 spinal cord segments, respectively, and its most caudal origin ranging from C2 to C6 spinal cord segments. Six and seven types of connections were identified between the SRAN and the posterior root of C1 (37.93%) and C2 (51.72%), respectively. While the connection types are largely consistent with the literature, a previously undescribed anatomical variation, type VI, in which the SRAN runs dorsally to the posterior root of C1 spinal nerve was detected in 1.7% of cases. Knowledge of fetal SRAN variations, may contribute to safer pediatric craniocervical surgical procedures, help reduce the risk of iatrogenic nerve injury and a better understanding of torticollis.