The preservation of the spinal accessory nerve represents a key goal in head and neck oncologic surgery during selective neck dissection. This study aims to illustrate the anatomical variants of the XI cranial nerve, delving into the relationship between the spinal nerve and the internal jugular vein, as well as the surgical implications. Two cases of patients who underwent oncologic surgery with neck dissection are described. Both cases found the spinal accessory nerve passing through the fenestration of the internal jugular vein. Alongside this case series, an independent literature review was conducted using the Medline and PubMed databases. In the majority of cases (67% - 96%), the spinal accessory nerve traces a lateral course to the internal jugular vein. Less frequently, the XI cranial nerve courses medial to the internal jugular vein. More rarely, as described in this case series, the nerve crosses through the fenestration of the vein (0.48% - 3.3%).