Variations of the accessory nerve: anatomical study including previously undocumented findings-expanding our misunderstanding of this nerve. 
The anatomy of the accessory nerve has been well described but continued new clinical and anatomical findings exemplify our lack of a full understanding of the course of this nerve.  Therefore, this study aimed to expand on our knowledge of the course of the 11th cranial nerve via anatomical dissections.  Fifty-six cadavers (112 sides) underwent dissection of the accessory nerve from its cranial and spinal origins to its emergence into the posterior cervical triangle.  Immunohistochemistry was performed when appropriate.  Our findings included two cases (1.8%) where the nerve was duplicated, one intracranially and one extracranially.  One accessory nerve (0.9%) was found to enter its own dural compartment within the jugular foramen.  The majority of sides (80%) were found to have a cranial root of the accessory nerve.  Thirty-one sides (28%) had connections to cervical dorsal roots medially and three sides (2.7%) laterally.  Medial connections were most common with the C1 nerve.  Medial components of these dorsal root connections were all sensory in nature.  However, lateral components were motor on two sides (1.8%).  Nerves traveled anterior to the internal jugular vein on 88% of sides.  One (0.9%) left side nerve joined an interneural anastomosis between the dorsal rootlets.  Macroganglia were found on the spinal part of the intracranial nerve on 13% of sides.  The lesser occipital nerve arose directly from the accessory nerve on two sides (1.8%) and communicated with the accessory nerve on 5.4% of sides.  One side (0.9%) was found to communicate with the facial nerve with both nerves innervating the sternocleidomastoid muscle.  Additional anatomical knowledge of the variants of the accessory nerve may benefit patient care when this nerve is pathologically involved.