Intracisternal accessory nerve schwannoma
Intracisternal accessory nerve schwannoma variant occupy the cisterna magna, the fourth ventricle, spinal canal or the foramen magnum 1) 2)
Till 2015 only 27 cases of the cisternal variant have been published so far. Out of these, 13 cases were located in the cisterna magna, 5 in the cervical canal, 5 in the cervicomedullary location, 2 in the cranio-vertebral junction and only 2 in the fourth ventricle 3)
The lesion of Krishnan et al., was also located predominantly in the fourth ventricle but with a large extension unto C2 across the cervicomedullary junction 4).
In spite of their origin from the accessory nerve, these tumors tend to be located in the midline and posteriorly, probably because the cisterna magna allows sufficient space for the tumor to expand 5).
This makes it appear more as a midline lesion and occupy the cisterna magna or the fourth ventricle, making it difficult to differentiate from other midline posterior fossa lesions 6).
Thus, the cisternal variant of accessory nerve schwannomas by virtue of their extension in to various cisternal spaces can be classified by location as:
The intracisternal variant often present with neck stiffness, secondary to accessory nerve irritation.
Total removal is the primary treatment of schwannomas arising from the spinal portion of the accessory nerve. Excision of an involved segment or rootlet along with the lesion sparing the rest of the nerve in continuity, rarely results in any neurological deficit. This is because the insidious tumor growth in a portion of the nerve causes functional compensation by the remaining intact uninvolved nerve segment 8) 9)