Trapezius muscle denervation in accessorius palsy due to a posterior fossa arachnoid cyst
Presentation
A young man noticed an asymmetry about his neck while shaving in front of the mirror. He went to see an orthopedic surgeon, who referred him for an MRI of the neck.
Patient Data
Marked atrophy and increased T2 signal of the right trapezius muscle. The other muscles, including sternocleidomastoideus are normal. On the coronal T2-weighted images, there is a liquid mass in the right posterior cranial fossa.
Cranial MRI a few days later
There is a large cyst in the lateral cerebellomedullary cistern that extends from Luschka's foramen down to the jugular foramen and displaces the cranial nerves X and XI anteriorly.
Case Discussion
Cranial nerve palsies resulting from posterior fossa arachnoid cysts have been rarely described. In this case, typical signs of subacute muscle denervation are present, indicating the affected nerve.
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