Reversible Isolated Accessory Nerve Palsy due to a Large Thrombosed Vertebral Aneurysm
A 70-year-old woman complaining of transient numbness in the upper right and lower limbs was referred to our hospital. Physical and neurological examinations revealed no definite abnormalities. However, MRI indicated a large mass lesion in the posterior fossa. The maximal diameter was 22 mm. The mass severely compressed the medulla oblongata and caused a high signal intensity lesion, suggesting a vasogenic edema. Both T1- and T2-weighted MRI showed a flow void signal and mixed signal intensity area inside the mass, suggesting a partially thrombosed vertebral aneurysm (fig. ). MRA disclosed a thrombosed large aneurysm of the right vertebral artery (VA) (fig. ).\nThe proximal VA was exposed through right suboccipital craniotomy and was clipped with one titanium aneurysm clip in order to reduce the pressure inside the aneurysm. The postoperative course was uneventful. No neurological deterioration occurred. Postoperative MRA showed the disappearance of the flow void signal inside the aneurysm. One month later, however, cerebral angiography revealed a partial recanalization of the right VA, probably because one titanium aneurysm clip was not enough to obliterate the sclerotic VA. She then underwent coil embolization of the right VA just proximal to the aneurysm clip. Subsequently, the right VA was completely obliterated. She was discharged without any neurological deficit. However, a couple of weeks later she complained of mild hoarseness and right shoulder pain. Physical and neurological examinations showed the atrophy of the right trapezius and sternocleidomastoid muscle, leading to the deepening of the right supraclavicular fossa (fig. ). No other cranial nerve deficits were observed. The symptoms were considered to result from right isolated accessory nerve palsy. Radiological examinations showed no newly developed lesion such as cerebral infarction in the brain stem. There was no significant change in size of the VA aneurysm. As a result, the isolated accessory nerve palsy was considered to be a delayed complication due to aneurysmal compression on the intracranial portion of the accessory nerve.\nFollow-up MRI showed that the VA aneurysm gradually decreased in size over a period of several months. The deformity of the medulla oblongata markedly improved and its high signal intensity lesion completely disappeared (fig. ). At the same time, the patient's hoarseness completely resolved. The deepening of the right supraclavicular fossa also disappeared completely (fig. ).