Remote Paraparesis due to a Traumatic Extradural Arachnoid Cyst Developing 2 Years after Brachial Plexus Root Avulsion Injury: Case Report and Review of the Literature.

Traumatic extradural arachnoid cyst is a rare entity. However, late appearance of paraparesis due to formation of an extradural arachnoid cyst as a sequel of brachial plexus injury is extremely rare and the literature regarding this issue is scarce revealing only 11 cases. Herein, we report a patient with delayed progressive spastic paraparesis appearing after a multilevel brachial plexus root avulsion injury where imaging revealed formation of a large traumatic extradural arachnoid cyst at the cervicothoracic region. Furthermore, to propose that a high-energy trauma might simultaneously result in delayed formation of an extradural arachnoid cyst. However, preganglionic root avulsion injury with pseudomeningocele formation in association with extradural arachnoid cyst is not reported previously. A case of a 36-year-old man with spastic paraparesis developing 2 years after a multilevel brachial plexus root avulsion injury is presented. Root avulsion had immediately resulted in complete paralysis of the left upper limb that had not ameliorated. Imaging studies of the cervicothoracic region disclosed left-sided multilevel pseudomeningoceles and a large extradural arachnoid cyst extending from C5 to T2. After appropriate en bloc laminotomy, the cyst was excised and the causative dural tear was closed. Subsequently, three large defects of pseudomeningoceles were obliterated with artificial dural patch for the prevention of cord herniation. This was followed with laminoplasty of the corresponding levels after dural closure. The postoperative course was uneventful and paraparesis recovered steadily within 2 months. Paraparesis even years after brachial plexus injury should be regarded as a serious event that deserves extensive imaging survey for the possibility of the formation of an extradural arachnoid cyst. Careful review of the literature disclosed that the current case is the 12th case that an extradural arachnoid cyst has developed after brachial plexus injury and the first example that the pathogenic factor that might be implicated in occurrence of this rare association could be clarified with review of the MRI features. Actually, the presence of posttraumatic pseudomeningoceles in association with an arachnoid cyst in the current case is in favor of the belief that only preganglionic root injuries that are in close proximity to the spinal canal had been the cause dural tear with remote formation of extradural arachnoid cyst.