cervicomedullary compression caused by various abnormalities in bony and soft tissue is a common and well - characterized condition1,6,7 ) . in contrast , cervicomedullary compression due to an anomalous change in the vertebral artery ( va ) , as in dolichoectasia , is a relatively rare condition . intracranial arterial dolichoectasia is defined as an increase in the length and diameter of the intracranial arteries , and the vertebrobasilar system is the most commonly affected segment17,22 ) . dolichoectatic changes in the va without involvement of the basilar artery are quite rare and can cause a pulsatile mass effect in the surrounding areas . for example , va anomalies have been previously reported to cause a variety of symptoms , including neck and arm pain , occipital neuralgia , torticollis , myelopathy , drop attack , radiculopathy , pyramidal tract signs , and cranial nerve defects4,5,8,9,11,12,13,15,16,20,23,24,25,26 ) . the few reported cases of this condition showed improvement in symptoms following microsurgical decompression2,4,5,15,21,23,24,25,26 ) . however , adhesion or indentation of the va with the low cranial nerve , spinal cord , and rootlet is common in dolichoectasia . therefore , the potential for intraoperative complications due to damage to these adjacent structures during decompression should be carefully considered . in this case report , we show that the use of intraoperative monitoring ( iom ) of somatosensory evoked potentials ( ssep ) and motor evoked potentials ( mep ) aided in checking for potential nerve root or spinal cord damage during microvascular decompression in a case of cervicomedullary compression caused by an anomalous va . a 68-year - old woman had a 10-year history of posterior neck pain and a 3-year history of gait disturbance . her symptoms worsened gradually . a neurological examination revealed normal muscle strength in all extremities , but mri revealed multiple abnormalities , including an anomalous tortuous va compressing the dorsal portion of the spinal cord bilaterally at the cervicomedullary junction , spinal cord signal changes , and atrophy ( fig . no congenital anomalies of the posterior fossa or any degenerative changes in the spinal column were observed . iom of ssep and mep using an intraoperative monitoring system ( isis iom system , inomed medizintechnik gmbh , teningen , germany ) was initiated under general anesthesia . after making a midline incision , suboccipital craniectomy with c1 laminectomy the muscles inserting into c2 were preserved . to protect the extradural va , the back muscle was very carefully stripped using doppler monitoring . next , the dura was opened to form a y shape revealing the tortuous vas , which appeared somewhat sclerotic . the vas were intertwined and they had formed severe adhesions with the c2 rootlet and spinal cord . we also found an indentation of the vas with the spinal cord , and va pulsations compressed the spinal cord ( fig . , the ssep signal of the right tibialis anterior muscle changed , with the amplitude dropping to below 50% of baseline ( fig . subsequently , the vas were dissected with extreme care and then lifted gently without causing any changes in ssep . in comparison with the initial dissection an increase in mep amplitude compared to baseline was , however , observed after dural closure ( fig . the wound was closed layer - by - layer , and there were no other procedural complications . postoperatively , the patient experienced marked improvement in her symptoms . the day after surgery , six months after the surgery , the patient complained of no symptoms except numbness in the occipital area . a 68-year - old woman had a 10-year history of posterior neck pain and a 3-year history of gait disturbance . her symptoms worsened gradually . a neurological examination revealed normal muscle strength in all extremities , but mri revealed multiple abnormalities , including an anomalous tortuous va compressing the dorsal portion of the spinal cord bilaterally at the cervicomedullary junction , spinal cord signal changes , and atrophy ( fig . no congenital anomalies of the posterior fossa or any degenerative changes in the spinal column were observed . iom of ssep and mep using an intraoperative monitoring system ( isis iom system , inomed medizintechnik gmbh , teningen , germany ) was initiated under general anesthesia . after making a midline incision , suboccipital craniectomy with c1 laminectomy the muscles inserting into c2 were preserved . to protect the extradural va , the back muscle was very carefully stripped using doppler monitoring . next , the dura was opened to form a y shape revealing the tortuous vas , which appeared somewhat sclerotic . the vas were intertwined and they had formed severe adhesions with the c2 rootlet and spinal cord . we also found an indentation of the vas with the spinal cord , and va pulsations compressed the spinal cord ( fig . , the ssep signal of the right tibialis anterior muscle changed , with the amplitude dropping to below 50% of baseline ( fig . subsequently , the vas were dissected with extreme care and then lifted gently without causing any changes in ssep . in comparison with the initial dissection an increase in mep amplitude compared to baseline was , however , observed after dural closure ( fig . the wound was closed layer - by - layer , and there were no other procedural complications . postoperatively , the patient experienced marked improvement in her symptoms . the day after surgery , her posterior neck pain improved . six months after the surgery , the patient complained of no symptoms except numbness in the occipital area . many patients with condition have been successfully treated by microvascular decompression using various materials2,4,5,15,21,23,24,25,26 ) . the first is spinal cord damage during va dissection , and the second is instability of the spinal column following surgery . given the complex structure of the cervicomedullary junction , vascular compromise and resulting damage to the spine during surgery is a major concern . the main arteries supplying blood to medulla and spinal cord are the posterior inferior cerebellar artery , anterior spinal artery , and posterior spinal artery . surgical manipulation of the va does not affect these main arteries supplying blood to the spinal cord , but it may affect microcirculation in the spinal cord . it is difficult to detect damage to microvessels using standard intraoperative vascular monitoring techniques , such as intraoperative indocyanine green videoangiography or doppler sonography . therefore , we performed continuous iom of ssep and mep to monitor potential spinal cord damage . in the field of spinal surgery , intraoperative monitoring of ssep was first introduced to avoid undesirable neurological complications14 ) . however , ssep is a measure of sensory nerve function that is mainly localized in the dorsal column . therefore , ssep can not indicate any anterior spinal column damage , including damage to the corticospinal and motor tracts27 ) . as a result , surgeons have questioned the reliability of ssep for monitoring damage throughout the spinal cord . improved technology has enabled intraoperative mep monitoring of the motor component of the spinal cord . thus , both mep and ssep can now be monitored during spinal surgery , increasing the sensitivity for detecting spinal cord damage3,10 ) . however , the patient was at risk of not only damage to the dorsal column , but also intraoperative damage to the motor tract . during decompression in standard surgical decompression for vas that compress the spinal cord and entangle rootlets , the vas are retracted dorsolaterally , and the spinal cord is released . upon retraction of tangled rootlets , spinal cord traction may ensue and lead to spinal cord damage associated with a change in ssep . generally , mep signal is not checked during such decompression , because of concerns over further damaging the spinal cord . in this case , a change in the ssep signal was detected during surgery , and we were able to act appropriately to prevent damage to the spinal cord . furthermore , an increase in the mep signal was observed , indicating that the spinal cord had been decompressed and the motor functions were spared . when using the posterior approach to operate on cervical spinal lesions , preservation of the c2 insertion muscle ( the semispinaliscervicis muscle ) reduces subsequent posterior neck pain and instability18,19 ) . because the main symptom experienced by our patient was posterior neck pain , it was essential that the surgery did not cause any further posterior neck pain since c2 laminectomy was not performed , the muscles inserting into c2 were preserved ; nevertheless , the operating field was wide enough . the symptoms associated with cervicomedullary compression caused by an anomalous va can be markedly improved following microsurgical decompression .
we report a case of cervicomedullary compression by an anomalous vertebral artery treated using microsurgical decompression with intraoperative monitoring . a 68-year - old woman presented with posterior neck pain and gait disturbance . 
 mri revealed multiple abnormalities , including an anomalous vertebral artery that compressed the spinal cord at the cervicomedullary junction . 
 suboccipital craniectomy with c1 laminectomy was performed . 
 the spinal cord was found to be compressed by the vertebral arteries , which were retracted dorsolaterally . at that time , the somatosensory evoked potential ( ssep ) changed . 
 after release of the vertebral artery , the ssep signal normalized instantly . 
 the vertebral artery was then lifted gently and anchored to the dura . 
 there was no other procedural complication . 
 the patient 's symptoms improved . 
 this case demonstrates that intraoperative monitoring may be useful for preventing procedural complications during spinal cord microsurgical decompression .