The patient came to the clinic 22-November-2014 complaining of LBP for 50 days without sciatica. Difficult walking that she cannot walk more than 300 meters, after what getting left hip pain. The condition of the patient is deteriorating.

On examination, the patient is limping with exaggerated scoliotic stance. SLRS 70 degrees both sides with weak both lower limbs 4/5 both sides.

The patient was sent for MRI of the dorsal and lumbar spine with contrast and single voxel spectroscopy. There is a cystic intramedullary lesion inside the conus medullaris and it is stuck to the posterior wall of the dura. The content of the cyst is CSF like consistency and spectroscopy ruled out malignant changes of the lesion.

Using the C-arm, laminectomy of L1 was performed. The dura was opened longitudinally, trying during that to preserve the adherent to it the underlying arachnoid which was separated from the dura by sharp dissection. It was necessary to dissect the arachnoid circumferentially to remove the arachnoid cyst and part of it was sent for histologic verification and after its removal the spinal cord was hanging free. Using Inomed with DNS revealed no response even with 10 mA and it was assumed that the ISIS Inomed was troubleshooting. The dura was closed water-tightly and routine closure of the wound. Before weaning off the patient, she was sent for MRI investigation, which confirmed the still presenting intramedullary cyst. The wound was opened and a 3 mm incision over the nonfunctioning part of the spinal cord was performed. The fluid was sent for histologic verification and the spinal cord collapsed completely and running nearby roots were seen. The roots were responding well even with DNS below 2 mA both sides. Routine closure of the wound.

Smooth postoperative recovery. The power of both lower limbs normalized.

When you have suspicion, always check. The no response of the spinal cord to DNS at the end of first stage of surgery led to perform intraoperative MRI which confirmed the still persisting intramedullary cyst. The pathologic non-functioning posterior spinal cord was opened to evacuate the cystic cavity, after what the functioning neural tissues came to the field.

It is rare to see syringomeyletic cavity at the conus medullaris level. This was mostly triggered by the presenting arachnoidal adhesions of this area to the dural wall.

Even with the best MRI available technology, a misleading data can lead the neurosurgeon to wrong conclusions. All the time check when you suspect.