A 69 year old man consulted the emergency department reporting a progressive and unexplained decrease in strength in the right lower limb of about fifteen days' duration. He also presented with paraesthesia in the distal areas of both feet. She did not report back pain and the symptoms began after pain in the knee. There was no history of interest except for hypertension, which was treated and well controlled. Examination by the emergency physician revealed a step gait and a decrease in strength 4/5 for dorsiflexion of the right foot. He was diagnosed in the emergency department with possible neuropraxia of the right external popliteal sciatic nerve and was referred to the rehabilitation department, where, two months after the onset of the symptoms, he was referred to the neurosurgery department after observing an intramedullary lesion at the level of L1, rounded, ill-defined, 1x1 cm, with an isointense centre and hypointense periphery in T1, which after the administration of gadolinium enhanced in a diffuse manner and showed thickening of the diameter of the conus medullaris. As a first diagnosis, the possibility of a conus medullaris ependymoma was reported, without being able to rule out the possibility of an astrocytoma. There was no mention of any mass other than the one described above and no other process was evident on MRI. The patient was admitted to the neurosurgery department with hypoaesthesia in the tips of the toes of both feet, together with a decrease in distal strength of 2/5 in the right lower limb and 3/5 in the left lower limb. On admission, he retained sphincter control and the Karnofsky index was 70. Chest X-ray was reported as normal.

The patient underwent an osteoplastic laminotomy and total resection of a l x l cm mass, easily resectable and not very haemorrhagic. Histological examination showed the presence of a metastasis of clear cell carcinoma of probable renal origin. This diagnosis was confirmed by a thoracic-abdominal CT scan, which showed a giant renal mass (11 x 1 x 1 x 14 cm) and several abdominal and pulmonary metastases of less than 1 cm in size that were not evident on plain radiology. The patient recovered practically all of his paraparesis during his stay in the neurosurgery department. The control MRI study performed at 3 months showed no signs of recurrence. The patient evolved favourably, with no neurological symptoms, 14 months after the operation.