Cavernous malformations of the spinal cord are rare relative to their cousins in the brain. They co-exist in both locations in 16-25% of cases. The thoracic segments of the spinal cord are most commonly affected followed by the cervical cord.The malformations usually occupy space dorsal to the equator of the cord and their exact relationship to the fibres passing them in the cord determine what symptoms they may cause. At the back of the cord in the dorsal coloumns (made up of gracile and cuneate bundles of fibres- see figure on right) information tracking the position of joints, touch-discrimination and vibration. Fibres that initate voluntary movement are located further forward and at the periphery of the cord. There is almost no redundant tissue in the spinal cord and disturbance produces deficits.
In approximately 55% of cases a cavernoma of the cord is discovered when haemorrhage results in sudden and catastrophic loss of function below the level of the cavernoma. The true risk of a first ever symptomatic haemorrhage from a cavernoma is not known because of their relative rarity. In a review of all the published cases to date it was estimated at approximately 2.1% annum. A haemorhage from a thoracic cavernoma may produce sudden loss of power and feeling of the legs together with loss of badder, bowel and sexual function. If a similar event were to occur in a malformation located in the cervical cord then the upper limbs could be additionally involved and perhaps the main muscle of repsiration, the diaphragm.
As with cavernomas in other locations the development of symptoms may be more insidious as blood products slowly accumulate in the tissue around the cavernoma. Early microsurgical removal is often advocated in such cases. In truth the actual incidence of neurological deterioration in those who harbour an asymptomatic spinal cord cavernoma is not known. The medical literature for the most part consists of reports on what happened to those who became known to us because of their symptoms. Consequently a decision to remove spinal cord cavernoma requires careful balance of the benefits against the likely consequences of intervening.
The definitive treatment of a spinal cord cavernoma is microsurgical removal. In our hands the procedure is carried out with the help of intraoperative neurophysiological monitoring. Electrodes in the scalp send tiny electric shocks through the spinal cord and these may be recorded from peripheral nerves. Changes in the quality of these signals indicate that the nervous tissue in the cord may be being hurt and afford and opportunity to try and modify the operation in hopes of mitigating any harm. Contact electrodes placed against the spinal cord itself provide reliable information on the condition of the most important tracts facilitating voluntary movements.
A cavernoma may not be visible on the surface of the cord in which case it can be located with ultrasound. Techniques to demonstrate blood vessels within the cord may also give a clue to its location as the cord overlying with appear as relatively poor in blood supply. The interior of the cord is usually accessible through tiny incisions (myelotomy) made between the dorsal coloumns or at the point where sensory nerves enter the cord to the side- the dorsal root entry zone.
The cavernoma is gently seperated from the surrounding nervous tissue. There is usually vey little bleeding from the lesion itself. No attempt is made to remove the golden coloured nervous tissue surrounding the malformation. in the brain this is often done to ensure complete removal or to increase the likelihood that a seizure disorder would be helped. In the spinal cord however such dissection is likely to harm the cord and it is prudent to leave it be.
Once satisfied that the cavernoma has been completely removed the incisions are closed with tiny sutures, thinner than a hair. The very best of outcomes will usually mean that there is a temporary disturbance of ones ability to co-ordinate movements, affecting the ability to walk or use the hands. For most uncomplicated cases this will gradually recover.