Spinal cord and spinal vascular diseases
The spinal cord, similar to the brain, can develop arteriovenous malformations, dural arteriovenous fistulas, and tumors amenable to endovascular treatment. Aneurysms often occur in association with arteriovenous malformations; it is very rare for them to appear independently in the spinal cord vessels. Furthermore, the vertebrae and soft tissue surrounding the spinal cord are also sites of arteriovenous malformations and tumors amenable to endovascular treatment. Experience holds much importance in safely and effectively treating diseases around the spinal cord by endovascular treatment. Below are common diseases of the spine and the spinal cord, and the application of endovascular treatment for each disease.
Tumors
Just as brain tumors, spinal cord tumors can be classified into intradural and extradural lesions. Almost all of intradural lesions amenable to endovascular treatment are hemangioblastomas. Indication for endovascular embolization is mostly preoperative in order to decrease blood loss during open surgery. Since the feeding vessels are much smaller than those in the case of arteriovenous malformations, it is difficult to insert tubes (micro-catheters) into the peripheral vessels. Also, because vessels on the back of the spinal cord can be treated easily by surgery, endovascular treatments are rarely used to treat intradural tumors, unless the tumor is excessively large.
Amongst extradural tumors, the following are amenable to endovascular treatment: metastatic tumors that metastasized from the kidney, thyroid gland or breast, hemangiomas, aneurysmal bone cysts, giant cell tumors, hemangiopericytomas, sarcomas, and benign or malignant primary bone tumors such as plasmacytomas. Endovascular treatment is often conducted preoperatively in order to minimize bleeding during surgery. In some cases when surgery is difficult, endovascular treatment is conducted in order to slow the progression of symptoms or to temporarily alleviate neural symptoms and pain. The main risks of conducting endovascular treatment for extradural diseases is spinal cord ischemia that occurs when embolization is conducted without the realization of the existence of spinal cord vessels because of dense staining of the tumor by contrast dye distortion of the spinal cord vessels caused from previous treatments, or due to deterioration of angiogram images caused by the use of metallic instruments.
Diseases that cause arteriovenous shunts
Just as diseases of the head, spinal lesions can be classified as intradural, dural and extradural. Intradural lesions can be categorized into arteriovenous fistulas which do not have nidus and arteriovenous malformations which have nidus. Arteriovenous fistulas account for 20% of all intradural spinal cord shunt diseases, and can be categorized by the size of the fistula into either macro or micro. Micro arteriovenous fistulas often occur in adults and macro in infants. Macro arteriovenous fistulas often coexist with Hereditary Hemorrhagic Telangiectasia (HHT).
Diagnosis and examination
When spinal cord arteriovenous malformation is suspected, the first diagnostic imaging test that will be conducted is the non-invasive MRI. Spinal cord arteriovenous malformations will almost always cause an abnormal finding in the MRI. The main observations of spinal cord arteriovenous malformations are expanded vessels or nidus inside and/or on the surface of the spinal cord, and edema or hematoma in the spinal cord. In some cases the following can also be observed: clotting in the spinal veins, cyst formation inside the spinal cord, spinal atrophy, changes in the bone such as deformation of vertebrae and expansion of theneural foramen caused by expanded veins. Furthermore, when there is association of vascular malformations outside the spinal cord, they will be observed in the bone and soft tissue as well. CT is effective for examining the changes in the bones or for the evaluation of subarachnoid hemorrhage, but otherwise MRI is a better examination method. When there is dural arteriovenous fistula, the spinal cord will appear swollen and expanded veins will be observed. In the chronic phase, the spinal cord will become atrophic and appear smaller. These days, the possibility to identify the location of the lesion by MR angiography has increased, but the standard method of examination still remains to be catheter angiography when taking treatment into consideration.
Angiography
In order to examine the vascular anatomy of the spinal cord vascular malformations in detail while keeping treatment in mind, angiography using a catheter is necessary. In some cases, in order not to overlook nomal spinal cord arteries that are the size of hundreds of microns, angiography is conducted while the patient’s breath is controlled under general anesthesia, for minimum body movements and for the best imaging quality. It is quite common to stop the breathing and control the intestinal movement to take the best picture. Furthermore, with spinal cord angiography, you not only can examine the lesion’s vascular anatomy, but also examine the hemodynamics of the spinal cord and its lesions. For example, if you take an angiography of the anterior spinal artery in a spinal cord dural arteriovenous fistula case, you will find that the circulation time is delayed and that the venous return is not visualized, which are indications of venous hypertension in the spinal cord.
a）Intradural lesions
Symptoms
Many of the diseases that cause intradural arteriovenous shunts mainly show their initial symptoms by the age of 30, and about half of them develop during childhood before age 16. The most important symptoms are subarachnoid hemorrhage and intramedullary bleeding which occur in about half of the cases. These symptoms appear as a sudden acute pain in the back or in between the scapulas. When there is large amount of bleeding from the subarachnoid hemorrhage, it causes headaches, stiffness of the back of the neck, and disturbance of consciousness. These symptoms appear for subarchanoid hemorrhage due to cerebral aneurysm rupture as well, and CT also shows similar findings, so it is important to distinguish them from one another. In addition to pain, disturbance of sensory and motor functions in the limbs below the level ot the bleeding and dysfunction of the bladder and bowel are also common, and these symptoms are severer in the case of intramedullary hemorrhage. The frequency of re-bleeding is high in the long-term, but the risk in the early stage after the initial bleeding seems to be lower than previously acknowledged. Non-bleeding neurological deficits can occur suddenly, increasingly worsen, or continually progress. This is thought to be caused by a circulation disorder in the spinal cord due to hypertension in the veins or by spinal cord compression caused by expanded veins. There are cases where pain appears in the back and along the nerves. Cases where the pain worsens according to the patient’s posture are thought to be caused by nerve root compression due to expanded veins. In rare cases, asymptomatic spinal cord arteriovenous malformations are discovered due to coexisting vascular lesions in the skin.
Treatment
Endovascular treatment for arteriovenous fistulas is conducted by blocking the arterial or venous side of the fistula by placing coils or liquid adhesive (N Butyl-cyanoacrylate (NBCA)). Aneurysms can be treated by blocking the inside of the aneurysm by coil or NBCA. In cases of nidus-type arteriovenous malformations, it is best to treat them by using NBCA, if the micro-catheter can enter the nidus. The treatment strategy for nidus-type arteriovenous malformations does not aim complete cure but blocks the aneurysm or arteriovenous fistulas in order to improve symptoms or prevent their development. If you aim complete cure, the risk of complications becomes high. Aneurysms are relatively common observations in spinal cord arteriovenous malformations, and are also diverse in location (in feeding arteries, inside the nidus, in arteriovenous fistulas) and cause (increase in blood flow, pseudo-aneurysms associated with bleeding, thrombosis of the venous side of the arteriovenous fistula). These are all targets of embolization treatment. When expansion or change in the shape of the aneurysm is observed, it must be blocked as soon as possible because it is unstable. In cases where the micro-catheter cannot fully reach the nidus, the vessels can be blocked using particulate substances.
There are cases where coexisting vascular malformations occur in the spine, muscle, or skin at the same level of the spinal cord as the spinal cord arteriovenous malformations. In principle, all lesions that cause symptoms should be treated, but many of the treatment targets are intradural lesions.
b）Dural lesions
Symptoms
Dural lesions are called dural arteriovenous fistulas. These occur most frequently amongst all vascular malformations in the spinal cord and spine. They most commonly occur in men above 40. The cause of this disease is unknown, but it is an acquired lesion in which an arteriovenous shunt developsbetween the dural artery and a vein inside the dura matter. The typical clinical symptom is progressive paralysis of the lower limbs, and during examination, most cases will show sensory dysfunction of the lower limbs, dysfunction of the bladder and bowel and sexual dysfunction. The symptoms can either continually worsen, slowly progress while repeating improvement and worsening, or worsen in a stepladder pattern. Furthermore, in 10-20% of the cases, acute exacerbation can be observed. In some cases, backaches may coexist, and movements that increase intra-abdominal pressure such as bowel movement, forward leaning and holding one’s breath may worsen the symptoms.
Treatment
On one hand, this disease can lead to complete paraplegia if left untreated, but on the other hand, it can be treated with low risk and a high success rate. Therefore, even when severe symptoms are observed, treatment is indicated in almost all cases in order to at least stop progression of the symptoms. Treatment can be conducted either by surgery or endovascular embolization. The surgical treatment is relatively simple, consisting of cutting the draining vein of the arteriovenous fistula located inside the dura matter. When conducting endovascular embolization, a liquid embolic substance such as NBCA is injected in the feeding artery using a micro-catheter so that the substance will reach the venous side of the arteriovenous fistula. Particulate embolic substances are not used because the effect of treatment tend to be temporarybecause ofhigh possibility of recannalization. In cases where the feeding artery of the arteriovenous fistula and a spinal cord artery derive from the same location, embolization is contraindicated because there is a high risk of spinal cord ischemia. If the lesion is not completely obliterated by embolization, it is important to perform surgery successively without delay. In cases where the blood flow through the spinal cord artery is extremely slow or where significant stagnation of radiopaque dye can be observed in the venous return of the arteriovenous fistulas, medication (heparin) that lowers the blood’s clotting function is used in order to prevent the spinal veins from clogging. The advantages of embolization treatment compared to surgical treatment are; 1. It can be conducted in succession in the same setting as the spinal angiography, 2. It is less invasive and complications such as pain and infection occur less frequently compared to surgery, 3. The patient can get out of the bed and start rehabilitation next day after operation, 4. Heparin can be used from right after the operation in order to prevent blood from clotting, and 5. When the lesion cannot be completely obliterated by embolization, surgery can be conducted in succession. The disadvantage is that when the venous side of the arteriovenous fistula is not completely embolized by a liquid embolization substance, there is a risk of recurrence even when the lesion is not visualized on the angiography after the treatment. Our treatment strategy is to perform embolization as the first choice following angiography. When embolization is risky or the lesion cannot be completely cured by embolization, we perform surgical treatment during the same admision.
Treatment prognosis
If the treatment is successful and the arteriovenous fistula is completely obliterated by embolization, there will be some kind of neurological improvement in almost all cases. Recovery after the treatment tends to be better when the interval between the occurrence of the symptoms and treatment is short, and when pre-treatment neurological symptoms are mild. In general, the motor function and position sensation of the joints recover sooner, while warmth and pain sensation and bladder and bowel functions recover later, often incompletely. Immediate treatment is necessary when clinical symptoms exacerbate acutely, because favorable recovery is possible after the treatment even when pre-treatment neurological symptoms are severe.
In cases where symptoms, that once improved after treatment, start to deteriorate again, it is necessary to investigate whether the arteriovenous fistula has recurred or not by MRI or spinal cord angiography. When there is no recurrence of the arteriovenous fistula, it is possible that the worsening symptoms are due to development of a blood clot in the spinal cord vein. In this case, symptoms may improve with the systemic administration of heparin. In addition, it should be also kept in mind that intervertebral disc hernia and stenotic lesions in the peripheral vessels can cause symptoms similar to those of a spinal dural arteriovenous fistula.
c）Extradural lesions
Many of the extradural arteriovenous malformations are arteriovenous fistulas.Malformations draining to the intradural veins and present with neurological symptoms similar to those of dural arteriovenous fistulas are treated in the same way as the dural arteriovenous fistula. Extradural malformations can rarely causeintradural or extradural bleeding. Arteriovenous fistulas beside the spine can occur independently or in association with a spinal cord vascular malformation. Symptomatic extradural lesions should be treated by endovascular embolization, but complete cure is often difficult because many of them are high flow and extensive. The arteriovenous fistula along the spinal nerve is usually a high flow single hole lesion. Those occur at the cervical level are sometimes due to trauma or associated with a connective tissue disease.These can be treated by endovascular embolization using coils or liquid embolization substances. Most of the arteriovenous malformations in the spine coexist with arteriovenous malformations in the spinal cord. Those lesions that cause pain or destruction of bones are a target of endovascular treatment. When treating these lesions, it is important to consider the possibility of a coexisting spinal cord lesion.