Syringomyelia

　　1. Causes of disease

　　The exact etiology is not clear, and can be divided into two types: congenital developmental abnormalities and secondary syringomyelia, the latter is rare.

　　1. Congenital incomplete closure of the spinal cord neural tube, this disease is often accompanied by other congenital abnormalities such as spina bifida, cervical rib, scoliosis, and occipital-cervical deformities, which support this view.

　　2. Abnormal spinal cord blood circulation causes spinal cord ischemia, necrosis, softening, and the formation of a cavity.

　　3. Mechanical factors, due to congenital factors leading to obstruction of the fourth ventricle outlet, cerebrospinal fluid flow from the fourth ventricle to the subarachnoid cavity is blocked, cerebrospinal fluid pulsation wave impacts the central canal of the spinal cord downward, causing the central canal to expand and break through the wall of the central canal to form a cavity.

　　4. Others, such as cystic transformation of spinal cord tumors, traumatic myelopathy, radiation myelopathy, spinal cord infarction softening, intramedullary hemorrhage, necrotizing myelitis, etc.

　　2. Pathogenesis

　　1. There are generally four theories of congenital causes

　　(1) Gardner's theory of fluid mechanics: Starting in 1958, Gardner reported a large number of cases of Chiari I malformation associated with syringomyelia. He speculated that due to obstruction in the occipital foramen area (congenital malformation or arachnoiditis, etc.), cerebrospinal fluid could not flow out of the fourth ventricle. Under the action of the plexus plexus arterial pulsation, cerebrospinal fluid would continuously impact the central canal of the spinal cord, causing it to expand and destroy the gray matter around the central canal, forming a cavity. In surgery, it was also found that the fourth ventricle and the central canal were communicating; in some patients, when performing ventriculography, it was possible to observe contrast medium entering the central canal from the fourth ventricle; by injecting air into the cavity through a skin puncture, the gas could also overflow into the fourth ventricle; and the protein content of the fluid in the cavity was low, similar to cerebrospinal fluid. However, there are also different opinions: in some patients, there was no communication between the fourth ventricle and the central canal found in angiography, surgery, and autopsy; although the contrast medium injected into the lumbar puncture did not flow into the fourth ventricle, the cavity could be visualized; some cavities were separated from the central canal and were multi-chambered. Some scholars calculated the pressure of the plexus arterial pulsation and found that the pressure was very small, which was impossible to cause a cavity. In addition, this theory cannot explain the occurrence of bulbar syringomyelia.

　　The theory of intracranial and intraspinal pressure separation by Williams: Since 1969, Williams has carried out a series of studies and measured the pressure of the ventricles, cavities, and subarachnoid spaces. It is believed that when a person coughs, sneezes, or exerts force, it can cause the intracranial and intraspinal venous pressure to rise, and the pressure in the subarachnoid space of the brain and spinal cord to rise accordingly. At this time, normal people balance it by the back and forth flow of cerebrospinal fluid in the subarachnoid space. However, in patients with mild herniation of the cerebellar tonsil, due to the obstruction of cerebrospinal fluid circulation, an imbalance in pressure occurs. Williams found that during the early stage of coughing, the pressure in the lumbar subarachnoid space was higher than that in the basal cistern, and then the opposite. From this, he speculated that the cerebellar tonsil may have a valve-like action. When the pressure in the subarachnoid space of the spinal cord rises, cerebrospinal fluid can push up the herniated tonsil and flow into the intracranial cavity; as the pressure in the subarachnoid space of the spinal cord decreases, the cerebellar tonsil herniates again, causing cerebrospinal fluid to be unable to return, leading to increased intracranial pressure, which promotes the perfusion of cerebrospinal fluid from the fourth ventricle to the central canal. This pressure difference between the intracranial and spinal cord, and between the central canal and the extraspinal cord, is called cerebrospinal fluid pressure separation by Williams. This pressure difference acts repeatedly and intermittently for many years, which can form a communicating spinal cord cavity. Through cavity puncture and animal experiments, it has also been found that the cavity has the characteristic of high pressure. There are also clinical reports that some patients have symptoms exacerbated during coughing and exertion. The communication between the central canal and the cavity in patients with syringomyelia is not always open. Due to the repeated pressure on the tissue at the foramen magnum and other reasons, it can close. Therefore, the theory of cerebrospinal fluid impact was proposed in the progression of the cavity. In patients with obvious pressure at the foramen magnum, when coughing and other exertions occur, the pressure in the subarachnoid space of the spinal cord suddenly rises. Since it cannot be transmitted to the intracranial cavity, it is transmitted to the cavity inside the spinal cord. Due to the closed opening or valve-like action of the cavity, the fluid inside the cavity cannot flow into the intracranial cavity and is impacted upwards to the gray matter next to the central canal. Over time, the cavity gradually expands upwards and forms a medullary cavity on the basis of the spinal cord cavity. This explains that the medullary cavity cannot exist alone, which is consistent with clinical observations.

　　The hypothesis of cerebrospinal fluid percolation through the spinal cord substance: In 1972, Ball discovered in the post-mortem examination of syringomyelia that there was a significant widening of the perivascular space around the spinal cord substance. He found that India ink injected into the cavity could spread along the perivascular space and form some small pools locally, especially in the dorsal white matter of the spinal cord. From this, it is speculated that due to the malformation of the occipital foramen magnum area, the venous pressure and the subarachnoid space pressure of the spinal cord are repeatedly transiently elevated, which acts on the spinal cord for a long time, causing the perivascular space to gradually expand, and cerebrospinal fluid seeps in to form a cavity. In 1979, Aboulker proposed that the neural axon tissue is permeable to water, and cerebrospinal fluid can渗透 through the neural tissue into the spinal cord. Clinically, there are also reports that in patients with no communication between the fourth ventricle and the central canal, the cavity can be visualized in the delayed cerebrospinal fluid imaging, and some cavities are far from the central canal, mostly located near the posterior horn of the spinal cord surface.

　　(4) The theory of circulatory disorders: Netsky found abnormal vessels in the spinal cord of syringomyelia patients during autopsies, especially in the posterior horn. He speculated that with the aging process, circulatory disorders can occur around abnormal vessels, leading to cavities. The spinal cord has a protective mechanism against damage from cerebrospinal fluid perfusion or impact, such as gliosis, which can affect the blood supply to the spinal cord substance, and ischemia may be one of the causes of cavity formation and progression. Congenital abnormalities in the spinal cord posterior horn are not the only factors in the etiology. Congenital abnormalities in the posterior horn of the spinal cord, combined with occipital foramen area畸形 and venous pressure factors, make cerebrospinal fluid easily侵入 the spinal cord posterior root on the side of congenital abnormalities, forming a cavity locally. As the cavity expands, it can communicate with the central canal, and then the central canal gradually expands, finally communicating with the fourth ventricle.

　　2. Acquired etiology is often caused by spinal cord tumors, arachnoiditis, and trauma, among other factors. Trauma can cause necrosis of the central part of the spinal cord, leading to the accumulation of exudate and destructive products, increasing osmotic pressure, and causing fluid retention. Due to the increased intramedullary pressure, surrounding tissues can be damaged, causing the cavity to gradually expand. Animal experiments have found that some small cysts appear near the cut end of the spinal cord, suggesting that the rupture and fusion of these cysts may be the cause of cavity formation. For syringomyelia following arachnoiditis, it is mainly due to ischemia and venous thrombosis. Syringomyelia caused by spinal cord tumors is mainly related to the secretion of proteinaceous fluid by tumor cells.

　　The pathogenesis of syringomyelia is complex, and malformation or obstruction in the occipital foramen area is one of the important factors leading to the formation of cavities. Due to the differences in etiology, constitution, and compensatory ability among individuals, the formation and development of cavities also vary. Therefore, different etiological discussions and comprehensive analyses should be conducted according to the clinical characteristics and different stages of the disease.

　　The syringomyelia often occurs near the central canal in the cervical and upper thoracic segments, close to one side of the posterior horn, forming a tubular cavity that can extend through multiple spinal segments and does not necessarily communicate with the central canal. On the cross-section of the spinal cord, the cavity occupies most of the medulla, and the dorsal aspect of the anterior horn can also be affected, with the commissural structures often being destroyed. As the cavity further develops, the posterior horn can also be affected, even including the ventral aspect of the posterior column. The cavity can be localized to one side of the spinal cord or occupy both sides. The shape of the cavity is not uniform, and it is possible for multiple cavities to exist at the same plane of the spinal cord, which can be separated or interconnected. Some cases of this condition coexist with syringobulbia. The cavity can extend upwards to the pons and midbrain. Syringomyelia below the lumbar segment is less common. In a few cases, small cavities are seen at the end of the spinal cord and coexist with spina bifida.

　　Compression and degeneration of the spinal cord is often the inevitable result of the expansion of the cavity. The spinal cord at the cavity site presents a fusiform bulge, the color becomes pale, and the pial vessels decrease. The cavity can be located centrally or on one side, or in front or behind, causing compression and degeneration of the gray matter, lateral column, and posterior column of the spinal cord. The wall of the cavity is smooth, composed of proliferating glioma and degenerating nerve fibers, which become pale, and the surrounding nerve fibers show edema. In the late stage, when the spinal cavity is huge, the spinal cord tissue becomes thin, which can cause obstruction of the vertebral canal.

　　According to the pathological condition, syringomyelia can be divided into two types: one is communicating syringomyelia, that is, the syringomyelia communicates with the fourth ventricle and subarachnoid cerebrospinal fluid, often combined with cerebellar tonsillar herniation type I and II malformations. It may be caused by some abnormal factors in the process of growth and development, such as the central canal of the spinal cord may leak continuously into the surrounding nerve tissue under the action of higher cerebrospinal fluid pressure, causing persistent expansion and forming the disease; another type is non-communicating syringomyelia, where the cavity does not communicate with the cerebrospinal fluid circulation pathway. Its formation is related to intramedullary tumors, traumatic paraplegia, and some degenerative diseases.

　　Syringomyelia often occurs with other congenital malformations, such as scoliosis or kyphosis, concealed spinal bifida, cervical occipital area malformation, cerebellar tonsillar herniation, and clubfoot.

　　After the lesion develops and affects the pyramidal tract and extrapyramidal tract, lower limb spastic paralysis gradually appears, and the pyramidal tract signs in both lower limbs are positive. When one side of the cervical spinal cord is damaged, the descending sympathetic fibers are destroyed, and Horner's syndrome may appear on the same side. Common autonomic disorders include skin nutrition disorders such as skin keratosis, hair loss, and vascular relaxation disorders. In the later stage of the disease, the cavity often involves the nucleus of the spinal tract of the trigeminal nerve, causing facial onion skin-like pain and thermal sensation loss, developing from the lateral side to the nasolabial area; involving the nucleus ambiguus causes difficulty in swallowing and coughing when drinking water; involving the hypoglossal nucleus causes tremors in the extrinsic muscles and muscle bundles; involving the facial nucleus causes peripheral facial paralysis; involvement of the vestibular cerebellar pathway causes dizziness, nystagmus, and gait instability.

　　1. Sensory symptoms

　　According to the cavity located in the cervical segment and upper thoracic segment of the spinal cord, biased on one side or located centrally, there is segmental sensory disturbance in the upper limb and upper thoracic segment, often characterized by segmental dissociative sensory disturbance, pain, and decreased or absent thermal sensation, while deep sensation remains. This symptom can also be bilateral.

　　2. Motor symptoms

　　The syringomyelia in the cervical and thoracic segments affects the anterior horn of the spinal cord, leading to flaccid paralysis symptoms in one or both upper limbs, characterized by muscle weakness and decreased muscle tone. The atrophy of the thenar and interosseous muscles of the hands is most obvious, and in severe cases, claw-like hand deformity may occur. When the descending root of the trigeminal nerve is affected, central-type pain and temperature sensation disturbances on the same side of the face may occur, with a so-called 'onion-like distribution' of sensory loss in the face, accompanied by weak masticatory muscle strength. If the vestibular cerebellar tract is involved, dizziness, nausea, vomiting, unsteady gait, and nystagmus may occur. On the other hand, unilateral or bilateral lower limb upper motor neuron partial paralysis, increased muscle tone, absent abdominal wall reflexes, and positive Babinski sign may occur in the late stage, with paralysis often worsening.

　　3. Autonomic nervous system damage symptoms

　　Syringomyelia involves the sympathetic spinal cord center at the junction of the lateral horn of the spinal cord (cervical 8 and thoracic 1), leading to Horner's syndrome. The lesion damages the corresponding segments, and the skin of the limbs and trunk may have abnormal secretion, with hyperhidrosis or hypohidrosis being the only clinical sign of secretion abnormalities. Hypohidrosis may be limited to one side of the body, known as 'hemihypohidrosis', and is more common in the upper half of the body, or in one upper limb or half of the face. Usually, the corneal reflex may also weaken or disappear, as keratitis sicca can lead to bilateral corneal perforation. Another strange phenomenon of sweating is an increase in sweat when exposed to cold, accompanied by a decrease in temperature, hyperkeratosis of the fingertips and nails, atrophy, and loss of luster. Due to the loss of pain and temperature sensation, it is easy to suffer burns and injuries. In the late stage, patients may experience urinary incontinence and recurrent urinary tract infections.

　　1. Maintain an optimistic and cheerful mood. Strong and long-term or recurrent emotional changes such as tension, anxiety, irritability, and pessimism can disrupt the balance of excitation and inhibition processes in the cerebral cortex, leading to increased muscle twitching and the progression of muscle atrophy.

　　2. Maintain a balanced diet and keep the digestive function normal. For patients with syringomyelia muscle atrophy, maintaining normal digestive function and reasonably adjusting the diet structure is the foundation of rehabilitation. Patients with syringomyelia muscle atrophy require high-protein, high-energy diet supplements to provide the necessary substances for the reconstruction of nerve cells and skeletal muscle cells, to enhance muscle strength and increase muscle mass. Early use of high-protein, vitamin-rich, phospholipid, and trace element-containing foods, and actively cooperate with medicinal diets such as yam, Job's tears, lotus seed core, tangerine peel,太子参, lily, etc., is recommended. Spicy foods should be avoided, and smoking and drinking should be abstained from. For patients in the middle and late stages, semi-liquid and liquid foods rich in protein, nutrition, and energy are mainly recommended, and a method of eating small meals frequently is adopted to maintain the patient's nutritional and electrolyte balance.

　　3. Pay attention to prevent colds and infections. Patients with syringomyelia muscle atrophy, due to low immune function or some kind of immune deficiency, may worsen their condition and prolong the course of the disease once they catch a cold, with increased muscle weakness and muscle twitching. Especially for patients with bulbar palsy, there is a high risk of concurrent pulmonary infection, which, if not treated promptly, can lead to poor prognosis and even threaten the patient's life. Gastroenteritis can lead to dysfunction of intestinal flora, especially viral gastroenteritis can cause varying degrees of damage to the anterior horn cells of the spinal cord, resulting in increased muscle twitching, decreased muscle strength, and recurrent or worsening symptoms.

　　Firstly, Laboratory Examination

　　Routine cerebrospinal fluid and dynamic examination show no characteristic changes. Large cavities can cause mild stenosis of the vertebral canal and increased CSF protein.

　　Secondly, Imaging Examination

　　1. CT scan

　　80% of cavities can be detected during CT scanning, showing a clear boundary low-density cystic cavity within the spinal cord. Its CT value is the same as that of the corresponding subarachnoid cerebrospinal fluid, on average 15Hu lower than that of the corresponding segment of the spinal cord CT value. The corresponding spinal cord外形is dilated. A few cavities have lower pressure and appear atrophic, with irregular shape. When the cavity is small or contains a high protein content, it may be missed on plain scan. Intramedullary iodinated water造影CT delayed scanning can show high-density contrast agent within the spinal cord cavity. When the cavity directly communicates with the subarachnoid space, the contrast agent can pass through the spinal cord vascular space or communicate with the fourth ventricle to enter the cavity. Therefore, there is a higher chance of detecting high-density shadows within the spinal cord after delayed scanning following contrast agent injection. In cases with associated spinal cord tumors, the spinal cord is irregularly dilated, with uneven density, and the cavity wall may be thicker. After trauma, the spinal cord cavity is often eccentric, and partitions are often visible inside.

　　2. MRI

　　MRI sagittal plane images can clearly show the overall appearance of the cavity. T1-weighted images show a tubular expansion with central low signal in the spinal cord, while T2-weighted images show high signal fluid within the cavity. Regardless of T1 or T2 weighting, the fluid signal within the cavity is uniform and consistent. The cavity is often circular on cross-sectional images, sometimes irregular or biconcave in shape, with clear and smooth edges. At the upper and lower ends of the cavity, there is often gliosis. When the gliotic tissue proliferates within the cavity, it forms partitions, making the cavity multilocular or sausagelike. The spinal cord at the corresponding segment of the cavity is uniformly dilated. Due to the pulsation of cerebrospinal fluid, it appears as low signal in the T2-weighted image, a phenomenon known as the cerebrospinal fluid flow void phenomenon. The fluid within the spinal cord cavity communicates with cerebrospinal fluid and can have pulsation, so these patients can be seen to have low signal flow void phenomenon on T2-weighted images, which is quite similar to what is seen on T1-weighted images. Due to the different degrees of pulsation within the cavity fluid, the shape of the signal loss area may not be consistent with the range of T1-weighted imaging. Multilocular cavities, due to the presence of partitions, have weaker pulsation and a lower incidence of flow void phenomenon. However, when they communicate, the incidence of flow void phenomenon within the cavity increases significantly. Therefore, the absence of flow void phenomenon suggests the presence of multilocular partitions. Non-pulsating cavities are often solitary, with small length and diameter. After分流 surgery, the pulsation within the cavity is weakened or even disappears. Therefore, the observation of flow void phenomenon within the cavity can also be used as one of the indicators for surgical efficacy. MRI is the most effective tool for diagnosis and can display the spinal cord cavity and its extension and size in the vast majority of cases.

　　3. Others

　　Using induced current to detect muscle contraction function, for patients with severe muscle paresis, an electrical变性 reaction may occur, and the detection of motor threshold often increases. Electromyographic examination is meaningful for any level of damage to the lower motor neuron pathways of the spinal cord.

　　1. The diet for syringomyelia patients should contain a lot of high-protein, high-vitamin, easily digestible foods. Through reasonable nutrition matching and appropriate cooking, the patient's appetite should be enhanced as much as possible to ensure that the nutrients and energy in the patient's diet meet the body's needs.

　　2. Patients with syringomyelia should avoid foods and刺激性 foods that are harmful to the condition, such as chili and coffee, especially for patients in the acute stage and those with Yin deficiency and fire hyperactivity, it is best to avoid these foods.

　　3. Patients with syringomyelia should follow the doctor's advice on diet, starting with soft and thin food and gradually adapting to other foods within the body. Pay attention not to consume too much greasy food. It is necessary to rationally match sugar, fat, protein, minerals, vitamins, and other nutrients to achieve scientific dieting.

　　1. Treatment

　　General treatment involves the use of neurotrophic drugs. In the past, radiotherapy was tried, but the efficacy was not confirmed. Given that the disease is a slowly progressive condition, and it often is accompanied by occipitocervical deformities and cerebellar tonsillar herniation, which are believed to be related to the etiology, surgical treatment should be adopted after an explicit diagnosis is made. However, there is currently a lack of a universally recognized and unified surgical method. The effectiveness of surgery still needs to be confirmed through the practice of a large number of cases and a long period of observation. The theoretical basis for surgery is: ① To decompress the craniovertebral junction area, handle any existing deformities and other pathological factors in the area, eliminate the cause of the disease, prevent the progression and deterioration of the lesion; ② To perform a fenestration and shunting operation to reduce the size of the cavity, relieve internal compressive factors, and alleviate symptoms.

　　I. Posterior Fossa, Cervical Junction Decompression Surgery is performed according to the conventional posterior fossa decompression surgery method, including resecting part of the occipital bone and upper cervical vertebral plates, widely opening the dura mater, separating adhesions, focusing on releasing the cerebellar tonsillar herniation and subarachnoid adhesions in the large foramen magnum area, allowing the cerebrospinal fluid to flow out smoothly from the fourth ventricle central aperture. It has a good effect on syringomyelia. If there are pathological factors such as tumors and cysts, they should be dealt with together.

　　II. Syringomyelia Drainage Surgery performs occipital and cervical incisions, cuts the dura mater, explores the syringomyelic location of the spinal cord, and usually finds spinal cord bulging. Choose a non-vascular area on the dorsal midline along the posterior median fissure at the most prominent part of the spinal cord, and cut the spinal cord longitudinally to reach the syringomyelic cavity. Expose the syringomyelic cavity, then cut the syringomyelic cavity and drain the fluid. Place a silicone film inside the cavity at the incision site and suture it to the edge of the dura mater with silk thread as a continuous drainage device, which can improve the symptoms.

　　III. Syringomyelia Diversion Surgery opens the occipito-cervical region according to the craniocervical operation method, places a thin silicone tube inside the syrinx for spinal cord syringomyelia-subarachnoid cavity drainage surgery; or sends the catheter to the cerebellar medullary cistern or pontine cistern for shunting surgery, which has a good effect on relieving the symptoms of syringomyelia.

　　Other treatments include vitamin B complex, vasodilators, and neurocytometric metabolic function activators, which can all be used. Physical therapy, physiotherapy, and acupuncture therapy can also be adopted according to the condition to promote the recovery of postoperative neurological function.

　　II. Prognosis

　　The progression of this disease is slow, often lasting for decades. The short-term efficacy of surgery is significant, but surgery is not a curative operation. Patients should be followed up after surgery and regularly observed for changes in the syrinx and spinal cord through MRI.