1. Definition: Syringomyelia, also known as hydrosyringomyelia. Abnormal fluid accumulation in the spinal cord comprises two pathological types. Enlarged central canal of the spinal cord was discovered by Olliver as early as 1827, and since it was thought that the central canal of the spinal cord did not exist in humans after birth, the term spinal cord cavernous was used to describe this state.Stilling (1859) demonstrated that the central canal of the spinal cord existed throughout life in both juvenile and adult vertebrates.Schüppel (1865) labeled pathologically enlarged central canal of the spinal cord as Hydrosyringomyelia (HS). Schüppel (1865) referred to the pathologically enlarged central canal of the spinal cord as Hydromyelia, and Simon (1875) referred to the intramedullary cavity discontinuous with the central canal as spinal cavitation. To date, no clinical diagnostic technique has been able to clearly distinguish between the two pathologic states in surviving patients. Therefore, they have been collectively referred to clinically as spinal hydrocele cavitation or spinal cord cavernous disease. Clinically, the disease is mainly characterized by segmental distribution of pain and temperature sensation decreased and touch sensation preserved on one side or both sides of the trunk, atrophy of the hand, forearm ulnar side, supraspinatus muscle group and sweating disorder. The onset of the disease is insidious and the progression is slow. MRI of the vast majority of patients we treated showed thick and long intramedullary cavities with very weak spinal cord tissue. However, the clinical manifestations were mild. The extent of sensory deficits differed considerably from the length of the cavity. Motor deficits were less than sensory deficits and were limited to varying degrees of atrophy of the hand muscles manifested by anterior horn cell damage. These manifestations are quite inconsistent with the degree of manifestation that should characterize lesions within the spinal cord parenchyma. Which makes more sense: spinal cord cavernous disease, spinal cord effusion, or spinal cord effusion cavernous disease? Personally, I think that hydrocele may account for a large proportion of our cases. Arnold-Chiari malformation (1891), customarily known clinically as subcerebellar tonsil herniation, is actually a developmental malformation. Arnold-Chiari malformation (1891), clinically known as subcerebellar tonsillar herniation, is actually a developmental malformation in which the brain tissue of the middle axis of the posterior cranial fossa is shifted downward mainly by the prolongation of the cerebellar tonsils and enters into the cervical spinal canal via the foramen magnum. Type III, based on type II, with hydrocephalus and spinal membrane, cerebellar bulge. Type I is the most common in adults and is often combined with spinal cord cavernous disease. Type I is the most common in adults, often combined with spinal cord cavernous disease, and type A is combined with spinal cord cavernous disease, and type B is without spinal cord cavernous disease. types II and III are mostly seen in infants and young children. in 1894, chiari listed cerebellar hypoplasia as type IV, which is not widely accepted due to the controversy. Pathogenesis: Cerebrospinal fluid kinetic abnormality theory: 1) Gardner water hammer effect theory: it is believed that the cavern is in communication with the central canal and the IVth ventricle. Congenital anomalies in the occipitocervical region block the entry of cerebrospinal fluid (CSF) into the subarachnoid space from the IV ventricle. The arterial pulsation wave of the lateral ventricular plexus passes through the cerebrospinal fluid to the IV ventricle to form a water hammer effect, which pushes the cerebrospinal fluid to enter the central canal of the spinal cord through the latch of the IV ventricle (obex). The central canal expands under this pressure and eventually ruptures to form a cavity in the spinal cord parenchyma. 2) Ball and Dayan perivascular gap infiltration theory: It is believed that when the thoracic and abdominal pressures rise as a result of coughing and other special maneuvers, the pressure in the vertebral canal rises dramatically due to the furious dilatation of the epidural venous plexus, and because of the congenital abnormality of the occipitocervical region, the flow of cerebrospinal fluid is impeded by the congenital abnormality of the occipital-neck area from the vertebral canal to the skull, and it enters into the spinal parenchyma along the perivascular gap. into the spinal cord parenchyma. As a result, the cerebrospinal fluid accumulates in the medulla oblongata and fuses to form a cavity. Later, secondary factors cause the cavity to expand and rupture, and then the traffic between the cavity and the central canal of the spinal cord occurs. 3) William (slosh) theory: It is believed that congenital malformations of the occipitocervical region, especially chiari malformations, form a flap obstruction to the flow of the cerebrospinal fluid in this region. During a sharp rise in the pressure in the spinal canal caused by a specific maneuver such as coughing, the cerebrospinal fluid flows from the spinal canal into the skull. When relaxation occurs, the pressure in the spinal canal decreases and the flap prevents the flow of cerebrospinal fluid from the intracranial to the intravertebral canal, and a cranio-spinal pressure separation occurs. At the same time, the central canal becomes negatively pressurized, causing cerebrospinal fluid to enter the central canal of the spinal cord through the latch (obex) of the IV ventricle. In this manner, the central canal gradually dilates and eventually ruptures to form a cavity in the spinal cord parenchyma. All three theories are based on obstruction of cerebrospinal fluid circulation in the region of the occipital foramen magnum, which is now so popular that it has become the basis of surgical treatment. However, it is rare to see the presence of transportation between the cavities and the IV compartment in clinical practice, which is easy to understand to explain the development of the cavities, but the explanation of the formation of the cavities has been questioned. Abnormal blood circulation theory: It is believed that abnormal blood circulation in the spinal cord can cause necrosis and liquefaction of intramedullary tissue, which is closely related to the formation of non-traffic spinal cord cavernous disease. Congenital anomalies theory: the disease is a congenital developmental anomaly. the Arnold-Chiari malformation is also a congenital developmental anomaly, and has been proposed to be associated with a narrowing of the posterior cranial fossa volume. Reflection: A disease containing two different pathologic states must have a different pathogenesis. The 176 cases admitted to our department since 1985 have the following clinical features: 1) the age of onset is seen as young as 3 months after birth (without surgery, not included in this group); 2) the clinical manifestations are relatively very mild. The extent of sensory deficits differed considerably from the length of the cavities. Motor deficits were less than sensory deficits and were limited to varying degrees of atrophy of the hand muscles manifested by anterior horn cell damage. Very few patients present with cone-bundle signs. In contrast, the cavities associated with trauma and spinal vascular malformations are relatively small but clinically severe.3) They are basically combined with developmental abnormalities in the occipitocervical region, such as flattened cranial base and Arnold-Chiari malformations, the latter being the most common, all of which are of type I. MRI showed that the dorsal surface of the tonsils of Arnold-Chiari malformation type I showed a turn in the region of the occipital foramen magnum, with obvious ingrowns.2,3 The dorsal surface of the tonsils of type III was a single line, with a clear ingrown. The dorsal surface of the tonsils in type II and III was a slope.4) MRIT2WI images showed cerebrospinal fluid obstruction around the tip of the tonsils in the region of the occipital foramen magnum, and the IV ventricle was normal in size, and no communication between the cavities and the IV ventricle was seen.2 cases of posterior median foramen abnormality were found, and surgical confirmation of thin film adhesion was made in 1 case; granular amyloid tissue was made in 1 case. 1 case of cerebral-spinal cord cavernosities was found in the rest of the cases which were mostly below the cervical dilatation.5) Improvement of the cerebral-spinal fluid circulation in the occipital-cervical subarachnoid space Various methods of cerebrospinal fluid circulation were seen in cavitation collapse. In some cases, cavernous collapse was seen on the 2nd postoperative day. In some cases, cavernous collapse was seen only after 3 months. Therefore, the formation and development of the disease should be explored separately. Since hydrocephalus occupies a large proportion of the spinal cord, the formation of the cavities should be related to embryonic development. The development of the cavities may be related to the poor circulation of cerebrospinal fluid and the poor closure structure of the spinal cord itself. The traffic between the cavities and the subarachnoid space of the spinal cord is difficult to determine, and the Gardner’s theory can not explain all the cases. Other secondary factors, such as spinal vascular malformation and trauma, can cause changes in the closed structure of the spinal cord itself and poor circulation of cerebrospinal fluid, and the cavitation occurs within the spinal cord parenchyma, so the clinical manifestations are heavier. How does atrophic spinal cord cavernosis develop? Diagnosis: 1) X-ray plain film; 2) myelography; 3) intraoperative real-time ultrasound; 4) CT and DMCT; 5) MRI.Currently, MRI and X-ray plain film are mainly used, the former can fully show the morphology of the spinal cord cavities and the circulation of cerebrospinal fluid, and the latter can help to detect bony deformities. The diagnosis of this disease is not difficult, relying on clinical manifestations and detailed clinical examination. The development of diagnostic imaging methods has improved the understanding of spinal cord cavernous disease, especially as the chance of combining Arnold-Chiari malformation is higher than previously thought, and the application of MRI has further updated the understanding. In turn, this has influenced the development of surgical management of the disease. The differential diagnosis of this disease consists mainly of combined cavernous intramedullary tumors. Traditionally, the disease has been divided into two categories: traffic and non-transit. The former refers to cavities that are in communication with the central canal and the IV ventricle, which are not yet easily detected on imaging data, and are now mostly referred to patients with combined occipitocervical malformations; the latter refers to independent intramedullary cavities, which are mostly seen in secondary spinal cavernous disease. Imaging data are also categorized into dilated and atrophic spinal cord cavernous disease, the former is suitable for surgical treatment. Preoperative preparation: 1) X-ray radiographs to understand the bony deformity, especially to assess the stability of the occipitocervical region, with or without joint dislocation.2) Pediatric patients are prone to postoperative deformities such as cervical lordosis, and the age of surgical treatment should be decided especially according to whether the disease is progressive.3) A history of tuberculous meningitis. Tuberculous arachnoid inflammation with adhesion causing cavitation is not good for surgical efficacy.4) Surgery for atrophic spinal cord cavernous disease is not good for surgical efficacy.5) Talking about the purpose of surgery is mainly to control the progression of the disease. 4. Surgical methods that have been used historically: suboccipital and superior cervical decompression + central canal occlusion; IVth ventricle – spinal subarachnoid shunt; myelotomy and/or cavernous-subarachnoid shunt; terminal ventricle opening (end-filament dissection); cavernous-pool drainage; cavernous suction or occlusion; and ventricular shunt. 5. Surgical methods that have been reported domestically: suboccipital and cervical 1-2 decompression: Suboccipital and cervical 1-2 decompression + cavotomy/shunt/; Suboccipital and cervical 1-2 decompression + occipital pool plication/subarachnoid release; Suboccipital and cervical 1-2 decompression + cerebellar tonsillectomy + occipital pool plication/subarachnoid release; Cavotomy-ventriculocephalic shunt; Trend: suboccipital decompression is on the rise, cavotomy is on the decline. Points of contention: arachnoid retention or not? Dural incision or not? Size of the occipitocervical decompression window (decompression of the occipital foramen magnum area or decompression of the enlarged posterior cranial fossa?) . Reflections: 1) If the results of various surgical treatments are close, should the surgical approach be chosen to complicate? Simplify? 2) Decompression of the posterior cranial fossa or decompression of the greater occipital foramen region? Classical decompression of the posterior cranial fossa (suboccipital decompression) covers the greater part of the squamous part of the occipital bone and the C1-2 vertebral plate, but the site of the cerebrospinal fluid obstruction is in the region of the greater occipital foramen. Craniospinal cerebrospinal fluid traffic may pass ventrally, bilaterally, and through the cerebellar valleys. So, should decompression be as extensive as possible? Or until it is reasonable? 3) Does removal or separation of the tonsils cause adhesions? Do adhesions no longer occur after localized subarachnoid release? 4) Is the cavity cut near the posterior root outlet or in the posterior median sulcus? Is it really possible to perform a posterior median sulcus dissection when the cavity is not so obvious? Are there any structures in the posterior median? Such as a comma bundle? 5) Does spinal stenosis combined with spinal cord cavernous disease require surgery? Currently, we mainly practice decompression of the occipital foramen magnum area + clipping of the dura to preserve the arachnoid under neuroendoscopy.