Vestibular aqueduct syndrome was discovered in the late 1970’s with the introduction of CT, and is characterized by fluctuating sensorineural hearing loss and vertigo in young children. Patients tend to develop the disease at the age of 3-4 years, and colds and trauma are often triggers for the onset of the disease, which can cause severe sensorineural hearing loss and vertigo even with minor trauma. What is the pathology of vestibular aqueduct syndrome? We know that the lymphatic system of the cochlea consists of two chemically distinct types of lymphatic fluid – ectolymph and endolymph. In the inner ear, the ectolymphatic fluid is found in the vestibular and tympanic steps of the cochlea and in the interspaces of the spiral apparatus, while the endolymphatic fluid is found in the middle steps of the cochlea. The two types of lymphatic fluid do not communicate with each other and together play an important role in the pressure regulation of the cochlear fluid. The total amount of ectolymphatic fluid is much larger than that of endolymphatic fluid, and its Na+ content is about 30 times higher than that of K+. This ionic concentration characteristic is similar to that of extracellular or intercellular fluid, which is widely present throughout the body, and its ionic composition is very similar to that of cerebrospinal fluid, but its protein content is much higher than that of cerebrospinal fluid. In anatomy, the vestibular aqueduct is a bony channel connecting the cochlea with the posterior cranial cerebrospinal fluid, which allows the ectolymphatic fluid in the cochlea to flow directly to the cerebrospinal fluid. The pressure of the ectolymphatic fluid in the inner ear is directly influenced by the pressure of the cerebrospinal fluid in the posterior cranial fossa, and if the diameter of this tube is too wide, when movements such as exercise or breath-holding are performed to induce a higher pressure of the cerebrospinal fluid, it can directly squeeze the vestibular balance receptors in the membrane vagus to appear vertigo symptoms. Secondly, the lumen of the vestibular aqueduct houses the endolymphatic duct. In fact, we can regard the endolymphatic duct as the part of the membrane vagus extending to the brain, but the difference between the endolymphatic duct and the vestibular aqueduct is that the end of the endolymphatic duct extending to the side of the brain is the blind end, which is not directly connected with the cerebrospinal fluid, and its contents are endolymphatic fluid, which belongs to the intracellular fluid, i.e., high potassium and low sodium components, and the concentration of K+ is about 30 times of Na+. The endolymphatic fluid penetrates into the cerebrospinal fluid from the membranous vagus once through the endolymphatic duct to the capsule end of the posterior cranial fossa and through the inner side of the dura mater. In the process of fluid exchange between the membranous vagus and the cerebrospinal fluid in the subarachnoid space through its own extensions, the endolymphatic ducts and endolymphatic sacs, this flow of endolymphatic fluid is unidirectional, i.e., toward the posterior cranial fossa. One of the reasons why this unidirectional flow of endolymphatic fluid toward the cerebral side is ensured, in addition to the presence of valves in the membranous vagus, is related to the presence of bony structures in the periphery of the endolymph – the vestibular aqueduct. During the flow of endolymphatic fluid toward the endolymphatic sac, the endolymphatic fluid on the side of the membranous vagus is mainly intracellular fluid, i.e., low in sodium and high in potassium. The K+-Na+ ion exchange pump exists on the vascular stripe in the endolymphatic vessels, which exchanges K+-Na+ with the endolymphatic fluid passing through it, causing the original potassium-rich endolymphatic fluid to gradually turn into a high Na+ solution, which is close to the sodium content of the cerebrospinal fluid, i.e., it becomes extracellular fluid. Apparently, the composition of endolymphatic fluid from the membrane vagus through the endolymphatic vessels to the endolymphatic sac changes from a high potassium to a high sodium solution, in other words, from an intracellular fluid to an extracellular fluid, and this change is closer to the cerebrospinal fluid on the inside of the endolymphatic sac, facilitating the absorption of endolymphatic fluid. This unidirectional flow and compositional change of endolymphatic fluid ensures the pressure stability and chemical equilibrium of the membrane vagus; at the same time, the unidirectional flow of endolymphatic fluid also prevents the high sodium solution on the side of the endolymphatic sac from returning to the membrane vagus, avoiding the poisoning of auditory cells. However, we cannot simply regard this flow as a direct flow or osmosis, because during the flow from the cochlea to the endolymphatic sac, the potassium and sodium content of the endolymphatic fluid undergoes a gradual change, i.e., from an intracellular fluid with high potassium and low sodium to an extracellular fluid with high sodium and low potassium close to the cerebrospinal fluid, and this shift in fluid composition may be related to the presence of absorptive epithelial structures and potassium and sodium ion pumps in the endolymphatic vessels . In this sense, the ectolymph in the vestibular aqueduct is in direct communication with the cerebrospinal fluid and has the same composition; therefore, the composition does not change whether the flow is in the direction of the cerebrospinal fluid or in the direction of the vagus; on the contrary, the flow of the endolymphatic fluid in the endolymphatic duct is unidirectional and can only flow in the direction of the cerebrospinal fluid, and the composition also changes from intracellular fluid to extracellular fluid. In brief, the flow of ectolymphatic fluid in the vestibular conduit is not changed in composition, whereas the flow of endolymphatic fluid in the endolymphatic ducts is changed, i.e., it changes from endolymphatic fluid to ectolymphatic fluid, i.e., extracellular fluid. The vestibular aqueduct is present in the temporal bone fissure-like structure surrounding the endolymphatic duct, forming a narrow part of the endolymphatic duct, which acts as a restriction of intracanalicular solution flow and pressure transmission, while ensuring the protection of the membranous vagus from cerebrospinal fluid pressure. Among them, the size of the vestibular aqueduct is very important; if it is too wide, it may lose this restrictive effect, and once the cerebrospinal fluid pressure changes, it will directly cause the change of pressure in the cochlea, forming the flow of endolymphatic fluid and the stimulation of vestibular receptors, which eventually triggers the vertigo symptoms. Secondly, the endolymphatic fluid of the membranous endolymphatic ducts has unidirectional mobility, so that it can ensure the balance of the internal environment for the metabolism of the auditory hair cells in the inner ear. Furthermore, if the vestibular aqueduct is too wide and the endolymphatic duct is also too wide, it will lead to the reflux of endolymphatic fluid and finally the mixing of internal and external lymphatic fluid in the membranous vagus, which will cause toxic damage to the cochlea and lead to sensorineural hearing loss. This shows that patients with vestibular aqueduct syndrome have two main problems, firstly, the loss of the normal flow limiting effect of the vestibular aqueduct makes the pressure change of cerebrospinal fluid easily cause the pressure fluctuation of the fluid in the cochlea, especially stimulating the vestibular receptors to show the symptoms of vertigo; secondly, the passive dilatation of the endolymphatic vessels makes the endolymphatic fluid backflow back to the membrane vagus, causing the confusion of the components of the internal and external lymphatic fluid and the poisoning of the auditory cells, which eventually causes hearing loss. of hearing loss eventually. Usually, the maximum anteroposterior diameter of the middle segment of the vestibular aqueduct is >1.5 mm, and the diameter of the external orifice of the vestibular aqueduct is >1.5 mm as the axial CT diagnostic criteria for vestibular syndrome. Although CT scans are often used in imaging to detect the presence and abnormality of the vestibular aqueduct, this only indicates the width of the bony lumen and does not reflect the actual condition of the membranous endolymphatic vessels within the vestibular aqueduct. Therefore, MRI hydroimaging of the cochlea is able to understand the thickness of the endolymphatic vessels and directly find the real cause of hearing damage. In China Hearing Online’s WeChat, parents often ask what to do about vestibular aqueduct syndrome? Does a cochlear implant mean a complete cure? We can only warn parents of such children that the principle of early detection, prevention and intervention is usually used to slow down the progression of the disease in patients with vestibular syndrome. Early treatment with neurotrophic agents is generally effective, and some children’s hearing can be restored to its original level, but it is still poorer than normal children’s hearing, and hearing is prone to fluctuations, and there is no specific treatment for the lesions of the vestibular aqueduct. Some children are born with nearly normal hearing, although in the subclinical stage, but careful parents will find that the child speaks late, slurred speech, hearing loss after a cold or trauma is sometimes reversible, if you can timely go to the hospital otology department for hearing and balance function examination can help diagnose, do temporal bone CT scan and MRI examination can confirm the diagnosis, early confirmation of this disease and take preventive measures. For children with significant hearing loss that affects language communication, they can be fitted with hearing aids at professional institutions for language training. For children with severe hearing loss, cochlear implants are the only way to improve hearing, but they are not a cure for vestibular damage, which means that patients with vestibular canal syndrome will continue to have symptoms such as vertigo and tinnitus.