Applied anatomy Composition of the skull base: The posterior wall of the frontal sinus forms the anterior border of the skull base, where the thicker frontal bone extends posteriorly to form the parietal wall of the septal sinus and continues with the sieve plate bilaterally. The sieve plate is connected to the sieve roof by a lateral plate. This connection is barely visible when the sieve plate and the sieve roof are at the same level, but it may be a vertical bone plate depending on the degree of sieve plate sinking into the nasal cavity. Posteriorly, the pterygoid sinus and posterior septal airspace form a lower part of the skull base. The most common site of spontaneous cerebrospinal fluid rhinorrhea is the location of the sieve plate, where the dura mater wraps around the olfactory nerve and crosses the sieve plate, making it highly susceptible to rupture. The other most common site of injury is from the well-pneumatized pterygoid sinus, and increased intracranial pressure is an important causative factor in these cases. Cerebrospinal fluid nasal leaks associated with nasal endoscopic surgery are often found with fistulae located in the lateral plate near the anterior septal artery. Post-traumatic cerebrospinal fluid nasal leaks usually originate from the sieve plate, sieve roof and posterior wall of the frontal sinus or pterygoid sinus. Overview The main risk of cerebrospinal fluid rhinorrhea is that it can be followed by serious intracranial bacterial infections, which can be life-threatening and should be taken seriously by clinicians. The advantages of nasal endoscopic repair of cerebrospinal fluid nasal leak are: 1. no damage to brain tissue, avoiding complications and dangers that tend to occur with traditional craniotomy; 2. no facial scar; 3. direct visualization of the sieve plate, pterygoid sinus, septal sinus and saddle area for repair, less damage, maximum protection of olfactory function, precise operation and good surgical results. Indications and contraindications of surgery Indications: 1, spontaneous cerebrospinal fluid nasal leakage, invalidated by conservative treatment; 2, traumatic (including surgical injury) cerebrospinal fluid nasal leakage; 3, tumor cerebrospinal fluid nasal leakage. Limitations of nasal endoscopic repair of cerebrospinal fluid nasal leak: inability to simultaneously manage intracranial lesions or remove intracranial tumors; difficulty in repairing larger dural defects via nasal endoscopy. 19.6.4 Preoperative preparation 1. nasal CT scan to observe the site of cerebrospinal fluid nasal leak (septal sinus, pterygoid sinus, frontal sinus); 2. nasal endoscopy can usually localize the specific site of cerebrospinal fluid leak. 3. glucose quantification: when a cerebrospinal fluid nasal leak is suspected, the effluent can be collected for glucose quantification. A sugar content of more than 1, 67 mmol/L can identify the cerebrospinal fluid. Transferrin β-2 is only found in cerebrospinal fluid and aqueous hyaline body fluid, not in tears, saliva, serum and physiological nasal secretions, and can be used as a specific test marker for cerebrospinal fluid. Position and anesthesia The patient is placed in the supine position with the head slightly elevated. Sterilization and sterile towel. General anesthesia. (1) Cerebrospinal fluid nasal leak from the horizontal plate of the sieve and the roof of the sieve First, endoscopic septal sinus excision is performed to thoroughly clean the granulation tissue and mucosal polyps from the horizontal plate of the sieve and the roof of the sieve, and to find and identify the site of cerebrospinal fluid nasal leak. If the middle turbinate obstructs the observation or affects the operation, partial middle turbinate resection can be done. The entire procedure should be performed with strict hemostasis to clearly reveal the site of the leak. If the leak is large, the airspace around the leak should be thoroughly cleaned up to the sieve roof or the horizontal plate of the sieve bone to expose part of the dura mater. At this point, care should be taken to remove the prolapsed dura and meninges rather than attempting to repair it, because the dura cannot provide the supporting force for repairing the defective tissue. In contrast, the skull base bone is hard, and the repair will naturally work better if it is based on this strong support. When the skull base is fractured or unstable small fragments of bone in the operative field should be removed prior to repair. Large pieces of bone should be left in place. and leave the dura open to the edge of the large bone fragment. The tissue around the leak is scratched to form a fresh wound with a ring approximately 2 to 3 mm wide. The broad fascia is laid on the surface of the leak. If possible, it is preferable to tuck the broad fascia above the sieve plate or the bony wall at the apex of the sieve sinus to ensure good fixation, but this is sometimes difficult to do. The muscle, gelatin sponge and iodoform gauze are placed under the broad fascia. When the skull base defect is larger than 2 cm, cartilage or bone is used to reinforce the repair site. Cartilage can be taken from the nasal septum or from the auricular cartilage via the postauricular route. Bone grafts can be taken from the pear bone or the inferior turbinate. A good free thick mucosal graft can be obtained by routine inferior turbinate resection. For cerebrospinal fluid nasal leaks caused by linear fractures of the septal roof, the key to surgical repair is to enlarge the leaky fracture into a visible fistula, then fill the fistula with pounded muscle and seal the entire septal roof with broad fascia. The fistula was fixed by compression with a gelatin sponge impregnated with antibiotics. The septal sinus and nasal cavity were filled with iodoform gauze. For good fixation of the broad fascia or muscle with the tissue around the leak, otocerebral glue can also be applied, which helps to improve the success rate of the procedure. The sieve plate is connected to the sieve roof through the lateral plate, and the defect around the lateral plate is the most difficult area to repair. Because the bone is extremely thin in this area, any manipulation may enlarge the defect. After trimming out a fresh wound around the defect, the defect is covered with fascia or turbinate mucosa, and fat is used as a filler. Alternatively, the bony part of the middle turbinate may be removed, but the middle turbinate mucosa is preserved, and then the middle turbinate mucosa flap is turned to the defect site. Cerebrospinal fluid rhinorrhea of the sieve plate is not easily repaired due to the difficulty of exposure. Because of the narrow olfactory sulcus and the immobility of the middle turbinate, adequate exposure of the area is achieved at the expense of changing the position of the middle turbinate. Either external displacement of the middle turbinate or removal of the middle turbinate is performed. The external displacement may result in new septal plate fractures or septal plate movement. Removal of the middle turbinate can sometimes damage the natural opening of the frontal sinus. For better access to the olfactory sulcus, septal sinus opening may be performed to improve access to the nasal roof. It is difficult to separate the mucosa from the septal plate because the bone is thin and can be broken with slight pressure. In addition, there is still a sheath of the olfactory nerve wrapped around the septum that crosses the sieve plate, which can easily form or aggravate cerebrospinal fluid sieve plate leakage during the exposure process. (2) Cerebrospinal fluid nasal leak from the pterygoid sinus Enter the pterygoid sinus through the nasal cavity and through the anterior wall of the pterygoid sinus to find the site of the cerebrospinal fluid leak. Carefully clean all the mucosa of the pterygoid sinus. Mucosal polyps and granulation tissue around the leak should be removed thoroughly. The lumen of the pterygoid sinus is filled with broad fascia and muscle. If possible, it is best to place a broad fascia through the cranial defect between the ruptured dura and the cranial bone wall (epidural space). The pterygoid sinus stoma is closed with broad fascia. The nasal cavity was filled with gelatin sponge and iodoform gauze, and the gauze filling was extracted around 10 days. The lateral wall of the hyperpneumatized pterygoid sinus forms the lateral crypt of the pterygoid sinus, where most of the cerebrospinal fluid nasal leaks occur in combination with meningeal bulges. In order to fully expose the lateral wall of the pterygoid sinus, the posterior wall of the maxillary sinus and the medial tissue of the pterygoid fossa are removed via the pterygopalatine fossa pathway. The main steps are: complete excision of the septal sinus airspace, full excision of the pterygoid sinus and maxillary sinus opening, and excision or abrasion of the posterior wall of the maxillary sinus to access the pterygopalatine fossa. The maxillary artery and its branches are identified, pushed down or clamped, and the deep area of the pterygopalatine fossa is exposed by separating them layer by layer, then the maxillary branches of the pterygopalatine and trigeminal nerves are dissected free and preserved as much as possible, and the posterior wall of the pterygopalatine fossa (i.e., the anterior wall of the pterygoid sinus) is further removed to reach the lateral crypt of the pterygoid sinus. Excision of part of the root of the medial plate of the pterygoid process is helpful in exposing the lateral crypt of the pterygoid sinus. Intraoperatively, the pterygopalatine artery and the distal maxillary artery are usually cut, which may result in severe bleeding. Rapid cautery of the bleeding vessels by bipolar electrocoagulation can be effective in stopping the bleeding. The posterior wall of the pterygopalatine fossa can be removed with a diamond O. Care should be taken not to damage the maxillary nerve that travels through the pterygopalatine fossa. When the defect is completely exposed, the cerebrospinal fluid nasal leak is then repaired. Some scholars have also adopted surgical repair by removing the posterior end of the nasal septum and then reaching the lateral crypt of the pterygoid sinus from the contralateral nasal cavity via the space after septal resection. Bing Zhou introduced the trans-pterygoid pathway to the lateral crypt of the pterygoid sinus, with the following main steps: ① complete anterior to posterior septal sinus opening, complete wide maxillary sinus opening through the middle nasal tract, open the posterior edge of the window to the vertical plate of the palate, and peel off the mucosa of the posterior lateral wall of the maxillary sinus left in the anterior inferior part of the sinus cavity. ②Open the pterygoid sinus, after widening the resection of the anterior (lateral) wall of the pterygoid sinus, from the root of the middle turbinate to the attachment of the lateral wall of the nasal cavity, separate the mucosa to expose the pterygopalatine foramen, bite off the vertical plate of the palatine bone and dissect the pterygopalatine artery. ③Laterally, after removing the bony wall of the posterior lateral wall of the maxillary sinus with the ridge of the infraorbital neural tube as the boundary, the anterior pterygopalatine orifice, pterygopalatine nerve, artery, pterygopalatine ganglion and other vascular nerve bundles were dissected and exposed with the pterygopalatine artery as the marker. Below the pterygopalatine artery, the pterygopalatine fossa fat was partially incised and coagulated by electrocoagulation, and bluntly peeled away to reveal the root of the pterygoid process and the anterior wall of the pterygoid sinus, which was separated upward and outward to the round hole, and the anterior wall of the lateral crypt of the pterygopalatine sinus was ground away below it as a marker to expose the lateral crypt. The mucosa in the cavity of the pterygoid sinus was peeled off, and the bony defect area of the skull base was completely exposed. The defect area is filled with fat or muscle tissue, embedded with bone fragments on the intracranial surface of the defect, covered with myofascial and/or mucosal membrane, and sprayed with bioprotein glue (3) Cerebrospinal fluid nasal leak from the frontal sinus Repairing cerebrospinal fluid leaks occurring in the frontal sinus through nasal endoscopy is usually difficult due to the pathway and viewpoint. Endoscopic repair is only possible if a small, forward-expanding defect is clearly visible after opening the frontal sulcus. If the defect is located in the posterior or lateral wall of the frontal sinus, the anterior wall of the frontal sinus can be opened through a coronal scalp incision or brow arch incision, and the fistula site can be determined by 70- or 30-degree endoscopic examination of each wall of the frontal sinus. The mucosa around the fistula is removed with a spatula under direct vision, and the mucosa at the bone defect should be gently separated from the dura mater if it is adherent to avoid damaging the dura mater and aggravating the cerebrospinal fluid nasal leakage. Fascial or fat-supported grafts can be used to repair the fistula after the defect site is clearly identified. If severe structural destruction is found at the frontal saphenous fossa, the frontal sinus should be closed with fat. In recent years, a new method of repairing cerebrospinal fluid nasal leaks has been developed more rapidly, namely the bath-plug technique for repairing cerebrospinal fluid nasal leaks. The main procedure is as follows: after the tissue around the skull base leak is processed, the size of the skull base defect is measured. The graft can be taken from the fat of the earlobe. If the defect is larger than 12 mm, fat can be extracted from the greater trochanteric area of the femur or from the abdomen. The fat plug should be the same diameter as the leaky hole defect and approximately 1.5-2 cm in length, and an absorbable suture is tied at one end of the fat plug and then passed through the long axis of the fat. A free mucosal flap is obtained on the lateral wall of the nasal cavity, positioned at the anterior aspect of the middle turbinate and measuring 3 cm × 3 cm (more is taken for larger defects). The fat plug is placed under the defect and gently inserted into the defect with a frontalisable sinus probe. It is important to note that only a small portion of fat is inserted into the skull at a time, which is safe because the probe will not enter the skull more than a few mm at a time, whereas attempting to insert a large piece of fat into the skull at a time requires a lot of force and the probe may slip deeper into the skull and damage intracranial structures. There may be blood vessels present at the site of the fat embolus, and this is especially likely when repairing a meningeal brain bulge, since there is a vascular blood supply to the prolapsed brain tissue and dura mater. However, if the fat embolus is introduced slowly and gently into the skull, the likelihood of damage to intracranial structures is minimal. Once the fat embolus is safely pressed into the skull, it is held in place with a probe in conjunction with gentle pulling of the sutures, allowing the fat embolus to spread flat over the intracranial defect site, which, together with the pressure of the cerebrospinal fluid, increases the fat containment. The sealing of the fat plug is further tested by placing the patient in a head-down position and having the anesthesiologist cause the patient to perform a deep inspiratory maneuver, at which point no cerebrospinal fluid should be visible in the nasal cavity. Further pressure is applied from above to fill the bony defect with the fat plug, and it is normal that a little fat may droop from the defect. After these steps, the patient is placed in a head high position (15 degrees) and the free mucosal flap is slid up along the sutures to close the defect and ensure that the mucosal side of the flap is facing the nasal cavity. The surgical field was coated with fibrin glue, the sutures were cut, and then the nasal cavity was filled with gelatin sponge and iodoform gauze. Postoperative management 1. lie in semi-sitting position, low salt diet, limit water intake, lie in semi-sitting position for 5-7 days; 2. apply antibiotics to prevent infection; 3. avoid forceful nose blowing, sneezing and forceful coughing, apply stool softeners for 3-5 days; 4. apply dehydrating drugs and diuretics as appropriate; 5. consult with neurosurgery whether to do lumbar drainage; 6. withdraw the filled iodoform gauze about 10 days after surgery. Complication prevention and control After nasal endoscopic skull base repair, cerebrospinal fluid nasal leakage may sometimes occur again, if it occurs for a short period of time after surgery, conservative treatment can be given first. Injury to intracranial vessels requires neurosurgical assistance. When intracranial operations are involved, be gentle and stop the bleeding properly during the operation. Evaluation 1. Accurately finding the leak is a prerequisite for successful surgery. We have learned that (1) if clear and bright fluid is seen flowing down intraoperatively, a suction device can be used to track it while suctioning until the leak is found. Cerebrospinal fluid leaks caused by septal sinus surgery are easily observed under nasal endoscopy and are characterized by a clear flow of fluid with thin, bloody fluid. If there is significant hemorrhage, the cerebrospinal fluid appears as a dark band in the blood because the cerebrospinal fluid is not as reflective as the surrounding blood. Obvious hemorrhage combined with cerebrospinal fluid leakage suggests the possibility of intracranial vascular injury. (2) In patients with longer disease duration, there is often mucosal hypertrophy, adhesions or granulation tissue around the leak, at which point the lesion should be scraped away and the area observed in detail to find the leak. (3) When searching for the leak under endoscopy, an assistant can assist in compressing the affected internal jugular vein to induce cerebrospinal fluid spillage; (4) According to foreign data, fluorophore can be injected into the spinal canal via lumbar puncture to assist in the localization of cerebrospinal fluid leaks. (5) In nasal endoscopic cerebrospinal fluid nasal leak repair, it is almost impossible to repair the cerebrospinal fluid leak in a dense manner if one wishes to do so surgically. The aim of the procedure is to provide a suitable graft piece as well as to create an environment suitable for repair. (6) The principles of successful repair are precise positioning of the defect, careful removal of the mucosa around the defect to prepare the graft bed for graft growth, and accurate alignment of the graft to the defect, requiring no dead space, no bulging or no tension. 2, after surgery should be noted: (1) for more cerebrospinal fluid leakage can be appropriate to reduce the cranial pressure. 25% mannitol 250ml, 2 times / day, intravenous drip, at least 5 days in a row. (2) The gelatin sponge filled with pressure at the top of the sieve can be removed and allowed to drain or be absorbed naturally. (3) Don’t let the patient do the examination of lowering the head and pressing the neck in order to observe the effect of surgery.