Skull base communicating tumors refer to tumors that originate from intracranial or extracranial penetration of the skull base bone and/or dura causing intracranial and extracranial communication. The anterior skull base is adjacent to the nose, orbit, and face, and is a common site for communicating tumors. The location of the communicating tumor is deep, and when found, it is often large in size. The surrounding anatomical relationships are complex and neurovascularly intertwined, making surgery difficult and risky, and often requires multidisciplinary collaboration. From 1994 to 2007, our department cooperated with the Department of Maxillofacial Surgery and the Department of Otolaryngology to treat 50 cases of anterior lateral skull base communicating tumors, which are reported as follows. 1. Subjects and methods 1.1 General situation 31 male cases and 19 female cases, age 3-71 years old, average 34 years old. Preoperative CT and MRI examinations were performed in all cases, 15 DSA examinations were performed, 9 preoperative embolizations were performed. 12 preoperative biopsies were performed. 5 cases applied dextroscope system for preoperative planning. 1.2 Clinical manifestations Local symptoms: facial swelling, nasal congestion, epistaxis, protruding eyes, headache, etc. Cranial nerve symptoms: facial numbness, diplopia, facial palsy, hearing loss, hoarseness, etc. 1.3 Tumor size: diameter 3.2-18 cm, average 5.7 cm. tumor site: cranial + orbit in 5 cases, cranial + sinus in 9 cases, cranial + sinus + pterygopalatine fossa in 5 cases, cranial + sinus + pterygopalatine fossa + infratemporal fossa in 12 cases, cranial + sinus + pterygopalatine fossa + parapharyngeal space in 9 cases, cranial + sinus + pterygopalatine fossa + infratemporal fossa + parapharyngeal space in 10 cases. 1.4 Surgical access Enlarged frontal base access in 4 cases, transmaxillary access in 8 cases, transcranial orbital access in 4 cases, transnasal access in 4 cases, frontal temporo-zygomatic access in 5 cases, transmandibular access in 11 cases, preauricular trans-temporal-inferior temporal fossa access in 5 cases, and combined frontal temporal-inferior temporal fossa access in 9 cases. Skull base reconstruction was performed in 18 cases. 2. Results 2.1 Excision: 31 cases of total excision, 15 cases of subtotal excision, and 4 cases of partial excision. 2.2 Postoperative complications: 23 cases had postoperative complications. There were 4 cases of wound infection, 1 case of intracranial hematoma, 4 cases of cerebrospinal fluid leakage, 1 case of central nervous system infection, 2 cases of mastication difficulty, 5 cases of cosmetic damage, 1 case of proptosis, and 9 cases of cranial nerve injury, including 1 case of olfactory nerve, 4 cases of trigeminal nerve, 1 case of abducens nerve, and 3 cases of facial nerve, with no surgery-related deaths. 2.3 Postoperative pathology: meningioma in 9 cases, epithelioid cyst in 5 cases, adenocarcinoma in 4 cases, angiofibroma in 4 cases, hemangiopericytoma in 2 cases, squamous cell carcinoma in 3 cases, sarcoma in 4 cases, teratoma in 3 cases, enucleated cell tumor in 2 cases, glial ectopic in 2 cases, hydatidiform fibrous tumor in 2 cases, osteoma in 1 case, papilloma in 1 case, neurofibroma in 5 cases, nerve sheath tumor in 2 cases, and benign tumor of neurogenic origin in 1 case. 2.4 Follow-up: 32 cases were followed up, 18 cases were lost, and the follow-up period was 6 months-7 years, with an average of 20 months. There were 8 cases of tumor recurrence, all of them were malignant tumors. The anterior skull base includes the frontal, sieve and pterygoid bones, among which the sieve bone is the weakest and the tumor can communicate intracranially and extracranially through the sieve plate or orbital roof. The lateral skull base refers to the triangle of the skull base at the intersection of the infraorbital fissure and the prolongation line of the occipital fissure, above which mainly corresponds to the middle skull base. This area communicates with the orbit via the superior and inferior orbital fissures, with the pterygopalatine fossa via the foramen ovale, foramen spinosum, and foramen rupture, with the infratemporal fossa and parapharyngeal space. The tumor can communicate intracranially and extracranially along these foramina and fissures or by destroying the middle skull base. The anterior and lateral skull base tumors can also cross the pterygoid pterygoid and saddle nodes to invade each other. Common anterior and lateral skull base communicating tumors include meningioma and nerve sheath tumor from intracranial origin, nasopharyngeal carcinoma, juvenile angiofibroma and olfactory blastoma from nasal cavity and paranasal sinuses, adenoid cystic carcinoma from salivary gland, osteoma and chondrosarcoma from bony structures. The selection of surgical cases should fully consider the patient’s symptoms, signs, life expectancy, natural history of the disease, tumor nature, scope, and involved structures. Preoperative biopsy is done as much as possible, and transnasal or sinus biopsy is preferred for most communicating tumors [1]. Surgery is generally not preferred for those sensitive to radiotherapy or chemotherapy, such as nasopharyngeal carcinoma, lymphoma, etc. If the tumor is huge and extensively invades important structures, such as cavernous sinus, ruptured orifice segment of internal carotid artery or bilateral orbits, surgery is prudent. For slow growing benign tumors, such as meningioma at the base of the skull, if the lesion is small, asymptomatic or mild, especially in elderly patients, they can be observed and followed up. For patients with suspected important vascular involvement or tumor with abundant blood supply, CTA, MRA or DSA examination is feasible. If the internal carotid artery is surrounded by the lesion, the risk of intraoperative occlusion of the vessel can be assessed by balloon occlusion test. Monitoring cerebral blood flow by Xenon CT after vessel balloon occlusion is highly sensitive and specific. For blood-rich tumors, such as meningiomas, angiofibromas, and paragangliomas, preoperative embolization of the blood supply vessels to reduce intraoperative bleeding can reduce the risk of surgery. In this group of 9 cases with preoperative embolization, the tumor blood supply mainly originated from the maxillary artery and pharyngeal ascending artery of the external carotid artery. During embolization, strict vascular superselection should be performed to embolize the embolization material into the tumor as much as possible and avoid the return of embolization material into the internal carotid artery, especially to avoid entering the dangerous anastomosis between the internal carotid artery, external carotid artery and vertebral artery. In the present case of neurogenic tumor in the pterygopalatine fossa, angiography did not show obvious tumor staining, but considering the unilateral maxillary sinus access via facial decortication to remove the lesion, it was easy to injure the pterygopalatine fossa segment of maxillary artery, and the location was deep and difficult to stop bleeding, so the pterygopalatine fossa segment of maxillary artery was embolized. Intraoperative bleeding was low. We believe that embolization is not only for the blood supplying artery of the tumor, but also for the large vessels that may be encountered in the surgical route, and if intraoperative bleeding is difficult to handle, preoperative embolization is feasible to reduce the risk of surgery. The embolization materials can be gelatin sponge, PVA granules, Onyx gum, etc. The skull base is uneven, with many foramina, complex structures and dense neurovascularity. 3D imaging is necessary to correctly understand the anatomical relationship between the tumor and its surrounding structures in this region. We applied dextroscope (software RadioDextra 1.0) surgical virtual reality (VR) system from Volume interaction, Singapore, for preoperative planning, and fused images such as CT and MRI from thin scan (1.0 mm) to obtain 3D stereoscopic images, which can be rotated, cut, abraded, recovered, and other simulated surgical operations. In this group of 5 cases, dextroscope system was applied for preoperative planning, which can judge the tumor size, location and its relationship with surrounding important structures more clearly, and apply different positions and accesses to reveal the tumor, observe the key points during surgery, simulate the resection of tumor and choose the best surgical access. As in the case shown in Figure 1, VR observation of the ICA was located posterior to the tumor, rather than being wrapped by it. The dura mater at the base of the skull was thickened and the tumor did not invade into the dura mater. The tumor was mainly supplied by the ascending pharyngeal artery, which was consistent with the DSA findings. A transmandibular approach was simulated, and the tumor was satisfactorily exposed. The surgery was performed according to the preoperative planning of VR with good results. The selection of the surgical approach was based on the following principles: good exposure; short route to avoid damage to important structures; use of potential cavities and foramina as much as possible; resection of bone to enlarge the operative field and reduce brain tissue traction; easy structural reconstruction; flap design to protect the neurovascular tip and facilitate possible flap transfer, while taking into account the effect of postoperative radiotherapy on blood flow and the possibility of reoperation; avoiding facial disfigurement; and choosing a combined approach when necessary. If necessary, a combined approach should be chosen. [2] The choice of the appropriate approach is based on the experience of the surgical team. Here, we will discuss only three approaches that are commonly used by our group but relatively rusty for neurosurgeons. Transmaxillary approach: A facial shift or decortication approach is used to expose the anterior wall of the maxillary sinus and access the pterygopalatine fossa through the maxillary sinus, which is suitable for resection of tumors whose main body is located in the maxillary sinus and pterygopalatine fossa. The Weber-Fugerson or its modified incision is mostly used for facial shift, which has good exposure but affects the facial appearance and is rarely used. Facial decortication approach, which has slightly poorer exposure but does not leave facial scarring, should be considered first. The infraorbital nerve and blood vessels should be protected as much as possible during the operation, and the main trunk of the pterygopalatine fossa segment of the maxillary artery should be treated early; otherwise, the operative field is deep in, hemostasis is difficult, and structures such as the maxillary nerve and pterygopalatine ganglion are easily damaged. The transmandibular approach: there are three types of approaches: anteromedial mandibular approach, paramedian approach and lateral approach. It is suitable for tumors in the parapharyngeal infratemporal region involving the skull base. Christian et al. treated three cases of pediatric skull base tumors with lateral mandibular approach, all of which transected the mandible above the mandibular foramen, and concluded that the anterior mandibular approach or the paramedian approach requires splitting the lower lip and chin area and is not suitable for pediatric surgery [3]. Lateral osteotomy requires dissection of the parotid gland and facial nerve, which can easily damage the facial nerve. It is important to choose a suitable mandibular osteotomy according to the extent of the tumor and its position in relation to the mandible, to protect the inferior alveolar nerve vascular bundle as much as possible, to reduce the incidence of postoperative lip and gingival numbness and bone nonunion, and to avoid damage to the facial nerve and mandibular joint by excessive traction and rotation. The screw holes are drilled before the incision is positioned to facilitate titanium plate fixation of the mandible after tumor removal. This approach is less disturbing to important structures and we apply it more often. Inferior temporal-anterior infratemporal fossa approach: frontotemporal craniotomy, dissociation of the zygomatic arch, release and pulling away the facial nerve, and incision of the mandible can obtain good exposure and is suitable for most lateral skull base communicating tumors, especially for tumors in the lateral, superficial part of the internal carotid artery (Figure 3). Some scholars have classified malignant tumors located in the parapharyngeal space of the inferior temporal fossa and involving the base of the middle cranial fossa into lateral and medial internal carotid artery types according to their relationship with the internal carotid artery in the neck, and considered the lateral type or tumors located in the sheath of the internal carotid artery suitable for the anterior temporal approach to the ear and the medial type suitable for the transmandibular approach [4-6]. This approach is highly traumatic, bleeding and complicated to perform. It requires dissection of the facial nerve and is prone to facial nerve injury. Excision of the superficial parotid gland is prone to concave deformity of the posterior parotid jaw area. The temporalis muscle and the internal and external pterygoid muscles are severed, resulting in muscle atrophy and affecting the occlusal and masticatory functions. We have used less in recent years, mostly using combined frontotemporal-transmandibular approach. That is, frontotemporal craniotomy and transmandibular approach are used to remove intracranial and extracranial tumors respectively. For intracranial and extracranial communicating tumors, it is advisable to remove the intracranial part of the tumor first to avoid accidental pulling and damaging the intracranial tissues when removing the extracranial tumor. However, if the tumor is mainly located outside the skull and the intracranial invasion is slight, it is advisable to fully expose and remove the extracranial part first, and then deal with the invaded dura mater and the residual small amount of tumor tissues, and all surgical operations should facilitate the reconstruction of skull base after tumor removal. We should strive for total resection of the tumor in the first stage. Re-operation is difficult and damaging due to heavy adhesions and unclear levels. Complications are significantly increased [7]. If staged surgery has to be performed, it is advisable to operate again as early as possible. For malignant tumors, especially highly malignant tumors, the whole tumor, including the tissues surrounding the tumor, should be removed as much as possible to reduce the possibility of tumor dissemination and recurrence. For benign tumors, more emphasis is placed on maximizing the neurological integrity and removing the tumor as much as possible. Excessive stretching of brain tissue can be avoided by pre-emptive lumbar puncture or opening the arachnoid pool to release cerebrospinal fluid. The skull base tumor is mainly supplied by the maxillary artery and the ascending pharyngeal artery. If necessary, the blood supplying artery can be ligated at the early stage of surgery or the external carotid artery can be ligated by making an incision in the neck to reduce intraoperative bleeding. The posterior edge of the lateral plate of the pterygoid process is facing the foramen ovale, foramen spinosum, and pterygoid spine. When biting or grinding the middle skull base, do not go beyond this line to avoid damaging the bony canal of the internal carotid artery [8]. If it is necessary to separate the artery from the aneurysm, it is important to trace from the normal artery to the diseased segment and to control the proximal and distal ends of the artery before separating the aorta. Choose carefully to sacrifice the internal carotid artery or the distal and proximal vessels of the lesion for bypass, as it can easily lead to massive cerebral infarction [9]. Therefore, if the tumor is closely adherent to important vessels or nerves, total resection is not forced, and a small amount of residual tumor is treated postoperatively with gamma knife and other treatments [10]. The bleeding from the pterygoid plexus during the separation of soft tissues in infratemporal fossa surgery is high and can be stopped with bipolar electrocoagulation or hemostatic gauze. Intraoperative monitoring is best applied to preserve cranial nerve function as much as possible, and intraoperative monitoring can be done for both II-XII cranial nerves. For intraoperative repair of cranial nerve injury, in situ anastomosis or nerve grafting can be done. For tumors that can be reached through natural channels such as the nasal cavity and paranasal sinuses, endoscopy can be fully applied or combined with open surgery to remove the tumor, avoiding or minimizing the facial incision and avoiding complications such as facial nerve injury and masticatory muscle atrophy caused during layer-by-layer exposure. After resection of anterior skull base communicating tumor, the intracranial tissues are mostly connected with sinus, nasal cavity and oral cavity, which are prone to complications such as cerebrospinal fluid leakage and intracranial infection, therefore, skull base reconstruction is crucial, among which dural repair is the most critical. We use repair materials such as capitellar tendon membrane, temporalis fascia, skull bone periosteum and artificial materials to ensure tight sutures. Some parts are difficult to repair, such as the dural defect of the sieve plate which is tricky to repair because of the passage of olfactory filaments, and can be closed with bioprotein glue and temporalis muscle bonding. For small bone defects at the skull base, such as small orbital wall defects, as long as the orbital fascia is intact, they may not be repaired; for large defects, intracranial plates or titanium plates are used to repair them. The surgical dead space can be filled with autologous fat or muscle, and the most commonly used is the temporalis muscle flap. For larger defects, a transfer flap from an adjacent site such as the oblique muscle can be used; or a free skin flap with a vascular tip, such as the rectus abdominis skin flap. We have used the rectus abdominis dermatome flap to repair the huge surgical remnants of the patient’s facial cavity with good results, allowing maximum preservation of the patient’s function and appearance. If an intraoperative free muscle flap may be needed for repair, the flap should be pre-designed for the abdomen, femur, etc., and the surgical area should be prepared.