Endolymphatic sac tumor (ELST) is a tumor of temporal bone origin, also known as Low grade adenocarcinoma of probably endolymphatic sac or Hefner tumor, depending on its histological origin. ELST is rare and can occur alone or in association with Von-Hippel-Lindau syndrome (VHL), also known as Schilling’s disease. As the tumor increases in size, it may penetrate into the cerebral pontocerebellar horn or adjacent structures, causing corresponding occupying effects. The commonly involved cerebral nerve is the 8th cranial nerve (facial nerve), followed by the 9th, 10th, 12th and 5th pairs of cerebral nerves. Although its malignancy is low, it is located in the lateral skull base, and the lesion is deep, adjacent to important neurovascular and posterior cranial fossa, so it is difficult to diagnose before surgery, and the postoperative complications are more difficult and severe. VHL was first identified in 1895 by a German ophthalmologist, von Hippel, who first discovered that patients with retinal hemangioblastoma had familial characteristics. in 1926, a Swedish ophthalmologist, Arvid Lindau, discovered cases of retinal hemangioblastoma complicated by cerebellar hemangioma and abdominal organ lesions, thus calling the brain-eye-visceral hemangioma syndrome VHL disease. in 1964, Melon and Rosen summarized several clinical reports and officially named the central nervous system (CNS) hemangioblastoma combined with renal or pancreatic cysts, pheochromocytoma, renal carcinoma, and ectodermal cystadenoma as “von Hippel Lindau syndrome”, or VHL syndrome. Von Hippel-Lindau (VHL) syndrome is an autosomal dominant disorder. The prevalence is approximately 1/36,000 – 1/53,000, with an age of onset of 18-30 years and an epizootic rate of 95% at age 60 years. 10% of cases have childhood onset, and the main characteristic lesions are retinal and central nervous system hemangioblastoma and pheochromocytoma. Clinical diagnostic criteria: The diagnosis is made in patients with a family history of retinal hemangioma or CNS angiogenic tumor with the presence of any of retinal hemangioma, CNS angiogenic tumor, or substantial organ damage (renal cancer, multiple cysts or tumors of the pancreas, pheochromocytoma, papillary cystadenoma of the epididymis). In sporadic patients without a family history of hemangioma, the presence of two or more (including two) hemangiomas or one hemangioma and one substantial organ tumor is also diagnostic. The initial symptoms often do not appear in only one organ and do not occur at a fixed age, and the severity of the disease varies widely, with many family members having relatively harmless manifestations while others are very ill. In addition, the incidence of various tumors varies greatly among families and ethnic groups: the French are prone to nervous system tumors, the Germans to pheochromocytomas, and the Japanese to renal tumors more frequently. The concomitant conditions with the highest prevalence and lethality are renal cysts and renal cancer, followed by central nervous system hemangiomas. In the process of VHL recognition, the discovery of the importance of visceral manifestations, the recognition of new specific CNS manifestations (endolymphatic sac tumors) and adnexal tumors, and especially in recent years, advances in VHL gene characterization, function, and mutation detection have brought about great changes in the clinical diagnosis and management of patients. Endolymphatic sac tumor (ELST) ELST is a rare neuroectodermal temporal bone tumor. Since Treiter first reported a papillary adenoma of the temporal bone in 1898, the classification of ELST has been controversial for a century. There are various hypotheses regarding the origin of the tumor: cerumen of the external auditory canal, ectopic microsalivary glands, middle ear glands, middle ear mucosal epithelium, choroid plexus papilloma, etc. The nomenclature is also varied: it includes ceruminous adenoma of the pontocerebellar horn, adenoid cystic adenoma, pleomorphic adenoma, adenocarcinoma of the temporal bone, invasive papillary middle ear temporal bone tumor, etc. It was not until 1984, when Hassard and MacDougall reported successive cases of temporal bone tumors of endolymphatic sac origin, and 1989, when Heffner confirmed the hypothesis of endolymphatic sac origin of the tumor, that the name endolymphatic sac tumor was widely recognized. Although ELST has been reported in VHL since 1904, and in 2-11% of patients with VHL, it is only in the last decade or so that ELST has been recognized as a clinical manifestation of VHL. In fact, ELST is rarely seen in patients with non-VHL disease. About 30% of patients with VHL with ELST have bilateral onset, 95% have hearing loss, 92% have tinnitus, 62% have vertigo and balance disorders, 29% have external auditory canal fullness, and 8% have facial nerve damage. Hearing loss usually appears at an early age (mean age 22 years) and approximately 43% have an acute onset. The severity of clinical symptoms is not proportional to the size of the tumor, and Lonser’s histological study of the temporal bone in patients with VHL combined with micro-ELST suggests that acute endolymphatic hemorrhage and the resulting inflammation may be the main cause of acute hearing loss, while edema may explain the presence of Meniere’s-like symptoms (deafness, tinnitus and vertigo) in the disease. Imaging Imaging is essential for the detection of ELST. Mukherji et al. were the first to investigate the imaging features of ELST and concluded that the CT presentation of ELST is characteristic, with the tumor centered in the area of the vestibular aqueduct at the posterior border of the rock bone between the internal auditory canal and the sigmoid sinus, and that tumors <2 cm in diameter appear as soft tissue masses in the area of the external foramen of the vestibular aqueduct behind the rock bone labyrinth and As the tumor increases in size, it may involve the inner ear peripheral structures such as tympanic ventricle, vagus bone and jugular foramen area. The tumor may involve the periaryngeal structures such as the tympanic cavity, vagus bone and the jugular foramen. Histologically, the center of the tumor contains bone pins and foveal mesh-like bony structures, while EI ST itself does not produce bone-like tissue. Therefore, the high-density bone shadow shown on HRCT may be an encapsulated calcified margin of residual bone formation caused by tumor infiltration and encapsulation. The signal is mixed on MRI, and the more specific manifestations include increased signal density on unenhanced T1WI, with various intra-tumor lesions showing speckle-like; scattered signal enhancement areas and flow-through phenomenon on T2WI, with signature high signal after enhancement. Treatment Complete surgical resection of ELST is the main treatment. Any patient with tumor or hemorrhage on MRI who still has hearing needs surgery to prevent deterioration of the disease. If hearing loss is accompanied by other neurological symptoms, surgery should also be performed. However, if a patient has symptoms associated with ELST and no abnormalities are found on imaging, more clinical studies are needed to determine whether surgery should be performed to prevent hearing loss and other symptoms. As for the choice of surgical approach, the posterior auricular approach is generally used because the primary lesion is located behind the vagus, and the combined auriculocervical approach is feasible for extensive lesions. The posterior wall of the bony external auditory canal can be preserved if the external auditory canal is not involved, and the external auditory canal should be closed if the lesion invades the external auditory canal. -If the lesion invades the dura mater, the dura mater should be excised and repaired with temporalis fasciae, and the cavity can be filled with temporalis sternocleidomastoid muscle or fat. The tumor is mostly supplied by the external carotid artery and the anterior inferior cerebellar artery, so vascular embolization should be performed before surgery to reduce intraoperative bleeding, shorten the operation time and reduce complications. The tumor may recur if surgical resection is not complete, but no metastasis has been reported. Conventional radiotherapy and chemotherapy are not effective for postoperative residual tumor eradication, but gamma knife treatment is effective for this disease. The VHL gene is a typical oncogene, which was discovered by Latif et al. in 1993, localized at 3p 25-26, and successfully isolated by positional cloning. the VHL gene is 4.5 kb in length and is distributed in about 20 kb of DNA space. The VHL gene contains three exons and encodes a protein containing 213 amino acids and a molecular weight of 30,000, also known as VHL protein. Mutations in the VHL gene can result in loss of function of the protein, elevated VEGF expression, and the development of vascular-rich hemangioblastomas. Initially, the detection rate of VHL gene mutations was about 39-75%, but through the improvement of experimental methods, Southern blot, fluorescence in situ hybridization (FISH) and direct sequencing, the detection rate of VHL gene mutations in VHL gene lines is now nearly 100%. To date, there are no effective drugs to prevent or treat patients with clinically manifest VHL. This is because of the large number of tumors that cannot be surgically removed and the high recurrence rate. Recent functional studies of pVHL have confirmed the important role of pVHL in regulating VEGP and angiogenesis, which may provide new strategies for the treatment of VHL and related diseases. In vitro, VEGF is an important survival factor for neoplastic vessels, and withdrawal of VEGF can lead to hemorrhage, necrosis and vascular degeneration. In recent studies, the growth rate of rat VHL tumors was significantly suppressed and the angiogenesis rate and volume were significantly reduced when angiogenesis-inhibiting drugs were used. The population carriage rate of VHL mutations is estimated to be about 3/100,000, with an ectopic rate of nearly 100%. The genetic profile is autosomal dominant, and children have a 50% chance of developing the disease, so their children should also be closely followed. Conclusion In conclusion, ELST is an extremely rare tumor of the temporal bone rock or can extend to the pontocerebellar horn and peripheral structures, and is highly likely to accompany patients with VHL disease. Molecular diagnosis is very important for presymptomatic diagnosis of suspicious patients and high-risk patients, and close follow-up of detected carriers can lead to early detection of the tumor and early treatment.