Meningeal melanocytoma is a rare intracranial tumor. 1.Case report 1.1.Basic data There were 3 cases in this group, 1 male and 2 female, aged 35-53 years (average 44.6 years), with 2 supratentorial cases and 1 infratentorial case. No tumor recurrence was seen in 1-10 years of follow-up after total excision. 1.2. Typical case Wang, male, 52 years old, was admitted to the hospital with headache and dizziness for 2 months and unstable walking for 1 month. He had persistent headache and dizziness, nausea, no vomiting, choking and coughing with water, hoarseness, no dysphagia, no nystagmus, bilateral optic papilla edema, weakness of the right lower limb, unstable walking, skewing to the right, and Romberg’s sign (+). MRI is shown in Figure 1. After opening the dura mater, a 4 cm diameter spherical mass with smooth surface and clear borders was seen, soft in texture, with envelope and no obvious adhesion to the dura mater (Figure 2). Pathological diagnosis: meningeal melanocytoma (Figure 3). Now one year later, the patient was reviewed and all symptoms disappeared, and no recurrence was seen on MRI examination (Figure 4). 2, Discussion 2.1, Overview Meningeal melanocytoma was also called melanocytic meningioma in the past literature, and it was found that the disease is still histologically distinct from melanocytic meningioma [1]. It can occur anywhere in the skull and tends to be located near the skull base and meningeal structures, with the skull base being the most common and approximately 1/3 located in the craniocervical junction. The clinical presentation of the disease is similar to that of meningioma, with symptoms of high cranial pressure and focal neurological damage caused by progressive cerebral compression, and those with lesions in the posterior cranial fossa are often seen due to difficulty walking. The history of the disease varies from a few months to several years. 2.2, diagnosis 2.2.1, histopathological features Meningeal melanocytoma is mostly solitary, with complete envelope, clear boundary, smooth surface, black or gray-brown-black color, large tumor volume, black or brown-black liquid content. The tumor is mostly located outside the brain tissue, and its base is rarely adherent to the dura, mainly compressing the adjacent brain tissue but not growing invasively. The tumor cells were well differentiated by light microscopy, and the nuclear division phase was rare or absent. The main feature was a large amount of melanin deposition in the cytoplasm, and ultrastructural observation showed melanosomes in different stages of maturation. The histological origin of the tumor is thought to be from melanocytes in the soft meninges, and also from meningeal epithelial cells, but immunohistochemical studies of meningeal melanocytoma have shown that the lesions are strongly positive for S-100, Vimentin and HMB45, while EMA, Cytokeratin and GFAP are negative[1] . 2.2.2, Imaging characteristics Intracranial meningeal melanocytoma appears as a round or round-like nodular slightly high or high-density extracerebral occupying lesion with obvious uniform enhancement effect and varying degrees of edema around the tumor, sometimes the tumor can be connected to the dura mater or other dural appendages at the base of the skull, which is similar to the CT appearance of meningioma, but is not related to the dura mater. T1, slightly long T2 signal shadow, uneven signal, and speckled long T1, long T2 signal shadow, which can be different from meningioma. It is generally believed that the presentation of tumors on MRI depends mainly on the amount of intratumoral melanin content, while Maiuri et al [2] further suggested that the steady-state free radicals within melanin are the main factor affecting MRI signals. 2.2.3, Diagnostic basis Integrating the above data and literature, the diagnosis of melanocytoma is based on 1 a long medical history, excluding melanotic lesions in other parts of the body; 2 CT and MRI morphology similar to meningioma and nerve sheath tumor; 3 intraoperative visualization of intact envelope, black or brown; 4 light microscopic observation of tumor cells without heterotypy, nuclear schizophrenia is absent or occasionally seen; 5 immunophenotype HMB45 , S- 100, vimentin protein positive, EMA, Leu-7 negative. Reticulocyte staining showed that reticulocytes surrounded by nests of tumor cells and single tumor cells; 6 electron microscopy showed that the tumor cells contained melanosomes or pre-melanosomes in the plasma, with few intercellular connections and no extensive basement membrane-like material surrounding the tumor cells. [1] [3] 2.3. Treatment Meningeal melanocytoma is histologically benign with an intact envelope, so surgical total excision of the tumor is the treatment of choice, [4] especially microsurgical total excision of the tumor, its envelope and adjacent invaded tissues is expected to achieve a cure. Some scholars suggest that the tumor should be routinely treated with radiotherapy after surgery, but statistics in the literature show that there is no significant difference in the prognosis of patients after total resection plus radiotherapy, but it is still recommended that postoperative radiotherapy should be considered in cases where total resection is not possible [5], and Hamasaki O [6] concluded that partial resection followed by gamma knife treatment has significant efficacy. At present, most believe that the biological behavior of this tumor is benign and grows slowly, and although it may recur after surgery, it does not metastasize, but there are reports of metastasis and malignant change in the literature [7-8], so it is emphasized that patients should pay attention to close follow-up and regular review after surgery. 2.4, Differential diagnosis The disease should be differentiated from the following lesions: 1 Malignant melanoma: Intracranial malignant melanoma has few primary cases and is mostly metastatic from extracranial lesions, with rapid onset, short course, and poor prognosis, often dying within 1 year. The clinical symptoms are mainly increased intracranial pressure, neurological dysfunction and subarachnoid hemorrhage. The tumor has no clear boundaries and often invades the surrounding brain tissue and bone. The cerebrospinal fluid is often blackish to the naked eye, and the brain surface may be black. [1] Metastatic melanoma should be found in other parts of the patient’s body as the primary foci. Meningeal metastases are multiple, with the same histologic morphology as the primary foci and signal shadows without clear borders on imaging.2 Melanotic meningioma: It is a benign tumor originating from the meningeal epithelium and is difficult to distinguish from meningeal melanocytoma by visual inspection. The typical vortex-like structure is visible under light microscopy, often containing sand granules or focal calcifications. Electron microscopy shows special intercellular junctions and bridging granules, without melanosomes and pre-melanosomes in the cytoplasm. 2.5 Reasons for misdiagnosis and prevention The disease is similar to meningioma in imaging, so it is easy to be misdiagnosed as meningioma before surgery, and the color of the tumor seen during surgery is like malignant melanoma, if not differentiated, it will have adverse effects on the treatment and prognosis of the patient. The main method to avoid misdiagnosis is postoperative pathology, and if it is not easy to identify under light microscopy, immunohistochemistry and/or electron microscopy should be added. The differential diagnosis of this disease is not very accurate due to our inexperience in the diagnosis and treatment of this disease, and the immunohistochemical and electron microscopic data are not well utilized, so it needs to be improved in the future work.