Hemangiopericytoma, also known as hemangiopericytoma, is an extremely rare mesenchymal tumor. HPC originating in the central nervous system accounts for about 1% of brain tumors and was first proposed by Stout and Murray in 1942 [3]. In 1995, Joseph et al. [4] confirmed that HPC originated from Zimmerman epithelial cells on capillaries from the molecular and genetic level. It is a kind of contractile spindle cells distributed around the capillaries and venules behind the capillaries, regulating blood flow and permeability, and distributed in any part of the human body [5, 6]. In the 2000 edition of the WHO classification of nervous system tumors, hemangiopericytoma was classified as "mesenial tumors, non-meningeal epithelial tumors" in meningeal tumors, and intracranial HPC was classified as anaplastic HPC in the 2007 edition of the WHO classification of central nervous system. (AHPC, WHO level III) and HPC (level II), were recognized as a new entity in the 2016 edition of the WHO classification of the central nervous system. The recurrence rate of HPC and the rate of metastasis outside the nervous system are lower than AHPC [1, 2]. Although the tumor is a non-meningingepithelial cell tumor, it is highly similar to meningioma and synovial sarcoma in morphology and histology. Because of the non-specific clinical manifestations, most of the imaging examinations are diagnosed as meningioma, so it is easy to be misdiagnosed in the clinic. The diagnosis still depends on the combination of pathological diagnosis and imaging.
HPC can occur in any part of the body, especially the lower limbs, pelvis and retroperitoneum. Intracranial HPC is more common in men. The age of onset is mostly between 38-50 years old. The median age at diagnosis is about 40-50 years old [7, 8]. Its clinical manifestations are non-specific, mainly depending on the location of the tumor, the invasion and compression of the peripheral nerves by the tumor, and can be manifested as headache, dizziness, visual and hearing impairment, numbness and weakness of the limbs and seizures caused by increased intracranial pressure [9, 10]. Intracranial HPC is a tumor with aggressive behavior, including local recurrence and distant metastasis such as liver, bone, lung, kidney, abdominal cavity, lymph nodes, skeletal muscle, pancreas, skin and subcutaneous tissue, etc., and its recurrence within 12 years The rate is as high as 90% [11]. Of the 4 patients in this article, 2 died of tumor recurrence and metastasis after surgery, and the survival time was 60 months. The clinical follow-up of 2 cases was 5 months and 32 months without special.On the image, intracranial hemangiopericytoma is mostly irregular or lobulated, meningiomas have smooth edges, lobes are rare, and mostly round or elliptical. This irregular shape is mainly due to the rapid growth of the tumor, Caused by violations [12, 13]. On T1WI and T2W1 signals and DWI signals, meningioma generally have more uniform signals, while intracranial hemangiopericytoma cysts and necrosis are more common than meningioma, so intracranial hemangiopericytoma T1WI and T2WI signals and DWI signals are usually More mixed; intracranial hemangiopericytoma is more invasive, mostly connected to the meninges, with high signal changes on DWI, meningioma with iso-signal or slightly high signal changes [12]. In addition, hemangiopericytoma usually has Wide base dura mater is attached, and there may be a dural tail sign [8, 14]. A retrospective analysis of 22 cases found that SFT showed high attenuation signal on CT, and showed equal intensity signal and low signal intensity on MR image, as well as obvious enhancement. These features may have certain suggestive significance for SFT [14, 15].
The final diagnosis of intracranial SFT/HPC depends on pathological examination. In general, HPC has a clear boundary, soft texture, brown, dark red, or off-white leaf-like structure, which is wrapped into a leaflet or nodular mass by a covered pseudocapsule with abundant blood supply [16, 17]. Microscopically, the tumor tissue cells are abundant and dense, uniform in size, and composed of short spindle, oval or polygonal cells. The tumor cells are unclear, and the cytoplasm is slightly eosinophilic; the nucleus is oval, short spindle, and chromatin. Medium-density diffuse distribution, tumor cells generally have inconspicuous nucleoli, lack of nuclear inclusion bodies, and can see nuclear atypia and mitotic figures; the stroma is rich in blood vessels, showing fissures, staghorn-shaped blood vessels, lined with flat endothelial cells, tumors Cells surround the abundant thin-walled blood vessels, the size of the blood vessels varies, and a large number of branches are seen. These branches are attached and wrapped by collagen and run through the cells and the interstitium, showing a stag horn-like structure; some tumors have coagulative necrosis and hemorrhage, Can also infiltrate adjacent brain tissue and skull. One patient showed hemorrhage and necrosis under the microscope, and one case was diagnosed as a recurrence of meningeal hemangiopericytoma (low-grade sarcoma), and the mitosis was about 5/10 HPF where the cells were actively growing. The other two patients were consistent with the literature report under the microscope, the Ki-67 index was relatively low, and there was no recurrence temporarily. In the past, SFT/HPC was considered to be different pathological solid tumors, but the latest research confirmed by immunohistochemistry and gene sequencing that they are a common solid tumor with many similar histological features [18]. Some scholars performed whole-genome sequencing by isolating the DNA of SFTs, and found that the inversion in chromosome 12 caused the NAB2 and STAT6 genes to be juxtaposed, and thus showed that NAB2-STAT6 fusion is a unique molecular feature of SFT [19, 20], related literature It is believed that the presence of NAB2-STAT6 fusion protein was strongly positive in STAT6 immunohistochemistry, and the tissues without NAB2-STAT6 fusion protein showed the nuclear expression of NAB2 and the cytoplasmic expression of STAT6 protein [18]. Therefore, the 2016 WHO classification of the central nervous system proposed that the nuclear expression of STAT6 protein can be used to diagnose HPC/SFT and other mesenchymal tumors [2]. Relevant experiments have shown that the specificity and sensitivity of STAT6 to SFT/HPC are 100% and 96.6%, respectively [21]. Karen et al. [22] used 30 cases of tumors that were initially diagnosed as SFT/HPC meninges and found that all tumors expressed expression NAB2-STAT6 fusion, and it is believed that the fusion of NAB2 exon 4-STAT6 exon 3 is related to the classic SFT morphology and higher age, and shows a trend of decreased mitotic activity. Among the abnormal genes detected, NAB2 exon 6-STAT6 exon 16/17/18 are mostly located in the meninges, soft tissue and SFT of the head and neck, while NAB2 exon 4-STAT6 exon 2/3 It is mostly located in the SFT of the pleura and lung. The recurrence frequency of SFT with NAB2 exon 6-STAT6 exon 16/17/18 is compared with SFT with NAB2 exon 4-STAT6 exon 2/3 The frequency of recurrence is higher [23].
For the treatment of intracranial HPC, it is recognized that the most effective is surgical resection supplemented by radiotherapy. The combination of the two strategies can hinder the progression of the tumor, but has no effect on the median survival rate and the occurrence of metastasis [5, 6], and Total surgical resection has a better therapeutic effect than subtotal resection [7–9]. According to the results of pathological diagnosis, Kim et al. [24] conducted a statistical analysis on the overall survival rate. The results showed that the median time to local recurrence in patients with WHO II HPC and WHO III HPC was 66.2 months and 38.1 months, respectively [9]. Among the 4 patients diagnosed by us, 2 cases had recurrence time consistent with those reported in the literature. In terms of differential diagnosis, it is mainly differentiated from meningioma and synovial sarcoma. First, SFT/HPC has now been confirmed as a new solid tumor, which has a patternless structure with alternating bottom cell and high cell area in the omics. The cell area usually appears as a thicker collagen band, and the high cell area shows the presence of staghorn-shaped blood vessels. Both have similar structure and immunohistological characteristics in omics because they have the same spectrum system. Interestingly, someone compared the ALDHIA1 gene with soft tissue sarcoma and found that ALDHIA1 gene is highly expressed in SFT/HPC, and its sensitivity and specificity in SFT are 84% and 98.8%, respectively, and in HPC it is 84.5% and 98.7%. In meningioma and synovial sarcoma, only 1.2% and 7.1%. In addition, the analysis of the immunohistochemical expression pattern of SFT/HPC and meningioma in the literature shows that the nuclear expression of STAT6 has the highest specificity for SFT/HPC (100%), followed by CD34 (93.6%), and CD34 in meningiomas The positive expression is only 6.4% [25]. If CD34 and ALDHIA1 are diagnosed in combination, the positive predictive value and negative predictive value are both 100%. Therefore, imaging and microscopic performance combined with the current new immunohistochemical markers can distinguish meningiomas from synovial sarcoma.