Clinical Study On The Solitary Fibrous Tumor Of The Skull Base

Objective Solitary fibrous tumor is a spindle cell neoplasm of mesenchymal origin,most frequently arising in the pleura and less frequently in other sites such as the abdominal cavity,pelvic cavity,retroperitoneum,head and neck.Intracranial solitary fibrous tumor is a rare primary central nervous system tumor that accounts for less than 1% of all intracranial tumors.In the latest（2021 WHO classification of tumor of the central nervous system）,solitary fibrous tumor of the central nervous system is classified as grades 1,2,and 3: Grade 1 is a benign tumor and has a good prognosis;Grade 2 is a low-grade tumor and has a better prognosis;Grade 3 is more malignant and has a poor prognosis with intracranial and extracranial metastases.Solitary fibrous tumors of the skull base originating in the meninges,orbits,and nasal cavities of the skull base are more rare compared with solitary fibrous tumors of the skull.It is only reported in cases,with high malignancy and strong invasion ability,which is very easy to invade the surrounding normal tissues.Moreover,malignant solitary fibrous tumors（grade 2 and 3）will also have extracranial metastasis and worse prognosis.The clinical and imaging features of solitary fibrous tumor of skull base are lack of specificity and are easily misdiagnosed before surgery.The disease is currently poorly recognized and there is no standard treatment scheme.The clinical data of 10 cases of solitary fibrous tumors of skull base treated in the Cancer Hospital of Chinese Academy of Medical Sciences and the Second Affiliated Hospital of Anhui Medical University from September 2015 to September 2019 were analyzed retrospectively.We summarize the clinical characteristics of solitary fibrous tumors of the skull base and discuss the treatment strategies by combining relevant literatures from China and abroad.Methods The clinical data of 10 cases of solitary fibrous tumor of the skull base who underwent surgical treatment from September 2015 to September 2019 at the Department of Neurosurgery,cancer hospital,Chinese Academy of Medical Sciences and the Department of Neurosurgery,the Second Affiliated Hospital of Anhui Medical University were collected.And it includes: admission records,course records,imaging data,operation records,postoperative pathology and follow-up results.Literature search was conducted on Pub Med,CNKI and Wan Fang medical websites.Cases showing features consistent with solitary fibrous tumors of the skull base were selected from cases described in the literature,and clinical data were collected.Then the clinical characteristics and treatment strategies of solitary fibrous tumors of skull base were analyzed and summarized.Results The 10 cases of solitary fibrous tumors of the skull base that we treated and 37 cases of solitary fibrous tumors of the skull base that were screened after literature search were analyzed and summarized.Among the 47 cases of solitary fibrous tumors of the skull base,25 were male and 22 were female.The age at presentation was 18-74 years old,with a median age of 47 years.The common clinical symptoms of skull base solitary fibrous tumor included headache in 19 cases,vision loss in 15 cases,dizziness in 12 cases,hearing loss in 6 cases,head and neck mass in 3 cases,hyposmia in 2 cases,tinnitus in 1 case,and epilepsy in 1 case.Its common signs include unstable walking in 7 cases,limb numbness in 4 cases,eyesight difficulty standing in 3 cases,limb weakness in 1 case,facial paralysis in 1 case,dysphagia with hoarseness in 2 cases,and tongue muscle atrophy in 2 cases.In addition,the first symptom was head and neck mass in 3 cases and hearing loss in 2 cases.There were also abnormal endocrine changes in sellar tumors,such as PRL increased in 3 cases;ACTH,GH increased in 1 case;LH,FSH,TSH,ACTH decreased in 1 case.The disease duration was 15-34 days,with a median of 24 days.The predominant sites of skull base SFT were sellar area（15 cases）,cerebellopontine angle area（12 cases）,jugular foramen area（5 cases）,middle skull base（5 cases）,anterior skull base（4 cases）,posterior skull base（2 cases）,craniocervical junction area（2 cases）and ethmoid sinus（1 case）.The maximum diameter of the tumor is 2-7 cm,mostly 3-5 cm.The tumor features described in this group and the literature are as follows: 2 cases were multiple nodular,4 cases were lobulated;There were 26 cases with abundant blood supply and 1 case with general blood supply;There were 13 cases with clear boundary and 5 cases with unclear boundary;The capsule was intact in 2 cases and no obvious capsule in 1 case;There were 5 cases of cystic necrosis and 3 cases of non cystic necrosis;Peritumoral edema occurred in 1 case.On plain CT scans,most of the features were isodensity（7 cases）and high density（4 cases）,and low density was rare（2 cases）;the tumors mostly invaded the bone（5 cases）;enhanced scans were mostly heterogeneous enhancement（5 cases）,Homogeneous enhancement was less（3 cases）.MRI plain T1 WI was mainly iso-intensity（10 cases）or low-signal（6 cases）,and low-iso-intensity mixed shadows were also seen（4 cases）.T2 WI was mainly high signal（14 cases）;There were some mixed signals of equal and high intensity（3 cases）,forming a special "Yin-Yang sign",which is also considered to be the characteristic manifestation of skull base SFT;Isosignal was rare（3 cases）.Magnetic resonance FLAIR showed high signal intensity（2 cases）;high signal intensity was common in DWI（7 cases）,and low signal intensity was rare（2 cases）;enhanced scan enhancement was uneven（7 cases）,and homogeneous enhancement（6 cases）.Among the 10 cases of solitary fibrous tumors in the skull base,1 case of internal and external communication tumor in the cranial cervical junction and 1 case of multiple giant cranial cervical communication tumor were treated with embolization before operation because of the huge tumor and abundant blood supply.One craniocervical junction region spinal canal internal and external communication tumor,4 craniocervical communication tumors in the jugular foramen region and 1 multiple giant craniocervical communication tumor were resected using a combined craniocervical approach,3 tumors in the cerebellopontine angle region were microsurgically resected using a posterior sigmoid sinus approach,and 1 middle skull base temporal inferior fossa tumor was resected endoscopically using a lower lip transmaxillary sinus approach.The literature reported that 7 cases of solitary fibrous tumors in the sellar region were treated by transsphenoidal endoscopy,3 cases of larger sellar tumors were treated by frontal craniotomy,and 1 case of sellar tumors was treated by transsphenoidal endoscopy + frontal craniotomy;One case of tumors in cerebellopontine angle region underwent suboccipital craniotomy;Two patients with sphenoid ridge tumors underwent craniotomy through frontotemporal zygomatic arch approach;Two patients with posterior skull base tumors underwent suboccipital paraoccipital median craniotomy;One case of jugular foramen tumor was treated by infratemporal cranial fossa and transcondylar approach;One case of middle skull base tumor underwent orbital pterygoid craniotomy;One case involved ethmoid sinus and underwent transnasal endoscopic resection.During the operation,the tumor texture was softer in 10 cases and tougher in 12 cases.Total tumor resection was performed in 14 cases,subtotal tumor resection in 3 cases,and partial tumor resection in 6 cases.HE stain: Most of the tumor cells were dense spindle / spindle shaped,and nuclear atypia and mitosis were common.There are many antler vessels arranged by endothelial cells and a large amount of reticular fibrin around the tumor cells.Immunohistochemistry: Most of the skull base SFT tumor cells were strongly positive for nab2-stat6,VIM,and CD34,and some of the tumor cells were also positive for Bcl-2,CD99,p53,mib-1l1,and CD68.In addition,the pathological features of grade 1,2 and 3 skull base SFT were different.Grade 1: HE staining showed that short spindle tumor cells inserted between long collagen fibers to form a typical mat pattern;Immunohistochemistry showed that tumor cells were positive for STAT6 and CD34,and Ki-67 proliferation index was about 4%.Grade 2: HE staining showed typical staghorn like vessels;Immunohistochemistry showed that tumor cells were positive for STAT6,with a decreasing trend in CD34 positivity and an increasing Ki-67 index.Grade 3: HE staining showed increased cellularity,moderate atypia,and mitotic figures;Immunohistochemistry showed that tumor cells were positive for myogenin,the phenomenon of decreased CD34 positivity was more obvious,and the Ki-67 index was significantly increased.The 10 patients in our series who had both radiotherapy information and progression free survival and overall survival were uniformly analyzed with a total of 25 patients from 15 patients reported in the literature.The median PFS was 16.5 months in the radiotherapy group,which was higher than 12 months in the no radiotherapy group,but p = 0.98,not statistically significant.The median OS was 32.5 months in the radiotherapy group,which was higher than 31 months in the no radiotherapy group,but p = 0.68,which was not significant.Conclusions Skull base SFT is an extremely rare CNS tumor with high malignancy,low total resection rate,and easy recurrence and metastasis compared with intracranial SFT and other intracranial tumors.Imaging features such as "" Yin Yang sign "" are helpful in distinguishing them from other tumors.According to the existing research results,we advocate:（1）Surgical treatment is preferred for skull base SFT,with individualized surgical options selected based on the site of tumor occurrence;（2）Adjuvant radiotherapy is required after surgery,which can improve the local control rate of the tumor to a certain extent;（3）Postoperative tumor tissue underwent genetic testing to guide possible targeted therapy and immunotherapy.The overall therapeutic effect of skull base SFT is still unsatisfactory,and further exploration at the molecular level is urgently needed to find possible molecular therapeutic targets.