intracranial hemangiopericytoma ( hpc ) was first reported by begg and garret4 ) , who noted its microscopic characteristics including meningiomas . hpc arises from zimmerman pericytes around capillaries and postcapillary venules ; therefore , these tumors can occur anywhere capillaries are found , especially in the lower extremities , retroperitoneum and pelvis24,45 ) . intracranial hpcs rarely present in the central nervous system , and they account for 2.5% of all meningeal tumors and less than 1% of all cns tumors22,23 ) . these tumors also have malignant features , such as a tendency to recur locally and metastasize distantly . despite the high rate of local recurrence and distant metastasis , we reviewed our experiences with 13 patients with intracranial hpcs to analyze the disease features , treatment strategies and clinical courses . in particular , we focused on the efficacy of resection and adjuvant radiotherapy ( rt ) . a total of 13 patients underwent microsurgical resection for intracranial hpc at least once at our institute from january 1995 to may 2013 . four patients had preoperative digital subtraction angiography ( dsa ) and only one patient underwent tumor embolization using dimethyl sulfoxide ( dmso ) and onyx . a total of 20 operations were performed for the resection of either primary or recurrent intracranial hpcs . after 2002 , all operations were performed by assisted neuronavigation . and intraoperative electrophysiologic monitoring was performed after 2009 . we reviewed the original operation records to determine the estimated blood loss ( ebl ) , macroscopic features and extent of tumor resection . immunohistochemistry was examined in all cases , including ema , s-100 , cd34 and the ki-67 proliferative index . the mean follow - up period was 54.3 months , with a range of 13 to 185 months . information regarding postoperative status was obtained from our outpatient department medical records and phone contacts . statistical analysis was carried out using kaplan - meier method , and the comparison of recurrence free survival rate between different two groups was conducted using log - rank test . the patient group consisted of 12 ( 92.3% ) males and 1 ( 7.7% ) female . patient ages at the time of initial diagnosis ranged from 26 to 73 years , with a mean of 48 years . the most common presenting symptom was headache , and four patients had visual field defects due to a tumor in the occipital lobe . during the study period , we diagnosed 13 intracranial hpcs and 598 meningiomas . the ratio of intracranial hpcs to meningiomas was 1 : 46 , and the proportion of hpcs was only 2.2% . the preferential areas of tumor origin were parasagittal ( 5 patients , 38% ) and falx ( 3 patients , 23% ) . one patient had a homogeneous enhancing pineal gland tumor which turned out to be hpc . distributions of the remaining tumor locations were as follows : two convexity , one sphenoid wing and one cerebellopontine angle . the preoperative contrast - enhanced ct scans of 12 patients ( ct was not available for one patient ) revealed hyperdense and homogeneous or heterogeneous enhancing lesions with no evidence of calcification . radiologic findings of osteolysis of the skull were noted in 2 patients ( 15.4% ) ( fig . enhanced mr images , all patients had well demarcated tumor margins and detailed features of mr images are described in table 1 . preoperative dsas were performed on 4 patients ( 30.8% ) because they had many fluid void signals on the t2-weighted images . each dsa image showed a hypervascular contrast staining mass with an arterial feeder from the middle meningeal artery ( case no . 8) , distal branches of the pericallosal artery and some posterior choroidal arteries ( case no . two patients ( 15.4% ) showed hemorrhage from the hpc on the initial ct scans ( case nos . 1 , 2 ) one day preceding the operation for tumor resection , embolization was performed by dmso and onyx via the left distal mca . post - embolic angiography showed a decrease in the size of the hypervascular contrast staining mass ( fig . 3 ) . an mr image obtained immediately after embolization of the tumor showed no acute infarction or venous congestion . all patients were initially treated with surgical resections and there were no perioperative mortalities . at the initial operation , a grossly total resection ( gtr ) was accomplished in 9 patients ( 69.2% ) , a partial resection ( pr ) in 2 patients ( 15.4% ) and an endoscopic biopsy in 1 patient , while results were not available for one patient . one patient underwent only an endoscopic biopsy because of a deep seated tumor ( pineal lesion , case no . another patient underwent the initial operation at an outside institution , so we could not estimate the extent of the resection . according to the original operation records , ebl ranged from 350 ml to 1200 ml and the mean ebl was 850 ml , for all patients . postoperative external beam radiotherapy ( ebrt ) was delivered in 11 patients ( 84.6% ) regardless of the extent of resection . 9 ) rejected an active treatment after the initial surgery and another patient ( case no . 4 ) was not irradiated postoperatively due to misdiagnosis . however , he received irradiation ( 1500 cgy ) by cyberknife 3 months later . the mean total ebrt dose was 5770 cgy ( range : 5400 - 6000 cgy ) . two patients ( 15.4% ) underwent stereotactic radiosurgery using a cyberknife for treatment of recurrent tumors . his initial pathologic diagnosis was pineal parenchymal neoplasm with intermediate undifferentiation , and he received a total of 2 cycles of ice chemotherapy ( a regimen employing ifosfamide , carboplatin and etoposide ) . but , the tumor progressed during chemotherapy and mental confusion developed due to an obstructed hydrocephalus . six patients ( 46.1% ) had low grade hpcs ( who grade ii ) and 7 patients ( 53.9% ) had anaplastic hpcs ( who grade iii ) , a percentage that is relatively higher than in other studies . interestingly , the pathologic diagnosis of the resected recurrent tumors changed from low grade to anaplastic hpcs in 2 patients ( 15.4% , case nos . 2 , 4 ) . low grade hpcs ( who grade ii ) showed dense cellularity with branched thin walled vessels ( fig . anaplastic hpcs ( who grade iii ) showed cellular pleomorphism with frequent mitosis and necrosis ( fig . all resected tumors had well developed reticulin fibers , and cd34 was positive in 10 patients ( 83.3% ) and negative in 2 patients ( 16.7% ) . the ki-67 proliferative index ranged from 1% to 30% , wi th a mean of 11.3% . the mean ki-67 proliferative index was 2.2% in the low grade hpc group , and 18.3% in the anaplastic hpc groups . six patients ( 46.2% ) developed local recurrences at 104 , 73 , 19 , 4 and 3 ( two patients ) months after initial surgery . of the 6 patients , one underwent five operations , another underwent four operations and the other two underwent two operations . the two remaining patients underwent only the initial operation because of their poor general medical condition . five and 10-year recurrence - free survival ( rfs ) rate was 62% and 20.5% , respectively . mean time for local recurrence was 24.6 months in patients who treated with pr or biopsy against 105.7 months in patients who treated with gtr ( p=0.012 by log - rank test ) ( fig . 7 ) . regarding adjuvant rt , mean time for local recurrence was 10.7 months in patients who did not received rt against 85.4 months in patients who received rt ( p=0.052 by log - rank test ) ( fig . 8) . there were no distant metastases , based on clinical follow - up and whole body pet - ct scan . the outcomes of treatment were estimated according to the karnofsky performance scale ( kps ) . the mean kps at the final outcome was 64.6 ( initial mean kps was 70.8 ) . the mean follow - up period was 54.3 months ( range : 13 - 185 months ) . five year overall survival rate was 84% and mean overall survival was 158 months ( fig . the patient group consisted of 12 ( 92.3% ) males and 1 ( 7.7% ) female . patient ages at the time of initial diagnosis ranged from 26 to 73 years , with a mean of 48 years . the most common presenting symptom was headache , and four patients had visual field defects due to a tumor in the occipital lobe . the ratio of intracranial hpcs to meningiomas was 1 : 46 , and the proportion of hpcs was only 2.2% . the preferential areas of tumor origin were parasagittal ( 5 patients , 38% ) and falx ( 3 patients , 23% ) . one patient had a homogeneous enhancing pineal gland tumor which turned out to be hpc . distributions of the remaining tumor locations were as follows : two convexity , one sphenoid wing and one cerebellopontine angle . the preoperative contrast - enhanced ct scans of 12 patients ( ct was not available for one patient ) revealed hyperdense and homogeneous or heterogeneous enhancing lesions with no evidence of calcification . radiologic findings of osteolysis of the skull were noted in 2 patients ( 15.4% ) ( fig . enhanced mr images , all patients had well demarcated tumor margins and detailed features of mr images are described in table 1 . preoperative dsas were performed on 4 patients ( 30.8% ) because they had many fluid void signals on the t2-weighted images . each dsa image showed a hypervascular contrast staining mass with an arterial feeder from the middle meningeal artery ( case no . 8) , distal branches of the pericallosal artery and some posterior choroidal arteries ( case no . two patients ( 15.4% ) showed hemorrhage from the hpc on the initial ct scans ( case nos . 1 , 2 ) one day preceding the operation for tumor resection , embolization was performed by dmso and onyx via the left distal mca . post - embolic angiography showed a decrease in the size of the hypervascular contrast staining mass ( fig . 3 ) . an mr image obtained immediately after embolization of the tumor showed no acute infarction or venous congestion . additionally , the patient had no neurological deterioration after embolization . all patients were initially treated with surgical resections and there were no perioperative mortalities . at the initial operation , a grossly total resection ( gtr ) was accomplished in 9 patients ( 69.2% ) , a partial resection ( pr ) in 2 patients ( 15.4% ) and an endoscopic biopsy in 1 patient , while results were not available for one patient . two patients had aborted operations because of intraoperative bleeding that resulted in partial resection . one patient underwent only an endoscopic biopsy because of a deep seated tumor ( pineal lesion , case no . another patient underwent the initial operation at an outside institution , so we could not estimate the extent of the resection . according to the original operation records , ebl ranged from 350 ml to 1200 ml and the mean ebl was 850 ml , for all patients . postoperative external beam radiotherapy ( ebrt ) was delivered in 11 patients ( 84.6% ) regardless of the extent of resection . 9 ) rejected an active treatment after the initial surgery and another patient ( case no . 4 ) was not irradiated postoperatively due to misdiagnosis . however , he received irradiation ( 1500 cgy ) by cyberknife 3 months later . the mean total ebrt dose was 5770 cgy ( range : 5400 - 6000 cgy ) . two patients ( 15.4% ) underwent stereotactic radiosurgery using a cyberknife for treatment of recurrent tumors . his initial pathologic diagnosis was pineal parenchymal neoplasm with intermediate undifferentiation , and he received a total of 2 cycles of ice chemotherapy ( a regimen employing ifosfamide , carboplatin and etoposide ) . but , the tumor progressed during chemotherapy and mental confusion developed due to an obstructed hydrocephalus . one day preceding the operation for tumor resection , embolization was performed by dmso and onyx via the left distal mca . post - embolic angiography showed a decrease in the size of the hypervascular contrast staining mass ( fig . 3 ) . an mr image obtained immediately after embolization of the tumor showed no acute infarction or venous congestion . all patients were initially treated with surgical resections and there were no perioperative mortalities . at the initial operation , a grossly total resection ( gtr ) was accomplished in 9 patients ( 69.2% ) , a partial resection ( pr ) in 2 patients ( 15.4% ) and an endoscopic biopsy in 1 patient , while results were not available for one patient . one patient underwent only an endoscopic biopsy because of a deep seated tumor ( pineal lesion , case no . another patient underwent the initial operation at an outside institution , so we could not estimate the extent of the resection . according to the original operation records , ebl ranged from 350 ml to 1200 ml and the mean ebl was 850 ml , for all patients . postoperative external beam radiotherapy ( ebrt ) was delivered in 11 patients ( 84.6% ) regardless of the extent of resection . 9 ) rejected an active treatment after the initial surgery and another patient ( case no . 4 ) was not irradiated postoperatively due to misdiagnosis . however , he received irradiation ( 1500 cgy ) by cyberknife 3 months later . the mean total ebrt dose was 5770 cgy ( range : 5400 - 6000 cgy ) . two patients ( 15.4% ) underwent stereotactic radiosurgery using a cyberknife for treatment of recurrent tumors . his initial pathologic diagnosis was pineal parenchymal neoplasm with intermediate undifferentiation , and he received a total of 2 cycles of ice chemotherapy ( a regimen employing ifosfamide , carboplatin and etoposide ) . but , the tumor progressed during chemotherapy and mental confusion developed due to an obstructed hydrocephalus . six patients ( 46.1% ) had low grade hpcs ( who grade ii ) and 7 patients ( 53.9% ) had anaplastic hpcs ( who grade iii ) , a percentage that is relatively higher than in other studies . interestingly , the pathologic diagnosis of the resected recurrent tumors changed from low grade to anaplastic hpcs in 2 patients ( 15.4% , case nos . 2 , 4 ) . low grade hpcs ( who grade ii ) showed dense cellularity with branched thin walled vessels ( fig . tumor cells had diffuse cd34 positivity ( fig . 4b ) and the ki-67 proliferative index was 10% ( fig . anaplastic hpcs ( who grade iii ) showed cellular pleomorphism with frequent mitosis and necrosis ( fig . all resected tumors had well developed reticulin fibers , and cd34 was positive in 10 patients ( 83.3% ) and negative in 2 patients ( 16.7% ) . the ki-67 proliferative index ranged from 1% to 30% , wi th a mean of 11.3% . the mean ki-67 proliferative index was 2.2% in the low grade hpc group , and 18.3% in the anaplastic hpc groups . six patients ( 46.2% ) developed local recurrences at 104 , 73 , 19 , 4 and 3 ( two patients ) months after initial surgery . of the 6 patients , one underwent five operations , another underwent four operations and the other two underwent two operations . the two remaining patients underwent only the initial operation because of their poor general medical condition . five and 10-year recurrence - free survival ( rfs ) rate was 62% and 20.5% , respectively . mean time for local recurrence was 24.6 months in patients who treated with pr or biopsy against 105.7 months in patients who treated with gtr ( p=0.012 by log - rank test ) ( fig . regarding adjuvant rt , mean time for local recurrence was 10.7 months in patients who did not received rt against 85.4 months in patients who received rt ( p=0.052 by log - rank test ) ( fig . 8) . there were no distant metastases , based on clinical follow - up and whole body pet - ct scan . the outcomes of treatment were estimated according to the karnofsky performance scale ( kps ) . the mean kps at the final outcome was 64.6 ( initial mean kps was 70.8 ) . the mean follow - up period was 54.3 months ( range : 13 - 185 months ) . five year overall survival rate was 84% and mean overall survival was 158 months ( fig . intracranial hpcs are very rare tumors with an incidence of less than 1% , and they represented 2.2% of all meningiomas diagnosed over the last 18 years in our institute . it is widely known that intracranial hpcs , unlike meningiomas , are more common in males than females , which was also true in our data , where 92% of the patients were males5,18,25 ) . in previous studies on intracranial hpcs , the mean age at the time of diagnosis ranged from 38 to 44.9 years , which was lower than that of meningiomas1,5,22,23,25,48 ) . in our series , our study included two patients ( 15.4% ) with intracerebral hemorrhage on an initial ct scan . the majority of hpcs arise in the supratentorial area with dural attachment23,41 ) . however , non - dural attached hpcs , such as in the pineal region ( case no.4 ) , and purely intraparenchymal hpcs have also been reported28,39,41 ) . distinguishing hpcs from benign meningiomas before surgery can be difficult , but is very important because of the aggressiveness of hpcs and their high rates of local recurrence and distant metastasis . chiechi et al.9 ) reported that intracranial hpcs are more multilobulated than benign meningiomas , and have narrow based dural attachment on ct and conventional mr images . additionally , hyperostosis and intralesional calcification are not found in intracranial hpcs , which is distinct from meningiomas . many other papers have reported that intracranial hpcs may show osteolytic features on plain films , ct and mr images6,11,33 ) . in the current study , osteolysis of the skull on ct scan was noted in 2 patients ( case nos . 5 , 11 ) who were diagnosed with anaplastic hpc . it has been found that osteolysis is more prevalent in anaplastic hpcs than in low grade hpcs9 ) . it has also been found that ct perfusion is valuable in preoperative grading of intracranial gliomas13 ) , in distinguishing between glioblastomas , metastasis and abscesses8,12 ) and in evaluating the prognosis of recurrent brain tumors after stereotactic radiosurgery26 ) . similarly , ren et al.34 ) reported that ct perfusion can provide crucial information on hpcs and benign meningiomas . as mri technology has advanced , liu et al.30 ) demonstrated that minimum apparent diffusion coefficient ( adc ) values may be helpful for distinguishing hpcs from meningiomas . they found that the mean minimum adc values of hpcs were significantly higher than that of meningiomas . the frailty of the conventional surgical approach was intractable intraoperative bleeding from the meningeal artery during the initial stage of the operation . thus , several authors have proposed multi - stage operations , included feeding artery embolization27 ) . matsushige et al.31 ) reported a giant hpc treated with preoperative tumor embolization , where embolization was used to overcome intraoperative bleeding . the use of preoperative tumor embolization has also decreased operation - related mortality and morbidity1 ) . after devascularization of the tumor from the main feeding artery using embolization , we were also able to markedly reduce intraoperative bleeding in case no . 10 . the blood loss during operation was much lower compared to non - embolized patients ( 350 ml vs. 990 ml ) , but we could not draw statistically significant conclusions due to the limited sample size of our study . surgical resection of the tumors offers the advantage of pathologic confirmation and reduction of mass effects . a simpson grade i resection has been found to be associated with a high long - term control rate2,18 ) . similarly , rutkowski et al.36 ) reported that , regardless of adjuvant therapy , gtr was associated with significantly improved survival rates compared with pr . in our series , a total of 9 patients ( 69% ) achieved a gtr at the initial surgery , which was a much higher rate compared to other studies . a literature review on intracranial hpcs showed an average gtr rate of 56.7% ( table 2 ) . we conducted a statistical analysis about correlation between extent of resection and recurrence , and we found statistical significance like other several series ( mean rfs 105.7 months vs. 24.6 months , p=0.012 ) ( fig . interestingly , the average mortality rate in the recent literature was 31.5%1,2,15,16,18,21,28,35,37,42,44 ) , but was only 15.4% in our study . though adjuvant therapy and follow - up period also affect the mortality rate , we cautiously suggest that gtr also contributed to the decreased mortality rate . staples et al.43 ) reported that the 5-year rfs improved from 28% with operation alone to 57% with adjuvant rt after gtr . similarly , we could find that the patients who had been recieved adjuvant rt had tendency of longer rfs ( mean rfs 85.4 months vs. 10.7 months , p=0.052 ) ( fig . a review of the recent literature shows that adjuvant rt is not applied consistently ( range : 17 - 91% , mean : 47.4% ) . on the other hand , we performed adjuvant rt regardless of the pathologic grade and extent of resection in most of the patients , 11 out of 13 patients received adjuvant rt to a mean dose of 5770 cgy . serious side effects from irradiation , such as cerebral edema , leucencephalopathy , radiation - induced necrosis and death have been reported42 ) . in our study , there were no significant radiation - related complications . chemotherapy provided only insignificant benefits3,20 ) , but chamberlain and glantz7 ) reported that chemotherapy ( cyclophosphamide+adriamycin+vincristine , followed by -ifn , followed by ice ) may be helpful for recurrent intractable intracranial hpcs . in our study , one patient was treated with chemotherapy ( ice regimen ) due to an initial misdiagnosis of pineal sarcoma . the histological criteria for anaplastic hpcs ( who grade iii ) include more than five mitoses in 10 high power fields and/or necrosis and moderate to high nuclear atypia and moderate to high cellularity after hemorrhage . moreover , the pathologic features of low grade hpcs ( who grade ii ) show monomorphous round to oval tumor cells having staghorn - like vessels . the tumors contain well developed reticulin fibers and diffuse cd34 immunopositivity . in our data , the mean ki-67 proliferative indexes in low grade and anaplastic hpc were 2.2% and 18.3% , respectively . in recurrent hpc , the mean ki-67 was 14.6% , while in non - recurrent hpc , it was 7.8% . reported that the patients with a ki-67 index less than 5% tended to survive longer , but this finding could not correlate the clinical outcome46,47 ) . also we conducted statistical analysis of rfs depending on the who grade , but we could not find statistical significance ( p=0.644 ) . galanis et al.20 ) found that , out of 32 recurrences , 19 ( 59% ) recurred at the primary site , eleven ( 34% ) recurred at both the primary and other cns sites and the remaining 2 ( 7% ) had diffuse leptomeningeal spread without local recurrence at the primary site . in our series , we would define ' recurrence ' as increased tumor sized by follow - up radiologic study and any apparent deterioration in clinical status to need reoperation . in the strict sense , initially partial resection or biopsy cases should be described as ' progression ' when reoperation were needed , but number of our cases were too small to analyze about progression cases , separately . unfortunately , several authors reported that the extent of tumor resection has been less definitely correlated with the local recurrence of hpcs compared to meningiomas29 ) . this feature of intracranial hpcs might be explained by the strategy to aggressively irradiate partially resected tumors to reduce local recurrence . recently , du et al.14 ) reported only a 3.8% recurrence rate , but their follow - up period was very limited ( mean : 22 months ) . in our series , the recurrence rate was 46.2% ( 6/13 ) , with the mean follow - up period of 54.3 months ( range : 13 - 185 months ) . it is widely known that after the first recurrence , hpc tends to recur at brief intervals . guthrie et al.23 ) reported that the average periods to the second , third and fourth surgeries for recurrence were 38 , 35 and 17 months , respectively . schrder et al.38 ) found 5- , 10- and 15-year survival rates of 65% , 45% and 15% , respectively . in their broad literature review , rutkowski et al.36 ) found 1- , 5- , 10- and 20-year survival rates of 95% , 82% , 60% and 23% , respectively . mena et al.32 ) reported a recurrence rate of 70% ( 57/94 ) , while kochanek et al.29 ) reported 41% ( 7/17 ) . it seems that rarity of intracranial hpcs along with the absence of a well formulated treatment strategy might lead to highly fluctuating survival and local recurrence rates . we believe that adjuvant radiation therapy is helpful , even if maximal tumor resection was performed in low grade hpcs . molecular biologic analysis and studies of the efficacy of chemotherapy are required for better outcomes in relentlessly recurrent hpcs .
objectiveintracranial hemangiopericytomas ( hpcs ) are rare tumors with aggressive behavior , including local recurrence and distant metastasis . 
 we conducted this retrospective study to evaluate the efficacy of grossly total resection and adjuvant radiotherapy ( rt ) for these tumors.methodsa total of 13 patients treated for intracranial hpc from january 1995 through may 2013 were included in this retrospective study . 
 we analyzed the clinical presentations , radiologic appearances , treatment results , and follow - up outcomes , as well as reviewed other studies.resultsthe ages of the patients at the time of diagnosis ranged from 26 to 73 years ( mean : 48 years ) . 
 the majority of the patients were male ( 92.3% ) , and the majority of the tumors were located in the parasagittal and falx . 
 the ratio of intracranial hpcs to meningiomas was 13 : 598 in same period , or 2.2% . 
 seven patients ( 53.8% ) had anaplastic hpcs . 
 nine patients ( 69.2% ) underwent gross total tumor resection in the first operation without mortality . 
 eleven patients ( 84.6% ) underwent postoperative adjuvant rt . 
 follow - up period ranged from 13 to 185 months ( mean : 54.3 months ) . 
 the local recurrence rate was 46.2% ( 6/13 ) , and there were no distant metastases . 
 the 10-year survival rate after initial surgery was 83.9% . 
 the initial mean karnofsky performance scale ( kps ) was 70.8 and the final mean kps was 64.6.conclusiongross total tumor resection upon initial surgery is very important . 
 we believe that adjuvant rt is helpful even with maximal tumor resection . molecular biologic analyses and chemotherapy studies 
 are required to achieve better outcomes in recurrent intracranial hpcs .