collision tumors occur when two pathologic tumor types are intermingled and identified histopathologically from a single specimen.1 
 2 metastasis from prostate adenocarcinoma commonly involves the bone and other organ systems a 67-year - old - right - handed man presented with a history of progressive confusion , abulia , and urinary incontinence . magnetic resonance imaging revealed a 5.3    4.8    4.2 cm extra - axial lesion arising from the anterior skull base with associated vasogenic cerebral edema in the frontal lobes bilaterally ( fig . 1 ) . on examination , although his affect was dull , there was no focal neurologic deficit . on digital rectal examination , the prostate - specific antigen ( psa ) level was 49.6 ng / ml ( normal : 04 ) . given the large extra - axial tumor , with vasogenic edema , mass effect , and neurologic symptoms , a bifrontal craniotomy was performed , with gross total resection of the lesion.3 
 
 neuroimaging . ( a ) sagittal postcontrast t1-weighted magnetic resonance ( mr ) scan demonstrating a contrast - enhancing mass ( white arrow ) arising from the anterior skull base with mass effect on the adjacent frontal lobes . ( b ) coronal mr demonstrating a contrast - enhancing lesion ( arrowhead ) with heterogeneous areas within the tumor mass appearing to arise from the region of the olfactory groove characteristic of an olfactory groove meningioma . ( c ) axial contrast - enhancing mr images demonstrate lobulated lesion ( white arrowhead ) with mass effect and adjacent perilesional edema ( black arrowheads ) . ( d ) axial fluid - attenuated inversion recovery images revealing significant bifrontal edema ( arrowheads ) . 2 ) ; the adenocarcinoma cells stained immunohistochemically for antibody directed against the psa.2 
 
 microscopic views of the lesions . ( a ) a world health organization grade i meningothelial meningioma with a focally disordered architecture and psammoma bodies was present . ( b ) nests of atypical - appearing cells consistent with metastatic adenocarcinoma were observed within the meningioma . ( d ) focal positive immunoreactivity with antibody to prostate - specific antigen was observed in the metastatic tumor . the metastasis additionally demonstrated positive staining with antibodies to chromogranin and neuron - specific enolase , indicative of neuroendocrine differentiation . the tumor stained with cytokeratin 7 and 20 antibodies and did not stain with antibody to thyroid transcription factor 1 . intracranial dural - based metastasis is relatively uncommon in comparison with the intraparenchymal disease burden . several neoplastic and nonneoplastic lesions have been reported to mimic both the radiologic imaging and clinical features of meningioma.4 
  prostate carcinoma has a predilection to metastasize to the bones and lymph nodes ; central nervous system involvement is rare.5 brain metastases in patients with prostate cancer range from 0.2% to 0.63% . dural - based metastases from prostate carcinoma have been reported and may mimic meningioma.6 
 7 
 8 most uncommon is metastasis of a prostatic adenocarcinoma to a preexisting intracranial tumor , a so - called collision tumor . dring reported the first case of prostate cancer metastasizing to a meningioma in 1975 , subsequently followed by other reports.9 
 10 there has been a report of metastatic prostate cancer presenting with a subdural hematoma.11 elderly men with known prostate carcinoma have been reported to have intracranial metastatic disease on routine surveillance and autopsy.12 intra - axial brain metastases are a rare and typically terminal event in patients with advanced systemic metastases . dural spread could be hematogenous or because of direct colonization of tumor cells , with another speculation being the increased tumor vascularity from the anterior skull base meningioma potentially having a higher predilection for metastatic cells to develop within a primarily meningeal tumor.13 only five cases of prostate cancer collision tumors have been reported previously.14 all the previous reports of a collision tumor have been in patients with a known prostate cancer that had already metastasized widely and systemically prior to central nervous system involvement . to our knowledge , this is the first case where metastatic prostate adenocarcinoma has presented initially and primarily with neurologic symptoms . although collision tumors are rare , the imaging characteristics make it difficult to discern different dural - based pathology , with malignant lesions posing as benign tumors thus mandating a thorough clinical , laboratory , and imaging work - up of elderly patients .
background  dural lesions in the anterior skull base may occur secondary to benign or malignant pathology that may be difficult to differentiate on imaging . 
 detailed clinical evaluation in many cases will narrow the differential diagnosis . in spite of using all the available information , in certain cases the underlying etiology of a lesion 
 remains unclear . 
 participant  we report a rare case of metastatic prostate adenocarcinoma to a meningioma in a 67-year - old - man who presented with progressive confusion and mental status alterations with no prior history of malignancy . 
 neuroimaging revealed a large anterior skull base lesion . 
 results  the lesion was surgically resected , and histopathology revealed a collision tumor , in which prostate adenocarcinoma was found admixed with a world health organization grade i meningioma . 
 conclusion  anterior dural skull base lesions can be either benign or malignant . 
 although infrequently reported , a benign - appearing dural - based lesion may be a manifestation of an underlying malignancy , and a thorough clinical , radiologic , and pathologic examination may be necessary , especially in the elderly .