pilomyxoid astrocytoma ( pma ) has been included as a novel clinico - pathological entity in the 2007 world health organization classification of tumors of the central nervous system . pma has a poor prognosis when compared to pilocytic astrocytoma ( pa ) because of the propensity of the tumor to metastasize through the cerebrospinal fluid ( csf ) . pma occurs typically in the hypothalamic / chiasmatic region similar to the pilocytic variety , and there have been a few reports regarding the image features that differentiate pma from pa . we report a rare case of pma of the third ventricle in a 24-year - old male . a 24-year - old male presented with a 3-month history of dull headache that had progressively worsened over the past 1 week and was associated with nausea and vomiting . on examination , he had no neurological deficit . noncontrast - enhanced ct scan showed mild hydrocephalus with a uniform hypoattenuated lesion in the third ventricle [ figure 1a ] . brain mri showed a well - defined mass measuring about 2.7  2.4  2.3 cm in the third ventricle causing hydrocephalus . it showed hypointensity on a t1-weighted image , hyperintensity on a t2-weighted image , and thick peripheral contrast enhancement . there was no dissemination on brain [ figure 1b  d ] and spinal mri [ figure 1e and f ] . the radiological differential diagnosis was pma , pa , germinoma , or craniopharyngioma with difficult differentiation . 24-year - old male presented with a 3-month history of dull headache that had progressively worsened over 1 week with nausea and vomiting . ( a ) axial noncontrast ct image shows a homogenously hypoattenuated mass in the third ventricle without hemorrhage or calcification ( arrow ) . ( b ) axial flair image shows a mass of high signal intensity in the third ventricle ( arrow ) . ( d ) contrast - enhanced t1-weighted image shows thick peripheral enhancement ( arrow ) . ( e , f ) contrast - enhanced t1-weighted images of spine show no cerebrospinal fluid dissemination . ( g ) postoperative contrast - enhanced t1-weighted image shows remnant tumor in the floor of the third ventricle ( arrow ) . the patient underwent a navigation - guided craniotomy and partial resection of the tumor . at surgery , most of the lesion was found to be soft and whitish in color . although it looked well circumscribed initially , the tumor infiltrated the walls of the third ventricle . we left the tumor which was adherent to the floor of the third ventricle to minimize the hypothalamus injury [ figure 1 g ] . histologically , it consisted of monomorphous and bipolar piloid cells in a substantial amount of myxoid background [ figure 2a ] . no rosenthal fibers or eosinophilic granular bodies immunohistochemically , the tumor cells were strongly positive for glial fibrillary acidic protein [ figure 2b ] . anti - ki-67 monoclonal antibody ( mib-1 ) is one of the most useful markers for evaluating cellular proliferation in human neoplasm , including intracranial tumors . rathi et al . , demonstrated significant relation between tumor grade and mib-1 labeling index . they found that mean mib-1 labeling index values of astrocytomas were lower than those of anaplastic astrocytomas and glioblastomas . in our case , the fraction of mib-1positive tumor cells ( mib-1 labeling index ) was low [ figure 2c ] . 24-year - old male presented with a 3-month history of dull headache that had progressively worsened over 1 week with nausea and vomiting . ( a ) photomicrograph ( hematoxylin  eosin stain , original magnification 400 ) shows overall monomorphic tumor cells ( arrow ) and prominent myxoid background without rosenthal fibers or eosinophilic granular bodies . ( b ) immunohistochemically , the tumor is strongly positive for glial fibrillary acidic protein , confirming its astrocytic origin ( glial fibrillary acidic protein , original magnification 400 , arrow ) . ( c ) proliferation of anti - ki-67 monoclonal antibody ( mib-1)-positive tumor cells is low ( mib-1 , original magnification 400 , arrow ) . , pma shows a prominent mucoid matrix and an angiocentric pattern of monomorphous bipolar tumor cells without eosinophilic granular bodies , rosenthal fibers , or hyaline droplets . rosenthal fibers and eosinophilic granular bodies are characteristic of pa , and calcification is more common in pa than pma . the tumor predominantly occurs in children of different age groups , ranging from the newborn to young adult . due to the more aggressive behavior , komotar et al . , reported that the mean duration of progression - free survival for pma and pa was 26 and 147 months , respectively . pma is usually found at the hypothalamic / chiasmatic region , but may occur anywhere along the central neuroaxis . the reported radiologic findings of pma are a well - defined , predominant solid mass , hypointense on t1-weighted images and hyperintense on t2-weighted images , and homogeneous contrast enhancement . , reported that unlike pa , pma is predominantly solid , with only a minimal cystic component . the presence of lesion , mainly solid , with non - enhancing portion of the tumor may be helpful differential features of pma as compared to pa . other characteristics on imaging that help in differential diagnosis would be the predilection for suprasellar area , intratumoral hemorrhage , and early leptomeningeal dissemination . similarly , t2-weighted image in our case demonstrated a bright hyperintense mass with well - defined margin . marked hyperintensity on t2-weighted image may reflect the characteristic histopathologic finding of pma with prominent myxoid component . however , contrast - enhanced t1-weighted image showed a solid mass with central necrosis and thick peripheral enhancement . it appears that it is difficult to differentiate pma from pa on the basis of imaging findings . linscott et al . , reported a much broader imaging spectrum with variable contrast enhancement patterns including rim enhancement but no contrast enhancement , and so they concluded that there were no definitive pathognomonic image findings to distinguish pma from pa in their study . moreover , lee et al . , reported that the two tumors could not be diff erentiated based on the presence of hemorrhage . the differential diagnosis of pma in the third ventricle also includes meningioma , craniopharyngioma , or germ cell tumor . the mass in our case showed no fat or calcification , but demonstrated thick peripheral enhancement . horger et al . , reported that apparent diffusion coefficient values and t2 signal intensity are generally higher in the latter , reflecting the proportion of myxoid matrix in these tumors . preliminary investigations with the use of mr spectroscopy in two cases of pediatric optic - chiasmatic pma revealed an increase in choline concentration in the intratumoral region of pa in comparison with pma . they attributed this elevation to the more cellular components in pa in comparison with the myxoid background of pma . , reported that elevated choline / creatine outside pma enhancing margin is usually present in high - grade tumors . currently , there is no standard guideline on the management of patients with pma . non - enhancing solid tumors give rise to diagnostic problem when they disseminate along the csf space . non - enhancing csf dissemination is more apparent on a fluid attenuation inversion recovery ( flair ) image . careful evaluation of signal changes of csf to detect csf dissemination on flair images may be helpful for surgical planning . we have reported a case of a 24-year - old male with a pilomyxoid astrocytoma ( pma ) arising in the third ventricle . recognition of this tumor may be of help to make an early diagnosis and appropriate treatment plan .