they complained about a lump in the back of the child s head that made it difficult to comb and plait the girl s hair . the child was entirely asymptomatic , and there was no relevant medical history , such as systemic ailment or associated long - bone disease . magnetic resonance imaging scans showed an occipital dural - based tumour of heterogeneous intensity slightly compressing the left occipital pole and apparently extending toward the superior sagittal sinus ( fig . the outer surface of the fixed specimen ( 662 cm ) was gray tan , smooth , and hard , yet the transverse cut surface contained yellow , pale , and pasty material with reddish kernel - like crusts , resulting in an overall appearance similar to a slice of butter - covered raspberry bread ( fig . under light microscopy , the pale yellow areas contained widespread coagulative necrosis , powdery calcification , numerous cholesterol clefts , foreign body - type giant cells , and foamy macrophages , while the red nodules were populated by giant cells ( fig . the entire lesion was demarcated by a thin fibrous wall consistent with compacted dura mater . closer examination of the nodular areas detailed a miscellaneous group of giant cells including mononucleated as well as multinucleated forms of foreign - body and touton types , the former with ground - glass amphophilic to flamboyantly eosinophilic cytoplasm and occasional empty vacuoles ( fig . 2c foci of a mixed inflammatory cell population could be recognized , including lymphocytes , neutrophils , and scarce eosinophils . intriguingly , some giant cells demonstrated phagocytosis of related tumoural elements ( cell cannibalism ) and uptake of inflammatory cells ( fig . disturbing bizarre nuclei were also present in some of these giant cells ; however , mitotic activity was not identified ( fig . the immunoperoxidase - coupled reactions revealed a fibrohistiocytic immunophenotype with cd68 , 1-antitrypsin ( data not shown ) , 1-antichymotrypsin ( data not shown ) , and vimentin positivity ( fig . cd34 immunostaining was negative but highlighted the delicate vascular branching , whereas the epithelial membrane antigen ( ema ) unexpectedly delineated the giant cell borders ( fig . likewise , staining for ps100 , cd1a , cd207 , fxiiia , smooth - muscle actin ( sma ) , muscle - specific actin ( msa ) , podoplanin ( d2 - 40 ) , microphthalmia transcription factor ( mitf ) , and glial fibrillary acidic protein ( gfap ) was also negative . ancillary histochemical stains were also requested ( ziehl - neelsen , auramine - rhodamine , fite - faraco , periodic acid - schiff , brown - hopps and grocott ) and did not detect either conventional or atypical mycobacteria . an additional dural fragment labeled as  implant attached to the superior sagittal sinus it had yellow macules constituted microscopically of foamy histiocytes and multinucleated foreign - body type giant cells engulfing cholesterol crystals . according to the aforementioned findings , the lesion was diagnosed as dural xanthogranuloma ( cholesterol granuloma with broad areas of coagulative necrosis and foci of giant cells ) . to date all procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 helsinki declaration and its later amendments or comparable ethical standards . informed consent was obtained from the patient s legal guardian , and anonymity of the patient was preserved . lesions of fibrohistiocytic origin seem to be quite rare among central nervous system ( cns ) tumours [ 1 - 3 ] . accumulation of foamy macrophages in the neural axis can arise from known metabolic / storage disorders or serum lipid disturbances ( secondary cns involvement ) but can also occur without an exact cause or triggering factor ( primary cns involvement ) [ 4 - 7 ] . at present , the pathogenesis of the latter remains poorly understood . nonetheless , two hypothetical pathways have been proposed to explain their formation [ 5 - 7 ] : ( 1 ) local trauma or haemorrhage with overstimulation of mesenchymal cells from dura mater or vascular adventitia and ( 2 ) synthesis of lipotrophic factors that cause undifferentiated mesenchymal cells to undergo xanthomatous transformation . these primary cns , lipidized fibrohistiocytic tumours have been traditionally dichotomized as intraventricular ( i.e. , affecting plexi choroidei ) or meningeal ( dural - associated ) [ 4 - 7 ] . this classification can be further expanded to include some other topographies , such as leptomeningeal or parenchymatous ( intracerebral or intracerebellar ) [ 8 - 10 ] . although plexi choroideorum xanthomas have been described since the beginning of the 20th century , the first observations of a non - ventricular fibrous xanthoma were presented in the 1973 work of kepes et al . . it was not until 1979 that lam and colah   reported the first dural - associated lesion of this kind . in contrast , cns cholesterol granulomas ( xanthogranulomas ) are uncommon lesions usually found incidentally in plexi choroidei during postmortem examination ( 1.6% to 7% of autopsies ) . they are thought to occur either because of desquamation of choroidal epithelial cells or from local histiocytes recruited , perhaps , as formerly described . they feature needle - like cholesterol clefts flanked by foreign - body type giant cells , foamy histiocytes , chronic inflammatory cells , and scattered haemosiderin granules . also , varying amounts of fibrosis can be present , becoming most marked in long - standing lesions . otherwise , solitary reticulohistiocytoma is a distinctive but rare lesion in adults . such tumours are seen as a yellow - brown to dark - red papule consisting of dense circumscribed nodules of deeply eosinophilic histiocytes often exhibiting multinucleation with no touton giant cells . immunoperoxidase reactions reveal expression of cd163 , cd68 , and vimentin , along with variable reactivity for ham56 , 1-antitrypsin , lysozyme , fxiiia , ps100 , msa , and mitf . a multicentric variant has also been described , but it is associated with autoimmune disorders and internal malignancies . interestingly , it has been suggested that the solitary form is similar to adult xanthogranuloma , with the distinction being largely based on predominance of multinucleated eosinophilic histiocytes . reports of solitary reticulohistiocytoma involving the neuroaxis are currently non - existent in the global medical literature . there were various differential diagnoses to consider in our case , such as xanthoma , fibrous histiocytoma ( fibroxanthoma ) , atypical fibrous histiocytoma , solitary ( juvenile ) xanthogranuloma , and erdheim - chester disease . as conveyed by weiss and enzinger , xanthomas are just collections of tissue histiocytes filled with lipids . these foamy macrophages are embedded within a loose stroma and organise in uniform sheets , occasionally divided into smaller nests by delicate fibrous bands . they are thought to be closely related to cholesterol granulomas , probably in an earlier stage . nevertheless , a comparative clinicopathological analysis of both lesions in plexi choroidei revealed some differences . intense siderosis and a higher male - to - female ratio were noted in cholesterol granulomas ( 14:3 vs 13:8 ) , while xanthomas were more frequently associated with dyslipidaemia . histologically , benign fibrous histiocytomas are characterized by a mixture of spindle fibroblast - like cells arranged in short fascicles , with or without focal storiform profiles , and plump histiocyte - like cells accompanied by variable numbers of foamy histiocytes , haemosiderin - laden macrophages , multinucleated giant cells of foreign - body or touton types , lymphocytes , plasma cells , and bundles of collagen [ 1 - 3 ] . the immunohistochemical profile shows an admixture of cd68 , fxiiia , cd34 , ps100 , sma , and d2 - 40 cells , in variable proportions . a subset of fibrous histiocytomas exhibits borderline histologic signs of malignancy , including significantly greater cellular atypia and increased mitotic activity . in spite of the nuclear pleomorphism focally detected in our case , mitotic activity was not present ; thus , the bizarre nuclei observed were considered a degenerative phenomenon such as that seen in ancient neurilemmoma or giant cell ependymoma . we also interpreted the small implant attached to the superior sagittal sinus as an additional lesion rather than direct extension from the larger one ( i.e. , an early multifocal process ) . juvenile ( solitary ) xanthogranuloma demonstrates a wavering time - dependent appearance and is a challenging diagnosis to eliminate [ 1 - 3,17 ] . despite its classic morphology showing foamy histiocytes accompanied by touton - type giant cells , conversely , longstanding lesions usually develop interstitial fibrosis and even assume a vague storiform pattern . additionally , the existence of transitional cases with or without xanthomatous features , with or without interspersed spindle cells , and containing multinucleated giant cells with or without touton configuration is also possible . usually , a modest number of acute and chronic inflammatory cells are also present , especially eosinophils . regardless of morphology , macrophages and touton cells show immunoreactivity for cd68 , 1-antitrypsin , 1-antichymotrypsin , lysozyme , cd31 , and fxiiia . the former can be ruled out by means of an appropriate immunohistochemistry panel ( ps100 , cd1a , and cd207 ) in a suitable clinical setting ( localized vs multiple sites of involvement ) . on the other hand , the latter can be troublesome , particularly when erdheim - chester disease is suspected , which is a rare disorder that most often becomes apparent in middle age and is typically seen in the context of long - bone and systemic disease . it is characterized by lipid - laden cd68 + , cd1a , and ps100 macrophages and touton - type multinucleated giant cells accompanied by scarce eosinophils . indeed , the reddish nodules described in our case displayed some of these features ; however , considering the lack of multiple organ involvement , we considered the multinucleated foreign - body type giant cells to represent a trait more akin to solitary reticulohistiocytoma than to erdheim - chester disease . tuberculosis was also a consideration ; however , the gross appearance of the lesion was not consistent with a tuberculoma , which is usually hard and chalky - white rather than soft , and pale - yellow . furthermore , there was no heubner arteritis or typical epithelioid granulomas of tuberculosis with caseous necrosis and langhan type giant cells . one might argue that it can be entirely feasible in an immunodeficient patient ; however , as previously stated , our patient was a completely healthy girl who had already received her bacillus calmette  gurin vaccine ( which only provides protection against the leptomeningeal form ) . other non - fibrohistiocytic neoplasms can show extensive xanthomatous changes , such as glioblastoma , pleomorphic xanthoastrocytoma , and metaplastic meningioma . nonetheless , immunoperoxidase - coupled assays for gfap and ema can be useful to achieve a diagnosis in these settings . though a dull peripheral rim was observed in the multinucleated giant cells through ema immunostaining , it was uncertain whether to dismiss it as an artifact . indeed , ema expression has been demonstrated in normal plasma cells , monoblasts , and in some hematological malignancies . xanthogranuloma and solitary reticulohistiocytoma are conditions grouped among the pathogenetically diverse category of fibrohistiocytic tumours . interestingly , these miscellaneous lesions sometimes show stunning overlapping morphological or immunophenotypical traits , which might be explained on the basis of the  facultative fibroblast  concept proposed by ozzello in 1963 . this concept features a cell with an inherent capacity to transdifferentiate to another morphologic and functional state , an assumption that could be true for the present case . nonetheless , it can simply represent a time - dependent phenomenon ( i.e. , evolving stages of the same process ) . hence , we report a lipidized fibrohistiocytic lesion arising in the dural coat of the cns with peculiar and unconventional traits that , as far as we know , have not been previously described .
we report a unique case of a 4-year - old girl with an intriguing fibrohistiocytic tumour . 
 magnetic resonance imaging scans showed a dural mass of variegated intensity compressing the left occipital pole and apparently extending toward the superior sagittal sinus . 
 grossly , the cut surface of the surgical specimen was yellow , pale , and soft with reddish kernel - like crusts . 
 histologically , the yellow areas resembled cholesterol granulomas with widespread coagulative necrosis , cholesterol clefts , powdery calcification , foreign body - type giant cells , and foamy macrophages , while the scattered red spots contained numerous multinucleated giant cells of foreign - body and touton types , the former with amphophilic to slightly eosinophilic cytoplasm . 
 immunoperoxidase reactions confirmed the expression of histiocytic markers and vimentin . 
 as far as we know , no tumour displaying these peculiar morphological features has yet been described .