Benign isolated fibrohistiocytic tumor arising from the central nervous system. Considerations about two cases.

Benign fibrous histiocytomas (BFHs) are tumors with fibroblastic and histiocytic components without histological anaplasia. Intracerebral lesions are exceptional and to our knowledge a spinal location was not yet described. We describe 2 cases of BFHs of the neural axis: the first, a 22-month-old boy with Down's syndrome, presented with a paraparesis and the magnetic resonance (MR) of the spine disclosed an intradural extramedullary, thoracic mass, totally resected; the second, a 13-year-old boy with left partial motor seizures, in whom the MR of the brain showed an intracerebral, right frontal tumor, also surgically removed. Both patients are free of recurrence, 6 years and 15 months after surgery, respectively. Histological examination and immunoreactivity for vimentin and histiocytic markers favored the diagnosis of BFH. It is likely that these tumors may originate from spinal dura mater mesenchymal stem cells and from the intracerebral perivascular pial sheath or the brain vessel walls themselves, respectively. Other benign, isolated, intracranial fibrohistiocytic neoplasms, namely the juvenile xanthogranuloma, can harbor a clinical, morphological and immunohistochemical profile overlapping the one of the BFH. Intracranial germ cell tumors may be associated with Down's syndrome, although harboring an unusual, non-pineal and non-chiasmatic location. One can speculate that a similar, still unknown genetic mechanism responsible for this association, could also induce the growth of other type of tumors in patients with this syndrome. BFHs should be added to the differential diagnosis of intracerebral or spinal dural attached tumors. Furthermore, we propose to name these intracranial tumors "benign isolated fibrohistiocytic tumors of the CNS".