Fibrohistiocytic tumors

Abstract

been the subject of controversy in recent decades,which has centered on whether they arise from histiocytic cells that may assume fibroblastic features or from fibroblastic stem cells. This continuing controversy is beyond the scope of the present chapter. Regardless of the pathogenesis of this disease, however, the term fibrohistiocytic remains fashionable in imaging literature to indicate a lesion composed of a mixture of cells with histiocytic and fibroblastic appearance. Fibrohistiocytic masses are divided into three categories according to their degree of malignancy: (1) benign fibrohistiocytic lesions, (2) lesions of intermediate malignancy, and (3) malignant fibrohistiocytic lesions. Benign fibrohistiocytic lesions consist of various lesions with similar morphology but different pathogenesis and biological behavior; i.e., true neoplasms (fibrous histiocytoma), tumor-like conditions (xanthoma, reticulohistiocytoma), and indeterminate processes (juvenile xanthogranuloma). Since juvenile xanthogranuloma, reticulohistiocytoma, and other superficial soft tissue masses are often confined to the skin, with a rather characteristic gross appearance, they are often detected and characterized by visual inspection or palpation,and usually not imaged. Imaging findings in cutaneous masses have therefore been published only occasionally in radiological literature. Furthermore, the contrast resolution in computed tomography (CT) is insufficient for imaging these small superficial lesions [49]. The development of a dedicated, high-resolution MR surface coil will facilitate MRI of cutaneous and subcutaneous lesions [102]. It has already been reported that MRI is the method of choice for estimating the depth and extent of cutaneous tumors [72, 102]. Fat-suppression techniques, masking high signal intensity (SI) of surrounding fat, may theoretically improve anatomical detail and contrast resolution [102]. Dermatofibrosarcoma protuberans, Bednr tumor, plexiform fibrohistiocytoma, giant cell fibroblastoma, and angiomatoid fibrous histiocytoma are considered as fibrohistiocytic tumors of intermediate malignancy, since they grow in a more infiltrative fashion and more often recur. Their potential to metastasize, however, is low. Malignant fibrohistiocytic tumors include the atypical fibroxanthoma and malignant fibrous histiocytoma (MFH). The latter accounts for the majority of reports on fibrohistiocytic tumors reported in the radiological literature. However, there is growing evidence indicating that MFH is not a definite fibrohistiocytic neoplasm. As a result, it has been omitted from the 2002 World Health Organization (WHO) classification (see 14.2.3.2 for further details) [36].