NeuroradiologyHistiocytoma, fibrous
pleomorphic
lesion that consists of a predominantly bicellular population of atypical fibroblastic and histiocytic cells in variable proportions. Its histogenesis is unclear, but the mixed cell population is thought to arise from a common precursor (i.e. the primitive mesenchymal cell), which forms both the fibroblastic and histiocytic elements. The cell population within these tumours may also vary greatly as far as cell differentiation and anaplasia are concerned. However, the
pathological criteria for the
malignant potential of fibrous histiocytoma have been a matter of controversy. Therfore, several classifiation schemes have been proposed for fibrous histiocytoma based on clincial and
pathological features.
Malignant fibrous histiocytoma is the most common soft tissue sarcoma found in adults; it occurs with greatest frequency in the seventh decade of life. This lesion typically arises in the deep soft tissues of the lower and upper extremities and retroperitoneum. Less frequently (1 3% of all cases), it is found in the head and neck. Malignant fibrous histiocytoma of the bone is often reported to arise as a consequence of irradiation, bone infarction, trauma, Paget's disease, and fibrous dysplasia. Benign fibrous histiocytoma is frequently found in sun-exposed skin of the extremities and of the head and neck, and is also often seen within the orbit. Affected persons are usually younger than 50 years. Benign fibrous histiocytoma involving the deeper soft tissues of the head and neck is rare, and involvement of the nasal cavity and paranasal sinuses is very unusual.
In general, malignant fibrous histiocytoma appears as a hypointense lesion on T1-weighted images, and as a mass of heterogeneous signal intensity on T2-weighted images, except in cases of intratumoural bleeding. In cases of abundant fibrous tissue, the lesion appears hypointense on T2-weighted images; alternatively it is hyperintense on T2-weighted images in cases in which the tumour contains mucinous components. The myxoid type of malignant fibrous histiocytoma is thought to be a variant, featuring less cellularity and a rich matrix; it also tends to be associated with a better prognosis than its more cellular counterparts. The rate of metastases of myxoid types decrases as their myxoid components increase. The significance of the myxomatous changes in these tumours is not clear, but it seems unlikely that this represents merely a degenerative change, as other degenerative changes are lacking. It is regarded as an area in which the tumour cells multiply more slowly but produce an abundant mucoid matrix as a form of differentiation. This may explain the better prognosis. Treatment of malignant fibrous histiocytoma included surgical removal followed by adjuvant chemotherapy and/or radiation. In a significant number of patients, local recurrence or metastasis develops within 2 years. The mean 5-year survival rate for patients with malignant fibrous histiocytoma originating from bone is 3450%.
Benign fibrous histiocytoma is a rare cause of nasal obstruction in a neonate, but it should be considered in the differential diagnosis of congenital intranasal masses. The MR and CT appearance of this tumour is nonspecific and may closely mimic that of a nasal glioma.
FS