Contributed by Matthias Reitz, Jozef Zustin, Jakob Matschke, Nils Ole Schmidt, Manfred WestphalDIAGNOSIS Cranial chondromyxoid fibroma of the sphenoid bone
DISCUSSION
Chondromyxoid fibroma (CMF) is a rare benign, primary bone tumor that was first described in 1948 by Jaffe and Lichtenstein as a "fibroma with focal chondroid metaplasia" [4], an entity which "needed to be distinguished from chondrosarcoma and chondroblastoma". CMFs account for <1% of all primary bone tumors and are mostly situated in the metaphyses adjacent to the epiphyseal growth-plate of long-bones, where they usually present as a lesion abutting the medullary cavity. Very few cases of cranial localization can be found in the literature [9]. At present, only about 50 cases of CMFs arising in cranial bones are documented [1]. None of these cases was found to be located within the lateral part of the sphenoid wing. When found cranially, the primary localization is in the skull base. Here, the lesion tends to be cortical, centrally located, and symmetrically expansive [6]. Around 80% of the patients diagnosed with CMF are less than 36 years-old, with a second group of disease-onset occurring around the age of sixty [3]. Local pain and swelling or tenderness are the most common presenting symptoms. Radiological findings include geographic bone destruction and either partial or complete cortical erosion with sharply defined tumor boarders and sclerotic margins [8]. In the conventional X-ray, CMFs present as expansive ovoid lesions with a radiolucent centre. Although CMF lesions can contain microscopic foci of calcifications, these are rarely visible in radiological imaging. This contrasts sharply to chondrosarcoma, in which the foci of matrix calcifications are easily seen. On MRI, depending on the histological composition and the amount of myxoid and cartilage tissue, the centre of the tumor is hyperintense in T2-weighted images and contrast enhancing.
The World Health Organization defines CMF as a "benign tumor, which is histologically characterized by lobulated areas of spindle-shaped or stellate cells with abundant myxoid or chondroid intracellular material, separated by zones of more cellular tissue rich in spindle-shaped or round cells with a varying number of multinucleated cells of different sizes" [7].
The great majority of CMFs show either a macrolobular or microlobular pattern, with the microlobular pattern being more present when the lesions are located in the skull or facial bone. [9]. The lobules present with a hypocellular centre and a hypercellular periphery, where multinucleated giant cells can be found. Another histological feature that occurs in a minority of CMFs is focal calcification, which is also more common in lesions involving the skull and the facial bones. [6;10]. Permeation of the bone is frequent in lesions of the skull and cranial bones and displayed in the presented case (Fig. 1). Both features (focal calcification and permeation of the bone) can serve as additional diagnostic tools regarding (neuro)-radiological imaging and leading to the correct diagnosis of a CMF.
Although in most cases, the distinctive morphology of CMF allows a quick and correct diagnosis, from time to time difficulties occur when distinguishing the tumor from myxoid chondrosarcoma. In most cases, the presence of calcification and the relative high degree of cellular polymorphism allows for a distinction of these two entities. For CMF, recurrence-rates vary from 5-60%, depending mainly on the surgical procedure and the age of the patient [6;9]. Recurrences occur more often in younger patients (under 20 years of age) and when a surgical curettage instead of total resection is performed [6;10]. Gross total resection of the lesion with tumor-free margins is, whenever possible, the treatment of choice [2]. In cases where complete surgical resection is not accomplishable, radiation therapy may be useful, despite the evident risk of sarcomatous conversion [10]. Spontaneous malignant transformation of CMF to chondrosarcoma has been suggested in the literature, although these cases might have been misdiagnosed myxoid chondrosarcoma in the first place [5]. Nevertheless neuroradiological controls on a regular basis are strongly recommended due to the aggressive rate of recurrences. It is of vital importance for the patient to accurately distinguish between CMF and malignant chondral tumors as chondrosarcoma. When complete surgical resection is possible, CMF has an excellent prognosis.
REFERENCES
Contributed by Matthias Reitz, Jozef Zustin, Jakob Matschke, Nils Ole Schmidt, Manfred Westphal
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