Clinical History
A 35-year old man with known polyostotic fibrous dysplasia presented with a painless swelling at the lateral side of the distal right upper arm which was present for 1.5 years.
Imaging Findings
A 35-year old man was referred to our hospital for further investigation of a swelling at the lateral side of the distal right upper arm. This swelling was painless and already present for 1.5 years. No growth was noted during this time-interval. The patient was in normal physical condition, there were no B-symptoms or fever. Blood cell counts were normal, only ALP were elevated (660 U/L, nl.
Discussion
The co-existence of polyostotic fibrous dysplasia with intramuscular myxoma was first described in the literature by Henschen in 1926, but since Mazabraud in 1967 emphasized the association as part of the spectrum of fibrous dysplasia, the entity is well-known as "Mazabraud's syndrome". It is a very rare syndrome with less than 50 cases reported in world literature [1]. Fibrous dysplasia typically precedes the development of myxomas [2]. In the majority of cases, the diagnosis of fibrous dyplasia is made in childhood, whereas the myxomas present in adult life. Most cases occurred in
women with a mean age of 46 years [3]. In typical cases, the myxomas occur in the vicinity of the most severely affected bones [4]. The most frequently affected sites are the thigh, buttock and pelvic muscles. Regarding location and patient's sex, this case is rather atypical. The radiological characteristics of the bony lesions in this syndrome are the same as in polyostotic fibrous dysplasia not associated with myxomas. The ribs, femur, tibia, gnathic bone, calvaria and humerus are most frequently involved in monostotic fibrous dysplasia (decreasing order of frequency). Polyostotic fibrous dysplasia more frequently involves the skull and facial bones, pelvis, spine and shoulder girdle [2]. It can be unilateral or bilateral and may effect several bones of one limb or both limbs,with or without axial skeletal involvement. Lesions in long bones are typically in a diaphyseal and metadiaphyseal localisation, although epiphyseal extent may occur. Most lesions are radio-lucent, although denser areas of ground-glass appearance and sclerosis may be encountered. The lesions are usually well-defined and often bordered by a reactive zone [2]. Endosteal scalloping can be seen, expansile remodeling contributes the regionally bulging contours that are a characteristic radiographic feature [2]. On MRI, lesions are typically of low intensity on T1WI and high intensity on T2WI. If fibrous tissue predominates however, lesions can be of low T1 and T2-signal intensity but enhancement occurs after gadolinium-administration [5]. The myxomas are typically intramuscular lesions with low signal intensity (usually iso-intense to adjacent skeletal muscle) on T1WI and high signal intensity on T2WI. Although they appear well defined on imaging studies, they have no capsule [2]. Contrast enhancement is variable but is most often heterogeneous with irregular rim-enhancement. Intralesional septal enhancement may occur. A small rim of fat representing atrophied surrounding muscle can be identified. This rim is usually most prominent at the superior and inferior extent of the lesion. Surrounding high signal caused by leakage of the myxomatous tissue into the surrounding muscle may be seen in 79 to 100 % of myxomas [6]. Patients with Mazabraud's syndrome are statistically at greater risk for malignant sarcomatous degeneration of bone lesions than are patients with fibrous dysplasia alone [1]. Therefore, closer clinical and radiological follow-up is recommended, with high suspicion in patients with sudden changes of clinical symptoms.
Differential Diagnosis List
