Teaching Case

A 48-year-old female patient was admitted to our hospital with left thigh and hip pain. The patient presented for the first time 26 years ago with similar complaints and was followed up by orthopaedics. The patient didn’t undergo any surgical operation and has no known malignancy and other diseases.

Plain X-ray, MRI, and sonographic images of lesions obtained for further evaluation. In plain X-Ray images at the left iliac bone and proximal femur, there were regions of increased radiolucency, with ground glass appearances, expansive features, with well-demarcated contours, endosteal remodelling, but no bone destruction, and no periosteal reaction (figure 1a and 1b). Also, there was a lesion in the left iliac bone which is surrounded by a layer of thick, sclerotic reactive bone ("rind sign").

MRI images of bone and soft tissue lesions were shown in Figures 2 and 3 respectively. MRI images showed heterogeneous masses with sharply demarcated borders and cystic degenerations in medullary regions of the iliac bone and proximal femur with minimal enhancement. Bone lesions remained the same in size and there was a gradual but little increase in the size of cystic mass (5.5 cm to 7.3 cm in four years). Also, there was a complex cystic soft tissue mass with peripheral enhancement within proximal fibres of the rectus femoris muscle. In figure 4, sonographic images of myxoma are demonstrated. Ultrasound-guided biopsy was taken from the soft tissue lesion and histologically confirmed that the lesion was a myxoma.

Mazabraud’s Syndrome is a rare syndrome with a prevalence of 1/1.000.000 [1]. The disease has a predilection of females (68-84%) [2]. The syndrome is characterized by cystic soft tissue masses (myxoma) accompanied by fibrous dysplasia and cystic lesions are usually located near the bony component. Fibrous dysplasia usually appears in the polyostotic form, but monostotic forms could also be encountered [3]. It may present with pain, skeletal deformity and, pathological bone fractures. The syndrome was reported to be associated with postzygotic GNAS1 gene mutations involved in cell proliferation [4].

Because of increasing size at later ages, myxomas may present as painful or painless palpable masses. Ultrasound provides important information for lesions that are superficial enough for sonographic imaging. On sonography, myxomas are seen as septated cystic lesions with a thick wall and dense content in the deep subcutaneous fat tissue and between muscle fibres. On MRI, myxomas demonstrate hypointense T1WI, homogeneous hyperintense T2WI signal, and poor wall enhancement after contrast administration can be seen. In these patients, fibrous dysplasia is usually detected incidentally on imaging. Fibrous dysplasia can develop in different localizations within the axial and appendicular skeleton such as femur, humerus, ribs, and skull [5]. Expansile masses with a ground-glass appearance on direct radiography are typical findings for fibrous dysplasia. At the bone lesions, MRI can demonstrate hyperintense cystic, hemorrhagic, or fatty areas on T2WI and hypointense signal changes in all sequences due to fibrocartilage tissues and calcifications. Heterogeneous or peripheral rim enhancement is generally expected in contrast-enhanced sequences [4]. Fibrous dysplasias are benign tumours that are classified as "Don't touch" bone tumours and pose a risk of pathological fracture, therefore, in addition to other radiological findings, FDG/PET imaging and biopsy findings (focused on the confirmation of myxomas) could be helpful for proving the diagnosis.

Lesions should be followed up radiologically and clinically. Pathological fractures, development of new myxoma, and (although rare) sarcomatous transformation in bony lesions can be seen during follow-up. In the case of sarcomatous transformation in fibrous dysplasia, the patient may present with symptoms such as pain and swelling [6]. In this case, the diagnosis should be confirmed by biopsy and the patient should be referred for appropriate surgical intervention (curettage or excision).

In summary, Mazabraud Syndrome should be suspected if cystic soft tissue lesions are found in combination with fibrous dysplasia. It should be known that the lesions that develop due to this syndrome are benign and should be followed clinically and radiologically. Radiologists should be aware that pathological fractures, newly developing or enlarging myxomas may be seen during follow-up, and sarcomatous transformation may develop in bony lesions.