Fibrous dysplasia, first described in 1938 by Lichtenstein,1 is a benign fibro-osseous lesion that can occur as an isolated skeletal lesion (monostotic form) or affect multiple skeletal sites (polyostotic form). In addition, fibrous dysplasia may be associated with single or multiple endocrinopathies, or with precocious puberty and cutaneous hyperpigmentation in McCune-Albright syndrome.2
Fibrous dysplasia usually appears as a well-defined radiolucent medullary lesion that is irregular and mildly expansive, with a hazy opacity classically described as having a ground-glass appearance. In the long tubular bones, fibrous dysplasia may cause expansion of the bone contour with cortical thinning and endosteal scalloping. The shaft typically is involved, but the metaphysis also may be affected.3 These changes usually are recognizable on plain radiographs, but in cases in which the lesion is difficult to visualize, computed tomography (CT) may be beneficial.4 However fibrous dysplasia may present with radiographic features that mimic other benign fibro-osseous lesions, be associated with other lesions,5 or even be confused with certain types of malignancies.6
This article presents a case of monostotic fibrous dysplasia in the proximal tibia of an 11-year-old girl with unusual radiologic features of multifocal lytic lesions and cortical disruption. The diagnosis was confirmed by open biopsy.
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| Figure 1: AP radiograph (A) showing irregular multiple lytic lesions in the tibial metaphysis close to the epiphyseal plate. Axial (B) and sagittal (C) CT showing multiple lytic lesions and violation of the cortex with soft-tissue extension. Axial T2-weighted MRI (D) showing multiple lytic lesions with soft-tissue swelling. |
An 11-year old girl presented with intermittent pain in her proximal left tibia of 12 months duration. She had no history of trauma, weight loss, medical illness, fever, or infection. The pain increased with physical activity and was partially relieved at rest.
Physical examination revealed local tenderness over the medial aspect of the upper left tibia without the presence of a soft-tissue mass. The patient had full range of motion of the left knee, and there was no intra-articular effusion. Endocrine and laboratory studies were normal, except for an elevated bone alkaline phosphatase value of 81.2 µg/L.
Radiographs revealed multiple lytic lesions with irregular borders on the medial aspect of the proximal tibial metaphysis, close to the epiphyseal growth plate (Figure 1A). The adjacent bone appeared thickened but without periosteal reaction, and there was no expansion of the proximal tibia. A bone technetium scan demonstrated isolated increased uptake in the proximal metaphysis of the left tibia.
Computed tomography showed multiple lytic lesions with irregular borders. There was no identifiable feature in the matrix but the lesion extended through the cortex into the soft tissue (Figures 1B and 1C). The density of the lesion was similar to that of the surrounding soft tissue.
Fat-suppressed magnetic resonance imaging (MRI) showed multiple lesions in the tibial metaphysis with low signal intensity on T1-weighted images and an increased intensity on T2-weighted images (Figure 1D). Soft-tissue swelling was noted without reactive cortical bone.
Figure 2: Low-power (A) and high-power (B) photomicrographs showing benign fibrous tissue containing thin, irregularly shaped trabeculae of woven bone focally lined by osteoblasts (hematoxylin-eosin stain).
An open biopsy was performed without attempting to excise the lesion. Material was submitted for bacteriologic analysis (ie, aerobic and anaerobic cultures, and fungal studies). Histologically, the lesion consisted of benign fibrous tissue containing thin, irregularly-shaped trabeculae of woven bone that were only focally lined by osteoblasts (Figure 2). The spindle cells in the fibrous component were bland, and mitotic figures were rare. These microscopic findings are typical for fibrous dysplasia. The fibro-osseous lesion involved the medullary cavity, which was highly vascularized. Some of the fragments consisted of reactive bone from the edges of the lesion.
The patient was managed nonoperatively, and analgesics relieved the pain somewhat. At the patients most recent follow-up evaluation, 18 months after the initial presentation, she was asymptomatic and fully active. The lesion was difficult to visualize on plain radiographs (Figure 3A). Computed tomography (Figures 3B and 3C) revealed partial filling in of the lytic areas with areas of sclerosis and almost complete restoration of the cortex.
Figure 3: AP radiograph (A) after 18 months of follow-up shows the lesion is difficult to visualize, and axial (B) and sagittal (C) CT demonstrate partial resolution of the lesion with filling in of the lytic areas, sclerosis, and reconstitution of the cortex.
The diagnosis of fibrous dysplasia usually is readily apparent on radiographic examination, but in cases in which there is a question, CT may be useful in clearly delineating the lesion.4 The lesion typically is well defined and has a ground-glass appearance caused by the finely scattered bone trabeculae within the tissue. There is medullary expansion of bone with surrounding cortical bone thickening, and a layer of reactive cortical bone on top of normal bone.
The lesion usually involves the diaphyseal region and also may involve the metaphyseal region; the epiphyseal area is rarely involved. The MRI appearance is variable, with a homogeneous intermediate to low signal intensity on T1-weighted images and an intermediate to high signal intensity on T2-weighted images.5
Although some authors have stated a smooth cortical contour is always maintained,5 others classify fibrous dysplasia as a tibial lesion that may cause cortical destruction.6 Resnick7 stated the external cortices are invariably smooth unless fracture or infection has supervened.
Although malignant degeneration of fibrous dysplasia is rare, the presence of cortical destruction and soft-tissue mass should raise suspicion to such a possibility.5 Fibrous dysplasia may present radiographic features consistent with other benign fibro-osseous lesions of the skeleton, and also may be confused with certain types of malignancies. In this respect, fibrous dysplasia remains a radiologic challenge.
In our patient, the appearance was atypical and did not correspond to the classic appearance of fibrous dysplasia. The radiographic differential diagnosis of the lesion included atypical presentation of fibrous dysplasia, osteofibrous dysplasia, adamantinoma, infection, aneurysmal bone cyst, eosinophilic granuloma, nonossifying fibroma, chondromyxoid fibroma, and malignancies such as Ewing sarcoma and low-grade central osteosarcoma. At the patients 18-month follow-up examination, there was partial resolution of the lesion.
It is believed fibrous dysplasia usually becomes quiescent at puberty and remains so throughout life.7 Although the clinical presentation, laboratory findings, and imaging studies usually permit the diagnosis of fibrous dysplasia, in certain cases, such as with our patient, this entity may pose a diagnostic challenge.
- Lichtenstein L. Polyostotic fibrous dysplasia. Arch Surg. 1938; 36(5):874-898.
- Lichtenstein L, Jaffe H. Fibrous dysplasia of bone: a condition affecting one, several or many bones, the graver cases of which may present abnormal pigmentation of skin, premature sexual development, hyperthyroidism, or still other extraskeletal abnormalities. Arch Pathol. 1942; 33(6):777-816.
- Harris WH, Dudley HR Jr, Barry RJ. The natural history of fibrous dysplasia: an orthopaedic, pathological, and roentgenographic study. J Bone Joint Surg Am. 1962; 44(2):207-233.
- Daffner RH, Kirks DR, Gehweiler JA Jr, Heaston DK. Computed tomography of fibrous dysplasia. AJR Am J Roentgenol. 1982; 139(5):943-948.
- Fitzpatrick KA, Taljanovic MS, Speer DP, et al. Imaging findings of fibrous dysplasia with histopathologic and intraoperative correlation. AJR Am J Roentgenol. 2004; 182(6):1389-1398.
- Levine SM, Lambiase RE, Petchprapa CN. Cortical lesions of the tibia: characteristic appearances at conventional radiography. Radiographics. 2003; 23(1):157-177.
- Resnick D. Fibrous dysplasia. In: Resnick D, ed. Diagnosis of Bone and Joint Disorders. 4th ed. Philadelphia, PA: WB Saunders; 2002:4825-4843.
Drs Lädermann, Ceroni, De Coulon, and Kaelin are from the Division of Pediatric Orthopedics, Childrens Hospital, Dr Stern is from the Orthopedic Surgery Service, and Dr Taylor is from the Department of Pathology, University Hospital of Geneva, Geneva, Switzerland.
Drs Lädermann, Stern, Ceroni, De Coulon, Taylor, and Kaelin have no relevant financial relationships to disclose.
Correspondence should be addressed to: Richard Stern, MD, Service de Chirurgie Orthopédique et Traumatologie de lAppareil Moteur, Hopitaux Universitaires de Genève, 24, Rue Micheli-du-Crest, 1211 Geneva 14, Switzerland.