AJR 2004; 182:1389-1398
© American Roentgen Ray Society
Imaging Findings of Fibrous Dysplasia with Histopathologic and Intraoperative Correlation
Kimberly A. Fitzpatrick1,
Mihra S. Taljanovic1,
Donald P. Speer2,
Anna R. Graham3,
Jon A. Jacobson4,
George R. Barnes1 and
Tim B. Hunter1
1 Department of Radiology, University of Arizona College of Medicine, 1501 N
Campbell Ave., PO Box 245067, Tucson, AZ 85724-5067.
2 Department of Orthopaedic Surgery, University of Arizona College of Medicine,
Tucson, AZ.
3 Department of Pathology, University of Arizona College of Medicine, Tucson,
AZ.
4 Department of Radiology, University of Michigan, Ann Arbor, MI.
Received July 22, 2003;
accepted after revision October 28, 2003.
Presented at the 2003 American Roentgen Ray Society meeting, San Diego,
CA.
Address correspondence to M. S. Taljanovic.
Introduction
Fibrous dysplasia is a noninherited bone disease in which abnormal
differentiation of osteoblasts leads to replacement of normal marrow and
cancellous bone by immature bone and fibrous stroma. It is usually an
incidental imaging finding, generally not requiring further investigation.
However, fibrous dysplasia may be complicated by pathologic fracture, and
rarely by malignant degeneration. It can also be associated with aneurysmal
bone cysts. Fibrous dysplasia is categorized as either monostotic or
polyostotic and may occur as a component of McCune-Albright syndrome or the
rare Mazabraud syndrome. This pictorial essay provides various imaging
findings of fibrous dysplasia and examples of the underlying histopathology,
gross intraoperative findings, and clinical characteristics.
Imaging Characteristics of Fibrous Dysplasia
Classically, fibrous dysplasia lesions are intramedullary, expansile, and
well defined (Fig. 1A,
1B,
1C,
1D,
1E). Although endosteal
scalloping may be present, a smooth cortical contour is always maintained.
Lesions show varying degrees of hazy density with a ground-glass quality,
although some may appear almost completely radiolucent or sclerotic. The
lesions usually show nonspecific increased uptake of radiotracer on bone
scans. CT and MRI are useful for evaluating the soft-tissue components and the
entire extent of a lesion [1].
The MRI characteristics of fibrous dysplasia are variable, typically showing
signal intensity that is intermediate to low on T1-weighted images,
intermediate to high on T2-weighted images, and heterogeneous enhancement
after administration of gadolinium
[2] (Figs.
1B,
1C,
1D).
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Fig. 1A. —17-year-old girl with classic lesion of fibrous dysplasia.
Frontal radiograph of knee shows well-defined lesion with smooth sclerotic
margins and hazy matrix in distal femur, confirmed as fibrous dysplasia at
histopathology.
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Fig. 1B. —17-year-old girl with classic lesion of fibrous dysplasia.
Coronal STIR MR image (TR/TE 4,166/81; inversion time, 110 msec) shows lesion
with signal intensity that is intermediate to high with low-signal-intensity
rim.
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Fig. 1D. —17-year-old girl with classic lesion of fibrous dysplasia.
Axial T1-weighted MR image (533/12) with fat saturation before administration
of gadolinium (D) and after administration of gadolinium (E)
show that there is mild to moderate heterogeneous enhancement of lesion. Note
smooth scalloping of posterior cortex (arrows).
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Fig. 1E. —17-year-old girl with classic lesion of fibrous dysplasia.
Axial T1-weighted MR image (533/12) with fat saturation before administration
of gadolinium (D) and after administration of gadolinium (E)
show that there is mild to moderate heterogeneous enhancement of lesion. Note
smooth scalloping of posterior cortex (arrows).
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Pathology of Fibrous Dysplasia
Surgical removal of fibrous dysplasia lesions is generally reserved for
equivocal cases or those with complications. The gross appearance of fibrous
dysplasia is a firm solid white mass replacing the medullary cavity
(Fig. 2). Typical microscopic
findings include irregular spindles of woven bone, usually nonmineralized,
scattered throughout a fibrocellular matrix
(Fig. 3). Foci of cartilage may
also be present, sometimes leading to the potentially devastating misdiagnosis
of chondrosarcoma. The degree of haziness shown radiographically by a given
fibrous dysplasia lesion directly correlates with its underlying
histopathology. More radiolucent lesions are composed of predominantly fibrous
elements, whereas more radiopaque lesions contain a greater proportion of
woven bone. A cystic appearance seen in some lesions corresponds with areas of
necrosis [3]. Variations in the
cellular constituents of fibrous dysplasia lesions also account for their
variable MRI appearance
[2].
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Fig. 3. —Photomicrograph of surgical specimen from 17-year-old girl
shows classic microscopic appearance of fibrous dysplasia consisting of small,
principally nonmineralized, trabeculae of woven bone (arrow) in bland
cellular and collagenous matrix. (H and E)
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Monostotic Fibrous Dysplasia
The monostotic form of fibrous dysplasia comprises approximately 80% of all
cases and is seen in patients between 10 and 70 years old. The most common
sites of involvement include the rib (Fig.
4), femur, tibia, mandible, skull, and humerus. Solitary
involvement of other bones is unusual. A variety of skull lesions may be seen,
most commonly involving the frontal, sphenoid, maxillary
(Fig. 5), and ethmoid bones.
Uncomplicated monostotic lesions are generally asymptomatic and usually do not
cause significant deformity. As a rule, monostotic fibrous dysplasia does not
convert to the polyostotic form, lesions do not increase in size over time,
and the disease becomes inactive at puberty
[1].
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Fig. 5. —Radiograph of facial bones of 16-year-old girl shows
sclerotic expansile fibrous dysplasia lesion (arrows) involving right
maxillary sinus and adjacent maxilla, with secondary narrowing of maxillary
sinus and right nasal cavity.
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Polyostotic Fibrous Dysplasia
The polyostotic form of fibrous dysplasia may involve many or few bones,
most commonly the skull and facial bones, pelvis, spine (Fig.
6A,
6B,
6C), and shoulder. Polyostotic
fibrous dysplasia is often unilateral, sometimes showing a monomelic pattern.
It tends to involve larger segments of bone and is frequently associated with
fractures and severe deformities.
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Fig. 6A. —65-year-old woman with unusually late presentation of
polyostotic fibrous dysplasia, confirmed at histopathology. Axial CT image
shows large expansile fibrous dysplasia lesion involving posterior right rib
(arrowhead), with associated mass effect on right kidney. Additional
lesions involve adjacent vertebral body (open arrow) and another
right rib (solid arrow).
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Fig. 6B. —65-year-old woman with unusually late presentation of
polyostotic fibrous dysplasia, confirmed at histopathology. Axial T2-weighted
MR image (TR/TE, 1,108/93) shows heterogeneous signal, relatively increased
compared with that of muscle, in corresponding large rib lesion
(arrowhead) and vertebral body lesion (arrow).
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Fig. 6C. —65-year-old woman with unusually late presentation of
polyostotic fibrous dysplasia, confirmed by histopathology. Frontal positron
emission tomography image shows markedly increased activity in two rib lesions
(black arrows). Increased activity is also present in adjacent
vertebral body lesion and in other lesions involving thoracic spine at higher
levels (arrowheads). Additional large lesion involving right sacrum
also shows increased activity (white arrow). Note presence of
excreted radiotracer in both intrarenal collecting systems, right ureter, and
urinary bladder. Normal cardiac activity is also apparent.
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The shepherd's crook deformity is a common bowing deformity with varus
angulation of the proximal femur
[1]
(Fig. 7). Involvement of the
skull (Fig. 8A,
8B) may cause cranial nerve
dysfunction with visual and hearing impairment. The term "leontiasis
ossea" describes a rare form of polyostotic disease that involves the
frontal and facial bones (Fig.
9) and results in marked deformities resembling a lion's face
[4]. Another craniofacial
entity, known as cherubism, is a hereditary fibrous lesion of bone,
symmetrically involving the mandible and often the maxilla
(Fig. 10). Although sometimes
classified as a variant of fibrous dysplasia, cherubism likely actually
represents a form of giant cell reparative granuloma, from which it is
histologically indistinguishable
[5]. Although the
manifestations of polyostotic fibrous dysplasia may be severe, it does not
spread or proliferate and generally becomes quiescent at puberty, but existing
deformities may progress
[1].
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Fig. 8A. —57-year-old man with polyostotic fibrous dysplasia of skull.
Lateral radiograph of skull shows mixed-density fibrous dysplasia lesion
(arrows) involving right frontal and parietal bones.
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Fig. 8B. —57-year-old man with polyostotic fibrous dysplasia of skull.
Axial T2-weighted MR image (TR/TE, 5,350/105) shows expansile lesion, which is
of heterogeneous, predominantly intermediate signal intensity
(arrows).
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Fig. 9. —Frontal radiograph of skull of 7-year-old girl shows
sclerotic fibrous dysplasia lesions involving right facial and frontal bones,
with resultant hypoplasia of right orbit. Outward appearance of these
deformities may resemble lion's face, such that this form of polyostotic
fibrous dysplasia has been termed "leontiasis ossea."
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Fig. 10. —Axial CT scan through facial bones at level of hard palate of
5-year-old boy with cherubism shows typical expansile lesions involving base
of maxilla and mandibular rami. Additional images from this study (not shown)
revealed uniform symmetric involvement of entire maxilla and mandible, typical
of cherubism.
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Complications of Fibrous Dysplasia
A common presentation of fibrous dysplasia is pain related to pathologic
fracture (Fig. 11A,
11B). These fractures
generally heal normally, but additional fractures may subsequently occur at
the same site [1,
3]. The risk of pathologic
fracture is accentuated when there is a coexisting aneurysmal bone cyst
further weakening the diseased bone
[6] (Fig.
12A,
12B).
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Fig. 11A. —Findings of fibrous dysplasia complicated by pathologic
fracture. Coronal STIR MR image (TR/TE, 5,000/60; inversion time, 160 msec) of
17-year-old girl shows fibrous dysplasia involving femoral neck with
pathologic fracture line extending through lesion (arrow), both
confirmed by histopathology.
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Fig. 11B. —Findings of fibrous dysplasia complicated by pathologic
fracture. Photomicrograph of surgical specimen from 15-year-old boy with
similar imaging findings as patient in A shows periosteum
(arrows) overlying cartilaginous metaplasia (arrowheads) in
region of subperiosteal new bone formation, secondary to pathologic fracture
through fibrous dysplasia. (H and E)
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Fig. 12A. —10-year-old girl with fibrous dysplasia associated with
aneurysmal bone cyst, both confirmed by histopathology. Sagittal T1-weighted
MR image (TR/TE, 500/5) with fat saturation and gadolinium enhancement shows
long expansile fibrous dysplasia lesion involving mid and proximal humeral
diaphysis and proximal metaphysis. Associated aneurysmal bone cyst components
are seen as centrally nonenhancing region with rim enhancement in proximal
aspect of lesion (open black arrows) and nonenhancing region in
distal aspect of lesion (open white arrows). Pathologic fracture is
also present at distal aspect of lesion, accounting for nonenhancing cystic
fluid (solid arrows) leaking into anterior soft tissues.
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Fig. 12B. —10-year-old girl with fibrous dysplasia associated with
aneurysmal bone cyst, both confirmed by histopathology. Lateral radiograph of
humerus, obtained 3 weeks after A, shows mildly expansile fibrous
dysplasia lesion with hazy matrix. Slightly more radiolucent appearance of
proximal and distal aspects of lesion (arrowheads) is attributable to
coexisting aneurysmal bone cyst. Healing fracture (arrow) is readily
apparent.
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Malignant degeneration of fibrous dysplasia complicates less than 1% of all
cases, presenting clinically as pain and swelling. Radiographic findings
include cortical destruction and associated soft-tissue masses (Fig.
13A,
13B,
13C,
13D). The most common
malignancies include osteosarcoma, fibrosarcoma, and malignant fibrous
histiocytoma. Transformation to chondrosarcoma has been reported, sometimes
erroneously on the basis of the incidental finding of cartilaginous nodules in
a specimen. The true number of cases of malignant degeneration is likely
overestimated given previous irradiation of involved bone in many cases
[7].
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Fig. 13A. —54-year-old man with malignant degeneration of fibrous
dysplasia due to osteosarcoma, which was confirmed at histopathology.
(Courtesy of Kransdorf M, Jacksonville, FL; Murphey M, Washington, DC) Frontal
radiograph of knee shows expansile lesion of proximal fibula with cortical
destruction and associated soft-tissue mass.
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Fig. 13B. —54-year-old man with malignant degeneration of fibrous
dysplasia due to osteosarcoma, which was confirmed at histopathology.
(Courtesy of Kransdorf M, Jacksonville, FL; Murphey M, Washington, DC) Axial
CT scan shows extent of cortical destruction and osteoid matrix in soft-tissue
mass.
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Fig. 13C. —54-year-old man with malignant degeneration of fibrous
dysplasia due to osteosarcoma, which was confirmed at histopathology.
(Courtesy of Kransdorf M, Jacksonville, FL; Murphey M, Washington, DC) Axial
T2-weighted MR image through same lesion better defines extent of soft-tissue
mass, which shows predominantly increased signal.
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Fig. 13D. —54-year-old man with malignant degeneration of fibrous
dysplasia due to osteosarcoma, which was confirmed at histopathology.
(Courtesy of Kransdorf M, Jacksonville, FL; Murphey M, Washington, DC)
Photograph shows gross specimen of resected bone and soft-tissue mass.
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Syndromes Associated with Fibrous Dysplasia
McCune-Albright syndrome is an endocrinopathy occurring mainly in girls,
consisting of the triad of precocious puberty, polyostotic fibrous dysplasia,
and characteristic cutaneous pigmentation (Fig.
14A,
14B,
14C,
14D). The cutaneous lesions
are flat pigmented macules, often referred to as "café au
lait" spots and likened to the coast of Maine because of their irregular
contour. Fibrous dysplasia lesions associated with McCune-Albright syndrome
tend to be more disabling than those of pure polyostotic disease
[1,
3].
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Fig. 14B. —McCune-Albright syndrome. Photograph of 17-year-old boy with
McCune-Albright syndrome shows gross appearance of shepherd's crook deformity
of hips and severe bowing and shortening of right tibia.
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Mazabraud syndrome is the rare combination of fibrous dysplasia and
soft-tissue myxomas (Fig. 15A,
15B,
15C). The benign, generally
asymptomatic, myxomatous tumors usually develop in muscle near the most
extensively involved bones years after the initial diagnosis of fibrous
dysplasia. The tumors are homogeneous soft-tissue masses, showing low
attenuation on CT. On MRI, they are hypointense to slightly hyperintense on
T1-weighted images and hyperintense on T2-weighted images and show a complex
pattern of enhancement after administration of gadolinium
[8]. Mazabraud syndrome is
associated with a higher incidence of transformation to osteosarcoma
[7].
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Fig. 15B. —30-year-old man with Mazabraud syndrome. Coronal STIR MR
image (TR/TE, 5,000/54; inversion time, 120 msec) with fat saturation through
elbow shows heterogeneous fibrous dysplasia lesions in distal humerus and
proximal radius and ulna. Well-defined soft-tissue mass with signal intensity
of intermediate to high (arrow) at medial aspect of distal humerus
represents myxoma.
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Fig. 15C. —30-year-old man with Mazabraud syndrome. Bone lesion, as well
as myxoma (arrow), show predominantly intermediate signal intensity
on this axial T1-weighted MR image (650/20) at level of distal humerus.
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Conclusion
Fibrous dysplasia is a common benign bone disease existing in monostotic
and polyostotic forms. It is sometimes associated with aneurysmal bone cysts,
and it is a component of McCune-Albright and Mazabraud syndromes.
Complications include occasional pathologic fracture and rare malignant
degeneration. The imaging features of fibrous dysplasia are characteristic,
although not specific, and depend on the underlying histopathology of a given
lesion. Knowledge of the various appearances, complications, and associations
of fibrous dysplasia is important to ensure the accurate diagnosis and
appropriate management of this disease.
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Introduction
Imaging Characteristics of...
