FIBROUS DYSPLASIA: IMAGING CHARACTERISTICS

H. ZAGHOUANI BEN ALAYA, A.BEN ABDALLAH,S. YAHYAOUI, S. MAJDOUB,T. RZIGUA, L. BEN CHRIFA,H. AMARA, D. BEKIR, CH. KRAIEMImaging department, Farhat Hached Hospital, Sousse, Tunisia

INTRODUCTION

Fibrous Dysplasia (FD) of bone is a rare non-inheritable congenital disease.

It is characterized by a focal proliferation of fibrous tissue in the bone marrow leading to osteolytic lesions deformities and fractures.

FD can be presented in a monostotic or polyostotic form.

The complications are represented mainly by bone deformities and nerve compression

The imaging appearance is often characteristic and allows in combination with the clinic findings the diagnosis

Authors attempted to highlight the interest of imaging in the diagnosis of FD.

The literature is reviewed to delineate radiologic features of monostotic and polyostotic fibrous dysplasia.

Introduction

PATIENTS AND METHODS

Retrospective study of 7 cases. FD was monostotic in 4 cases and

polystotic in 3 cases It involves proximal femurs in 1 case, ribs

in 2 cases4 reported cases were craniofacial form

and the involved bones were maxilla (n= 1), sphenoid (n = 1), temporal (n= 1), and frontal bone (n= 2)

Only 2 cases showed involvement of spine.

CASE N°1

A 19-year-old boy presented to his doctor because of shoulder pain of 1 year’s duration.

(a) Well-defined lytic lesions of the humerus and both bones of the forearm, which at times appear multilocular and expansile with thinnes but unruptured cortical (b) CT showed in the medullary cavity replacement of cancellous bone with a homogeneous hyperdense beach responsible for thinning of the cortical

a

b

Case n° 1

MR coronal images:*The lesions has low signal intensity on T1-weighted MR image (a ), high weighted intensity on T2 (b)* T1-weighted MR image with fat saturation and after administration of gadolinium (c ) show that there is mild to moderate heterogeneous

enhancement of lesion. a b c

*The same patient has cervical MRI for cervical pain that shows a lesion of the vertebral hemibody of D1which has low intensity signal on T1 without cortical lysis or soft tissue abnormality on sagittal T1-weighted MR image (d).* T1-weighted MR image with fat saturation and after administration of gadolinium (e ) show that there is an intense enhancement of lesion.

d

Polyostotic FD

e

CASE N°2

A 24-year-old man who presents with a meningeal syndrome. A cerebro-medullar MRI was indicated

*Sagittal T2-weighted MR image (a ) shows a low signal lesion of the vertebral body of D1 with an intense and homogene enhancement of the lesion on T1-weighted MR image (b ).*CT scan reveals increased bone density of D1 (c ).a b

c

MonostoticFD of spine

CASE N°3

Coronal MR images show a lesion interesting the left greater wing of sphenoid. This lesion has an intermediaire signal on T1 (a) , a low signal on T2 (b) and present an intense enhancement on contrast-enhanced T1-weighted MR image with fat-saturation (c ).

A 27-years-old woman , consultsfor diplopia lasting for 6 months. the clinical examination found left convergent squint and paralysis of the V and VI cranial nerves.

a b c

Axial and coronal CT scan show fibrous dysplasia involving body, the left greater wing of sphenoid bone (blue arrows). Note expanded left pterygoid process (arrowhead) and inflammatory changes in left sphenoid sinus (*).

Base of the skull(sphenoid) FD

Case n° 3

CASE N°4

*Axial T1-weighted MR (a ) and coronal T2-weighted MR (b) images reveal expansile lesion, with low signal intensity involving rleft frontal and parietal bones* Axial T1-weighted MR image with fat saturation and after administration of gadolinium (c ) show that there is mild to moderate heterogeneous enhancement of lesion.

a bc

Cranio-facial FD

A 35-year old woman who consulted for left frontal and orbital swelling

CASEN°5

A 12-years old boy who presented a ptosis of the left upper eyelid

*Axial CT scan (a) show thickening and increased fronto-orbital left bone density.*Coronal MR images show a lesion interesting left roof of orbit. This lesion has a low signal intensity on T1 (c) and T2 (b) .*T1-weighted MR image after administration of gadolinium (d ) show that there is intense and heterogeneous enhancement of the lesion.

Cranio-facial FD

a b c

d

DISCUSSION

Fibrous dysplasia (FD) is a congenital and noninherited benign bone disease

FD has been regarded as a developmental skeletal disorder characterized by replacement of normal bone with benign cellular fibrous connective tissue.

It affects both sexes with a slight female predominance and is diagnosed between 5 and 30 years on average

It affects both sexes with a slight female predominance and is diagnosed between 5 and 30 years on average

The lesions grow with the child, stabilize after puberty and appear exceptionally in adulthood

FD can affect one bone (monostotic form) or multiple bones (polyostotic form), and the latter may form part of the McCune-Albright syndrome (MAS) or Mazabraud syndrome

Discussion

Monostotic Fibrous Dysplasia

The monostotic form of FD comprises approximately 80% of all cases

It is seen in patients between 10 and 70years old.

The most common sites of involvement include the rib, femur, tibia, mandible, skull, and humerus

Solitary involvement of other bones is unusual

FD of the spine is rare. It most commonly involves the body and adjacent pedicle without particular predilection for a part of the spinal column

The skull and facial bones are the affected sites in 10–25%

All bones of the skull and the face may be affected

It concerns mainly the ethmoid (72%), sphenoid (43%), the frontal bone (33%), maxilla (24%) and less frequently the temporal, parietal, occipital or mandible bone.

Monostotic Fibrous Dysplasia

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

Monostotic Fibrous Dysplasia

Polyostotic Fibrous Dysplasia

The polyostotic form of FD may involve many or few bones, most commonly the skull and facial bones, pelvis, spine, and shoulder.

Polyostotic fibrous dysplasia is often unilateral, and may be bilateral, always asymmetric

It tends to involve larger segments of bone and is frequently associated with fractures and severe deformities.

Involvement of the skull may cause cranial nerve dysfunction with visual and hearing impairment

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

Polyostotic Fibrous Dysplasia

Syndromes Associated with Fibrous Dysplasia

1-McCune-Albright syndrome is an endocrinopathy occurring mainly in girls, consisting of the triad of precocious puberty, polyostotic FD, and characteristic cutaneous pigmentation referred to as “café au lait” spots

2-Mazabraud syndrome is the rare combination of fibrous dysplasia and soft-tissue myxomas

Classically, fibrous dysplasia lesions are intramedullary, expansile, and well defined lesion with thick sclerotic borders

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

Imaging findings: radiograh and CT

Three types of lesions are distinguished depending on the degree of hazy density :

*The ground-glass pattern *The homogeneously dense pattern:

increased bone density compared with adjacent normal bone

*The cystic variety: At times, a mubtilocubar, cystic lesion with well-defined margins can be seen

Occasionally, calcified cartilaginous and osseous foci may be present within the lesion

MRI findings

The MRI characteristics of FD are variable Typically showing signal intensity that is

intermediate to low on T1- weighted images Intermediate to high signal on T2-weighted

images These high signal intensities on T2- weighted

images correspond to nonmineralized areas and regions of cystic change

Fibrous dysplasia reveals varying degrees of enhancement after gadolinium infusion.

The fibrous tissues in FD are well vascularized and often show numerous small vessels in the center and large peripheral sinusoids. These histologic features explain why fibrous dysplasia enhances intensely after the injection of contrast material

MRI findings

Complications of Fibrous Dysplasia

1-Pathologic fracture These fractures generally heal normally, but

additional fractures may subsequently occur at the same site

2-Malignant degeneration of FD Complicates less than 1% of all cases Radiographic findings include cortical

destruction and associated soft-tissue masses The most common malignancies include

osteosarcoma, fibrosarcoma, and malignant fibrous histiocytoma.

CONCLUSION

Fibrous dysplasia is a common benign bone disease existing in monostotic and polyostotic forms

Complications, and associations of fibrous dysplasia is important to ensure the accurate diagnosis and appropriate management of this disease

The imaging features of fibrous dysplasia are characteristic, although not specific, and depend on the underlying histopathology of a given lesion.