King Edward Memorial Hospital - Departments: Radiology

Radiology

Case of the Month

Case No. :	50
Month :	Feburary
Year :	2003
Contributor :	Dr. Bhavna Chablani

Other Cases

Radiological Findings

Differential Diagnosis

Discussion

CLINICAL PROFILE :

A thirty-eight-year old lady presented with severe pain in the left arm associated with swelling and restriction The swelling had been present since three years. A plain radiograph of the arm taken three years ago had shown an expansible lytic lesion of meta-diaphysis of the left humerus with ground glass matrix and an ossified exophytic lesion arising from medial cortex (Figure: 1). The patient had undergone a biopsy of this lesion, which was suggestive of fibrous dysplasia (FD).

Repeat radiographs of the humerus were now obtained.

Fig.1

RADIOLOGICAL FINDINGS:

ARadiographs of her left arm showed an exuberant densely ossified lesion involving the proximal meta-diaphysis of the humerus along its anterior-posterior cortex with thinning of the cortices (Figure: 2). There was extensive new bone formation beyond the confines of the bone. The zone of transition was ill denied. These changes were suggestive of malignant transformation. A chest radiograph showed bilateral hilar prominences. These had lobulated outer margins along with multiple, tiny, nodular opacities scattered all over the lung parenchyma (Figure: 3). Plain and post contrast axial CT scans of the chest revealed bilateral lobulated parahilar and parenchymal masses with calcification of various sizes and shapes (Figures: 4, 5). These changes were suggestive of metastases. Tc 99 bone scan (Figure: 6) revealed increased uptake of the tracer element in the left the upper one third humerus and on both sides of the mediastinum.

This lesion was biopsied and revealed woven new bone formation along with scanty spindle cell tumor tissue between the bony fragments. The spindle cells focally showed nuclear pleomorphism with hyperchromasia. These features were suggestive of an osteogenic sarcoma.


Fig.2	Fig.3

Fig.4	Fig.5

Fig.6

DIFFERENTIAL DIAGNOSIS:

1. Secondary aneurysmal bone cyst in FD

2. Cystic degeneration of FD

DISCUSSION:

Fibrous dysplasia is a skeletal developmental anomaly of the bone-forming mesenchyme in which osteoblasts fail to undergo normal morphologic differentiation and maturation. It may affect one bone (mono-ostotic) or may affect more bones (poly-ostotic). When associated with endocrine dysfunction - typically manifested by precocious puberty and cutaneous pigmentation, it is known as the McCune-Albright syndrome.

Both poly and mono ostotic FD generally becomes quiescent at puberty and remain so through out remaining life. In some instances, progressive deformity supervenes. Reactivation of skeletal lesions in FD has been noted in the course of pregnancy and estrogen therapy.

Malignant transformation of FD is rare in both monoostotic and polyostotic varieties of the disease. Sarcomatous changes have been mentioned in the literature. The actual incidence of malignancy in FD is less than 1% but a higher incidence of 4% is reported in case of Albright syndrome. In most reported cases, the diagnoses of FD was made in childhood and the malignant transformation developed during third or fourth decades of life. Men and women were affected equally among all the reviewed cases in the literature. In mono-ostotic FD, malignant transformation is most often detected in the skull and facial bones where as in polyostotic FD, the femur and facial bones are most frequently affected. In the cranio-facial region, the mandible and maxilla were most common sites for the secondary sarcomas followed by the femur, tibia, and pelvic bones. Radiation is a definite risk factor for the development of a sarcoma in a previously diagnosed case of FD.

Increase in pain associated with swelling is the only presenting clinical symptom. Our patient had pain with swelling associated with restriction of the movement of the shoulder, as the lesion was in close proximity with the shoulder joint.

On plain radiography, poorly defined areas of osteolysis with cortical destruction in association with soft tissue shadow in the vicinity of disrupted cortices have been regarded as highly suggestive of malignant transformation in case of FD. CT is useful especially to evaluate metastasis and to look for cortical involvement of the bone under evaluation. MRI has an advantage over CT due to its better soft tissue resolution and to look for involvement of the medullary cavity. Metastatic involvement of the adjacent soft tissue, abdominal organs and lung is common in sarcomatous transformation. Two conditions occurring in FD may clinically mimic a sarcomatous change, the first is the occurrence of a secondary aneurysmal bone cyst with fibrous dysplasia and the second is a cystic degeneration of the lesions in FD itself, which is frequently seen in FD of the ribs. These were easy to exclude in our patient due to the malignant nature of the radiological findings and also due to new bone formation.