Peh, WCG

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Title Radiological conference. Non-ossifying fibromaAuthor(s) Peh, WCGCitation Hong Kong Practitioner, 1999, v. 21 n. 3, p. 133-135Issued Date 1999URL http://hdl.handle.net/10722/44675Rights Creative Commons: Attribution 3.0 Hong Kong LicenseClinical History:A 18-year-old boy sustained a right knee injury. He was previously well. Radiographs (Figures 1 & 2) wereobtained.Figure 1: Frontal radiograph of the right Figure 2: Lateral radiograph of the rightknee kneeAnsweronpage 134What is the diagnosis?a) Avulsion fractureb) Osteochondritis dissecansc) Giant cell tumourd) Ewing's sarcomae) Non-ossifying fibromaThis radiology case was prepared by: Professor W.C.G. Peh,Department of Diagnostic Radiology,The University of Hong Kong,Queen Mary Hospital.133Radiological ConferenceAnswer:e) Non-ossifying fibromaRadiological findingsRadiographs (Figures 3 & 4) show an ovoid lucentlesion in the posterolateral aspect of the right lowerfemur. It is located eccentrically in the diametaphysealregion of the femoral shaft. Its margins are well-definedwith a narrow zone of transition and a thin sclerotic rim.There is no associated lesion calcification, cortical breach,periosteal reaction or soft tissue swelling.Figure 3: Same radiograph as Figure 1 withthe addition of arrows. An ovoidlesion is located in the diameta-physeal junction of the lower femur.It has well-defined margins with athin sclerotic rim (arrows). Noperiosteal reactionFigure 4: Same radiograph as Figure 2 withthe addition of arrows. The thinsclerotic rim and smooth margins(arrows) are appreciated. No boneexpansion or cortical breachDiscussionNon-ossifying fibromaNon-ossifying fibromas are not true neoplasms butare considered to be developmental defects. They arefound in subjects ranging from 2 to 20 years of age, andare usually asymptomatic although occasionally largerones may be painful or may fracture. Non-ossifyingfibromas are histologically identical to fibrous corticaldefects. The latter lesions tend to arise on the corticalsurface, unlike non-ossifying fibroma which are primarilyintramedullary. Microscopically, these lesions arecomposed of fibrous tissue, xanthoma cells and giantcells.1 •Non-ossifying fibromas are located eccentricallywithin the medullary cavity of bone and are found134Hong Kong Practitioner 21 (3) March 1999RADIOLOGICAL CONFERENCEpredominantly in the lower extremities, especially aroundthe knee. Radiographically, they are geographical lucentlesions which are sharply demarcated by a thin scleroticr im . Their outer margins may be scalloped and theoverlying cortex may be thinned or thickened as a resultof reactive change. They arise near the growth plate butnormal bone growth gradually carries the lesion towardsthe diaphysis . Non-ossifying f ibromas usua l l y heals p o n t a n e o u s l y . The i m p o r t a n c e of r e c o g n i s i n gradiologically-typical non-ossifying fibromas is that theydo not require biopsy or treatment, and are regarded as"don't touch" lesions.1 2Avulsion fractureAvul s ion fractures may produce an aggressiveradiographica l appearance. They can however berecognised from the i r characterist ic location at theinsertion sites of tendons. Such sites around the kneeinclude the anterior tibial tubercle due to traction fromthe patellar tendon, the tibial spine by tension from theanterior cruciate ligament, and the inferior pole of thepatella where the infrapatellar tendon inserts.3 Delayedradiographs after several weeks would allow the diagnosisto be clearer. The absence of trauma and radiographicalappearance in our patient excludes this diagnosis.Osteochondritis dissecansOsteochondritis dissecans is a term applied to a formof osteochondral fracture. The mechanism of injury isthought to be trauma transmitted through the articularcartilage to the subchondral bone. Fracture healing andpossible osteonecrosis contribute to development of anisolated fracture fragment, which may or may not havean intact overlying articular cartilage. The loose fragmenthas been called a "joint mouse". In the knee, the commonsite of Osteochondritis dissecans is at the medial femoralcondyle.3 Radiographically, a well-defined oval fragmentadjacent to the condylar defect is seen. These featuresare not present in our patient.Giant cell tumourGiant cell tumour classically occurs in patients withclosed epiphyses, i.e. young adults. Radiographically, itis epiphyseal in site and abuts the articular surface. Thelesion is typically eccentrically located in the medullarycavity, and is well-defined with a non-sclerotic margin.2This diagnosis can be excluded in our patient based onage and location within bone.Ewing's sarcomaEwing's sarcoma is a highly malignant bone tumourfound in children and adolescents. Radiographically, itis typically seen as a permeative lesion with an onion-skintype of periosteal reaction, a l though sunburst oramorphous periosteal reaction may also be present.2 Ourpatient does not have any radiographical feature tosuggest Ewing's sarcoma. •ReferencesHudson TM, Stiles RG, Monson DK. Fibrous lesions of bone. Radiol ClinNorth Am. 1993:31:279-297.Helms CA. Fundamentals of Skeletal Radiology. 2nd ed. Philadelphia: WBSaunders. 1995;pp56-77.Chew FS. Skeletal Radiology - the Bare Bones. Rockville, Maryland:Aspen. 1989;pp79-94.135

Radiological conference. Non-ossifying fibroma

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Radiological conference. Non-ossifying fibroma

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