Teaching Case

A 7-year-old boy presented with left-sided limping for the past 6 months, without a history of trauma. Clinical examination revealed lower limb-length discrepancy of more than 2 cm and mild left genu valgus deformity. Routine lab investigations were normal. Past medical and family history were otherwise unremarkable

Plain radiographs revealed flame-like, sharply-defined radiolucent areas, located at the lateral aspect of the proximal tibial metaphyseal-diaphyseal region, the medial fibular metaphysis and distal femoral metaphysis. Most lesions were surrounded by sclerosis. The largest one contained speckled calcifications and was associated with a tilted physis, and thinned sclerotic cortex. CT images confirmed the presence of proximal tibial and fibular lytic lesions, causing tibial deformity, affecting both the cortical and medullary bone. Intralesional calcifications and sclerotic margins were also noted. Subsequent MRI showed epiphyseal-metaphyseal involvement of the proximal tibia, extending into the diaphysis, by a lesion exhibiting signal characteristics identical to cartilage in all sequences, blending with epiphyseal cartilage and containing low signal intensity calcifications. The lesion was associated with derangement of the lateral part of the proximal epiphysis, asymmetrical physeal arrest and obliquity of the knee joint. Lesions of identical signal intensity were noted at the fibula and distal femur.

Background

Enchondromatous lesions are characterized by the presence of aberrant rests of epiphyseal growth-plate chondrocytes which develop within the medullary cavity of the metaphysis and may extend into the diaphysis of bones [1]. They usually present as solitary lesions affecting predominantly the short tubular bones of the hands and feet; however, multifocal or diffuse involvement defined as enchondromatosis may occasionally occur [2]. The distribution of lesions, combined with associated features and the mode of inheritance define the different subtypes of enchondromatosis, mainly including Ollier disease and Maffucci syndrome [3]. It is generally believed that extension of a lesion from the metaphysis into the epiphysis occurs secondarily, after closure of the growth plate.

Epiphyseal-metaphyseal enchondromatosis, unlike other subtypes of enchondromatosis, is characterized by formation of excessive enchondromatous tissue within the epiphysis and direct metaphyseal extension through an open epiphyseal growth plate [4]. It represents a rare condition which shows unilateral involvement confined to the long tubular bones of the lower extremity. The pathogenetic basis remains unclear and it is currently unknown whether it represents a variant of Ollier disease or a distinct clinical entity [4].

Clinical Perspective

Epiphyseal-metaphyseal enchondromatosis, depending on the location and extent of enchondromas, may be complicated by limb-length discrepancy, premature physeal arrest, angular joint deformity and incongruity of articular surfaces [4]. Other complications include pathological fractures and malignant transformation to chondrosarcoma [4].

Imaging Perspective

Imaging plays a vital role for the diagnosis, treatment planning and life-long follow-up to identify malignant transformation. Similar to all chondrogenic tumours, enchondromatous lesions are characterized by predominantly high signal on fluid sensitive sequences and occasional presence of calcifications [4,5]. Epiphyseal-metaphyseal enchondromatosis typically appears as amorphous radiolucent frond-like lesions with speckled calcifications, invariably involving the epiphysis and extending to the metaphysis, coursing through an open growth plate [4]. CT and MRI can evaluate the anatomical structures involved and the extent of lesions in better advantage. Both modalities may assess disease complications including asymmetrical premature physeal closure, irregularities of articular surfaces, angular deformity, pathological fractures or malignant transformation [4]. Signs indicating malignant transformation mainly include change of size, bone destruction, loss of lesions’ sharp demarcation and soft tissue edema/mass [6].

Outcome

Treatment is aimed mainly at correcting morphological deformity. Repeated lengthening and realignment procedures by means of osteotomy are usually required [4]. The family refused operation.

Written informed consent for publication has been obtained by the child and the guardian.