Unusual presentation of chondroblastoma mimicking Trevor's disease.

Chondroblastoma is a benign bone tumor, represents 1%-2% of all primary bone tumors, typically seen in patients 10-25-year-old and more common in males. It occurs most frequently in the distal femur, proximal tibia, and proximal humerus. Soft tissue extension is extremely rare. Adjacent joints may develop effusions, but the tumor mass protruding into the joint has never been seen in case of chondroblastoma. We report a rare case of intra-articular chondroblastoma arising from proximal tibia in a 16-year-old boy and growing into the knee joint mimicking an intra-articular osteochondroma.

Introduction

Chondroblastoma is a rare benign bone tumor, typically occurs in patients 10–25-year-old, more common in males with a ratio of 2:1.[1] This tumor represents 1%–2% of all primary bone tumors and about 9% of all benign bone tumors.[2] The tumor occurs most frequently in the distal femur, proximal tibia, and proximal humerus. Radiographically, it presents as a well-defined lesion centered in an epiphysis of a long bone. Differential diagnosis includes infection in children or giant cell tumor, aneurysmal bone cyst, and clear cell chondrosarcoma in adults. Soft tissue extension is extremely rare. Joints adjacent to a chondroblastoma may develop effusions,[3] but the tumor mass protruding into the joint has never been seen in case of chondroblastoma. However, any growth arising from the epiphysis and protruding into the joint raise the suspicion of dysplasia epiphysealis hemimelica, also known as Trevor's disease, a rare developmental bone disorder with involvement of one-half of one or more epiphysis (hemimelica) in children[456] as a result of an overgrowth of cartilage.[7] In this disease, the epiphysis grows asymmetrically and forms an osteochondral protuberance that is macroscopically and microscopically similar to an osteochondroma.[7] We report a case of intra-articular chondroblastoma arising from proximal tibia and growing into the knee joint mimicking an intra-articular osteochondroma. Such presentation of chondroblastoma had never been reported in the English literature.

Case Report

A 16-year-old boy presented with pain and swelling over medial side of the left knee with the inability to extend the knee since 2 years. The swelling has slowly increased in size, especially during the past 6 months. Pain aggravates on walking and sitting cross-legged. No other swelling was found. There was no history of fever, weight loss, or loss of appetite. Past history was unremarkable. On clinical examination, the swelling was 3 cm × 4 cm in size, hard in consistency, well-defined margins, immobile, tender on deep palpation with normal overlying skin with no compressibility and reducibility. There was a flexion deformity of 30° of the knee joint with further flexion to 90°. There was no limb length discrepancy or coronal plane deformity of the knee. Anteroposterior and lateral radiographs of affected knee [Figure 1] revealed the presence of a bony growth arising from the medial part of tibial epiphysis extending into the joint cavity consistent with the clinical diagnosis of Trevor's disease. On the basis of clinical examination and radiographic findings, the diagnosis was felt definitively to be osteochondroma. Therefore, magnetic resonance imaging (MRI) was not performed. The patient underwent surgical excision of the mass under regional anesthesia using medial parapatellar approach, and send for histopathological examination. On gross examination, the lesion was 4 cm × 4 cm in size reddish in color, bony hard in consistency [Figure 2]. Histopathologically, the lesion consists of sheets of chondroblasts with dystrophic calcification surrounding individual cells giving the classical “chicken wire” appearance characteristic of chondroblastoma [Figure 3]. Full extension was achieved intraoperatively [Figure 4] and above knee plaster of Paris (POP) slab was applied in full extension. Postoperative lateral radiograph of knee confirmed the entire removal of the lesion [Figure 5]. Sutures removed at 2 weeks postoperatively, and knee range of motion (ROM) was initiated with full ROM at 4 weeks postoperatively.

Figure 1

Anteroposterior and lateral radiographs of the affected knee joint showing an exophytic mass arising from the anteromedial aspect of proximal tibial epiphysis

Figure 2

Clinical photograph of excised lesion

Figure 3

Chicken wire calcification as marked by the arrow (H and E, ×40)

Figure 4

Clinical photograph of affected knee postoperative, showing the full knee extension

Figure 5

Anteroposterior and lateral radiograph of the knee showing the entire removal of the lesion

Discussion

Chondroblastoma is an epiphyseal tumor occurring mainly in males around the second decade of life. It is well circumscribed lytic lesion limited to the epiphysis but in some cases may extend to involve the metaphysis leading to endosteal expansion or cortical destruction with periosteal new bone formation known as neocorticalization.[8] Despite epiphyseal involvement, joints adjacent to chondroblastoma are not involved. The case presented here had an intra-articular extension of the tumor from the medial tibial epiphysis with clinical restriction of joint movement similar to the presentation of intra-articular osteochondroma. This appears to be an unusual presentation of chondroblastoma confusing with Trevor's disease. Trevor's disease is an uncommon epiphyseal growth abnormality as rare as 1 in 1000,000 among the pediatric population.[9] Trevor hypothesized a congenital error or insult perpetrating the defect in the lower limb buds during early fetal life. He also speculated that the peculiarity in vascular arrangement of the epiphysis was responsible for the tendency of this lesion to be asymmetrically confined to only one side of the joint, preferentially the medial side.[10] Through this report, we want to emphasize in this particular case, that the first clinical and radiological impression derived from the presentation of the patient was an intra-articular variant of osteochondroma appearing in the knee joint. Even a surgical resection was performed with the same diagnosis in mind. However, the histopathological examination proved it to be a case of chondroblastoma. Hence, we have stressed on the unusual presentation of chondroblastoma of proximal tibia mimicking as intra-articular osteochondroma which was never seen previously. Hence, a keen eye should be kept in cases where a young patient presents with a complaint of pain in the knee with a flexion deformity and with radiographic evidence of Trevor's disease. In such cases, a rare possibility of chondroblastoma should be kept as a differential diagnosis. An MRI scan, before surgery might have given us a clue in our case.

The treatment of intra-articular osteochondroma is excision. Reith et al.[11] did not report any recurrence of the mass after surgical resection of intra-articular osteochondroma, although the follow-up was in all cases quite short. The treatment of chondroblastoma consists of curettage and filling up the defect with bone graft and/or bone cement. Despite better and more aggressive treatment methods, recurrence rates range from 8% to 30%, whereas systemic metastasis rates range from 0.8% to 6%.[1213] Factors contributing to recurrences include young age, aneurysmal bone cyst components, aggressiveness, anatomic site, and inadequate surgery. The suspicion that an open growth plate negatively impacts local recurrence has not been proven.[13] Patients with lesions in less accessible locations (e.g., talus, proximal tibia, and proximal humerus), or those with aggressive tumors, recurrences, and repeat surgery, or those with restricted joint movement and degenerative changes, had poorer outcomes.[14] Hence, in view of more aggressive nature of chondroblastoma as compared to osteochondroma, differential diagnosis of chondroblastoma must be kept in mind before definitive management.

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Conflicts of interest

There are no conflicts of interest.