Malignant Chondroblastoma of the Os Calcis

Patient. We describe a case of chondroblastoma of the os calcis which metastasized to the tibia, soft tissues and lung. A complete response of the lung lesions was noted with chemotherapy. Discussion. Review of the published literature shows that metastatic chondroblastoma only arises following local recurrence of the tumour.


Introduction
C hondroblastomas are recognized as benign prim ary bony lesions, ® rst described as a distinct entity by Jaffe and L ichtenstein in 1942. 1 These are rare tumours, the incidence being less than 1% of all prim ary bone tum ours. 2,3 M ales are affe cted m ore often than fem ales, the ratio being approxim ately 1.7; 1. 2 Chondroblastom as are usually located in the epiph ysis and are m ost com m only diagnosed in the second decade, while the epiphyseal plate is still open. 2,4 The m ost com m on sites are the proximal hum erus, fem ur and proxim al tibia. T hey occur less frequently around the ankle or in association with the apophyses. 2± 4 The radiological features are fairly typical: a lytic lesion arising in the epiphysis w ith an eccentric location, m ostly without periosteal reaction. T he lesion usually involves less than half of the epiph ysis and has a thin sclerotic border. 2,3 C linically, patients present w ith pain, swelling around the joint and a lim ited range of m ovem ents due to pain. At a later stage, the tumour could be asso ciated with a synovitis and a joint effu sion. Histologically the tum our is built up of round or polygonal chondroblasts surrounded by reticulin ® bres. T he m atrix is pinkstained chondroid, with occasional focal calci® cation. Scattered osteoclast-type multi-nucleated cells are often present. 2,3 The usual treatment is sim ple curettage of the lesion, with occasional bone grafting. M ost authors agree that, with intralesional curettage of the tum our, the local recurrence rate is between 5 and 16% . 2,4 Only a few cases have been reported in the literature 5± 15 which have m etastasized to the lungs, other bones or soft tissues.
In this report, we present the case of a 12-year-old boy with a chondroblastom a of the os calcis. F ollowing surgical treatm ent the tum our behaved in a m alignant m anner, with a local recurrence and m etastatic disease.

Case history
In March 1995, a 12-year-o ld boy was referred to our unit with a 3-m onth history of pain and sw elling of his right ankle region. Radiographs revealed a lytic expansile lesion of the os calcis containing calci® cation (Fig. 1). Biopsy w as carried out prior to referral and histology was consistent w ith a chondroblastoma. A careful curettage was perform ed with burring and brushing of the walls of the cavity and pulsed lavage irrigation.
Histology of the curettage specimen show ed som e necrotic areas and discrete reactive changes due to the previous biopsy, but was fully consistent with chondroblastoma.
Review at 6 weeks was satisfactory with absence of pain or swelling and radiographs showed som e early signs of consolidation of the os calcis. T hree m onths later the patient returned with further swelling and pain of the hind foot, with lim itation of m ovem ents of the ankle and subtalar joints. Radiographs now show ed total destruction of the os calcis identical to the appearances of the previous biopsies. Further scans (com puted tom ography (C T) chest and Tc isotope bone scan) excluded the presence of any other secondary tum ours. An above knee am putation w as perform ed.
Histology of the am putation specimen con® rm ed secondary lesions in the peroneal m uscles and several places in the soft tissues of the am putated leg. H istology of each tum our foci w as identical to the form er biopsies (Fig. 4).
He was restaged 12 weeks later follow ing the am putation when CT scans revealed the presence of lung m etastases. In view of this, he w as treated with chem otherapy (cisplatin 100 m g m 2 2 and doxorubicin 75 mg m 2 2 ) and after six cycles there was com plete resolution of the lung disease. He rem ained disease free for over 12 m onths before relapsing with further pulmonary disease. T his was resected surgically and histology again showed identical ® ndings to the previous lesions in the leg. H e has had post-operative whole-lung radiotherapy and remains alive and sym ptom free 3 years from diagnosis.

D iscussion
Since Jaffe and Lichtenstein ® rst described chonand m agnetic resonance im aging (M RI) revealed dram atic extension of the lesion into soft tissues and adjacent bones (Fig. 2). Chest X-ray was normal and a repeat biopsy was perform ed.
All previous histology slides were reviewed together with the new specim ens. Typical chondroblasts were seen in a rich chondroid m atrix (Fig. 3). A fairly high m itotic activity (more than 10 m itoses per high-po wer ® eld) was also seen along with unusual extended necrotic zones. The specim ens were reviewed by pathologists in the U K and the US and the consensus w as that the recurrent lesion was consistent w ith a diagnosis of chondroblastom a with atypical features. As no reconstruction was felt possible the patient w as prepared for a below -knee am putation. O n adm ission for this procedure the patient com plained of shin pain, and radiograph s and M RI now revealed two lytic lesions in his right tibia and a soft tissue m ass in the right calf. Biopsy of these lesions was carried out and all the lesions were histologically  **This patient had a hindquarter amputation following a m isdiagnosis of chondrosarcoma but the tumour was subsequently reclassi® ed as chondroblastoma. droblastom a, several hundred cases have been reported, the vast m ajority of them con® rming that the lesion is clinically benign.
O nly a few cases have been reported w here, despite the benign histological app earance, the tum our behaved aggressively, occasionally m etastasizing to neighbouring or distal bones, soft tissues, or more often the lungs. 5± 13 In Sirsat' s case 11 the tum our changed to a frankly m alignant ® brosarcom a but in all the others the histological appearance of the m etastases was identical to the prim ary tumour.
There appears to be som e confusion in the literature about the nam e m alignant chondroblastom a. Some authors consider locally aggressive chondroblastom as to be m alignant form s, although there was no evidence of m etastasis of the tum our. 1 There is a report of a case where a histologically benign looking chondroblastoma progressively increased in size w ith secondary spread to the lungs, but following surgery the lung m etastases rem ained unchanged in num ber and size. 5 Huvos and M irra 2,7 suggest that these lung m etastases represent self-lim ited`transplants' or implants' , and suggest the term`benign' m etastasis. K yriako s et al. 9 suggest the name`metastasizing chondroblastom a' , rather than m alignant chondroblastom a, for these cases.
All the reported cases of con® rm ed m etastatic lesions to the lungs where the histological app earance of the m etastases was identical w ith the prim ary tumour are identi® ed in Table 1. The single com m on feature of all these cases is that the m etastases only developed if there had been a previous local recurrence of the prim ary tum our. T he age and site of the tum ours correspond with the normal distribution of chondroblastom as. T he only case w here there w as not a local recurrence w as where the prim ary tumour had clearly been overtreated by a hindquarter am putation after a biopsy had (incorrectly) been interpreted as a chondrosarcom a. 13 The treatm ent of the m etastases has varied. In som e cases the m ultiplicity of the lesions led to a lack of treatment and was follow ed by death. In other cases, thoracotomy has produced apparent long-term cures, while in other cases the lesions have rem ained static following sim ple biopsy. C learly, the biological behaviour of these m etastatic tum ours is unpredictable and is rem arkably similar to that seen in m etastatic giant cell tum ours. 16 Chondroblastom as represent less than 1% of all bone tum ours and the num ber of patients with docum ented m etastases is less than 1% of all reported cases of chondroblastoma in the world literature. T he risk of m etastases developing in chondroblastoma is clearly low Ð and probably m uch less than 1% of all of these tumours.
From our review of the literature, we conclude that: (1) Lung m etastases have only been reported following local recurrence of the tum our (unless the patient has had an am putation). (2) F ull staging w ith chest radiographs and/or C T scan of the chest is advisable in any locally recurrent chondroblastom a. Bone scintigraph y and M RI w ill also be required to exclude spread to other bones or soft tissues, respectively. (3) In the presence of rapidly progressive chondroblastom a, chem otherapy may be indicated.