Periosteal chondroma

Clinical History

A 13-year-old boy presented a painless bone swelling of the proximal left tibia which was noticed after a trauma of the knee two months before. He explained that the mass was gradually growing. Physical examination revealed a painless mass 3 cm in diameter, in the proximal anterior left leg with no skin adherence.

Imaging Findings

Initial conventional radiographs revealed a lytic cortical lesion of the anterior metaphyseal-diaphyseal portion of the proximal left tibia, measuring 4x1 cm, not involving the growth cartilage, well circumscribed by sclerotic margins and no periosteal reaction (Fig. 1 and 2).

Magnetic resonance imaging showed an intracortical bone mass, well circumscribed with some lobulated margins. It presented hypointensity on T1 (Fig. 3) and hyperintensity on FAT-Saturated T2-weighted sequences (Fig. 4). The lesion enhanced peripherally after Gadolinium injection (Fig. 5). There were no other bone or soft tissue anomalies. The CT scan showed no internal calcifications of the lesion.
The child was operated for surgical resection and the resected tissue was a highly differentiated chondromatous neoplasm with slightly increased cellularity and minor differences in nuclear size. The majority of nuclei were small, round and contained dense chromatin. No significant nuclear atypia or mitosis was found.

Discussion

Periosteal chondroma is a rare benign chondromatous neoplasm that develops adjacent to the cortical surface, beneath the periosteal membrane [1]. It may occur in both children and adults with the highest frequency in the second decade. Typical sites of involvement are metaphyses of long tubular bones, hands and feet. [1] The most common clinical symptoms are a palpable mass and swelling or slowly progressive pain [2].

Signal characteristics on MR include hypo- to isointensity relative to muscle on T1-weighted images and commonly high signal intensity relative to fat on T2-weighted sequences due to the high water content of the hyalin cartilage [1]. The tumour often presents a lobulated configuration and can be associated with medullary bone or tissue oedema [3]. The majority of lesions are outlined by a rim of low signal intensity on all sequences which can be attributed to the presence of fibrous tissue and an intact periosteum covering the cartilage lobules [1]. The typical MR appearance includes peripheral contrast enhancement [1].

Differentiation of low-grade chondrosarcoma from chondroma may be difficult because low-grade chondrosarcoma often has a non-aggressive pattern [3]. Differentiating between these conditions may necessitate an excision biopsy, although it may also be difficult to differentiate them on the basis of histology [3]. Another differential diagnosis is sessile osteochondroma which may be distinguished by presenting continuity with its originating bone. In our patient, this finding was not detected. We can also consider non-ossifying fibroma which is usually asymptomatic.

Differential Diagnosis List

Final Diagnosis

Periosteal chondroma

URL:	https://www.eurorad.org/case/13533
DOI:	10.1594/EURORAD/CASE.13533
ISSN:	1563-4086