Tibial osteochondroma with thick cartilage which mimicked a chondrosarcoma: A case report

Abstract

We report a case of tibial osteochondroma in a 25-year-old female who presented with a palpable calf mass. This mass was associated with a thick cartilaginous cap on cross-sectional imaging, suggesting chondrosarcoma. A CT-guided biopsy was performed, and histology, however, was consistent with osteochondroma. Orthopedic oncology recommended surgical excision due to the potential high sampling error with chondroid lesions. The patient underwent surgical resection, resulting in a final diagnosis of osteochondroma. No post-surgical complications occurred, and a 12-month follow-up showed no evidence of local recurrence. This case highlights the atypical imaging feature of a thick cartilaginous cap in a benign etiology without malignant transformation.

Keywords: Cartilaginous cap; Chondrosarcoma; Osteochondroma.

Fig. 1

(A) Frontal and lateral radiography showed a large, exophytic, ossific lesion posterior to the proximal right tibia as arrow indicated. (B). Three-phase examination of the knees, with SPECT CT was performed to rule out other sites of disease. No significant abnormalities were seen on the flow of blood pool images. On the delayed views, intense tracer uptake is identified in the large exostosis at the posterior proximal right tibia as arrow indicated.

Fig. 2

(A-D) Multiple sequences of MRI remonstrated a large exostosis arising from the proximal tibial metaphysis which extends posteriorly. This measures 5.6 cm medial - lateral by 3.9 cm anterior - posterior by 4.9 cm craniocaudad. (A) T2 weighting demonstrates a cartilaginous cap which measures up to 2 cm in maximal thickness (as arrow indicated). (B). Marrow signal of tibia is otherwise preserved on PD sequence. The popliteal neurovascular bundle is displaced laterally by the lesion and the gastrocnemius musculature is displaced slightly posteriorly. (C) No edema is seen with the adjacent soft tissues on STIR sequence. (D) This confirmed cortical and medullary continuity best appreciated on T1 sequence, with an apparent osseous pedicle connecting the tumor and tibial cortex as arrow indicated. The findings are suggestive with an osteochondroma. Given the thick cartilaginous cap, an element of malignant degeneration is possible.

Fig. 3

(A) A biopsy of the osteochondroma the upper right tibia has been obtained as requested by orthopedics. Specimens have been obtained from the cartilaginous cap. as well as the adjacent ossified region. No complication occurred. (B) Immediate follow-up radiography post-surgery confirm the complete removal of the tumor.

Fig. 4

On gross examination, the cartilage cap measured up to 1.8 cm in thickness (measured perpendicular to the bone-cartilage interface) and had a glistening, slightly lobulated, gray-blue appearance.

Fig. 5

(A) Low power of the lesion showed the three layers with perichondrium cartilage, and bone (0.7x). The cartilage cap demonstrated the zonation seen in endochondral ossification with zone of reserve cells (B, 4x), zone of proliferation (C, 4x), zone of hypertrophy (D, 4x) and zone of degeneration (E, 4x). The interface of bone and cartilage demonstrated the zone of ossification (F, 10x).