The patient presented with a lump and vague pain in the posterolateral aspect of her proximal calf. The lump had been growing in the region for 11 years. Physical examination revealed a hard and tender mass in the lateral aspect of the right upper calf. Routine laboratory studies were normal.
Plain radiographs of the involved calf showed a large osseous excrescence arising from the external surface of the upper fibula and containing spongiosa and cortex that were continuous with those of the parent bone (Fig. 1). The bony outgrowth was sessile with a broad, flat base. On MR images, a solitary osteocartilaginous exostosis was seen (Figs. 2-4). There was continuity of the cortical and medullary bone in the lesion with that of the parent bone, a finding merely diagnostic of an osteochondroma. The cap of the osseous protuberance displayed the imaging characteristics of cartilage, showing high signal intensity on T2-weighted spin echo MR images. Due to the large size of the osteochondroma, tibiofibular synostosis (bony bridge) was produced with pressure deformity in the nearby tibia. There was bowing of the fibula, and minimal diastasis of the proximal tibiofibular joint.
Osteochondroma, also known as osteocartilaginous exostosis, is the most common benign bone tumour, representing 10-15% of all primary bone tumours and up to 50% of benign tumours [1]. Osteochondroma may develop after irradiation or may arise spontaneously. Lesions are composed of cortical and medullary bone with an overlying cartilage cap. The radiologic hallmark of osteochondroma is continuity of lesion with the marrow and cortex of the underlying parent bone.
Osteochondromas occur most commonly around the knee (40% of cases). The femur is the most-affected bone (30%), while tibial lesions account for 15-20% of cases [2]. Osteochondromas may be solitary or multiple as part of the hereditary multiple exostoses syndrome (HME) [1]. Complications are more common with multiple osteochondromas and include deformity (cosmetic and bone), fracture, vascular injury, neurologic compromise, overlying bursa formation, and malignant transformation. Bone deformity includes osseous bowing, malalignment and extrinsic pressure erosion of adjacent bones. When paired bones of the forearm or lower leg are involved, scalloping of the cortex may ensue.
The size of osteochondromas varies between 1-10 cm. Continued lesion growth after skeletal maturity, and a cartilage cap greater than 1.5 cm suggest malignant degeneration of an osteochondroma [3]. Solitary osteochondromas are usually asymptomatic with a male predilection ranging from 1.6-3.4 to 1. Small asymptomatic or minimally symptomatic lesions should be followed-up, while symptomatic lesions should be resected. Patients with HME require continued clinical and imaging surveillance to evaluate progression of lesions, or complications. Measurement of thickness of a cartilage cap can be accomplished with ultrasound, while CT or MR imaging are best suited for the evaluation of complex anatomic areas [1].
On radiographs, osteochondroma appears as a sessile or pedunculated bone excrescence, containing both spongiosa and cortex that are continuous with those of the parent bone. The cartilaginous cap has a variable degree of calcification.
Typically, osteochondromas tend to point away from the adjacent joint. Widening of the involved metaphysis of tubular bones may be noted. MR imaging often reveals yellow marrow centrally (which has high signal intensity on T1-weighted images and intermediate signal intensity on T2-weighted images) with a low-signal intensity cortex. The cartilage cap has low to intermediate signal on T1-weighted images and high signal on T2-weighted images. Mineralized portions in the cartilage cap remain low signal intensity with all MR sequences. After the intravenous administration of contrast, peripheral and septal enhancement in the cartilage cap can be seen.
Osteochondroma of the fibula
1. X-ray (Plain Film) Observations:
2. MRI Findings:
Overall, imaging features indicate a lesion with continuity of the bone cortex and marrow, a cartilaginous cap, and local calcification. These findings are consistent with a bony exostosis (osteochondroma-like lesion).
This is the most common benign bone tumor, formed by an outgrowth of bone cortex and marrow. It frequently occurs at the metaphysis of long bones, and imaging demonstrates continuity of the cortex and marrow with the parent bone. If the cartilage cap is thick (e.g., >1.5 cm) or continues to grow in adulthood, malignant transformation should be considered.
Occasionally, osteochondroma can undergo malignant transformation into chondrosarcoma, especially when the cartilaginous cap is significantly thickened or the lesion grows rapidly in adulthood with worsening pain. Typical chondrosarcoma often shows destructive growth with marked bone destruction and soft-tissue calcification (“ring” or “cluster-like” calcification).
These include osteoid osteoma, enchondroma, etc. However, these lesions typically do not present as a prominent outgrowth and often lack direct continuity with the bone cortex and marrow.
Based on the patient’s age (53-year-old female), history (11 years of slow growth, recent worsening pain), physical examination (hard mass), and imaging findings (bony outgrowth with continuity of marrow and cortex, a typical cartilaginous cap, and partial calcification), the most likely diagnosis is:
Osteochondroma.
If further examinations or follow-up imaging confirm a markedly thickened cartilage cap (>1.5 cm) or if the lesion exhibits rapid growth within a short period, the possibility of malignant transformation (e.g., chondrosarcoma) should be considered. A biopsy or higher-resolution MRI might be warranted to confirm the diagnosis.
1. Treatment Strategy:
2. Rehabilitation/Exercise Prescription:
Throughout the rehabilitation and exercise program, closely monitor both local and general pain, swelling, and fatigue levels. If symptoms worsen, seek medical evaluation promptly.
This report is based on the currently available imaging and clinical information and is provided for reference only. It does not replace a face-to-face consultation or the professional diagnosis and treatment advice of a physician. Patients should proceed with further examinations and treatment under the guidance of a specialist.
Osteochondroma of the fibula