Teaching Case

A 32-year-old male, presented with pain and swelling along the anterior aspect of the distal left leg for the past 4 months. On examination, a fluctuant swelling was palpated with a deep-seated hard projection. The patient underwent an X-ray of the left leg as well as a local site ultrasound for the swelling.

Anteroposterior and lateral radiographs (Figures 1a and 1b) of the left leg showed the presence of a well-marginated, sessile bony lesion arising from the anterolateral aspect of the distal diametaphyseal region of the left tibia with continuity of trabecular pattern with the underlying bone. Soft tissue swelling is visualised overlying the bony lesion as well as along the anterior aspect of the ankle joint.

Ultrasound images of the site of swelling show the bony lesion (Figures 2a and 2b), with its surface appearing echogenic with posterior shadowing and a thin hypoechoic covering of maximum thickness ~1.5 mm, suggesting the cartilage cap.

A thickened common tendinous sheath of the left extensor digitorum longus (EDL) and peroneus tertius with tenosynovial effusion, showing a predominantly clear appearance with few internal echoes, is seen (Figures 3a and 3b). The tendons appear mildly thickened, without significant internal vascularity; however, minimal synovial thickening surrounding them shows increased peritendinous vascularity (Figure 4).

Background

Osteochondromas are benign bone tumours arising from cartilage-capped bony projections on the surface of bones. Also considered to be developmental anomalies, they commonly occur in long bones like the femur or tibia, particularly in adolescents and young adults. Though usually asymptomatic, they can cause pain or functional issues.

Clinical Perspective

Osteochondromas can be multiple or solitary, with complications most commonly seen with multiple exostoses, as seen with multiple hereditary exostosis syndrome. Complications of osteochondromas include deformities, fractures, vascular compromise and pseudoaneurysm formation, neurologic sequelae, overlying bursa formation, mechanical irritation on surrounding soft tissues (for example, localised tenosynovitis) and malignant transformation [1].

Imaging Perspective

While X-rays are the ideal modality for diagnosing the primary features of an osteochondroma, an ultrasound or an MRI will help delineate the features of its associated complications. X-rays reveal the characteristic metaphyseal bony projection, with medullary continuity with parent bone, often accompanied by signs of surrounding soft tissue swelling or deformity [2]. MRI provides detailed views of the osteochondroma’s cartilage cap and highlights surrounding soft tissue inflammation, including thickening of the tendon sheath indicative of tenosynovitis. The tenosynovitis can be classified into active exudative (associated with infection or gout, predominant fluid accumulation), acute proliferative (seen with inflammatory conditions, synovial proliferation predominant), chronic and stenosing tenosynovitis, based on the imaging findings. Chronic synovitis is seen as marked (when active) or mild sheath thickening (when inactive), fluid accumulation, hyperaemia within and around tendons, and rice bodies formation.

Outcome

Treatment of such cases typically involves surgical resection of the tumour to relieve pressure on surrounding tendons. Concurrently, anti-inflammatory medications or corticosteroid injections may manage the symptoms related to tenosynovitis. Physical therapy can aid in recovery and restore tendon function.

Take Home Message / Teaching Points

Osteochondromas, even though benign, can become symptomatic in cases of fractures, vascular damage, compression of a peripheral nerve or spinal cord, mechanical irritation of soft tissues, or malignant transformation. It is important to identify these complications for appropriate patient management and prognosis, with some of them being able to be diagnosed on ultrasound, and without the need of an MRI.

Written informed patient consent for publication has been obtained.