Extraskeletal Chondroma

Case History: A 58-year-old male admitted to our institution with chief complaint of intermittent mild pain in his left knee. He first noticed the pain several years ago without worsening overtime. He reported no correlation between the pain and his daily physical activity. He denied any previous remarkable trauma to the knee. Clinical examination was unremarkable compared to the right side, as no swelling, tenderness, skin color change, motion limitation or palpable mass was noticed.

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Figure 1. Lateral radiograph of the knee revealed a juxta-articular soft-tissue mass located posteriorly to the patellar tendon, displacing the fat pad anteriorly. The mass seemed to be homogenous in nature, well-defined with some amorphous calcified foci inside. Mild degeneration of the left knee joint was also noted. No evidence of osteolysis, bony erosion or periosteal reaction.

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Figure 2. On ultrasound, the mass appeared to be solid, well-defined, heterogeneously hypoechoic with posterior enhancement. Multiple calcified foci distributed peripherally with acoustic shadowing were also seen. No evidence of hypervascularity. The anterior patellar tendon was preserved.

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Figure 3. MRI examination of the knee revealed a well-defined extraosseous mass along the anterolateral aspect of the proximal tibia. The lesion was in contact with the underlying bone without cortical breach or bony discontinuity, but causing displacement of the anterior fat pad without involvement to the patellar tendon. No evidence of joint effusion was present. The adjacent tendons and ligaments were normal with preserved fat planes. The mass was isointense to the muscle on T1W images and hyperintense on T2W images. There were some hypointense foci seen on both T1 and T2 images represent calcification proved on plain radiographs. After Gadolinium administration, the mass showed heterogeneously strong enhancement. MRI confirmed the extraosseous, extrasynovial location of the lesion. Various differential diagnoses were accounted for, including extraskeletal chondroma, extraskeletal osteochondroma, soft tissue chondrosarcoma, periosteal chondroma and periosteal chondromyxoid fibroma.

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Figure 4. Surgical excision of the lesion was performed. The mass was entirely extraskeletal, extra-articular and extrasynovial with a well-defined capsule. Gross specimen was a 3x2x3cm mass with smooth margins and the cross-section was white and shiny. Histopathological study confirmed benign chondroma.

Diagnosis: Extraskeletal chondroma

Discussion: Chondromas are generally classified as enchondroma, periosteal chondroma and extraskeletal chondroma according to their location, in which enchondroma is the most common and the rest are rare. These lesions are benign cartilage neoplasms and share the same basic pathology. Extraskeletal chondroma occurs mostly around hands and toes. The lesion can be found at any age, however it occurs more often in adults mainly from ages 30-60, and rare in children with only a few case reports in the literature.^1–3 Meanwhile, juxtacortical chondroma, also called periosteal chondroma, most commonly encounters in the diametaphyses of long bones in children and young adults.⁴

The typical clinical presentation of an extraskeletal chondroma is a painless, slow enlargement nodular soft tissue mass that may be present for a long time prior to diagnosis. On conventional radiography, the lesion may appear as a well-circumscribed, lobulated mass with dense central mineralization. Calcification is usually ring-like, punctuate or granular suggesting the presence of hyaline cartilage. The differential diagnosis of soft tissue tumors with calcification includes several entities, such as hemangioma, tumoral calcinosis, myositis ossificans, extraskeletal chondroma/osteochondroma or soft tissue chondrosarcoma, extraskeletal myxoid chondrosarcoma and synovial sarcoma.³ CT can confirm the extraskeleatal location of the mass and show foci of calcification or ossification that can direct the diagnosis towards extraskeletal chondroma. MRI helps delineate the lesion location and margins, but the appearance is nonspecific. Extraskeletal chondroma have been described as showing low to intermediate signal intensity on T1W images and heterogeneous intermediate to hyperintense signal from the cartilages on T2W images. Contrast enhanced MRI often shows diffuse enhancement within the mass. Marginal surgical excision is usually the treatment of choice with preservation of adjacent bone and soft tissue structures.² The diagnosis should be confirmed after correlating clinical, radiological and histopathological examination in order to avoid unnecessary, aggressive management.^2,4.

References
1. Turhan-Haktanir N, Demir Y, Haktanir A, Aktepe F, Sancaktar N. Concurrent soft tissue chondroma and periosteal chondroma of thumb. Eur J Gen Med 2009;6:257-261.
2. Adaletli I, Laor T, Yin H, Podberesky DJ. Extraskeletal chondroma: another diagnostic possibility for a soft tissue axillary mass in an adolescent. Case Reports in Orthopedics 2011;2011:309328.
3. Singh AP, Dhammi IK, Jain AK, Bhatt S. Extraskeletal juxtaarticular chondroma of the knee. Acta Orthop Traumatol Turc 2011;45:130-134.
4. Miller SF. Imaging features of juxtacortical chondroma in children. Pediatr Radiol 2014;44:56-63.