Age / Sex : 44 / M

Chief complaint: worsening knee pain after loss of consciousness due to ingestion of excessive alcohol

What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(답안은 한 개만 보내주시기 바랍니다)

Courtesy: 성미숙 (Mi Sook Sung), 가톨릭대 부천성모병원 (Catholic University of Korea, Bucheon St. Mary’s Hospital)

Giant cell tumor with secondary aneurysmal bone cyst

Discussion

Findings:

Fig. 1 Radiograph frontal view of left knee at initial presentation. An eccentric, lytic expansile lesion is present at meta-epiphyseal location in the distal femur with a single layer of solid periosteal reaction. An extraosseous soft tissue mass with ossification in the periphery and internal septa is seen medial to the intraosseous lesion

Fig. 2 Twelve-month follow-up radiograph demonstrates mild growth of the intraosseous lesion and increased ossification of the extraosseous soft tissue mass. A comminuted fracture is seen just proximal to the intraosseous lesion

Fig. 3 MRI of left knee demonstrates a multiloculated mass in the distal femur and the extraosseous soft tissue mass. A Coronal T2- and b coronal postcontrast fat-suppressed T1-

weighted images showing nonenhancing cystic portions in both the intraosseous and extraosseous components and lobular enhancing solid portions in the extraosseous soft tissue mass. C Axial T1-weighted image showing large cortical penetration in the anteromedial aspect of the femur, and multiple fluid–fluid levels in the intraosseous and extraosseous components.

Differential Diagnosis:

Diagnosis:  

Giant cell tumor with secondary aneurysmal bone cyst:

A unique presentation with an ossified extraosseous soft tissue mass

Discussion:

GCT of the bone is the most common precursor lesion of secondary ABC. These cystic areas may depict variable signal intensity, depending on their contents such as liquefaction, variable stages of hemorrhage, and necrosis. Fluid–fluid levels are often seen.

The present case is of interest due to the thin, delicate ossification along the margin and internal septa of the extraosseous soft tissue mass of the GCT at initial presentation. This finding is unexpected because matrix mineralization is reportedly rare in GCT of the bone. Soft tissue recurrences of GCT tend to ossify when soft tissue implantation occurs at the time of surgery or in cases with pathologic fractures.

The exact pathogenetic mechanism for the extraosseous soft tissue mass in the present case is not clear. It is possible that cortical penetration by the GCT led to the soft tissue mass without prior surgery or fracture. Considering the patient’s history of alcohol abuse with loss of conscious, it is conceivable that prior unrecognized subtle fracture might have resulted in implantation of GCT in the soft tissue.

Although soft tissue implantation of GCT has a tendency to ossify, we speculate that the soft tissue ossification in our case could be related to the prominent ABC component. This theory is supported by the fact that soft tissue implants of GCT show more coarse peripheral ossifications, whereas our case demonstrate thin, smooth calcifications along the margin and internal septa, more characteristic of ossifications in STABC. Furthermore, previously reported cases of soft tissue implants of GCT with ossifications were completely or predominately solid, whereas there were prominent ABC changes in the intraosseous and extraosseous components of our case which were histologically confirmed.

References:

1. Cooper KL, Beabout JW, Dahlin DC. Giant cell tumor: ossification in soft-tissue implants. Radiology. 1984;153(3):597–602.

2. Hong WS, Sung MS, Kim JH, etc. Giant cell tumor with secondary aneurysmal bone cyst: a unique presentation with an ossified extraosseous soft tissue mass. Skeletal Radiol. 2013 Nov;42(11):1605-10.