CASE 148

By: Dr. Nizar Al-Nakshabandi MD, FRCPC

HISTORY: 20-year-old male with left buttock pain.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

The AP radiograph of the pelvis [A] demonstrates a well-defined lytic lesion involving the left iliac wing extending into the left sacrum.

Axial T1 weighted sequence through pelvis [B] demonstrate a well-defined mass arising from the left iliac wing and extending anteriorly into the intra-abdominal pelvic cavity primarily of low signal intensity with central areas of high signal intensity. No extension into the neural foramina is present. It displaces the left psoas muscle anteromedially. Furthermore, it extends posteriorly into the left paraspinous muscles and into the subcutaneous tissues.

Axial T1-weighted with fat saturation sequence through the pelvis [C] and coronal T1 fat sat with gadolinium demonstrate the mass to be mildly heterogeneous enhancing lesion with central areas of necrosis. The left sciatic nerve is likely involved. Involvement of the left iliac wing, sacroiliac joint and sacrum is well demonstrated on the coronal sequence.

DIFFERENTIAL DIAGNOSIS:

The differential diagnosis is that of FEGNOMASHIC aneurysmal bone cyst, giant cell tumor, osteoblastoma, fibrous dysplasia, chondroblastoma and telangiectatic osteosarcoma. MFH, clear cell sarcoma, Ewing;s sarcoma LCH, and plasmacytoma could be added.

DIAGNOSIS:

Clear cell sarcoma of the bone.

PEARLS AND DISCUSSION:

Clear cell sarcoma is a rare soft tissue sarcoma of young adults with melanocytic differentiation. It occurs predominantly in the soft tissue of extremities, typically involving tendons and aponeuroses. Primary clear cell sarcoma of bone is extremely rare. This is not to be confused with clear cell sarcoma of the kidney.

It presents as a slow-growing mass especially around and affecting the tendons and aponeurosis and is deeply situated. Patient will have a lump or mass and can have pain or tenderness when it is large enough such as in our case.

Metastasis occurs in 50% of the cases and is usually to the bones, lymph nodes and lungs. 60% of patients are male.

Histologically infrequent occurrence of clear cell sarcoma in the general population leads to the erroneous diagnosis of metastatic melanoma particularly when the lesion is localized to the vicinity of the lymphatic plexus. There is why it is called malignant melanoma of the soft parts.

There is tendency for local recurrence and metastatic spread.

FURTHER READING:

1.      L.H. De Beuckeleer A.M. De Schepper J.E. Vandevenne et al. MR imaging of clear cell sarcoma (malignant melanoma of the soft parts): a multicenter correlative MRI-pathology study of 21 cases and literature review, Skeletal Radiol (2000) 29:187–195.

2.      Kransdorf MJ, Murphey MD. Neurogenic tumors. In: Kransdorf MJ, Murphey M, eds. Imaging of soft tissue tumors. Philadelphia: WB Saunders,1997: 255–273.

3.      Schnarkowski P, Peterfy CG, Johnston JO, Weidner N. Clear cell sarcoma mimicking peripheral nerve sheath tumor. Skeletal Radiol 1996; 25: 197–200