Age / Sex : 51 / M

Age / Sex : 34 / F

Chief complaint : Protruding mass on the right shoulder for 5 months

dermatofibrosarcoma protuberans

Discussion

Differential diagnosis:

Melanoma

Lymphoma

Metastatic disease

Sarcoid

Liposarcoma

Malignant fibrous histiocytoma

Granular cell tumor

Mycosis fungoides

Findings:

There is a 2.5 cm in size, well defined protuberant mass involving the skin and subcutaneous tissue of the posterior shoulder. The mass has iso signal to muscle on T1-weighted image, high signal on fat-suppressed T2-weighted fast spin echo image and intermediate signal on proton-weighted image with linear extension along the adjacent skin surface. After contrast injection, the mass shows homogeneous enhancement.

Discussion:

Dermatofibrosarcoma protuberans (DFSP) constitutes 6 % of all soft tissue sarcomas. It is associated with the chromosomal translocation t(17:22). Men are affected more frequently than women. It usually occurs in the third to fifth decade of life, although there are increasing reports of pediatric involvement. The clinical presentation is a slowly growing, reddish-brown to bluish, firm, superficial nodule fixed to the skin. The tumor originates in the dermis. Lesions may be multiple, and small nodules may coalesce to form a plaque. Large lesions may invade underlying structures, ulcerate, bleed, or become painful. Lesions most frequently involve the trunk (50%) and proximal upper and lower extremities (35 to 40%), followed by the head and neck (14%).

The radiographic appearance of DFSP is typically nodular soft tissue mass involving the skin and subcutaneous adipose tissue. The lesion also causes focal protuberance of the skin. CT or MR images are well suited to demonstrate this location and the distinct nodular or lobular architecture. The intrinsic signal intensity of the lesion on MR imaging is nonspecific (signal intensity similar to that of skeletal muscle on T1-weighted images and similar to or greater than that of fat on T2-weighted images). Fat-suppressed T2-weighted or STIR sequences typically reveal high signal intensity. Imaging may show heterogeneity compatible with hemorrhage and/or necrosis. Satellite nodules in the adjacent subcutaneous tissues may be seen on CT or MR imaging. Linear extensions along the skin surface can also be detected on long TR images. The hypervascularity is likely responsible for the moderate enhancement on CT or MR images after contrast injection. While the imaging features are not pathognomonic of the tumor, the characteristic location and shape should prompt inclusion in the differential diagnostic list.

Typical histologic features include spindle-shaped cells arranged in a storiform pattern on a background of fibrous stroma. Areas of higher grade sarcoma (more commonly fibrosarcoma) may be superimposed on conventional DFSP. Fibrosarcoma areas may be focally necrotic also.  

Treatment involves wide local excision with a margin of as least 3 cm and en bloc removal of the underlying subcutaneous tissue and fascia. Local recurrence is common (20 to 55%). MR imaging may be performed to monitor tumor recurrence. Metastases are rare, usually found in the lung.

References:

1. Torreggiani WC, Al-Ismail K, Munk PL, Nicolaou S, O'Connell JX, Knowling MA. Dermatofibrosarcoma protuberans: MR imaging features. AJR Am J Roentgenol. 2002;178(4):989-993

2.  Kransdorf MJ, Meis-Kindblom JM. Dermatofibrosarcoma protuberans: radiologic appearance. AJR Am J Roentgenol 1994;163:391-394

3.  Kransdorf MJ, Murphey MD. Malignant fibrous and fibrohistiocytic tumors. In: imaging of soft tissue tumors. 2^nd ed. Philadelphia, W.B. Saunders;2006:257-297

4.  Ono I, kaneko F. Magnetic resonance imaging for diagnosing skin tumors. Clin Dermatol  1995;13:393-399