Collagenous Fibroma (Desmoplastic Fibroblastoma) of the Shoulder

Abstract

AJR:183, December 2004 52-year-old woman presented with a palpable mass in her right shoulder. Findings of radiography of the humerus were normal. MRI revealed a solid 5.5 × 1.8 × 1.8 cm soft-tissue mass deep relative to the deltoid muscle with low signal intensity on both T1and T2-weighted pulse sequences (Figs. 1A and 1B). An excisional biopsy was performed, revealing a firm encapsulated mass. Histologic findings were consistent with a collagenous fibroma (desmoplastic fibroblastoma) (Fig. 1C). Desmoplastic fibroblastoma (collagenous fibroma) is a benign fibrous tumor that occurs most often in patients during the fifth and sixth decades of life with a male–female ratio of 5:1. Clinically, desmoplastic fibroblastoma presents as a firm mobile painless slowly growing mass located in the subcutaneous tissues or just deep relative to skeletal muscle. Fascial and muscle involvement are common. This entity has been reported in the arm, shoulder, posterior neck, upper back, abdominal wall, and hip joint. Size ranges have been reported from 1 to 20 cm. Histologically, these hypocellular tumors consist of stellate and spindle-shaped fibroblastlike cells that are widely separated by a collagenous to fibromyxoid matrix. Only a few case reports describe the MRI features of this tumor [1–3]. On MRI, the lesion has low signal on both T1-weighted and T2-weighted pulse sequences. The low signal intensity is attributed to the low cellularity of the mass in a background of abundant collagen [1]. It is important to distinguish a desmoplastic fibroblastoma from other potential causes of low T2 signal in a soft-tissue mass to assist with clinical management. Most soft-tissue masses have high signal intensity on T2-weighted images. Soft-tissue masses with low signal on T2-weighted images include neurofibroma, cicatricial fibroma, malignant fibrous histiocytoma, aggressive fibromatosis, and calcified masses (myositis ossificans, extraskeletal osteosarcoma or chondrosarcoma, and synovial sarcoma). In the absence of calcification, abundant collagen and marked hypocellularity in a soft-tissue tumor result in a decreased signal on T2-weighted pulse sequence [4]. Treatment of desmoplastic fibroblastoma is surgical excision with no reported incidence of local recurrence or metastases.