Infantile Fibromatosis

Infantile fibromatosis, originally described by Stout in 1954, seems to be genetic in origin although the mode of transmission is not clear. It refers to a family of soft tissue lesions characterized by proliferation of benign fibrous tissue, which is composed of uniform, elongated, fusiform, or spindle shaped cells surrounded and separated by abundant collagen. According to Enzinger and Weiss, they are classified into superficial and deep fibromatosis. Superficial tumors are usually purplish red as a result of intense vascularity. The intraabdominal organ involvement is also known which carries worse prognosis.

Fibromatosis is a group of related conditions having following common features; proliferation of well differentiated fibroblasts, infiltrative pattern of growth, presence of variable amount of collagen between the proliferating cells, lack of cytological features of malignancy and scanty or absent mitotic activity, aggressive clinical behavior characterized by repeated local recurrences but lack of capacity to metastasize distantly.

In infantile fibromatosis, the Characteristic feature is the presence of small, round intracytoplasmic inclusions. They are periodic acid- Schiff (PAS) negative and they apparently consist of actin filaments⁷. Morphologically, these lesions occur as unicentric gray white, firm poorly demarcated masses varying from 1 to 15 cm in greatest dimension.

Although histologically benign, this lesion tends to gradually infiltrate in skin subcutaneous tissue, muscles, nerves, blood vessels and even bone. They are rubbery, & tough. Clinically the presentation is of a slow-growing, firm, poorly circumscribed mass. Diagnosis is usually made histologically. The lack of malignant cells on histology differentiates infantile fibromatosis from infantile fibrosarcoma. It usually occurs in the anterior abdominal wall, buttocks, shoulder, upper arm and the head & neck. The scrotum & external genitalia are rare sites.

The progression is unpredictable. Wide local excision can provide cure if excision is complete with an adequate resection margin but this may be difficult due to infiltrative nature. Local recurrence occur usually within 18 months of original surgery. Wide local excision is the treatment of choice. Imaging is required for surgical planning. Radiographic examination reveals a soft tissue mass, usually noncalcified. CT appearances are nonspecific; MRI is the best modality for diagnosis & follow-up, specifically in deep fibromatosis.

The primary goal of treatment for fibromatosis is complete surgical resection to achieve negative margins. The management of children with unresectable or recurrent fibromatosis requires a multidisciplinary approach. Nonaggressive therapy with tamoxifen and diclofenac may be the first treatment choice in these patients, but in patients with progressive disease, cytotoxic chemotherapy is indicated. Weekly administration of vinblastine and methotrexate seems to be safe and effective in these children.