A Clinicopathologic Study of 45 Pediatric Soft Tissue Tumors With an Admixture of Adipose Tissue and Fibroblastic Elements, and a Proposal for Classification as Lipofibromatosis

Abstract

The tumor described here as lipofibromatosis is a rare pediatric neoplasm that has been variously interpreted as a type of infantile or juvenile fibromatosis, a variant of fibrous hamartoma of infancy, and a fibrosing lipoblastoma. This report details the clinicopathologic features associated with 45 cases of this soft tissue entity. The study group consisted of 32 males, 12 females, and one person of unstated gender. The patients presented with a soft tissue mass (range, 1-7 cm) involving the hand (n = 18), arm (n = 8), leg (n = 7), foot (n = 6), trunk (n = 5), or head (n = 1). Eight tumors were evident at birth. The individuals ranged in age from 11 days to 12 years (median age, 1 yr) at the time of initial biopsy or resection. Microscopic examination revealed abundant adipose tissue with a spindled fibroblastic element that chiefly involved the septa of fat and skeletal muscle. The process generally did not cause extensive architectural effacement of fat as is common with conventional fibromatoses, and it did not have a primitive nodular fibromyxoid component as is characteristic of fibrous hamartoma of infancy. The fibroblastic element exhibited focal fascicular growth and typically had limited mitotic activity (< or = 1 mitosis/ 10 high-power fields) and cytologic atypia. Oftentimes, small collections of univacuolated cells were present at the interface between some of the fibroblastic fascicles and the mature adipocytes. The tumors entrapped vessels (n = 45), nerves (n = 44), skin adnexa (n = 16), and skeletal muscle (n = 18). Focal immunoreactivity was present in some tumors for CD99, CD34, alpha-smooth muscle actin, BCL-2, and less frequently, S-100 protein, muscle actin (HUC 1-1), and EMA. However, no reactivity was detected for desmin (D33 and D-ER- 1 clones), keratins, or CD57. Follow-up data were available for 25 individuals (median follow-up period, 6 yrs 7 mos) with regrowth of the tumor or persistent disease documented in 17 (72%). The following events were more common in the group with recurrent or persistent disease: congenital onset, male sex, hand and foot location, incomplete excision, and mitotic activity in the fibroblastic element. Although it is likely this tumor comprises part of the spectrum of what has been referred to in the literature as infantile/juvenile fibromatosis, its clinicopathologic features and, in particular, its distinctive tendency to contain fat as an integral component, warrant separate classification as a "lipofibromatosis."

Soft Tissue Ankle Mass in a 15-month-old Girl

“…Lipofibromatosis is a rare pediatric tumor described by Fetsch et al in 2000 [5]. Since then, several case reports have been published.…”

“…However, Fetsch et al differentiated between infantile fibromatosis and lipofibromatosis by noting that the former had a more ''sheet-like'' pattern of growth and did not contain fat as an integral element. In addition, the anatomic location differs between the lesions, with fibromatosis more likely involving the head and neck [5]. Lipofibromatosis typically presents as an ill-defined, slowly growing, painless mass most commonly manifesting in the hands and feet.…”

Lipofibromatosis Arising in a Pediatric Forearm

“…The ages ranged from 11 days to 12 years (median age, 1 year) at the time of initial biopsy or resection. There was a more than 2:1 male predominance [1,3].…”

“…Lipofibromatosis is a rare pediatric tumour described by Fetsch et al in 2000 [1]. Since then, there have been few reports about this tumour and few descriptions of its image findings.…”

Fibromatosis in a Young Bernese Mountain Dog: Clinical, Imaging, and Histopathological Findings

“…The appearance of the cells range from primitive mesenchymal cells to fibroblasts. 8 Desmoid-type infantile fibromatosis is less common and is characterized by low cellularity, mature fibroblasts, and increased collagen bundles. 22,26 The histologic findings in the present case were compatible with desmoid-type infantile fibromatosis.…”