To our knowledge, this is the first comprehensive study in Korea describing the clinicopathologic features and follow-up results of patients diagnosed with FH at a single institution over 13 years. This lesion was first reported by Reye [
8] in 1956 as subdermal fibromatous tumor of infancy, and the current term was later coined by Enzinger [
3] in 1965. FHs are histologically characterized by an organoid mixture of 3 components: well-defined intersecting trabeculae of fibrocollagenous tissue; loosely textured areas of immature-appearing, small, rounded, primitive mesenchymal cells; and mature fat. In some cases, a pronounced sclerosing process replaces the majority of the lesion [
3].
FHs can be found in a variety of anatomical locations, although the principal sites are the axilla, shoulder, upper arm, back and groin. Cases involving the scalp, scrotum, perianal area and lower extremities have been also described [
3,
9-
13]. The most common site in this study was the lower back and gluteal region. Like other fibrous tumors in children, this lesion is more common in boys, but there is no evidence of familial tendency [
3,
9]. FH has been reported in an infant and a 4-year-old boy with desmoids-type fibromatosis and tuberous sclerosis (TS), respectively [
5,
14]. The genetic tendency for TS to give rise to hamartomas might explain the coexistence with FH, but more detailed studies are needed to prove a genetic link between FH and TS [
14]. A reciprocal translocation [t(2;3) (q31;q21)] was present in a previous report, and it is worthy of further study to determine whether chromosomal aberrations are related to its pathogenesis [
15]. The lesions were solitary in our series, but several cases of multiple nodules in the same patient have been described [
3,
16,
17]. Most FHs were less than 5 cm in diameter as described in the literature, and can reach up to larger than 10 cm [
7,
18]. They are usually firm, and may be affixed to the underlying tissue, thus causing the concern for malignancy [
7].
Despite its infiltrative growth and focal cellularity, the clinical course is benign [
5,
7,
18]. The treatment of choice for FH is complete excision with an envelope of normal tissue [
3,
7]. Although as many as 16% locally recur within a few months after primary excision, recurrences are non-destructive and cured by re-excision [
3-
5]. It was reported that the tumor capsule was developed in protracted and untreated FH. It continued to grow without regression, but delayed excision was not associated with an increased risk of postoperative complications [
18]. Clinical differential diagnosis includes a number of entities such as epidermal cyst, inclusion body fibromatosis, juvenile hyaline fibromatosis, palmoplantar fibromatosis, histiocytoma, dermatofibroma, leiomyosarcoma and fibrosarcoma [
12]. When the myofibroblastic areas predominate, the lesion may be difficult to distinguish from lipofibromatosis, infantile myofibromatosis and calcifying aponeurotic fibroma. However, the typical triphasic feature is readily recognized in most cases with sufficient sampling of the lesion. The overlying skin was grossly unremarkable, and was not sampled for histologic evaluation in such cases. However, eccrine changes, increased terminal hair follicles and epidermal basaloid follicular hyperplasia were frequently seen in previous reports, and these can be useful clues to consider a diagnosis of FH when the biopsy is superficial [
19,
20].
In conclusion, both the clinician and pathologist should be aware of this entity in order to avoid misdiagnosis of other fibromatosis and malignant tumor and unnecessary aggressive treatment.
Gee-Young Kwon, Suk-Koo Lee,1 and Jeong Meen Seo1
