A Clinical and Histopathological Study of 122 Cases of Dermatofibroma (Benign Fibrous Histiocytoma)

Dermatofibroma (benign fibrous histiocytoma) is a common skin lesion and it accounts for approximately 3% of the skin lesion specimens received by one dermatopathology laboratory1. There is a predilection for dermatofibroma to develop on the extremities, and particularly on the lower extremities of young adults. There is a female preponderance amongst the patients with dermatofibroma1. Dermatofibroma is round or ovoid, firm, dermal nodules and they are usually <1 cm in diameter2. The diagnosis is usually straightforward if the classical clinical and pathologic features are evident. However, many variants of dermatofibromas have been described, and knowledge of these variations is important to avoid a misdiagnosis of a possibly more aggressive tumor. The main histologic variants include fibrocollagenous, cellular3, histiocytic4, lipidized5, angiomatous6, aneurysmal7, clear cell8, monster cell9, myxoid10, keloidal11, palisading12, osteoclastic13 and epithelioid dermatofibroma14. There are no prior Korean reports regarding the detailed classification of the histologic features of dermatofibromas. Therefore, we report here on a series of 122 cases of dermatofibroma and we discuss the clinical and histopathologic features.

We performed a retrospective review of the medical records and 122 biopsy specimens of 92 patients who were diagnosed with dermatofibroma in the Department of Dermatology at Eulji Hospital of Eulji University between January 2000 and March 2010.

Dermatofibroma is one of the most common types of benign, cutaneous, soft tissue tumors. Dermatofibroma is most often found in the middle-aged adults and it has a slight female predominance. The majority of lesions are located on the limbs or the trunk, and they present as small, raised, hyperkeratotic, cutaneous nodules <1 cm in diameter with a red-brown surface. A significant proportion of cases are associated with minor local trauma, and especially insect bites15. The lesions are most often solitary, but 2~5 lesions are present in approximately 10% of individuals4. In the current study, most of the clinical characteristic features were consistent with those of the previous reports16, 17.

The results showed that most tumors presented at between 20 and 49 years of age with an overall predominance of females. Over 70% of the cases occurred on the extremities, and they appeared dusky brown in color with a smooth surface. However, unlike the previous reports, the most common diameter in our study was 1~2 cm (48.4%). Indeed, prior Korean studies have reported the most common diameter to be 1~5 mm16, 17. Only 3 cases of the tumor occurred at sites of insect bites and most of the tumors were asymptomatic (58.2%). In addition, more than 2 lesions were present in 14.7% of the patients.

Histopathologically, dermatofibroma is composed of a variable mixture of fibroblast-like cells, histiocytes (some of which may be xanthomatous or multinucleate) and blood vessels. The term 'nodular subepidermal fibrosis,' 'histiocytoma' and 'sclerosing hemangioma' have been used in the past for variants in which one of the three components predominated. The lesions are currently referred to as the fibrocollagenous, histiocytic, and aneurysmal variants to reflect the difference in composition18. In addition, numerous other variants have recently been described. The 122 cases of dermatofibromas were classified into variants according to the dominant pathologic features. The most common variant was a fibrocollagenous dermatofibroma (40.1%). The other variants included histiocytic (13.1%), cellular (11.5%), aneurysmal (7.4%), angiomatous (6.5%), sclerotic (6.5%), monster (4.9%), palisading (1.6%) and keloidal dermatofibroma (0.8%), in decreasing frequency. In addition, the tumors that occurred simultaneously in one patient tended to have similar histologic features.

The fibrocollagenous type of dermatofibroma has a predominance of collagen and fibroblast-like cells in an irregular or whorled arrangement18. One variant of the fibrocollagenous type, the 'palisading dermatofibroma,' has nuclear palisading and prominent verocay-like bodies in part of the lesion12. The cases with a prominent storiform pattern are referred to as cellular dermatofibroma3. The histiocytic variant has nests and sheets of histiocytes in a poorly cellular collagenous stroma. There are often many foam cells and giant cells, which may be the foreign body or touton type. Hemosiderin and lipid are commonly present4. In the angiomatous (vascular variant) type, there are numerous small branching vessels in a variable collagenous stroma6. The aneurysmal variant is distinct, with blood-filled spaces occupying up to one-half of the lesion. The vascular channels are surrounded by histiocytes that contain hemosiderin, foam cells and fibroblasts7. In addition, large, bizarre cells with abundant foamy cytoplasm and hyperchromatic nuclei have been reported in some dermatofibromas. These 'monster cells' can be binucleated or multinucleated9. Two other rare variants are the keloidal dermatofibroma with areas of thick eosinophilic collagen, and the sclerotic dermatofibroma with areas of sclerosis11, 19.

Dermatofibroma is a poorly demarcated tumor centered on the dermis. There is sometimes extension into the superficial subcutis, which may take the form of a septal extension or a well-demarcated bulge20. A pure subcutaneous form is exceedingly rare21. The results of the current study showed that 39.3% of the cases invade the subcutis and 3.3% of the cases invade the deep subcutis. Greater than one-half of the cases of the cellular (50%), aneurysmal (77.8%) and monster types (66.7%) had invaded the subcutaneous tissue. In addition, the aneurysmal type was statistically significant with respect to the depth of invasion (p<0.05). There were no cases with the pure subcutaneous form of a dermatofibroma.

Dermatofibromas, including the variants, may be associated with acanthosis or hyperplasia of the overlying epidermis and hyperpigmentation of the basal layer22. It has been suggested that epidermal growth factor may play a role in the pathogenesis of the epidermal hyperplasia23. In the current study, the aneurysmal type of dermatofibroma had a lower frequency of acanthosis (33.3%) and the cellular type of dermatofibroma had a lower frequency of basal pigmentation (42.9%; p<0.05). However, there were no specific subtype differences from the other subtypes according to the presence of the grenz zone. Other histologic changes observed with dermatofibroma include the presence of lymphoid nodules and mucin deposition10, 24. The presence of lymphoid nodules at the dermo-subcutaneous junction was observed in 9.8% of the cases in our study, and mucin deposition was noted in 18.9% of the cases. Lymphoid nodules were observed in 16.3% of the cases of the fibrocollagenous type of dermatofibroma (p<0.05).

The results of the current study are consistent with the previous reports on the clinical features of dermatofibroma. However, we observed several characteristic subtypes of dermatofibromas and we compared the frequency of the histologic subtypes. We assume the reason why most of the statistical results were nonsignificant was the small sample size in our study. Consequently, we suggest that a larger study or a multicenter-based study is needed to identify more subtypes, such as osteoclastic and epithelioid dermatofibroma, and to more accurately analyze the correlation between the subtypes and clinical/histologic features.