Recurring atypical (“pseudosarcomatous”) cutaneous fibrous histiocytoma

ARTICLE

Atypical ("pseudosarcomatous"), cutaneous, fibrous histiocytoma (ACFH) is a variant of benign, fibrous histiocytoma first reported by Fukamizu et al. in 1983 [1]. Rarely reported, this neoplasm is also known as dermatofibroma with "monster" cells [2]. We report an observation of recurring ACFH and review the main clinicopathological features of this tumor. The main differential diagnoses are discussed.

Case report

Clinical history

In October 1991, a 25-year-old woman presented with a 2.5 cm wide nodule on the front upper portion of the left leg. The lesion was incompletely resected. The patient refused further excision and follow-up.

In March 1993, she developed a blue, 4.5 cm wide recurrence on her scar which had developed over 6 months (Fig. 1). There was no palpable, peripheral lymphadenopathy. Magnetic resonance imaging of the left leg showed no muscle or bone invasion. Routine blood chemistry, chest X-ray and abdominal ultrasonography were normal. A surgically-enlarged excision of the lesion was performed. Additional radiotherapy (60 grays) was performed on the left leg. Four years later the patient had experienced no further recurrence.

Histopathology

The first excision (October 1991), showed, a dense dermal proliferation with numerous vascular cavities (Fig. 2) under an acanthotic epidermis. It was mainly composed of histiocyte-like cells and spindle cells. The cytoplasm of some large histiocyte-like cells contained lipid droplet inclusions or brown pigment. Some nuclei were atypical with large and hyperchromatic features including prominent nucleoli. Mitoses were identified (4/10 high power fields) (Fig. 3).

Examination of the recurring mass (March 1993), revealed a dermal, non-encapsulated tumor which was separated from a hyperplastic epidermis by a Grenz zone and which slighty invaded the hypodermis. Cellularity was the same as in the first excision. Immunohistochemical study showed a positivity in the cytoplasm of the spindle cells for vimentin and of the histiocyte-like cells for KP1 (CD68) (Fig. 4). Cytokeratin, S100 protein, desmin, actin, factor VIII and XIIIa were negative.

These findings were consistent with a diagnosis of ACFH.

Discussion

ACFH is a rarely reported lesion [1-5]. Beham and Fletcher found a 2% incidence among 376 cases of benign, cutaneous, fibrous histiocytoma [3]. Clinically, ACFH is a solitary nodule occurring on the trunk and limbs. Tumor size ranges between 0.5 and 3 cm. Light microscopy examination reveals a dermal and hypodermal, moderately circumscribed tumour which is occasionaly separated from an acanthotic epidermis by a Grenz zone. ACFH is composed of single and multinucleated histiocytes and fibroblasts with numerous capillaries. This neoplasm is also characterized by the presence of "monster" cells often having foamy cytoplasm or yellow-brown pigment. The term "monster" implies an atypical cell with a large hyperchromatic nucleus including one or more prominent nucleoli [2]. The extent of cellular atypia is variable and can represent more than 50% of the tumour bulk. Mitotic activity is low. Lymphocytic infiltration is occasionally present [4]. Immunoreactivity for KP1 and vimentin suggests a histiofibroblastic origin for this tumour.

The main differential diagnosis which must be discussed is atypical fibroxanthoma (AFX). Its typical presentation is an ulcerated nodule that arises on actinically damaged skin of the head or neck in the elderly (mean age 69 years). Histogically, pleomorphism is very marked with numerous atypical mitoses throughout the dermal lesion. The epidermis is ulcerated or atrophic [6]. However, a separate group was identified including younger adults whose lesions were located on the trunk or limbs [7, 8]. However, some authors consider that the clinicopathological features of these cases of so-called AFX indicate ACFH [3, 4]. The evolution of AFX is often benign after surgical treatment. Metastases are exceptional [7, 9-12].

In our case, owing to the existence of many vascular cavities, we discussed the diagnoses of aneurysmal fibrous histiocytoma (AH) and angiomatoid malignant fibrous histiocytoma (AMH). AH has no atypia or infiltration of the hypodermis, which precludes such a diagnosis [13]. AMH is excluded by the absence of a peripheral, dense pseudocapsule and prominent lymphoid cuff [14].

The possibility of sarcomatoid variants of malignant melanoma and squamous cell carcinoma is eliminated by the negativity of immunostaining for S100 protein and cytokeratin respectively.

As far as the treatment of ACFH is concerned, wide excision is indicated. Local recurrences, despite apparently complete resection, have been reported [5]. Protracted, postoperative follow-up is mandatory. Owing to the extent of recurrence, our patient received local radiotherapy.

CONCLUSION

ACFH is a rare, benign tumour which must be histogically well classified so that the condition is not confused with malignant, connective tissue tumors.

REFERENCES

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