(1)
Department of Pathology, University of Manitoba Max Rady College of Medicine, Winnipeg, MB, Canada
Keywords
Fibrohistiocytic lesionsFibrous histiocytomaNeurofibromaSolitary xanthogranulomaTenosynovial giant cell tumor
Fig. 6.1
(a) Spindle fibrous-like cells in a fibrous histiocytoma. (b) Histiocytic-appearing cells in a fibrous histiocytoma
6.1 Fibrous Histiocytoma
Fibrous histiocytoma, otherwise referred to as dermatofibroma , typically arises as a skin lesion in the extremities of adults between the second and fourth decades of life [2]. These clinically present as elevated and sometimes pigmented lesions that are usually less than 1 cm in diameter [3]. Approximately a third of affected patients can have multiple lesions, which have been reported to sometimes occur in patients who are immunosuppressed [4]. Rarely, benign fibrous histiocytomas can present as deeper lesions in the subcutaneous or soft tissue that are several centimeters in size [5]. These deep fibrous histiocytomas have been noted to occur at any age [6].
Pathology
Cutaneous fibrous histiocytomas are usually centered in the dermis and are composed of haphazardly arranged cells with fibrous and histiocytic features that percolate between dense sclerotic collagen fibers (Figs. 6.2 and 6.3). Scattered foamy histiocytes and multinucleated giant cells can be identified. There is typically only limited extension into the underlying subcutaneous adipose tissue [1].
Fig. 6.2
Cutaneous fibrous histiocytoma containing cells with a fibrohistiocytic appearance
Fig. 6.3
At the periphery of this fibrous histiocytoma , the cells percolate in between dense collagen fibers
The less frequent deep fibrous histiocytomas are more circumscribed. Microscopically, these neoplasms are typically cellular and can exhibit a more organized fascicular arrangement. Prominent branching vessels, similar to solitary fibrous tumor, can be identified (Fig. 6.4) [6].
Fig. 6.4
Deep fibrous histiocytoma with a branching vascular pattern
Histologic Variants
Ancillary Studies
Although neither sensitive nor specific, fibrous histiocytomas are often positive for Factor XIIIa and lack significant staining for CD34.
Differential Diagnosis
Dermatofibrosarcoma protuberans
Leiomyoma
Neurofibroma
Comments
- 1.
Fibrous histiocytoma can sometimes be difficult to distinguish from dermatofibrosarcoma protuberans, which is a more aggressive neoplasm.
- 2.
Dermatofibrosarcoma protuberans extensively infiltrates into the underlying subcutaneous adipose tissue.
- 3.
If the morphologic features are ambiguous, immunohistochemical stains for CD34 and Factor XIIIa can be helpful, as dermatofibrosarcoma protuberans is frequently strongly positive for CD34 and negative for Factor XIIIa.
- 4.
FISH studies can exclude dermatofibrosarcoma protuberans by confirming the absence of the COL1A-PDGFB fusion transcript.
- 5.
Fibrous histiocytoma can be confused with other dermal-based spindle cell lesions, such as neurofibroma or leiomyoma. Fibrous histiocytoma lacks the S100 or SOX-10 staining found in neurofibroma, or the desmin staining found in leiomyoma.
- 6.
Fibrous histiocytomas are benign neoplasms and are treated with conservative surgical resection. Once excised, they rarely recur [1].
- 7.
- 8.
Deep fibrous histiocytomas recur in approximately 20% of cases.
6.2 Solitary Xanthogranuloma
Solitary xanthogranuloma often occurs in children (sometimes referred to as juvenile xanthogranuloma ) but can also be seen in adults. These most commonly present as dermal lesions that frequently arise in the head and neck or trunk as skin papules. In occasional cases (particularly in very young children), patients can have multiple lesions arising on the skin and even organ involvement, such as the eye [9].
Pathology
Histologically, a solitary xanthogranuloma is composed of a dermal concentration of cells with eosinophilic or foamy cytoplasm that extends up to the epidermis and around associated adnexal structures (Fig. 6.7). Characteristic giant cells with peripherally arranged nuclei (Touton giant cells ) are present (Fig. 6.8). Associated inflammatory cells can also be identified [9, 10].
