Fibrous tumors

Dirk M. Elston

Many additional entities are included in the on-line atlas of fibrous and soft tissue tumors that accompanies this book.

Dermatofibroma

Key features

• Interstitial spindle cell proliferation

• Collagen trapping

• Overlying plate-like acanthosis

• Follicular induction common

• Ringed lipidized siderophages may be present

• Factor XIIIa+

• CD34−

All dermatofibromas demonstrate a proliferation of fibrohistiocytic cells. A curlicue pattern is typical. Another typical feature is that some areas of the tumor will be densely cellular, while others are sclerotic and hypocellular. The overlying epidermis is acanthotic and often demonstrates primitive follicular germs or sebaceous follicles. At the periphery of the tumor, collagen trapping (collagen balls) can be seen. The tumor may extend into the superficial fat in a lacy pattern.

When present, ringed lipidized siderophages are pathognomonic for dermatofibroma. These cells are like Touton giant cells with hemosiderin. They have central pink cytoplasm surrounded by a wreath of nuclei. There is both lipid and hemosiderin peripheral to the ring of nuclei.

Immunostaining can be helpful to separate cellular dermatofibromas from dermatofibrosarcoma protuberans. Large stellate cells within a dermatofibroma stain for factor XIIIa. The surrounding stroma will stain for CD34, but the central tumor is negative (except for endothelial cells).

Differential Diagnosis

• Densely cellular tumors are suspicious for dermatofibrosarcoma protuberans, even if overlying acanthosis and collagen trapping are present. CD34 and factor XIIIa staining should be performed

• Long fascicles of parallel nuclei suggest a melanocytic tumor. Nodular lymphoid aggregates suggest desmoplastic malignant melanoma. S100 staining should be performed

• Corkscrew nuclei running parallel to the epidermis suggest a dermatomyofibroma

Pearls

• Factor XIIIa is positive in dermatofibromas, fibrous papules of the face, angiofibromas, acquired digital fibrokeratomas, and pleomorphic undifferentiated sarcoma

• CD34 is positive in dermatofibrosarcoma protuberans, pleomorphic fibromas, sclerotic fibroma, spindle cell lipoma, and nephrogenic systemic fibrosis

• CD34 expression is lost in morphea

Fig 20-1 Dermatofibroma

Adult myofibroma

Key features

• Nodules with blue centers

• Myofibroblasts

• Peripheral fibrovascular proliferation

Fig 20-4 Dermatofibroma with monster cells

Fig 20-5 Adult myofibroma

The shade of blue in the center of the nodule resembles that of cartilage. The peripheral vascular proliferation may have staghorn vessels and resemble hemangiopericytoma.

Dermatomyofibroma

Key features

• Plaque-like tumor

• Spindle cells with east–west orientation

• Proliferation “respects” adnexal structures

• Corkscrew appearance of some myofibroblast nuclei

• Thick elastic fibers visible with Verhoeff–van Gieson stain

At scanning magnification, the most striking features of a dermatomyofibroma are the horizontal orientation of the spindle cell nuclei and the pattern of the proliferation with respect to the adnexal structures, especially hair follicles. The follicles are normal in appearance, and the proliferation extends up to each follicle, then continues on the other side without any displacement of the follicle.

Fig 20-6 Dermatomyofibroma. (d) Elastic stain or Verhoeff-van Gieson

Fibromatosis

Key features

• Myofibroblastic proliferation

• Locally infiltrative, but does not metastasize

• Corkscrew-shaped myofibroblasts

The fibromatoses include Dupuytren’s (hand) contracture, Peyronie’s (penis) disease and Ledderhose (foot) plantar fibromatosis. All forms demonstrate corkscrew-shaped myofibroblasts and collagen. Ledderhose disease tends to form large whorled nodules.

Fig 20-7 Dupuytren’s contracture

Fig 20-8 Ledderhose disease

Infantile myofibromatosis

Key features

• Myofibroblastic proliferation

• Locally infiltrative, but does not metastasize

• Corkscrew-shaped myofibroblasts

Fig 20-9 Infantile myofibromatosis

There is a tendency towards spontaneous regression. Superficial disease has an excellent prognosis. Visceral involvement may be fatal in some cases. In one series, more than half of the lesions were present at or soon after birth, approximately 80% were solitary, and 50% involved the head and neck. In the early stage, undifferentiated immature histiocytic cells may predominate. As the lesion matures, they develop characteristics of myofibroblasts. Regressing lesions become progressively less cellular and more fibrous.