Fibrous tumors

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Chapter 20

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

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.

Fig 20-10 Juvenile hyaline fibromatosis

Juvenile hyaline fibromatosis

Key features

• Autosomal recessive

• Nodular skin lesions of the hands, scalp, ears, and central face

• Gingival hypertrophy

• Joint contractures and osteopenia

• Nodular hyaline fibrosis in the dermis

• Linked to CMG2 or ANTXR2 mutations (gene encoding capillary morphogenesis protein-2 on chromosome 4q21)

Scar

Key features

• Fibroblasts with east–west orientation

• Blood vessels with north–south orientation

• Loss of elastic tissue (see Chapter 13)

Fig 20-11 Scar

Hypertrophic scar

Key features

• Whorled proliferation of fibroblasts and blood vessels

Keloid

Key features

• Whorled proliferation of fibroblasts and blood vessels

• Central bundles of amorphous “bubble gum” collagen

Fibrous hamartoma of infancy

Key features

• Disorderly growth of benign tissues

• Myxoid areas, mature fibrous areas, and fat

• Organoid (compartmentalized) appearance

• Surrounding skin has features of “kid” skin

A young child’s skin (“kid” skin) is characterized by delicate collagen bundles that stain deeply red. Many fibroblast nuclei are present. Lipocytes and adnexal structures tend to be small.

Fig 20-12 Hypertrophic scar

Fig 20-13 Keloid

Fig 20-14 Fibrous hamartoma of infancy

Infantile digital fibroma (inclusion body fibroma)

Key features

• Acral skin

• Criss-cross fascicles

• Spindle cells with red inclusion bodies

Infantile digital fibroma is also called recurrent infantile digital fibroma or aggressive digital fibromatosis. It is benign, but often extends deeply and has a high recurrence rate after excision. The inclusions stain purple with phosphotungstic acid hematoxylin (PTAH) and red with both H&E and Masson’s trichrome. They are actin positive.

Giant cell tumor of the tendon sheath

Key features

• Osteoclast-like giant cells

• Plump fibroblasts

• Focal dense collagen

• Hemosiderin pigment common

Fig 20-15 Infantile digital fibroma

Fig 20-16 Giant cell tumor of tendon sheath

Osteoclast-like giant cells have randomly distributed nuclei. The cytoplasm stains deeply pink to amphophilic and has scalloped edges where the cell exhibits molding against adjoining tissue.

Fibroma of tendon sheath

Key features

• Giant cell tumor of tendon sheath without the giant cells

• Characteristic plump fibroblasts often present

Elastofibroma dorsi

Key features

• Large fibrous tumor

• Elastin deposits throughout tumor

• Beaded elastic fibers

Fig 20-17 Fibroma of tendon sheath

As the name implies, elastofibroma dorsi is typically found on the back.

Sclerotic fibroma

Key features

• Collagen pattern resembles van Gogh’s “Starry night”

• Hypocellular

• May be a marker for Cowden’s syndrome

Because of the association with Cowden’s syndrome, sclerotic fibromas should be considered a distinct entity. Similar hypocellular areas have been seen in other fibrous tumors, especially dermatofibromas.

Fig 20-18 Elastofibroma dorsi, D Verhoeff-van Gieson

Fig 20-19 Sclerotic fibroma

Pleomorphic fibroma

Key features

• Scattered large hyperchromatic stellate nuclei

• Never hypercellular

• No mitoses

Despite the large hyperchromatic nuclei, pleomorphic fibromas are benign. They are peppered with hyperchromatic stellate nuclei that resemble the stellate nuclei in fibrous papules. Although the stellate cells resemble those of a fibrous papule, they are usually CD34 positive. Multinucleated cells may be present, but mitoses are absent. Tumors with overlapping features of sclerotic and pleomorphic fibroma have been described.

Sclerosing perineurioma

Key features

• Whorled, nodular, or storiform appearance

• Epithelial membrane antigen+

Angiofibromas

Key features

• Concentric perivascular fibrosis

• Stellate, factor XIIIa+ stromal cells

Fig 20-20 Pleomorphic fibroma

Fig 20-21 Sclerosing perineurioma

In tuberous sclerosis, we call them adenoma sebaceum or Koenen’s periungual fibromas. Multiple angiofibromas may also be seen in multiple endocrine neoplasia type I (MEN 1) and in type II neurofibromatosis.

On the face, we refer to the most common variant of solitary angiofibroma as fibrous papule of the face. On the penis, we call them pearly penile papules. Acquired digital fibrokeratoma is a closely related lesion.

Fibrous papule of the face (benign fibrous papule, solitary angiofibroma)

Key features

• Common variant of angiofibroma

• Concentric perivascular fibrosis

• Stellate, factor XIIIa+ stromal cells

• Large pyramid-shaped melanocytes may be present at the dermal–epidermal junction

Fig 20-22 Angiofibroma

Fig 20-23 Fibrous papule of the face

Fig 20-24 Acquired digital fibrokeratoma

A superficial shave biopsy of a fibrous papule may suggest a melanocytic lesion, because of the large melanocytes at the dermal–epidermal junction. Before the advent of immunostains, the stellate dermal cells were thought to be degenerated melanocytes.

Acquired digital fibrokeratoma

Key features

• Acral skin

• Hyperkeratosis, acanthosis, hypergranulosis

• Spindle cells and collagen often perpendicular to the surrounding skin surface

• Stellate, factor XIIIa+ stromal cells may be present

Nodular fasciitis

Key features

• “Tissue culture” fibroblasts

• Erythrocyte extravasation

• Loose myxoid pattern

• Foci of inflammatory cells

Fig 20-25 Nodular fasciitis

With time, nodular fasciitis develops thick red collagen bundles, but young lesions appear loose and myxoid, with erythrocyte extravasation and nodular aggregates of inflammatory cells. The stellate fibroblasts look like those in tissue culture.

Cranial fasciitis

Key features

• Variant of nodular fasciitis that occurs on the head of a child

Proliferative fasciitis

Key features

• Variant of nodular fasciitis

• Ganglion-like giant cells

• Collagen trapping at periphery

Calcifying aponeurotic fibroma

Key features

• Plump, epithelioid fibroblasts palisading around chondroid foci with or without calcification, occasionally with osteoclast-like cells

• Distal extremities

• Commonly found in children and adolescents

Fig 20-26 Proliferative fasciitis

Fig 20-27 Calcifying aponeurotic fibroma

Borderline tumors

Desmoid tumor (aggressive fibromatosis)

Key features

• Myofibroblastic proliferation

• Bland nuclei

• Tendency for deep infiltration and recurrence

• Beta catenin expressed

• Most are sporadic but can be associated with Gardner’s syndrome

Fig 20-28 Desmoid tumor

Fig 20-29 Plexiform fibrohistiocytic tumor

Plexiform fibrohistiocytic tumor

Key features

• Plexiform fascicles of myofibroblast-like fusiform and spindle cells

• Nodules of histiocytic cells and osteoclast-like giant cells (biphasic tumor)

• Variable pleomorphism and mitotic rate

Plexiform fibrohistiocytic tumor is a tumor of intermediate malignant behavior that occurs in children and young adults. It commonly involves an arm.

Malignant tumors

Dermatofibrosarcoma protuberans (DFSP)

Key features

• Densely hypercellular

• Storiform (woven) pattern

• Infiltrates fat in a honeycomb pattern

• Forms fibrous layers in the fat, parallel to the surface epidermis

• Epidermal rete pattern usually effaced

• CD34+, factor XIIIa−

Dermatofibrosarcoma protuberans infiltrates the fat in a honeycomb pattern. As the tumor progresses, parallel layers of tumor form in the fat, like a layer cake with lipocytes (frosting) in between the layers. The nuclei appear as dark spindle cells when cut across, and as pale gray oval nuclei when cut en face. Chromosomal translocations, especially t(17;22) sometimes present. A pigmented dermatofibrosarcoma protuberans is referred to as a Bednar tumor.

Pearl

Occasionally, overlying acanthosis and collagen trapping may be present in a dermatofibrosarcoma protuberans. If the tumor is densely hypercellular and infiltrates fat, CD34 staining should be performed.