Sclerotic fibroma was first described in association with Cowden's disease by Weary et al. in 1972.  In 1989, Rapini and Golitz described 11 cases of solitary sclerotic fibroma in the absence of Cowden's disease, suggesting the term 'solitary sclerotic fibroma' of the skin.

The terms hypocellular fibroma and circumscribed storiform collagenoma have also been used for this entity.

Gross:  They are small white or flesh-colored waxy papules ranging in size from 0.5 to 1.2 cm. Multiple lesions of this type have been reported in the multiple hamartoma syndrome (Cowden's disease).

Microscopic features:

   IMAGE1 ; IMAGE2 ;  IMAGE3

 These are well-circumscribed , unencapsulated dermal nodules  characterized by epidermal atrophy, a whorled appearance of sclerotic collagen bundles separated by clefts containing mucin, and sharp demarcation of the lesions from the surrounding normal skin.  The hyaline collagen bands are virtually acellular.

Immunohistochemistry: The tumour cells express CD34, vimentin and factor XIIIa, but are negative for markers of neural or melanocytic differentiation.  In some cases alpha-smooth-muscle actin positive myofibroblasts are present.

Differential Diagnosis : Sclerotic fibroma shares a common immunoprofile with Pleomorphic Fibroma (discussed later), but is distinct from dermatofibroma (Sclerotic variant of dermatofibroma) and other common spindle cell lesions of skin.

Variants:

Giant cell Collagenoma: Presents as solitary slow-growing flesh-coloured nodules in young and middle-aged adults.

Microscopic feature:  These lesions are characterized by sharply demarcated matrix consisting of coarse hyalinized collagen bundles arranged in a prominent storiform pattern and separated by mucin-containing clefts.  Admixed with the collagen matrix, there are two distinct cell populations -(i) spindle-shaped mononuclear cells, and (ii) bizarre multinucleated giant cells.  Atypical nuclei or mitotic figures are not present.

Immunohistochemistry:  Mononuclear cells expressed vimentin and actin HHF35. Multinucleated cells only expressed vimentin.  The cells are negative for cytokeratin,   desmin, S-100 protein, CD34, factor XIIIa, and the macrophage markers KP1, Mac 387.

Differential diagnosis: Pleomorphic fibroma ;Dermatofibroma ; solitary myofibroma

Pacinian  collagenoma:  Abstract  Composed of paucicellular collagen fibres arranged in concentric lamellations giving rise to an onion-skin appearance. The cells are CD34 positive. D/D: Perineurioma

Pleomorphic sclerotic fibroma:  In the superficial portion the tumour showed features of a pleomorphic fibroma, the deeper portion showed features of a sclerotic fibroma, and a transitional area is present in between.  According to some authors, pleomorphic fibroma, sclerotic fibroma, and pleomorphic sclerotic fibroma form a spectrum.

                                     
This lesion was described by Kamino et al in 1989.

Clinically presents as a slow-growing polypoid skin tag-like or dome shaped lesion in middle aged and elderly patients.

Site: on the trunk or extremities and rarely in head, neck, and subungual locations.

Microscopic features: IMAGE1  IMAGE2 IMAGE3

Well-circumscribed tumour composed of pleomorphic mononucleated and multinucleated cells with atypical nuclei with rare mitotic figures. The cytologic pleomorphism is considered as a degenerative process as seen in a number of other mesenchymal tumours.

Immunohistochemistry:  Vimentin and CD34- positive.  Desmin, Ki-M1p antibodies (pan-monocytic/macrophage marker) or S100 protein-Negative.  Staining for factor XIIIa has been patchy.

Differential diagnosis:

Benign tumours:  Dermatofibroma with atypical cells ; Giant cell fibroblastoma, pleomorphic lipoma ; sclerotic fibroma

Malignant tumours: Malignant fibrous histiocytoma ; Atypical fibroxanthoma;

Limited local recurrence may occur but there have been no reports of regional extension or metastatic spread.