|
The term 'Atypical Fibroxanthoma, was
introduced by Helwig EB (Texas J Med 1963;59: 664-667 ). Similar cases
were reported as Paradoxical fibrosarcoma of the skin or pseudosarcoma by Bourne RG (Med J Aus 1963;1:5 04-510).
Clinical presentation:
- The tumour usually presents as solitary, rapidly growing dome shaped
ulcerated and crusted nodule, usually less than 2 cm in diameter, on the
head or neck region of the elderly. The lesion usually occurs in
sun-damaged or radiation damaged skin.
- A rare clinical variant occurs in younger patients. The tumour is
larger and slow growing and are usually located on the trunk and
extremities.
Microscopic features:
Image
Link1
;
Image Link2
;
Image Link3
;
Image Link4
- Exophytic , well circumscribed, non encapsulated tumour.
- Located in the dermis.
- Expansile growth. The tumour is usually bordered by mononuclear
inflammatory cells in the deeper aspect.
- The adjacent adnexal structures are usually compressed. Adnexal
structures within the tumour are always intact.
- The overlying epidermis is thin and usually ulcerated with crust
formation , but there may be peripheral epidermal acanthosis with
formation of 'epithelial collarette'.
- A thin grenz zone may be present separating the tumour from the
epidermis or the tumour may stream out from the basal layer. In the latter
case the dermo-epidermal junction is not always clear.
- The tumour is characterized by marked pleomorphism and polymorphism .
- There is an admixture of three main cell types:
- Plump spindle shaped cells with vesicular nucleus,
arranged in fascicles
- Large polyhedral cells. Some of these cells are
vacuolated.
- Bizarre giant cells (mononucleate or multinucleate)
with hyperchromatic nuclei.
Note: Oil red O stain on frozen sections show variable amount of
lipid in the polyhedral and giant cells.
- Typical and atypical mitotic figures are noted (one per high power
field).
- The epidermis overlying the tumour usually do not show evidence of
atypia, junctional activity or atypical melanocytes. However, epidermis
adjacent to the tumour may show evidence of actinic keratosis.
- Dermis adjacent to the main lesion show features of solar elastosis.
Telangiectatic blood vessels may be present near the surface.
- In rare cases foci of osteoid and chondroid differentiation and
osteoclast like giant cells may be present.
- Spindle cell variant is entirely composed of monomorphic palely
eosinophilic spindle shaped cells arranged in fascicles . There is only
mild pleomorphism. (D/D- leiomyosarcoma, spindle cell squamous carcinoma
and spindle cell melanoma).
|
|
Differential
diagnosis of Atypical Fibroxanthoma:
1.
Spindle cell squamous Cell Carcinoma:
Infiltrative tumour and
overlying epidermal dysplasia is present. Cytokeratin is positive.
2.
Malignant melanoma:
S100 protein and HMB45
positive. Spindle cell melanomas are usually amelanotic,infiltrative
tumour with uniform cytology and are often associated with desmoplasia.
Neural invasion may be present.
3.
Leiomyosarcoma:
Infiltrative, poorly
circumscribed tumour composed of bundles of spindle cells. Primary
cutaneous leiomyosarcoma shows minimal cytological atypia. Metastatic
tumours are well circumscribed and demonstrates prominent cellular atypia.
Desmin is positive.
Note: Immunohistochemical
analysis is absolutely essential to confirm the diagnosis.
4.
Malignant fibrous histiocytoma: Deep soft tissue tumour.
CD74 is strongly positive.
5.
Dermatofibrosarcoma protuberance: Characteristic monomorphic
cytology , storiform arrangement.
6. Reticulohistiocytoma:
Composed of epithelioid
cells with 'ground glass' cytoplasm.
7. Post irradiation:
Features similar to atypical
fibroxanthoma may be present in post irradiated skin.
|
