Cellular dermatofibroma

Often larger, more cellular and more deeply extending than ordinary dermatofibroma, sometimes involving subcutis.
Can mimic dermatofibrosarcoma protuberans clinically and histologically because of size, cellularity and fascicular growth.
CD34 is usually negative in dermatofibroma but cellular dermatofibroma can show focal peripheral CD34 positivity; DFSP is typically diffuse CD34 positive.
Complete excision is reasonable when diagnosis is cellular DF, particularly if margins are involved or the lesion is large/recurrent.
Recurrence risk is higher than for ordinary dermatofibroma, so patients should be advised to return if a scar nodule develops.

Aneurysmal dermatofibroma

Presents as a blue-brown, violaceous, rapidly enlarging or haemorrhagic nodule/plaque and can mimic melanoma or a vascular tumour.
Histology shows blood-filled pseudovascular spaces without endothelial lining within a dermatofibroma background.
Endothelial markers stain true vessels but not the aneurysmal spaces, helping separate it from vascular neoplasia.
Because growth and colour can be alarming, diagnostic excision is often needed.
Recurrence risk is higher than in ordinary dermatofibroma, especially after incomplete removal.

Shows marked cytological atypia, pleomorphic or “monster” cells and sometimes atypical mitoses, while retaining features of dermatofibroma.
Clinical and histological overlap includes atypical fibroxanthoma, pleomorphic dermal sarcoma, melanoma and other spindle-cell tumours.
Specialist dermatopathology review and an appropriate immunohistochemical panel are important before accepting the diagnosis.
Complete excision with clear margins is generally preferred because rare metastasis has been reported in atypical/deep variants.
Follow-up should be individualised around margin status, depth, recurrence and pathology confidence.

Deep/plexiform dermatofibroma can extend into subcutis and mimic DFSP or soft-tissue sarcoma.
Other described variants include lipidised, hemosiderotic, clear-cell, palisading, granular-cell and atrophic forms.
Variant names should not distract from the key clinical question: is this a benign DF variant, DFSP, melanoma or another sarcoma mimic?
Large, rapidly growing, ulcerated, painful, recurrent or deeply fixed lesions need biopsy/excision rather than reassurance.
Clinicopathological correlation is essential if the clinical lesion appears more aggressive than the initial histology suggests.

Ordinary stable dermatofibromas can be observed; variant lesions are more often excised because diagnosis and margins matter.
Ask pathology specifically about DFSP, AFX/PDS and melanoma mimics when the lesion is large, cellular, atypical or recurrent.
For cellular, aneurysmal, atypical or deep DF with involved margins, consider re-excision according to pathology confidence, site and recurrence risk.
If DFSP remains in the differential, test for diffuse CD34 and consider molecular testing for COL1A1-PDGFB where appropriate.
Follow-up is not standardised; document a return plan for recurrent scar nodularity or new rapid growth.