Dermatofibroma

Circumscribed

Grenz zone

Collagen trapping

Epithelial, follicular and sebaceous induction

Hemosiderin

Factor XIIIa, CD68 and CD163 CD34 Masson trichrome stain highlights fibrous tissue as blue Dermatofibrosarcoma protuberans

Infiltration and expansion of fibrous septa.

Interdigitation of fat lobules in a honeycomb pattern

Sparing of adnexal structures

Herringbone pattern and significant atypia and mitotic figures in sarcomatous variant

CD34 Factor XIIIA, S 100, Melan A and SMA

Pigmented DFSP stains for fontanna masson stain but not Prussian blue

Myxoid DFSP stains with alcian blue, colloidal iron

Rosai-Dorfman disease Emperipolesis S100 and CD68 CD1a - Spindle cell xanthogranulom is a variant of juvenile xanthogranuloma Touton giant cells with vacuolated histiocytes Factor XIIIa, Mac 387, lysozyme, CD 68 and vimentin S100 protein, actin, desmin and keratin AE1.3 Sudan III stain highlights intracytoplasmic fat granules Sarcomatoid is a variant of anaplastic large cell lymphoma Large, bizarre-looking, spindle-shaped cells CD4, CD5, CD30, TIA-1 and ALK while CD3+/‒ CD8, CD15, CD20, CD56, CD68, desmin and SMA - Angiomyofibroblastoma Alternating areas of hypercellular and hypocellular region Desmin, estrogen receptor, progesterone receptor and SMA Masson trichrome stain smooth muscle cytoplasm as red and collagenous fibrous tissue as blue Superficial CD34-positive fibroblastic tumour

Neoplastic cells with polymorphic nuclei

Granular cytoplasm

Intranuclear cytoplasmic pseudoinclusions

Extremely low mitotic rate

CD34 and focal positivity for keratin (AE1/AE3) S-100 protein, EMA, SMA, myosin, desmin, myogenin, CD56 and FLI-1 Masson trichrome stain for fibrous tissue, which highlights as blue Malignant peripheral nerve sheath tumour Elongated wavy nuclei and bubblegum or wispy cytoplasm with mitotic activity CD34 and S100 Silver impregnation (Bodian and Beilschowsky stain) highlights nerve cells Erythema elevatum diutenum Leukocytoclastic vasculitis with onion ring fibrosis - EMA, CD34 and S100 Fibrohistiocytic lipoma Honeycomb fat cells with spindle cells Vimentin, calponin and CD34 Sudan III stain highlights fat tissue Superficial acral fibromyxoma

Prominent microvasculature

Mast cells

Multinucleated stromal cells

EMA, CD34 and CD99 Alcian blue and colloidal iron highlights mucin Granular cell tumour Pustulo-ovoid bodies of Milian S-100, CD31, CD56, CD68, CD117, inhibin, p53, calretinin, EMA and MIB-1

Periodic acid Schiff highlights granules and are resistant to diastase

These granules also stain with Sudan black B

Trichrome stain shows magenta colouration

Cutaneous histiocytic sarcoma Signet-ring cell type tumour cells with areas of cellular cannibalism and emperipolesis CD68, CD163 and lysozyme S100 and CD1a - Neurofibroma Elongated wavy nuclei and bubblegum or wispy cytoplasm S100 Glial fibrillary acidic protein Silver impregnation (Bodian and Beilschowsky stain) highlights nerve cells Neurothekeoma Intranuclear pseudo inclusion Strong positivity of S100A, MiTF, EMA, NSE, NKI/C3 and PGP 9.5 and focal positivity for claudin-1, Glut-1 and CD34 Silver impregnation (Bodian and Beilschowsky stain) highlights nerve cells Nodular fasciitis Tissue culture appearance SMA, calponin, vimentin, KP-1 and HSP47 Desmin, CD34, S100 and cytokeratin

Masson trichrome stain smooth muscle cytoplasm as red and collagenous fibrous tissue as blue

Alcian and colloidal iron stain for mucin

Perineuroma Lamellar-like structures CD34, EMA, vimentin, S-100 protein, desmoplakin and neurofilament - Hybrid schwannoma and perineuroma Well-circumscribed unencapsulated tumours Alternating S100, EMA stain with no co-expression; Claudin 1, GFAP and CD34 Silver impregnation (Bodian and Beilschowsky stain) highlights nerve cells Progressive nodular histiocytosis Spindle-shaped, vacuolated, stellate, oncocytic (ground glass) and foamy cells CD68, CD163, vimentin and fascin S 100 and CD1a - Pseudomyogenic (epithelioid sarcoma-like) hemangioendothelioma Cells with a rhabdomyoblast-like morphology may be seen ERG with retained INI-1, pancytokeratin AE1/AE3 and CD31 S100, CD34, desmin, EMA, MNF116, SMA, caldesmon, myogenin, MyoD1, HHV-8 and CD163 Spitz Naevus Kamino bodies, zonation and absent pagetoid spread S100, Melan A, HMB45, SOX 10, ALK, NTRK and ROS SMA, EMA, BRAF and cytokeratin

Masson’s fontana stain shows mild positivity in naevus cells

Schmorl method stains melanin blue green

Storiform collagenoma Hypocellular area of abundant collagen with ‘plywood-like’ clefts CD34 Masson trichrome stain to highlight collagenous fibrous tissue as blue and nuclei as black Myofibroma

Biphasic pattern

Spindle cells with eosinophilic cytoplasm and elongated nuclei

Hemangiopericytoma like vascular pattern

SMA, MSA, vimentin and calponin P63, desmin and h-caldesmon Masson trichrome stain smooth muscle cytoplasm as red and collagenous fibrous tissue as blue Solitary fibrous tumour Spindle-to-ovoid collagen with inconspicuous cytoplasm CD 34, STAT 6 and vimentin CD 99, CD 31, S100, AML, desmin and SOX 10 - IgG4-related disease Lymphoid aggregates, plenty of plasma cells and fibroblast in storiform pattern CD 138 and IgG4 Elastin Van Gieson stain to highlight obliterative venulitis