Non-malignant skin disease

Non-malignant skin disease is relatively common. The pathology may or may not be specific. Some diseases require clinical information to diagnose.

An introduction to dermatopathology is in the dermatopathology article. Nevi (moles) and other melanocytic lesions are dealt with in the article melanocytic lesions. Inflammatory skin conditions are dealt with in inflammatory skin disorders.

Other

Lichen simplex chronicus

• Abbreviated LSC.
• AKA squamous cell hyperplasia.

General

• May be considered a variant of spongiotic dermatitis.; more specifically, some think it is an atopic dermatitis (which fits in the large spongiotic dermatitis category).
• It is lumped with the psoriasiform dermatitides.

Etiology:

• Pruritus (itchness) -> mechanical trauma -> lichenification (thickened/leathery.

Microscopic

Features:

• Acanthosis (epithelial thickening) - irregular.
• Hyperkeratosis.

Other features:

• Spongiosis (epidermal intercellular edema -- cells appear to have a clear halo around 'em).
• Parakeratosis = retention of nuclei in the stratum corneum.

DDx:

• Prurigo nodularis - focal process (nodule or papule).

Images:

• LSC - low mag. (WC).
• LSC - high mag. (WC).

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SKIN, PUNCH BIOPSY:
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	- NEGATIVE FOR MALIGNANCY.

Prurigo nodularis

• Abbreviated PN.
• AKA chronic prurigo and picker nodule.

General

• Can be thought of as a localized/focal version of lichen simplex chronicus (LSC).

Gross

• Dome-shaped/raised - papular (<1 cm) or nodular (>1 cm).

Microscopic

• See lichen simplex chronicus.

DDx:

• Lichen simplex chronicus - a more diffuse process, not a raised lesion.

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SKIN LESION, LEFT CHIN, BIOPSY: 
	- PRURIGO NODULARIS.

Micro

The sections show a raised lesion with compact hyperkeratosis and irregular acanthosis. Spongiosis is seen focally. There is minimal hypergranulosis.

There is no thinning of the suprapapillary plate and no dilated superficial blood vessels. There is no interface activity.

Very common

Dermatomycosis

General

• Fungal infection of skin.

Note:

• Dermatophytosis (ring worm) is a type of dermatomycosis.

Microscopic

Features:

• Microorganisms - key feature.
  • Often hyphae (candida) - like twigs of a tree... branching.
• Perivascular inflammation.
• Exocytosis - blood cell infiltrate the epidermis.

Images:

• Dermatomycosis - intermed. mag. (WC).
• Dermatomycosis - high mag. (WC).
• Dermatomycosis - GMS - low mag. (WC).
• Dermatomycosis - GMS stain - high mag. (WC).

Stains

• GMS.
• PAS.

Cicatrix

• AKA scar, dermal scar.

General

• Previous surgery, biopsy, trauma.

Microscopic

Features:

• Loss of dermal papilla.
• Dense collagen - fibers run parallel to the dermal-epidermal (DE) junction - key feature.
• Loss of adnexal structures.

Other feature:

• Thin-walled blood vessels.
  • Described as running perpendicular to the surface - this may not be apparent.

DDx:

• Malignant melanoma, desmoplastic-neurotropic type.
• Dermatofibroma.
• Desmoplastic Spitz nevus.
• Sclerosing blue nevus.

Image:

• Scar (WC).

IHC

• S100 focal/scattered +ve.
  • Desmoplastic melanoma strong +ve.
• HMB-45 -ve.
  • Sclerosing blue nevus +ve.

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SKIN, LOWER MID BACK, RE-EXCISION:
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	- SOLAR ELASTOSIS.

Micro

The sections show skin with a dermis with dense collagen fibres that run parallel to the skin surface without adnexal structures. The overlying dermal-epidermis interface lacks the typical undulation.

Fibroepithelial polyp

• AKA acrochordon, skin tag.

General

• Benign.
• Older people.
• May be associated with pregnancy, diabetes, intestinal polyposis.
• Component of Birt–Hogg–Dubé syndrome - see: Hereditary RCC.

Gross

• Raised skin-coloured lesion.

Image:

• Skin tag (WC).

Microscopic

Features:

• On a stalk / epithelium on three sides.
• Benign epidermis.

Image:

• Fibroepithelial polyp (dermatlas.med.jhmi.edu).

Actinic keratosis

Bowenoid actinic keratosis redirects to here.

• Abbreviated AK.
• AKA solar keratosis.^{[citation needed]}

General

Risk factors:

• Sun exposure.
• Immune suppression (e.g. organ transplant recipients).

Gross

Features:

• Yellow-brown scaly, patches.
• Sandpaper sensation - on touching.

Note:

• May be pigmented.

Microscopic

Features:

• Epidermal nuclear atypia:
  • Variation is size, shape and staining - must involve basilar layer.
    • Nuclear enlargement - key feature.
    • Hyperchromasia.
• Abnormal epidermal architecture:
  • Palisading.^{[citation needed]}
• +/-Parakeratosis - may alternate with orthokeratosis, esp. early lesions.
• +/-Irregular acanthosis.

Note:

• May be full thickness - known as bowenoid actinic keratosis.

DDx:

• Bowen's disease - full thickness involvement - with involvement of adnexal epithelium and follicular epithelium.
• Paget disease of the breast.
• Squamous cell carcinoma of the skin.
• Lentigo maligna (melanoma in situ on sun damaged skin) - esp. for pigmented AK.
• Seborrheic keratosis - should not have basilar nuclear atypia.

Images:

• Actinic keratosis (WC).
• Actinic keratosis (WC).
• Actinic keartosis (WC).
• Bowenoid actinic keratosis - high mag. (WC).
• Bowenoid actinic keratosis - very high mag. (WC).

Histologic subtypes

Like most common things, there are several variants:

• Hypertrophic actinic keratosis.
• Acantholytic actinic keratosis.
• Proliferative actinic keratosis - downward finger-like projections of the epidermis.
• Pigmented actinic keratosis - DDx lentigo maligna.
• Lichenoid actinic keratosis.

Seborrheic keratosis

• Abbreviated SK.

General

• Benign.
• Most common tumour in older people.
• "Large number" of SKs = paraneoplastic syndrome (Leser–Trélat sign).

Epidemiology:

• Old people.
• Usually in sun exposed area.

Gross

• "Stuck-on" appearance - raised lesion.

Image(s):

• SK - gross image (dermatlas.org).

Microscopic

Features:

• Raised above skin surface.
• Border sharply demarcated.
• Hyperkeratosis - stratum corneum extra thick.
• Horn cysts - intraepidermal collections of keratin - key feature.
  • Actually invaginations - not true cysts; thus, they may more accurately be called pseudohorn cysts.
• Clusters of cells with brown granular material in the superficial dermis/dermoepidermal junction - pigmented melanocytes.

DDx:

• Actinic keratosis - especially, irritated SKs; have nuclear atypia and parakeratosis.
• Verruca vulgaris - SK may have papillomatous projections.
• Basal cell carcinoma, fibroepitheliomatous pattern - esp. reticulated SK.
• Melanocytic nevus.

Images:

• Seborrheic keratosis - low mag. (WC).
• Seborrheic keratosis - high mag. (WC).
• Seborrheic keratosis - high mag. (dermatlas.org).
• Seborrheic keratosis - low mag. (dermatlas.org).

Histologic subtypes

Like very common lesion, there are subtypes:

• Acanthotic seborrheic keratosis - thickened stratum spinosum; thick epidermis.
• Reticulated seborrheic keratosis - vaguely resembles fibroepithelioma of Pinkus (BCC, fibroepitheliomatous pattern).
• Irritated seborrheic keratosis - spongiosis (epidermal intercellular edema) and inflammation.
• Digitated seborrheic keratosis - papillomatous projections.

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SKIN, MID BACK, SHAVE BIOPSY:
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Micro

The sections show skin with acanthosis, pseudohorn cysts, parakeratosis, hyperkeratosis and focal basal epidermal pigmentation. There is no basal nuclear atypia, no mitoses and no melanocytic nests. There is minimal dermal inflammation. There is no solar elastosis.

Pilomatricoma

• AKA calcifying epithelioma of Malherbe, AKA pilomatrixoma.

General

• Benign skin tumour.
• Most common solid skin tumour of children.
• CTNNB1 gene mutation important in pathogenesis.

Clinical:

• Hard nodule - calcification.
• +/-Painful.

Treatment:

• Surgical excision.

Microscopic

Features:

• Lower dermis/subcutaneous adipose lesion; thus, usu. surrounded by connective tissue.
  • Sharpy demarcated island of cells.
  • Calcification in 75% - with calcium staining (von Kossa).
• Cells:
  • Basaloid epithelial cells - have prominent nucleoli.
  • Anucleate squamous cells ("ghost cells").
  • Giant cell foreign body type granulomas (form in reaction to keratin).

Notes:

• Keratin a prominent feature on cytology - lots of orange stuff.
• May ossify.

Images:

• Pilomatrixoma - cytology (bccancer.bc.ca).
• Pilomatrixoma - histology (dermrounds.com).
• Pilomatrixoma - high mag. (WC).
• Pilomatrixoma - intermed. mag. (WC).

DDx:

• Epidermal inclusion cyst.

Dermatofibroma

• Abbreviated DF.

General

• AKA fibrous histiocytoma.
• Reactive process -- it is not a neoplasm.
• Usually associated with previous trauma.
  • In women... usually legs.

Microscopic

Features:

• Prominent fibrous bundles, especially at the edge of the lesion.
  • Surrounded by spindle cells (fibroblasts).
    • Usually thought of as fibroblasts surrounded by fibrous material ("collagen-trapping").
• Lack of adnexal structures, i.e. no sweat glands, no hair.
• +/-Epidermal changes - known as "dirty fingers":
  • Acanthosis (thickened epithelial layer - specifically thickened stratum spinosum).
  • Basal keratinocyte hyperpigmentation.

DDx:

• Dermatofibrosarcoma protuberans (DFSP) - usu. deeper, classically has adnexal structures and fat within lesion.
• Neurofibroma.
• Blue nevus.
• Melanoma, esp. desmoplastic neurotropic-type.
• Fibromatosis.

Images:

• Dermatofibroma (ucsf.edu).
• DF - several images (pacificderm.org).
• DF stained with factor XIIIa (biocare.net).

Subtypes

Like all common things... there are subtypes:

• Cellular.
• Deep penetrating.
• Lipidized - with foamy macrophages, hemorrhage and Touton-like giant cells.
• Epithelioid cell histiocytoma.
• Fibrotic.
• Aneurysmal - large blood filled + features of lipidized.
• Granular cell dermatofibroma.
• Dermatofibroma with monster cells.

Cellular dermatofibroma

Features:

• High cell density in the dermis - "blue" at low power.
• Collagen bundles - key feature.

Images:

• Cellular dermatofibroma (surgicalpathologyatlas.com).
• Cellular dermatofibroma (dermpedia.org).

IHC

Features:

• Factor XIIIa +ve.
  • Usually negative in DFSP.
• CD34 -ve.
  • Usually positive in DFSP.
• D2-40 +ve.
  • Usually negative in DFSP.

Ezcema

General

• A nebulous thingy.
• Very common.

DDx:

• Contact allergy.
• Drug reaction.
• Food allergy.

Microscopic

Features:

• Spongiosis (epidermal edema); keratinocytes spacing increased - key feature.
• +/-Interdermal vesicles.
• +/-Eosinophils (may suggest Rx reaction).
• Perivascular lymphocytes.

Acne vulgaris

General

• Extremely common - esp. among adolescents.
• Very rarely seen by pathologists.

Treatments:

• Antibiotic (minocycline).
• Isotretinoin AKA all-trans retinoic acid (ATRA).

Gross

• Papules, pustules, nodules or cysts.
  • White, black or erythematous.

Images:

• Blackheads (WC).

Microscopic

Features:

• Folliculitis:
  • Neutrophils around hair follicle and infiltrate into it - including the follicular canal.
• Epidermal invagination or cyst at site of a hair follicle - contains:
  • Sebum.
  • +/-Bacteria (Propionibacterium acnes) and inflammatory cells - typically neurophils.

Subtyped into:

1. Open comedones ("blackheads") - no extension to epidermal surface.
2. Closed comedones ("whiteheads") - to epidermal surface have wide opening.

DDx - acneiform disorder:

• Rosacea.
• Infective folliculitis.
• Perioral dermatitis.
• Acne vulgaris.

Image:

• Acne (dermnet.com).

Very common - viral

Verruca vulgaris

General

• AKA common wart.
• Etiology - HPV.

Notes:

• Related to condyloma acuminatum.

Microscopic

Features:

• Hyperkeratosis (more keratin - thick stratum corneum).
• Hypergranulosis (thicker stratum granulosum).
• Acanthosis (thickening of the stratum spinosum).
• Rete ridges lengthened (~7-10x normal).
• Large blood vessels at the dermal-epidermal junction.

Memory device: there is more of everything - more s. corneum, s. granulosum, s. spinosum, longer rete ridges, more (larger) blood vessels.

Images:

• Verruca vulgaris - very low mag. (WC).
• Verruca vulgaris - intermed mag. (WC).

Verruca plana

General

• Common.
• Usu. hands and face.

Microscopic

Features:

• Orthokeratosis with basketweave pattern.
• Hypergranulosis.
• Viral keratohyaline.
• Koilocytes.
• Acanthosis - yet flat surface and base.

Notes:

• It differs from verruca vulgaris... (1) orthokeratosis, (2) flat surface and base.

Less common

Clear cell acanthoma

General

• Benign.
• Elderly.
• Classically on the leg.
• Rare.
• Clinically not distinct.
  • Suspected clinically in only ~3% of cases.

Microscopic

Features:

• Psoriasiform pattern - epidermal thickening (acanthosis).
• Keratinocytes:
  • Pale or light pink cytoplasm (when compared to surrounding non-lesional keratinocytes).
  • Separated from one another (spongiosis).
• +/-Stratum corneum neutrophils.

DDx:

• Psoriasis vulgaris.

Images:

• CCA (drmihm.com).
• CCA - low mag. (dermatlas.com).
• CCA - high mag. (dermatlas.com).

Chondrodermatitis nodularis chronica helicis

• AKA chondrodermatitis nodularis helicis.
• Abbreviated CNCH.

General

• Tender/painful - key clinical feature.
• Typically right ear - people more often sleep on this one.
• Usually >40 years old.

Etiology:

• Trauma/mechanical.

Clinical DDx:

• BCC.
• SCC.

Microscopic

Features:

• Dermal inflammation.
• Epithelial hyperlasia.
• Fibrosis.
• Cartilaginous pathology:
  • Perichondrial inflammation - key feature.
  • Perichondrial disruption.
  • +/-Necrosis.
  • +/-Hemorrhage.

Images:

• CNCH (dermpedia.org).
• CNCH (surgicalpathologyatlas.com).
• CNCH (dermatlas.med.jhmi.edu).

Cutaneous calcinosis

• AKA calcinosis cutis.

General

• Benign in itself; underlying cause may not be benign.
• May be a scrotal lesion - known as scrotal calcinosis.

Subtypes:

1. Dystrophic - due to death of cells; may be related to a tumour.
2. Metastatic - due to chronic renal failure; hyperkalemia; paraneoplastic phenomenon.
3. Iatrogenic - post surgical.
4. Idiopathic.

Microscopic

Features:

• Dermal calcification:
  • Acellular purple blobs on H&E.
    • +/-Artefactual tearing of surrounding tissue due to processing (cutting).
    • +/-Small artefactual lines ~1-2 micrometers due to processing (cutting).
  • Usu. well-circumscribed.

Images:

• Calcinosis cutis (blogspot.com).

Dilated pore of Winer

General

• Benign.
• Looks like zit.

Microscopic

Features:

• Dilated hair follicle with keratin.
• Acanthosis.
• Budding of epidermis (into dermis).

Lichenoid keratosis

• AKA lichen planus-like keratosis.

General

• Caucasians - middle age or older.
• May be a variant of seborrheic keratosis (with marked inflammation).

Clinical DDx:

• Basal cell carcinoma, squamous cell carcinoma of the skin, melanocytic neoplasm.

Microscopic

Features:

• Hyperkeratosis.
• Parakeratosis.
• Band of inflammatory cells at DE junction (lichenoid inflammation).
• Dead keratinocytes (Civatte bodies).
• Dermal melanophages.

DDx:

• Lichen planus - need clinical correlation (mucosal lesions).
• Drug reaction.
• Cutaneous T-cell lymphoma.
• Regressed melanocytic lesion.
• Lichenoid actinic keratosis - has atypical hyperchromatic basal cells - esp. at edge of lesion, usu. in the context of solar elastosis.

Images:

• Lichenoid keratosis (dermpathexpert.com).

Granuloma annulare

General

• Benign and self-limited condition.
• Etiology unknown - may be assoc. with trauma.

Gross

• Typically extremities - usu. arms and hands.

Microscopic

Features:

• Dermal palisading granuloma - typically superficial-to-mid dermis - surrounds:
  • Necrotic collagen - key feature.
    • Nuclei "missing" - have undergone karyolysis.
  • Mucin - important.
    • Loose/pale, paucicellular, eosinophilic.
• Chronic inflammatory cells.

Notes:

1. There may be multiple small foci with intervening normal dermis.
2. Granuloma annulare can be subclassified into subcutaneous and interstitial.
3. Histomorphologically similar to Rheumatoid nodule.

DDx:

• Necrobiosis lipoidica - little mucin, no normal dermis between foci, plasma cells - common, may involve the fat - tend to be deeper.
• Rheumatoid nodule - has fibrin in the core of the granuloma (instead of mucin).
• Epithelioid sarcoma - esp. if the lesion appears to be mid-to-deep dermis.

Images:

• WC:
  • Granuloma annulare - intermed. mag. (WC).
  • Granuloma annulare - high mag. (WC).
  • Granuloma annular - palisaded granuloma - high mag. (WC).
• www:
  • Granuloma annulare (dermaamin.com).

Stains

• Alcian blue (pH 2.5) +ve (for mucin).

Image:

• Granuloma annulare (nih.gov).

Necrobiosis lipoidica

General

Associated with:

• Diabetes mellitus - known as necrobiosis lipoidica diabeticorum.
• Rheumatoid arthritis.

Microscopic

Features:

• Dermal palisading granuloma around:
  • Necrotic collagen - key feature.
    • Nuclei "missing" - have undergone karyolysis.
• Little mucin, no normal dermis between foci.
• Plasma cells - common.
• May involve adipose tissue.

DDx:

• Granuloma annulare - more mucin, normal dermis between foci, plasma cells uncommon, no fat involvement - usu. more superficial.
• Rheumatoid nodule.

Images:

• Necrobiosis lipoidica (dermatology.cdlib.org).
• Necrobiosis lipoidica (drmihm.com).
• Necrobiosis lipoidica (dermnetnz.org).

Keloid

• Hypertrophic scar redirects to this section.

General

• Sites of previous trauma/surgery, esp. in dark skinned individuals.

Microscopic

Features:

• Thick collagen bundles - surrounded by paler staining fibroblasts - key feature.
• Lesion replaces adnexal structures, e.g. hair, sweat glands.

DDx:

• Hypertrophic scar.

NB:

• Reported as "keloidal-type collagen"; the clinician decides between hypertrophic scar and keloid.

Images:

• WC:
  • Keloid - low mag. (WC).
  • Keloid - intermed. mag. (WC).
  • Keloid - high mag. (WC).
• www:
  • Keloid (ucsf.edu).

Angiofibroma

See also: nasopharyngeal angiofibroma.

Should not be confused with angiokeratoma.

Fibrous papule redirects here.

General

• May be seen in the context of tuberous sclerosis - especially "butterfly area of the face".
• Solitary lesions in adults are known as fibrous papules and classically arise on the nose.

Clinical:

• Firm, dome-shaped, flesh coloured.

Microscopic

Features:

• Dome-shaped.
• Fibrotic dermis.
  • Enlarged fibroblasts.
• Dilated small vessels.

Image:

• Angiofibroma (drdittmar.lu).

Molluscum contagiosum

General

• Etiology: caused by molluscum contagiosum virus.

Microscopic

Features:

• A suprabasilar epidermal lesion consisting of "molluscum bodies", i.e. molluscum bodies are found above the stratum basale.
• Molluscum bodies - key feature:
  • Large cells with abundant granular eosinophilic cytoplasm.
  • Small peripheral nucleus.

Image(s):

• Molluscum contagiosum - high mag. (WC).
• Molluscum contagiosum - low magnification (WC).

Notes:

• Molluscum bodies very vaguely resemble signet ring cells -- but:
  • Cytoplasm eosinophilic and granular.
  • Nucleus usually smaller than in signet ring cell.
  • Molluscum bodies are only the epidermis - an uncommon place to find SRCs without finding them elsewhere.
• The granular eosinophilic cytoplasm represents accumulated virons.

Superficial dermal infiltrates

Discussed in detail by Alsaad and Ghazarian.

Dermal perivascular lymphoeosinophilic infiltration

• Abbreviated DPLI.

Microscopic appearance is just what it is called:

• Lymphocytes and eosinophils around the vessels in the superficial dermis.

DDx:

• Insect bite - classically wedge-shaped.
• Drug reaction.
• Urticarial reaction.
• Prevesicular early stage of bullous pemphigoid.
• HIV related dermatoses.

Notes:

• May superficially resemble cutaneous lymphoma.

Images:

• DPLI - very low mag. (WC).
• DPLI - very high mag. (WC).

Congenital dermal melanocytosis

• AKA Mongolian spots.
• Classically seen in asian children.

Gross:

• Brown or blue-grey patch in the lumbosacral area.

Mastocytosis

General

• Abundance of mast cells.

Classification:

1. Cutaneous (only) - usually children.
   • Urticaria pigmentosa.
   • Others.
2. Systemic - usually adults.
   • Indolent subvariant.
   • Aggressive subvariant.
   • Leukemic subvariant.

Microscopic

Features:

• Cells in the superficial/mid dermis that are:
  • Lymphocyte-like with more cytoplasm that is granular.
    • Cells may have spindled or stellate morphology.
    • Tend to be more abundant around vessels.
• +/-Eosinophils (common).
• +/-Edema - often prominent; gives cells a white halo.

Notes:

• Lymphocyte vs. mast cell:
  • Lymphocytes = round; mast cells = ovoid.

Images:

• www:
  • Mastocytosis - low res. (jameswpattersonmd.com).
  • Mastocytosis - bone marrow - several images (upmc.edu).
• WC:
  • Mastocytosis - high mag. (WC).
  • Mastocytosis - very high mag. (WC).
  • Systemic mastocytosis - several images (upmc.edu).

Stains

• Toluidine blue -- highlights the granules.

IHC

• CD117 +ve.
• Tryptase +ve.

Ichthyosis

General

• Comes in different flavours.
• Usu. inherited... thus a pediatric condition.

Gross

• Fish scale-like appearance.

Image:

• Ichtyosis (WC).

Microscopic

Features:

• Thick stratum corneum without basket-weave pattern.

Palmar fibromatosis

Main article: Fibromatosis

General

• AKA Dupuytren's contracture.

Clinical:

• Usually older 60-70s.
• Male > female.
• Associated with:
  • Alcohol abuse.
• May be familial.

Microscopic

Features:

• Bland spindle cells in dense collagen.
  • No nuclear atypia.
• Giant cells.
• +/-Mitotic figures.

Images:

• Palmer fibromatosis (biomedsearch.com).

Angiomyoma

• Do not confuse with angiomyxoma.

General

• Benign.
• Female > male.

Microscopic

Features:

• Well-circumscribed lesion with fascicular architecture.
• Spindle cells/epithelioid cell with moderate eosinophilic (pink) cytoplasm.
• Thick-walled blood vessels. (???)

Images:

• Angiomymoma (WC).
• Angiomymoma (WC).

Angiokeratoma

General

• Rare.
• May be seen in the context of Fabry disease.

Notes:

• Shouldn't be confused with angiofibroma which is associated tuberous sclerosis.

Microscopic

Features:

• Ectatic superficial dermal vessels.
• Overlying hyperkeratosis (thick stratum corneum).

Others features:^{[citation needed]}

• Irregular acanthosis.
• Longer rete ridges.

DDx:

• Venous lake.

Images:

• WC:
  • Angiokeratoma - low mag. (WC).
  • Angiokeratoma - intermed. mag. (WC).
• www:
  • Angiokeratoma (pathologyoutlines.com).

Inverted follicular keratosis

General

• Benign skin lesion.
• Central face - middle age.
• Uncommon.
• May be considered a variant of seborrheic keratosis that is predominantly endophytic.

Clinical DDx:

• BCC.
• Wart.

Microscopic

Features:

• Keratinocyte of cytologically benign proliferation.
• "Squamous eddies" (whorls of keratin).
• Coarse keratohyaline granules.

DDx:

• Squamous cell carcinoma of the skin.
• Trichilemmoma.
• Seborrheic keratosis - larger exophytic component.

Images:

• Inverted follicular keratosis - low mag. (flickr.com).
• Inverted follicular keratosis - high mag. (flickr.com).

Focal cutaneous mucinosis

General

• Benign.
• May be associated with systemic disease.

Microscopic

Features:

• Light blue whispy material in the dermis - key feature.

DDx:

• Dermal edema.
• Digital mucous cyst.

Panniculitis

Main article: Panniculitis

This is dealt with in the panniculitis article.

DDx for panniculitis:

• Erythema nodosum.
• Erythema induratum.
• Self-inflicted trauma.
• Systemic lupus erythematosus.
• Weird stuff.

Rare

Necrotizing fasciitis

Not to be confused with nodular fasciitis.

• AKA flesh-eating disease.

General

• High mortality.
• May be diagnosed at frozen section.
• Classically associated with Group A streptococcus.

Treatment:

• Operative debridement.

Microscopic

Features:

• Necrosis of fascia - key feature.
  • PMNs and necrotic debris (amorphous grey or pink material).

Note:

• Fat lobules between septae may be normal.

DDx:

• Cellulitis.

Images:

• Necrotizing fasciitis - intermed. mag. (WC).
• Necrotizing fasciitis - high mag. (WC).

Porokeratosis

General

• Genetic.
• Several subtypes.

Notes:

• Not the same as punctate porokeratotic keratoderma.

Microscopic

Features:

• Cornoid lamella (pathognomonic) - key feature:
  • Compact keratosis over a hair follicle.
• +/-Rete ridge loss.

Images:

• WC:
  • Porokeratosis - intermed. mag. (WC).
  • Porokeratosis - very high mag. (WC).

Nevus sebaceous

• AKA nevus sebaceous of Jadassohn.

General

• Congenital.
• Face or scalp.

Microscopic

Features:

• Abundant sebaceous glands.

Nevus lipomatosus superficialis

• Abbreviated NLS.

General

• Rare.
• Congenital.
• Usually lower trunk or gluteal region.

Microscopic

Features:

• Benign adipose tissue in the superficial dermis.

DDx:

• Lipoma.

Image:

• NLS (dermamin.com).

Bullous disease

Main article: Bullous disease

Cysts

Main article: Dermal cysts

See also

• Dermatopathology introduction.
• Malignant skin disease.