Benign Skin Tumours

Benign skin tumours are localised, non-malignant proliferations of one or more skin components — keratinocytes, melanocytes, fibroblasts, adipocytes, vessels or adnexa. For NEET PG the recurring theme is clinical morphology + a signature clinical sign + the histological hallmark + the correct procedure, with occasional questions on malignant transformation risk. This note builds a clean, comparison-driven framework so you can identify the lesion from a one-line stem.

Classification by tissue of origin

A quick mental map prevents confusion between look-alike lumps.

Origin	Representative benign tumours
Keratinocyte / epidermal	Seborrhoeic keratosis, epidermal naevus, clear-cell acanthoma
Cystic (epithelial-lined)	Epidermoid (infundibular) cyst, trichilemmal (pilar) cyst, milium
Fibrohistiocytic	Dermatofibroma (benign fibrous histiocytoma), skin tag (acrochordon)
Adipocytic	Lipoma, angiolipoma
Vascular	Pyogenic granuloma (lobular capillary haemangioma), cherry angioma, infantile haemangioma
Reactive fibrous proliferation	Keloid, hypertrophic scar
Adnexal	Syringoma, cylindroma, trichoepithelioma, pilomatricoma

High-yield: Most NEET PG stems give a single discriminating feature — stuck-on (seborrhoeic keratosis), dimple/buttonhole sign (dermatofibroma), central punctum (epidermoid cyst), bleeds easily after minor trauma (pyogenic granuloma), grows beyond wound margins (keloid). Lock these triggers.

Seborrhoeic keratosis

The commonest benign epidermal tumour of older adults; prevalence rises sharply after age 50. It arises from proliferation of immature keratinocytes.

Clinical features

• Well-demarcated, "stuck-on" (pasted-on) appearance — looks as if it could be flicked off the skin.
• Greasy, verrucous, hyperkeratotic surface; colour ranges tan to dark brown/black.
• Distribution on trunk, face, scalp; multiple lesions common.
• Asymptomatic; occasionally itchy or irritated.

Histology — hyperkeratosis, acanthosis, papillomatosis, and the pathognomonic horn pseudocysts (keratin-filled invaginations) plus pseudo-horn cysts. Basaloid keratinocyte proliferation with "string of pearls" basal layer.

High-yield — Leser–Trélat sign: Sudden eruption of multiple seborrhoeic keratoses (often with pruritus) is a paraneoplastic marker, classically of gastric adenocarcinoma (other GI/lung malignancies). A favourite single-best-answer link.

Differentials

• Melanoma / pigmented BCC — pigmented, irregular SK can mimic melanoma; dermoscopy shows milia-like cysts and comedo-like openings in SK.
• Dermatosis papulosa nigra — small, dark SK variant on the face of darker-skinned individuals.
• Stucco keratosis — white, dry, on lower legs.

Management — reassurance; remove for cosmesis/irritation by cryotherapy (liquid nitrogen), curettage, shave excision, or electrodessication. No malignant potential.

Dermatofibroma (benign fibrous histiocytoma)

A common fibrohistiocytic nodule, often considered a reactive proliferation following minor trauma or insect bite, typically in young-to-middle-aged women on the lower legs.

Clinical features

• Firm, button-like dermal papule/nodule, 0.5–1 cm, brown to red-brown.
• Dimple sign (Fitzpatrick sign): lateral pinch of the surrounding skin causes the lesion to dimple/retract inward rather than protrude — a classic exam tell.
• Slow-growing, asymptomatic; tethered to overlying epidermis but mobile over deeper tissue.

Histology — ill-defined dermal proliferation of fibroblasts and histiocytes in storiform (cartwheel) pattern, overlying epidermal hyperplasia with basal hyperpigmentation (induction of the epidermis), and peripheral collagen trapping ("collagen balls"). Factor XIIIa positive, CD34 negative (contrast with DFSP).

High-yield: Dermatofibroma is CD34-negative / Factor XIIIa-positive; dermatofibrosarcoma protuberans (DFSP) is CD34-positive. This single marker pair is repeatedly tested as the benign-vs-malignant discriminator.

Management — none needed; excision if symptomatic or diagnostically uncertain.

Epidermoid (epidermal inclusion / infundibular) cyst

The commonest cutaneous cyst, lined by stratified squamous epithelium with a granular layer, filled with laminated keratin.

Clinical features

• Dome-shaped, mobile dermal/subcutaneous nodule with a central punctum (dilated pore).
• Discharges cheesy, foul-smelling keratin when expressed.
• Common on face, neck, trunk, scrotum.
• May become inflamed/infected (ruptured cyst → foreign-body granulomatous reaction, red, tender, "abscess-like").

Distinguish from related cysts

Cyst	Lining	Key point
Epidermoid cyst	Epidermis-like with granular layer	Central punctum; keratin
Trichilemmal (pilar) cyst	Outer root sheath; no granular layer	Scalp; familial; firmer, no punctum
Milium	Tiny epidermoid cyst	1–2 mm white papule; face of newborns/adults
Steatocystoma	Sebaceous-gland-lined	Oily fluid; steatocystoma multiplex
Dermoid cyst	Has adnexal structures	Congenital; midline / lateral eyebrow

High-yield: A "sebaceous cyst" is a misnomer — the epidermoid cyst contains keratin, not sebum. Gardner syndrome associates multiple epidermoid cysts + osteomas + intestinal polyposis (FAP).

Management — complete excision of the cyst with its wall/capsule (incomplete removal → recurrence). If acutely inflamed, incise/drain and add antibiotics, then excise electively when quiescent.

Lipoma

The commonest benign soft-tissue (mesenchymal) tumour — a lobulated proliferation of mature adipocytes.

Clinical features

• Soft, doughy, mobile, painless subcutaneous mass; "slips away" under palpating fingers (slip sign).
• Trunk, neck, shoulders, proximal limbs.
• Multiple lipomas → familial multiple lipomatosis; tender multiple lipomas in women → Dercum disease (adiposis dolorosa); angiolipomas are tender.

Histology — encapsulated mature adipocytes, indistinguishable from normal fat except for the capsule.

High-yield: A deep, rapidly enlarging, painful or >5 cm fatty mass, especially in retroperitoneum/thigh, raises liposarcoma — image (MRI) and biopsy rather than blind excision. Most superficial lipomas need only reassurance.

Management — observation; surgical excision/enucleation or liposuction for cosmesis or symptoms.

Pyogenic granuloma (lobular capillary haemangioma)

Despite the name it is neither pyogenic (infective) nor a true granuloma — it is a benign, rapidly growing vascular proliferation, often post-trauma or hormonal (pregnancy → "granuloma gravidarum/epulis").

Clinical features

• Solitary, bright-red, friable, pedunculated papule/nodule developing over days–weeks.
• Bleeds profusely on minor trauma — the hallmark history.
• Common sites: fingers, lips, gingiva, face; gingival in pregnancy.
• A surrounding "collarette" of scale at the base is characteristic.

Histology — lobular proliferation of capillaries in an oedematous stroma (lobular capillary haemangioma), often with surface ulceration and epidermal collarette.

High-yield: Always consider amelanotic melanoma in the differential of a bleeding red nodule, especially acral — histology of any excised pyogenic granuloma is prudent.

Management — complete removal: shave/curettage with electrocautery of the base, or excision. Incomplete destruction → recurrence (satellite lesions). Pregnancy lesions may regress post-partum.

Keloid vs hypertrophic scar

Both are excessive dermal collagen responses to wounding, but they behave very differently — a perennial exam comparison.

Feature	Hypertrophic scar	Keloid
Relation to wound margin	Confined within original wound	Extends beyond original wound margin
Onset	Soon after injury (weeks)	Often delayed (months)
Natural course	Tends to regress with time	Persists/progresses; rarely regresses
Sites	Flexor surfaces, across joints	Ear lobes, presternal chest, shoulders, deltoid, upper back
Race/genetics	Any	More common in darker skin; familial
Histology	Fine collagen parallel to surface, abundant myofibroblasts	Thick, hyalinised, glassy eosinophilic "keloidal" collagen bundles, haphazard
Response to excision alone	Good	High recurrence (excision alone often worsens)

High-yield: Thick, glassy, hyalinised eosinophilic collagen bundles = keloid on histology. Keloid grows beyond wound margins; hypertrophic scar stays within. This pair is one of the most repeated dermatology MCQs.

Management flow (keloid): First line → intralesional triamcinolone (steroid) injections (± with 5-FU) → silicone gel sheeting/pressure therapy as adjunct → surgical excision only WITH adjuvant (intralesional steroid and/or post-op radiotherapy) to curb recurrence → cryotherapy, laser, or intralesional 5-FU/bleomycin for resistant lesions.

Adnexal benign tumours (quick recall)

• Syringoma — multiple small skin-coloured papules around the lower eyelids; eccrine duct tumour; "tadpole/comma-shaped" ducts on histology.
• Trichoepithelioma — multiple papules around the nasolabial folds; can be familial (Brooke–Spiegler).
• Cylindroma — "turban tumour" on the scalp; jigsaw-puzzle islands of basaloid cells.
• Pilomatricoma (calcifying epithelioma of Malherbe) — firm, hard nodule in children; "shadow/ghost" cells + calcification on histology.

High-yield eponym pairs: Syringoma → tadpole ducts; Pilomatricoma → ghost cells + calcium; Cylindroma → jigsaw pattern; Trichilemmal cyst → no granular layer.

Diagnosis and investigation of choice

For most benign skin tumours the diagnosis is clinical (morphology + signature sign), aided by dermoscopy (e.g., milia-like cysts/comedo openings in seborrhoeic keratosis; central white patch + peripheral pigment network in dermatofibroma).

The definitive / confirmatory investigation of choice is histopathology (skin biopsy / excision biopsy) whenever:

• diagnosis is uncertain,
• there is rapid growth, bleeding, ulceration or pigmentation suggesting malignancy,
• a pyogenic-granuloma-like or atypical lesion is excised (to exclude amelanotic melanoma).

For a suspected deep lipoma/liposarcoma, the imaging of choice is MRI.

Malignant transformation risk

Lesion	Malignant potential
Seborrhoeic keratosis	Essentially none (benign); Leser–Trélat is a marker of internal cancer, not transformation
Dermatofibroma	None (but distinguish from DFSP)
Epidermoid cyst	Negligible; rare SCC in long-standing cysts
Lipoma	None for typical superficial lipoma; liposarcoma is a separate de-novo tumour
Pyogenic granuloma	None; mimics amelanotic melanoma
Keloid	None

Key differentials at a glance

• Bleeding red nodule: pyogenic granuloma vs amelanotic melanoma vs cherry angioma vs Kaposi.
• Pigmented stuck-on plaque: seborrhoeic keratosis vs melanoma vs pigmented BCC.
• Firm leg nodule with dimple sign: dermatofibroma vs DFSP (CD34+) vs scar.
• Subcutaneous lump: lipoma vs epidermoid cyst (punctum) vs liposarcoma (deep, large, painful).
• Raised scar: hypertrophic scar (within margins) vs keloid (beyond margins).

Procedures — when to use what

1. Cryotherapy / curettage → seborrhoeic keratosis, small superficial lesions.
2. Shave + electrocautery of base → pyogenic granuloma.
3. Complete excision with capsule/wall → epidermoid cyst, lipoma, dermatofibroma (if removed).
4. Intralesional triamcinolone → keloid/hypertrophic scar (first line), and inflamed cysts can be settled with intralesional steroid.
5. Excision + adjuvant (steroid/radiotherapy) → keloid (never excision alone).

High-yield: Drug/injection of choice for keloid and hypertrophic scar = intralesional triamcinolone (corticosteroid). Procedure of choice for epidermoid cyst = complete excision of the cyst wall.

Mnemonics

• Seborrhoeic keratosis features — "SPHERE": Stuck-on, Papillomatosis, Horn pseudocysts, Elderly, Rough greasy surface, Eruptive (Leser–Trélat).
• Keloid high-risk sites — "DESS": Deltoid, Ear lobe, Sternum (presternal), Shoulder/upper back.
• Dimple sign → Dermatofibroma (both start with D).

Recently asked / exam angle

• "Stuck-on greasy plaque on the back of an elderly man; histology shows horn pseudocysts" → Seborrhoeic keratosis.
• "Sudden eruption of multiple seborrhoeic keratoses" → Leser–Trélat sign → look for gastric adenocarcinoma.
• "Pinching the skin around a firm leg nodule produces central dimpling" → Dermatofibroma (Fitzpatrick/dimple sign); marker to differentiate from DFSP is CD34 (negative in dermatofibroma, positive in DFSP).
• "Cheesy material from a nodule with a central punctum" → Epidermoid cyst; treat by complete excision with the wall.
• "Rapidly growing bright-red friable lesion on the finger of a pregnant woman that bleeds easily" → Pyogenic granuloma (granuloma gravidarum); exclude amelanotic melanoma.
• "Scar growing beyond the wound margin on the chest/ear lobe; glassy hyalinised collagen" → Keloid; first-line intralesional steroid.
• "Hard nodule in a child with ghost cells and calcification" → Pilomatricoma.
• "Multiple small papules on lower eyelids with tadpole-shaped ducts" → Syringoma.
• Gardner syndrome triad → epidermoid cysts + osteomas + colonic polyposis (FAP).

Rapid revision

1. Seborrhoeic keratosis = stuck-on, greasy; histology = horn pseudocysts; benign, no malignant potential.
2. Leser–Trélat sign = eruptive seborrhoeic keratoses → paraneoplastic, classically gastric adenocarcinoma.
3. Dermatofibroma = dimple/Fitzpatrick sign; CD34-negative, Factor XIIIa-positive; DFSP is CD34-positive.
4. Epidermoid cyst has a granular layer + keratin + central punctum; trichilemmal (pilar) cyst has no granular layer, scalp, familial.
5. "Sebaceous cyst" contains keratin, not sebum — a misnomer.
6. Gardner syndrome = multiple epidermoid cysts + osteomas + FAP.
7. Lipoma = soft, mobile, slip sign; painful/multiple → Dercum disease or angiolipoma; large/deep/painful → suspect liposarcoma (MRI).
8. Pyogenic granuloma = lobular capillary haemangioma, bright-red, friable, bleeds easily; treat with shave + cautery; exclude amelanotic melanoma.
9. Keloid extends beyond wound margins; hypertrophic scar stays within and regresses.
10. Keloid histology = thick glassy hyalinised collagen; first-line treatment = intralesional triamcinolone; never excise alone.
11. Pilomatricoma = ghost cells + calcification in a child; Syringoma = tadpole ducts on eyelids.
12. Investigation of choice when in doubt = histopathology (biopsy/excision); for deep fatty mass = MRI.