Benign Skin Tumors

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Epidermal Wonders - Surface Stars

  • Seborrheic Keratosis (SK):

    • Elderly; "stuck-on" waxy papules/plaques.
    • Micro: Horn cysts, pseudohorn cysts, acanthosis.

    ⭐ 📌 Leser-Trélat sign: Sudden ↑ SKs → internal malignancy (GI, esp. gastric adenocarcinoma).

  • Acanthosis Nigricans:

    • Velvety, hyperpigmented plaques (axilla, neck).
    • Assoc: Insulin resistance (DM, obesity), malignancy (gastric adenocarcinoma).
  • Epidermal Nevus:

    • Congenital; linear verrucous plaques (Lines of Blaschko).
    • Variants exist (e.g., ILVEN - inflammatory).
  • Keratoacanthoma (KA):

    • Rapid growth; dome-shaped nodule, central keratin plug. Sun-exposed.
    • Spontaneous regression common; often treated as SCC due to similarity.
  • Clear Cell Acanthoma:

    • Solitary, red-brown, "stuck-on" plaque (lower limbs).
    • Micro: Sharply demarcated pale, glycogen-rich keratinocytes (PAS+).

Melanocytic Marvels - Pigment Powerhouses

  • Melanocytic Nevi (Moles): Benign melanocyte clusters.
    • Junctional Nevus: Nests at dermoepidermal junction (DEJ). Flat, dark.
    • Compound Nevus: Nests at DEJ & in dermis. Raised, pigmented.
    • Intradermal Nevus: Dermal nests. Dome-shaped, often flesh-colored.
  • Blue Nevus: Deep dermal dendritic melanocytes. Blue hue (Tyndall effect). Common type < 1 cm.
  • Spitz Nevus: Usually children < 10 yrs. Pink/red nodule. Spindle/epithelioid cells. Kamino bodies (eosinophilic globules). Spitz nevus histology with Kamino bodies
  • Halo Nevus (Sutton's Nevus): Central nevus with surrounding depigmented halo. Immune (lymphocytic) reaction.
  • Becker's Nevus: Androgen-sensitive hamartoma. Unilateral hyperpigmented patch, often with hypertrichosis. Not true melanocytic nevus.

⭐ Spitz Nevus: Benign, but can mimic melanoma histologically. Key diagnostic feature: Kamino bodies (eosinophilic, PAS-D positive globules within the epidermis).

Dermal Delights - Connective Characters

  • Dermatofibroma (DF)
    • Fibroblasts, histiocytes, storiform pattern.
    • 📌 "Dimple sign" (Fitzpatrick's) on compression.
    • Factor XIIIa+. Peripheral collagen trapping (collagen balls).
  • Neurofibroma
    • Schwann cells, perineurial cells, fibroblasts in loose/myxoid stroma.
    • Associated with Neurofibromatosis Type 1 (NF1).
    • S100+ (often focal).
  • Schwannoma (Neurilemmoma)
    • Encapsulated. Pure Schwann cells.
    • Biphasic: Antoni A (cellular, Verocay bodies) & Antoni B (myxoid).
    • Strongly S100+.
  • Lipoma
    • Benign tumor of mature adipocytes.
    • Most common mesenchymal tumor.
  • Leiomyoma
    • From smooth muscle (e.g., arrector pili - piloleiomyoma).
    • Often painful.
  • Keloid
    • Overgrowth of dense, hyalinized collagen (Type I & III) beyond original wound.
    • Thick, eosinophilic collagen bundles.

⭐ Verocay bodies, palisading arrangements of Schwann cell nuclei around acellular eosinophilic areas, are characteristic of Antoni A tissue in Schwannomas. Neurofibroma with floret-like giant cells

Appendageal Aces - Glandular & Hairy Heroes

  • Glandular (Sweat & Sebaceous):
    • Syringoma: Periorbital; "tadpole" ducts (epithelial strands, comma-like tails).
    • Eccrine Spiradenoma: Painful blue nodule (📌 "Blue Suede Shoe"); two cell types.
    • Cylindroma: "Jigsaw puzzle" epithelial nests; "Turban tumor"; CYLD gene.
    • Sebaceous Adenoma: Foamy sebocytes & basaloid cells; Muir-Torre Syndrome link.
    • Syringocystadenoma Papilliferum: Papillary fronds, plasma cells; often in nevus sebaceus.
  • Follicular (Hairy):
    • Trichoepithelioma: Basaloid cells, horn cysts, abortive hair papillae.
    • Pilomatricoma: Firm nodule; "ghost cells" (shadow cells), basaloid cells, calcification. CTNNB1 gene.

      ⭐ Muir-Torre Syndrome: Sebaceous neoplasms + keratoacanthomas. DNA mismatch repair gene mutations (MSH2, MLH1). ↑ risk of visceral cancers (colorectal, GU).

Pilomatricoma histopathologyoka

High‑Yield Points - ⚡ Biggest Takeaways

  • Seborrheic Keratosis: Leser-Trélat sign (paraneoplastic). Horn cysts, "stuck-on" appearance.
  • Keratoacanthoma: Rapid growth, volcano-like nodule with central keratin plug. May spontaneously regress.
  • Dermatofibroma: Dimple sign (Fitzpatrick sign) on lateral pressure. Factor XIIIa positive.
  • Epidermal Cyst: Most common cutaneous cyst; contains keratin from hair follicle infundibulum.
  • Pilar Cyst (Trichilemmal): Commonly on scalp. Dense eosinophilic keratin, absent granular layer.
  • Syringoma: Benign eccrine duct tumor. Multiple small, periorbital papules. Tadpole/comma-shaped ducts histologically.
  • Nevus: Spitz nevus can clinically and histologically resemble melanoma. Congenital nevi carry an increased risk of melanoma development.
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Practice Questions: Benign Skin Tumors

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Which of the following conditions is associated with acanthosis nigricans?

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Flashcards: Benign Skin Tumors

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_____ nevus is a non-nested dermal infiltration of highly dendritic heavily pigmented nevus cells

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_____ nevus is a non-nested dermal infiltration of highly dendritic heavily pigmented nevus cells

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