Atlas of Dermatopathology

Differential diagnosis is at its most accurate and efficient when clinical presentation and histopathological features are considered in correlation with one another. With this being so, the expert team behind this atlas has integrated both perspectives to create an innovative and essential resource for all those involved with the diagnosis of tumors, cysts, and nevi. Almost 1,400 full-color images clearly illustrate common patterns and variants of tumorous lesions of the skin and are helpfully contextualized by concise, straightforward descriptions of key features and diagnostic clues. Whether they are aspiring or experienced practitioners, dermatologists and pathologists of all levels will find this an insightful and practically applicable addition to their bookshelf. Its far-reaching and easy-to-navigate coverage of relevant diseases of the skin provides trainees with an excellent grounding in the area, while practicing specialists may benefit from its use as a tool for the differential diagnoses of borderline cases. Atlas of Dermatopathology: Tumors, Nevi, and Cysts offers a uniquely balanced, clear, and comprehensive guide to what can be a difficult process, and will be of tremendous assistance tostudents, dermatologists, dermatopathologists, and pathologists everywhere.

Preface xv Acknowledgments xvii 1 EPIDERMIS 1 Nevi 2 Epidermal Nevus 2 Variant: Inflammatory Linear Verrucous Epidermal Nevus (ILVEN) 3 Keratoses 4 Seborrheic Keratosis (SK) and Variants 4 Variant: Acanthotic Seborrheic Keratosis 4 Variant: Reticulated, Pigmented Seborrheic Keratosis 6 Variant: Flat Seborrheic Keratosis 6 Variant: Papillomatous Seborrheic Keratosis 7 Variant: Activated (Irritated) Seborrheic Keratosis 7 Variant: Dermatosis Papulosa Nigra 7 Variant: Melanoacanthoma (Pigmented Seborrheic Keratosis) 8 Variant: Clonal (Intraepidermal) Seborrheic Keratosis (Borst– Jadassohn) 9 Variant: Seborrheic Keratosis with Monster Cells (Bowenoid) 10 Variant: Hyperkeratotic Seborrheic Keratosis (Stucco Keratosis) 11 Confluent and Reticulate Papillomatosis (Gougerot and Carteaud) 12 Reticulate Pigmented Anomaly of the Flexures (Dowling–Degos Disease) 13 Acanthosis Nigricans 14 Solar (Actinic) Keratosis 15 Variant: Acantholytic Solar Keratosis 16 Variant: Atrophic Solar Keratosis 16 Variant: Lichen Planus‐Like Solar Keratosis 17 Variant: Hypertrophic (Bowenoid) Solar Keratosis 18 Cornu Cutaneum 18 Acanthomas, Non‐Viral 19 Solar Lentigo 19 Callus, Factitial Acanthoma 20 Knuckle Pads (Chewing Pads) 21 Pale (Clear) Cell Acanthoma 22 Large Cell Acanthoma 23 Differential Diagnosis: Epidermolytic Acanthoma 24 Differential Diagnosis: Congenital Ichthyosiform Erythroderma 25 Acantholytic Acanthoma 26 Warty Dyskeratoma 27 Porokeratoma (Porokeratosis Mibelli) 30 Acanthomas, Viral 31 Verruca Vulgaris 31 Variant: Verruca Plana 33 Variant: Condyloma Acuminatum 34 Bowenoid Papulosis 35 Acrokeratosis Verruciformis (Hopf) 37 Molluscum Contagiosum 38 “Pseudocarcinomas” and Neoplasms with Intermediate Malignant Potential 40 Keratoacanthoma (KA) 40 Epithelioma Cuniculatum (Verrucous Carcinoma) (EC/VC) 44 Papillomatosis Cutis Carcinoides 45 Florid Papillomatosis of the Oral Cavity (Oral Verrucous Carcinoma) 46 Buschke–Löwenstein Tumor (Giant Condyloma) 47 Malignant Epidermal Neoplasms 48 Bowen’s Disease (Carcinoma in situ) 48 Variant: Clear Cell Bowen’s Disease 50 Variant: Cutaneous Horn (Cornu Cutaneum) on Bowen’s Disease 51 Variant: Pigmented (Anogenital) and Clonal Bowen’s Disease 52 Variant: Erythroplasia of Queyrat and Vulvar Intraepithelial Neoplasia 53 Basal Cell Carcinoma (BCC) 54 Variant: Nodular BCC 54 Variant: Infundibulocystic BCC 56 Variants of BCC With Ductal, Matrical or Sebaceous Differentiation 57 Variant: Superficial BCC 60 Variant: Pigmented BCC 61 Variant: Adenoid‐Cystic BCC 62 Variant: Sclerodermiform (Morpheaform) BCC 64 Clinical Variants: Ulcerating BCCs 66 Histological Variants: Metatypic BCC with Squamoid Differentiation 67 Syndromatic BCC (Basal Cell Nevus Syndrome, Gorlin–Goltz) 69 Fibroepithelioma of Pinkus 70 Squamous Cell Carcinoma (SCC) 72 Variant: Well‐Differentiated SCC 72 Variant: Acantholytic SCC (Epithelioma Spinocellulare Segregans of Delacretaz) 74 Variant: Myxoid SCC 76 Variant: Follicular (Infundibular) SCC 77 Variant: Spindle Cell (Fusicellular) SCC 78 Squamous Cell Carcinomas in Special Sites 79 2 ADNEXAL 85 Sweat Gland Differentiation 86 Nevi, Hyperplasias, and Benign Adnexal Neoplasms (BAN) 86 Eccrine Differentiation 86 Apocrine Differentiation 93 Malignant Adnexal Neoplasms 105 Eccrine Differentiation 105 Apocrine Differentiation 109 Sebaceous Differentiation 110 Hyperplasias and Hamartomas 111 Ectopic (Heterotopic) Sebaceous Glands (Fordyce Glands) 111 (Senile) Sebaceous Gland Hyperplasia 112 Nevus Sebaceous (Jadassohn) 113 Variant: Pilo‐Sebaceous Hamartoma 114 Benign Neoplasms 114 Sebaceous Adenoma 114 Muir–Torre Syndrome 115 Sebaceous Epithelioma (Sebaceoma) 116 Malignant Neoplasms 118 Sebaceous Carcinoma 118 Hair Follicle Differentiation 119 Nevi, Hyperplasia, and Hamartomas 119 Hair Follicle Nevus 119 Conical Infundibular Acanthoma (Giant Dilated Pore of Winer) 120 Benign Neoplasms 121 Pilar Sheath Acanthoma 121 Trichilemmoma (Tricholemmoma) 122 Tumor of the Follicular Infundibulum (Infundibuloma) 124 Trichoepithelioma (Superficial Trichoblastoma) 125 Trichoblastoma (Trichoblastic Fibroma; Immature Trichoepithelioma) 127 Trichoepithelioma (Sclerosing Epithelial Hamartoma) 131 Trichofolliculoma (Folliculosebaceous Cystic Hamartoma) 133 Trichoadenoma (Nikolowski) 136 Pilomatricoma (Calcifying Epithelioma Malherbe) 137 Proliferating Trichilemmal (Pilar) Tumor (PTT) (Proliferating Trichilemmal Cyst) 138 Malignant Neoplasms 140 Malignant Pilomatricoma (Pilomatrical Carcinoma) 140 Trichilemmal Carcinoma 141 Trichoblastic Carcinoma 142 Pilosebaceous Mesenchyme 143 Benign Neoplasm 143 Trichodiscoma (Follicular Fibroma, Fibrofolliculoma, Perifollicular Fibroma) 143 3 PAGET’S DISEASE 145 Mammary Paget’s Disease 146 Extramammary Paget’s Disease 146 4 MELANOCYTES 149 Non‐Neoplastic Hyperpigmentations 150 Ephelides (Genuine Freckles) 150 PUVA (Psoralen UVA) Lentigo 150 “Nevus” Spilus (Speckled Lentiginous Nevus; Café‐Au‐Lait Spot) 151 “Ink” Spot Lentigo (Reticulated Melanocytic Macule) 152 Senile Freckles (Solar [Actinic] Lentigo) 153 Mucosal Lentiginous Spots (Lip, Buccal, and Genital Mucosa) 154 Nevi 155 Common Acquired Melanocytic Nevi 155 Melanosis Neviformis (Pigmented Hairy Epidermal Nevus; Becker Nevus) 155 Junctional Nevus 156 Compound Nevus 157 Dermal Nevus 158 Variant: Miescher’s Nevus (Dermal Nevus) 160 Variant: Balloon Cell Nevus 161 Variant: “Activated” Acral (Lentiginous) Melanocytic Nevus 161 Variant: (Atypical) Genital Melanocytic Nevus 162 Variant: Halo Nevus (Leukoderma Centrifugum Acquisitum; Sutton Nevus) 163 Variant: Eczematoid Melanocytic (Meyerson’s) Nevus 165 Variant: Osteo‐Nevus of Nanta 166 Variant: Combined Epithelioid Spitzoid Nevus, “Wiesner Nevus” (BAP-1 Deficient Epithelioid Melanocytic Tumor) 167 Variant: Recurrent (Persistent) Melanocytic Nevus (Pseudomelanoma) 167 Variant: Nevus in Pregnancy 168 Variant: Ancient Nevus 170 Blue Nevi 171 Common Blue Nevus 171 Common Blue Nevus 172 Dermal Melanocytosis 177 Nevus Fuscoceruleus (Ota; Ito; Mongolian Spot) 177 Spindle and/or Epithelioid Cell Nevus 178 Common Nevus of Spitz 178 Variants of Spindle and Epithelioid Cell Nevus 179 Variant: Pigmented Spindle Cell Nevus (Reed) 182 Benign Melanocytic Lesions with Peculiar Structural Features 183 Melanocytic Nevus with Clonal Proliferation 183 Atypical (Dysplastic) Melanocytic (Clark’s) Nevus (B‐K Mole Syndrome) 185 Congenital Nevi, Small and Medium‐Sized (1.5–20 cm) 186 Malignant Melanocytic Neoplasms 188 Lentigo Maligna Dubreuilh (Hutchinson’s Freckle) 188 Malignant Melanoma 189 Variant: Superficial Spreading Melanoma (SSM) 190 Variant: Lentigo Maligna Melanoma (LMM) 192 Variant: Nodular Melanoma (NM) 193 Variant: Acral Lentiginous Melanoma (ALM) 194 Variant: Melanoma in Large Congenital Melanocytic Nevus (LCMN) 196 Variant: Cutaneous Metastasis of Melanoma 197 Special Localisations of Malignant Melanoma 204 Tumor Thickness and Levels 205 Common Clinical Differential Diagnoses of Malignant Melanoma 205 5 CONNECTIVE TISSUE 207 Nevi 208 Connective Tissue Nevus (Shagreen Patch; Cobblestone Nevus; Nevus Collagenicus) 208 Fibrous Neoplasms 209 Soft Fibroma (Skin Tag; Acrochordon) 209 Perifollicular Fibroma (Fibrofolliculoma; Trichodiscoma) 210 Variant: Sclerotic Fibroma (Plywood Fibroma; Storiform Collagenoma) 211 Variant: Fibrous Papule of the Nose 212 Variant: Pleomorphic Sclerosing Fibroma with Multinucleated Cells 212 Keloid 213 Infantile Digital Fibromatosis (Inclusion Body Fibromatosis; Recurring Digital Fibrous Tumor of Children; Reye’s Tumor) 214 Malformations with Supernumerary Tissue Elements 216 Supernumerary Digit (Rudimentary Digit; Rudimentary Polydactyly) 216 Differential Diagnosis: Acral Acquired Fibrokeratoma 216 Accessory Tragus (Preauricular Tag) 217 Accessory Nipple (Ectopic Breast; Polythelia) 218 Fibrohistiocytic Neoplasms 218 Dermatofibroma (Benign Fibrous Histiocytoma; Fibroma Durum; Sclerosing Hemangioma) 218 Dermatofibrosarcoma Protuberans 227 Variant: Pigmented Dermatofibrosarcoma Protuberans (Bednar’s Tumor) 230 Variant: Giant Cell Fibroblastoma 231 Pleomorphic Dermal Sarcoma (PDS) 231 Miscellaneous Tumors 234 Epithelioid Sarcoma 234 Dermatomyofibroma 236 6 VESSELS 239 Hamartomas, Nevi, and Malformations 240 Phacomatosis Pigmentovascularis 240 Eccrine Angiomatous Hamartoma 241 Nevus Anemicus 242 Capillary Malformations 242 Nevus Flammeus (Port-Wine Stain) 242 Nevus Araneus (Spider Angioma) 244 Cutis Marmorata Telangiectatica (van Lohuizen) (Nevus Vascularis Reticularis) 245 Congenital Telangiectatic Erythema (Bloom’s Syndrome) 247 Venous Malformations 248 Blue Rubber Bleb Nevus Syndrome (Familial Venous Malformation) 248 Hereditary Hemorrhagic Telangiectasia (Osler–Weber–Rendu) 249 Angioma Serpiginosum 250 Venular Aneurysm (Venous Lake) 251 Cavernous Hemangioma (in Maffucci Syndrome) 252 Sinusoidal Hemangioma 253 Spindle Cell Hemangioma (Formerly Spindle Cell Hemangioendothelioma) 254 Arteriovenous Malformations 256 Acral Arteriovenous Hemangioma (Cirsoid Aneurysm) 256 Glomuvenular Malformation (“Glomangioma”) 257 Lymphatic Malformations 259 Superficial Lymphatic Malformation (Superficial Lymphangioma) 259 Cystic Lymphatic Malformation (Cystic Hygroma) 260 Targetoid Hemosiderotic (Hobnail) Hemangioma 261 Progressive Lymphangioma (Benign Lymphangioendothelioma) 262 Lymphangiomatosis 263 Angiokeratomas 264 Verrucous Hemangioma (Venous Malformation) 265 Variant: Solitary Angiokeratoma 268 Variant: Angiokeratoma Circumscriptum Naeviformis 269 Variant: Fordyce Angiokeratoma 269 Variant: Angiokeratoma Acroasphycticum Digitorum (Mibelli) 269 Variant: Multiple “Pinpoint” Angiokeratomas (Angiokeratoma Corporis Diffusum; Fabry’s Disease) 269 Variant: Acral Pseudolymphomatous Angiokeratoma of Children (APACHE) 269 Hyperplasias 270 Granuloma Pyogenicum (Lobular Capillary Hemangioma; Botryomykoma) 270 Differential Diagnosis: Pyogenic Granuloma‐Like Granulation Tissue 272 Bacillary Angiomatosis 273 Verruga Peruana 274 Intravascular Papillary Endothelial Hyperplasia (Masson) 275 Acroangiodermatitis Mali (Pseudo‑Kaposi’s Sarcoma) 276 Benign Vascular Neoplasms 278 Epithelioid Hemangioma (Angiolymphoid Hyperplasia with Eosinophilia, ALHE) 278 Endothelial Differentiation 280 Infantile Capillary and Congenital Hemangioma 280 Cherry Angioma (Senile Hemangioma) 281 Microvenular (Microcapillary) Hemangioma 282 Tufted Angioma 283 Kaposiform Hemangioendothelioma 285 Glomeruloid Hemangioma in POEMS Syndrome 287 Pericytic Differentiation 288 Imitator: Solitary Fibrous Tumor of the Skin (SFT) 289 Myopericytoma (Infantile Myofibromatosis; Perivascular Myoma (incl. Myofibroma)) 290 Glomoid and Myoid Differentiation 292 Glomus Tumor 292 Angioleiomyoma (Angiomyoma; Vascular Leiomyoma) 294 Recently Described Benign Vascular Tumors 296 Symplastic Hemangioma 296 Papillary Hemangioma 297 Vascular Neoplasms of Intermediate Malignant Potential 298 Kaposi’s Sarcoma (KS) 298 Retiform Hemangioendothelioma 305 Composite Hemangioendothelioma 306 Papillary Intralymphatic Angioendothelioma (PILA) (Malignant Endovascular Papillary Angioendothelioma (Dabska Tumor); Endovascular Papillary Hemangioendothelioma) 306 Radiation‐Induced Atypical Vascular Lesion (AVL) (Benign Lymphangiomatous Papule (BLAP)) 308 Vascular Neoplasms with High Malignant Potential 309 Cutaneous Angiosarcoma 309 Radiation‐Induced (Postradiation) Angiosarcoma 312 Epithelioid Hemangioendothelioma 312 Epithelioid Angiosarcoma 315 Differential Diagnosis: Acantholytic (Angiosarcoma‐Like) Squamous Cell Carcinoma 316 Glomangiosarcoma (Malignant Glomus Tumor) 317 Other Neoplasms with Significant Vascular Component 318 Multinucleate Angiohistiocytoma 318 Angiofibroma (Adenoma Sebaceum Associated with Pringle–Bourneville Disease) 319 Angiolipoma 321 Angiolipoleiomyoma (Angiomyolipoma) 322 Angiomyxoma 322 Intralymphatic Histiocytosis 324 Kimura’s Disease 325 7 FAT 327 Nevus (Hamartoma) 328 Nevus Lipomatosus Superficialis Hoffmann Zurhelle 328 Neoplasms of Fat Tissue 329 Benign Neoplasms 329 Common Lipoma and Lipomatosis 329 Angiolipoma (see Vessels, Chapter 6) 330 Angiomyolipoma (see Vessels, Chapter 6) 330 Spindle Cell Lipoma 330 Pleomorphic Lipoma (see Pleomorphic Liposarcoma) 332 Hibernoma 332 Malignant Neoplasms 333 Cutaneous Liposarcoma 333 8 MUSCLE 337 Benign Neoplasms 338 Piloleiomyoma (Pilar Leiomyoma) 338 Angioleiomyoma (see Vessels, Chapter 6) 340 Rhabdomyoma, Adult Type 340 Malignant Neoplasms 341 Rhabdomyosarcoma 341 Superficial Leiomyosarcoma 342 9 NERVES 345 Benign Neoplasms 346 Schwannoma (Neurilemmoma) 349 Solitary Neuroma (“Palisaded Encapsulated Neuroma”) 352 Variant: Traumatic Neuroma 353 Granular Cell Tumor (Abrikossoff) 354 Dermal Nerve Sheath Myxoma (Myxoid Neurothekeoma) 356 Variant: Cellular Neurothekeoma 357 Pacinian Neurofibroma (Pacinoma) 358 Malignant Neoplasms 358 Malignant Peripheral Nerve Sheath Tumor (Malignant Schwannoma) 358 Malignant Granular Cell Tumor 360 Neuroendocrine Neoplasm 360 Primary Neuroendocrine (Merkel Cell, Trabecular) Carcinoma of the Skin 360 10 MAST CELLS 363 Solitary Cutaneous Mast Cell Proliferation 364 Cutaneous Mastocytoma 364 Diffuse Cutaneous Mast Cell Proliferations 365 Urticaria Pigmentosa (Juvenile Maculopapular Mastocytosis) 365 Telangiectasia Macularis Eruptiva Perstans (Adults) 365 Systemic Mast Cell Proliferation 367 Involvement of Skin and Bone Marrow 367 11 HISTIOCYTES 369 Langerhans Cell Histiocytoses (LCH) 370 Precursors of Langerhans Cell Histiocytoses 370 Congenital Self‐healing Reticulohistiocytosis (Hashimoto–Pritzker) 370 Indeterminate Cell Histiocytosis 371 Langerhans Cell Histiocytoses (Histiocytosis X) 371 Congenital Langerhans Cell Histiocytosis (Letterer–Siwe Disease) 372 Hand–Schüller–Christian Adult LHC Histiocytosis 374 Solitary Langerhans Cell Tumor (Eosinophilic Granuloma) 375 Non‐Langerhans Cell Histiocytoses 376 Proliferative 376 Proliferative Histiocytoma (Progressive Nodular Histiocytosis, PNH) 376 Benign Cephalic Histiocytosis 377 Multicentric Reticulohistiocytosis (Lipoid Dermatoarthritis) (Solitary Reticulohistiocytoma) 378 Sinus Histiocytosis With Massive Lymphadenopathy 379 Granulomatous Storing 380 Juvenile Xanthogranuloma (Nevoxanthoendothelioma; Xanthoma Multiplex; Juvenile Giant Cell Granuloma) 380 Xanthelasma Palpebrarum 383 Verruciform Xanthoma 384 Necrobiotic Xanthogranuloma (with Paraproteinemia) 385 Hereditary Progressive Mucinous Histiocytosis 386 Hemophagocytic 387 Familial Hemophagocytic Lymphohistiocytosis 387 Histiocytic Cytophagic Panniculitis 388 12 HEMATOPOIETIC DISORDERS 389 Lymphoid Skin Infiltrates 389 Cytomorphology, Major Cell Types 390 T‐Cells 390 B‐Cells 391 Pattern of Small Cell Lymphocytic Infiltrates 392 T‐Cell Pattern 392 B‐Cell Pattern 392 Pseudolymphoma (PL) 393 Nodular B‐Cell PL 393 Lymphadenosis Cutis Benigna (Lymphocytoma Cutis) 393 Differentiation between B‑Pseudolymphoma (PL) and Cutaneous B‐Cell Lymphoma (CBCL) 395 Nodular T‐Cell PL 396 CD30+ Pseudolymphoma in Scabies 396 Papular (Secondary) Syphilis 398 Pseudo‐Mycosis Fungoides (Mycosis Fungoides Simulators) 399 Lymphomatoid Contact Dermatitis 399 Lichen Planus 399 Drug Reactions 400 Early Vitiligo 400 Lichen Sclerosus et Atrophicus 400 Pityriasis Lichenoides Chronica 401 Graft Versus Host Reaction (Acute) 401 Pityriasis Lichenoides et Varioliformis Acuta (PLEVA) 402 Pigmented Purpuric Dermatitis (Lichen Aureus) 403 Lymphocytic Infiltration Jessner–Kanof 404 Cutaneous Mature T‐Cell Lymphoid Neoplasms (CTCL) 405 Mycosis Fungoides, Classic Alibert–Bazin Type 405 Mycosis Fungoides Patch Stage I 405 Mycosis Fungoides Plaque Stage II (CD4+; CD8−) 407 Variant: CD8+ Mycosis Fungoides 409 Mycosis Fungoides Tumor Stage III 409 Large Cell Transformation 410 Simulators and Variants of Mycosis Fungoides: “Parapsoriasis” 411 Simulator: Small Plaque Parapsoriasis (SPP) (Brocq’s Disease, Digitate Dermatosis) 411 Large Plaque Parapsoriasis (LPP) 412 Pigmented Purpuric Mycosis Fungoides 412 Erythrodermic Mycosis Fungoides 412 Folliculotropic (Pilotropic) Mycosis Fungoides 413 Syringotropic Mycosis Fungoides (Syringolymphoid Hyperplasia with Alopecia) 414 Granulomatous Mycosis Fungoides 415 Granulomatous Slack Skin 415 Pagetoid Reticulosis (PR), Unilesional (Woringer–Kolopp) 417 Sézary Syndrome (SS) 418 Variant: Sézary Syndrome, Large Cell Transformation 420 CD30‐Positive Lymphoproliferative Disorders (LPD) of the Skin 423 Anaplastic Large Cell Lymphoma (ALCL) 424 Neutrophil‐Rich (Pyogenic) Anaplastic Large Cell Lymphoma 426 Lymphomatoid Papulosis 427 Differential Diagnosis: Hodgkin’s Lymphoma, Lymphocyte Predominance 429 Subcutaneous Panniculitis‐Like Lymphoma 431 Subcutaneous (Panniculitis-Like; Alpha/Beta) T‐Cell Lymphoma 431 Differential Diagnosis: Subcutaneous (Panniculitis‐Like) Gamma/Delta lymphoma 432 Differential Diagnosis: Lupus Panniculitis (Lupus Profundus) 433 Primary Cutaneous Peripheral Lymphoma (PTL), Unspecified (NOS) 434 Primary Cutaneous CD4‐positive (Acral) Small/Medium‐Sized T‐Cell Lymphoproliferative Disorder 435 Cutaneous Aggressive Epidermotropic CD8‐positive T‐Cell Lymphoma (Berti) 436 Differential Diagnosis: Febrile Ulceronecrotic PLEVA (Mucha–Habermann Disease) 437 Extranodal NK/T‐Cell Lymphoma, Nasal Type (Subcutaneous) 439 Hydroa Vacciniforme‐Like Lymphoma 440 Angioimmunoblastic T‐Cell Lymphoma 441 Cutaneous Mature B‐Cell Lymphoid Neoplasms (CBCL) 443 Cutaneous Marginal Zone B‐Cell Lymphoma (MZL; MALT Type) 444 Variant: Immunocytoma 447 Differential Diagnoses: Multiple Myeloma/Plasmacytoma 448 Primary Cutaneous Follicle Center Lymphoma (FCL) 449 Diffuse Large B‐Cell Lymphoma (DLBCL) 451 Variant: Cutaneous Diffuse Large B‐Cell Lymphoma (Leg Type) 451 Variant: T‐Cell‐Rich B‐Cell Lymphoma (DLBCL) 454 Cutaneous Spindle B‐Cell Lymphoma 455 Extracutaneous B‐Cell Lymphoma (BCL) with Frequent Skin Involvement 457 Mantle Cell Lymphoma 457 Burkitt’s Lymphoma (BL) 458 Lymphomatoid Granulomatosis (Liebow) (LYG) 460 Intravascular Lymphomas 461 Intravascular Large B‐Cell Lymphoma (IV‐LBCL) (Systemic Angioendotheliomatosis) 461 Intravascular T Cell Lymphoma 462 Secondary Skin Involvement in Leukemias/Lymphomas 463 Chronic Lymphocytic Leukemia (CLL) 463 Myeloid and Monocytic Leukemias 464 T‐Zone Lymphoma 466 Adult T‐Cell Leukemia/ Lymphoma (ATLL) 467 Immature Hematopoietic Malignancies 468 Blastic Plasmacytoid Dendritic Cell Neoplasm 468 Precursor Lymphoblastic Leukemia/Lymphoma 470 13 CUTANEOUS CYSTS 471 Cysts with Epithelial Lining 472 Stratified Squamous Epithelium 472 Epidermal (Infundibular) Cysts 472 Variant: Epidermal Proliferating Cyst 473 Variant: Epidermal Cyst with Pigment and Vellus Hairs 473 Vellus Hair Cyst 474 Trichilemmal (Isthmus‐Catagen) Cyst 475 Milia 476 Follicular Hybrid Cyst 477 Hidrocystoma (Cystadenoma) 478 Steatocystoma, Multiplex and Simplex 481 Dermoid Cyst 482 Pilonidal Sinus (Pilonidal Cyst) 484 Non‐Stratified Squamous Epithelium 485 Cutaneous Ciliated Cyst of the Lower Limb 485 Median Raphe Cyst 486 Cysts without Epithelial Lining (Pseudocysts) 487 Oral Mucous Cyst and Superficial Mucocele of the Lip 487 Digital Myxoid Cyst 488 Synovial Cyst (Ganglion) 490 Index 491