Epidermal
Inclusion Cyst
(Epidermoid cyst)

Well-demarcated skin-colored nodule, ± visible central punctum

Cyst lined by stratified squamous epithelium with granular layer and contains lamellated keratin; multiple cysts in Gardner syndrome

Pilar Cyst
(Trichilemmal cyst)

Clinically indistinguishable from EIC but located on scalp, frequently multiple

Lined by stratified squamous epithelium, no granular layer, cyst contains homogenized keratin, ± foci of calcification

Proliferating
Trichilemmal Cyst

{Neoplastic cells undergoing trichilemmal keratinization}

Slow-growing nodule on scalp

Well-circumscribed nodule in deep dermis with solid and cystic patterns, neoplastic cells with some degree of hyperchromasia and mitotic figures, “horn pearls,” foreign body giant cell reaction, tumor with pushing margins, ± foci of calcification

Congenital cyst often on face (often lateral eyebrow)

Lined by squamous epithelium with granular layer and cyst contains lamellated keratin and ± hair shafts, multiple pilosebaceous units appear near cyst lining

Tiny dome-shaped skin-colored to pigmented papules on trunk in children

Lined by squamous epithelium with granular layer and cyst contains lamellated keratin and ± vellus hairs

Dermal skin-colored to yellow nodule in dermis that drains oily fluid if punctured, common in chest, axilla, and groin

Cyst lined by stratified squamous epithelium with granular layer with thin, corrugated eosinophilic cuticle, adjacent sebaceous lobules next to cyst wall

{Multiple seen in steatocystoma multiplex}

Translucent, skin-colored to bluish cyst commonly on face

Unilocular or multilocular cyst lined by layers of epithelial cells and luminal decapitation secretion, cyst appears empty

Solitary cyst mainly in suprasternal notch or anterior neck at birth

Lined by pseudostratified ciliated columnar epithelium with interspersed goblet cells, cyst lining often surrounded by smooth muscle, mucous glands, cartilage, or lymphoid follicles

Cystic nodule commonly over midline anterior neck in children or young adults

Lined with cuboidal, columnar, or stratified squamous epithelium, may contain some ciliated columnar cells, characteristic thyroid follicles in cyst wall (low cuboidal cells surrounding pink homogenous material)

Congenital cyst often arising on lateral neck; due to incomplete involution of branchial cleft structures

Lined by stratified squamous epithelium or pseudostratified ciliated columnar epithelium, surrounded by lymphoid tissue; prudent to delineate extent of lesion by CT or MRI before cyst removal

Fluid-filled cavity in the cartilaginous portion of ear

Intracartilaginous cavity without epithelial lining, surrounding degenerated cartilage and hyalinized material