Two of the most common benign skin and subcutaneous tumors; soft mobile fatty mass vs. tense punctate-pored cyst.
Also known as: lipoma, epidermoid cyst, sebaceous cyst, epidermal inclusion cyst, EIC
Overview
Lipoma: benign, slow-growing tumor of mature adipocytes encased in a thin fibrous capsule, located in subcutaneous tissue. Epidermoid (epidermal inclusion) cyst: benign, dermal, encapsulated keratin-filled cyst lined by keratinizing squamous epithelium, typically connected to the surface by a central punctum (the term 'sebaceous cyst' is a misnomer because the cyst contents are keratin, not sebum).
Epidemiology
Lipomas are the most common soft tissue tumor; estimated 1% of the general population has at least one. Peak onset 40-60 years. Epidermoid cysts are equally common, particularly on the face, scalp, neck, trunk, and scrotum. Familial multiple lipomatosis and Gardner syndrome (associated with epidermoid cysts and colonic polyposis) are noteworthy syndromic presentations.
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Lipomas arise from mature adipocytes proliferating within a thin fibrous capsule; molecular studies show frequent rearrangement of HMGA2 (chromosome 12q14). Epidermoid cysts arise from implanted or proliferating follicular infundibular epithelium, often after pilosebaceous follicle occlusion or trauma; the keratinizing squamous lining sheds keratin into the cyst cavity.
Clinical presentation
Symptoms
Lipoma: gradual, painless, soft subcutaneous mass; most commonly asymptomatic; cosmetic concern or rare pressure on adjacent structures
Epidermoid cyst: dome-shaped dermal nodule with central punctum, slowly enlarging; may discharge cheesy, foul-smelling keratin material
Inflamed/ruptured epidermoid cyst: acute painful, red, swollen nodule mimicking abscess; rupture releases keratin into the dermis triggering a foreign-body response
Signs / physical exam
Lipoma: soft, doughy, freely mobile, well-circumscribed, painless mass under intact skin; classically on neck, trunk, and proximal extremities; transilluminates poorly; 'slippage sign' (gentle pressure causes the lipoma to slide laterally)
Epidermoid cyst: firm, mobile, dermal cyst with a visible central punctum; expression of cheesy keratin contents from the punctum confirms the diagnosis
Inflamed cyst: erythema, warmth, tenderness, possible spontaneous drainage of pasty foul-smelling material
Classic findings
Soft, mobile, painless subcutaneous mass with slippage sign (lipoma); firm dermal cyst with a central punctum and expressible cheesy keratin (epidermoid cyst).
Differential diagnosis
Liposarcoma — Rapid growth, size >5 cm, deep (subfascial) location, firmness, pain — MRI and biopsy/excision are warranted
Angiolipoma — Multiple small tender lipomas in young adults, often forearms; benign but painful
Pilar (trichilemmal) cyst — Scalp; no punctum; lined by trichilemmal-type epithelium; cheesy contents
Steatocystoma — Multiple small cysts (steatocystoma multiplex) on trunk; sebaceous lining; contains oil
Dermoid cyst — Lateral brow or midline scalp; congenital; may extend to bone
Abscess — Acute warm, erythematous, fluctuant mass with systemic symptoms; requires drainage; distinct from a quietly inflamed cyst
Lymph node, ganglion cyst, or hernia (depending on site) — Anatomic location and exam differentiate
Diagnostic workup
Diagnostic criteria
Clinical diagnosis in straightforward cases. Histopathology of an excised lesion is definitive when malignancy concerns exist or for atypical lesions.
Labs
Generally none required for typical lesions
Bacterial culture if abscess vs. inflamed cyst is unclear
Genetic and gastroenterology evaluation for Gardner syndrome if multiple cysts, osteomas, or family history of colon cancer/polyposis
Imaging
Ultrasound when lesion depth or character is uncertain — distinguishes lipoma (well-defined homogeneous hyperechoic mass) from cyst (anechoic to hypoechoic with posterior enhancement)
MRI for large (>5 cm), deep, painful, or rapidly growing fatty masses to exclude liposarcoma (look for thick septa, nodularity, non-fatty components, contrast enhancement)
CT/MRI if Gardner syndrome under consideration (mesenteric desmoid tumors, osteomas)
Diagnostic algorithm
Feature
Lipoma
Epidermoid (Sebaceous) Cyst
Layer
Subcutaneous (deep to dermis)
Dermal (within skin)
Consistency
Soft, doughy, lobulated
Firm, mobile
Mobility
Slips under finger ('slippage sign')
Moves with skin
Surface clue
Skin entirely normal
Central punctum visible
Contents
Mature adipocytes
Cheesy keratin
Inflammation/drainage
Rare
Common when ruptured
Red-flag features
>5 cm, rapid growth, pain, deep/subfascial → MRI
Recurrent or atypical → look for Gardner syndrome
First-line therapy
Observation or excision
Excision with full capsule removal
Lipoma vs. epidermoid cyst — distinguishing exam and management features.
Treatment
First-line
Lipoma: observation if asymptomatic and cosmetically acceptable; surgical excision (simple enucleation with capsule) is the definitive treatment for symptomatic, cosmetically bothersome, large, or atypical lesions
Epidermoid cyst (non-inflamed): elliptical excision with removal of the entire cyst wall — incomplete capsule removal is the most common cause of recurrence; minimal-incision technique with punch-and-squeeze acceptable for small cysts
Inflamed/ruptured epidermoid cyst: incision and drainage of pus, packing if abscess; defer formal excision for 4-6 weeks until inflammation resolves; intralesional triamcinolone 10-20 mg/mL can quiet inflammation
Add oral antibiotics (cephalexin, doxycycline, TMP-SMX) only for surrounding cellulitis or systemic signs
Second-line / adjunct
Liposuction or endoscopic lipoma removal for cosmetic concerns or multiple lipomas
Recurrent cysts: re-excise with wider margin to capture residual capsule
Intralesional steroids can reduce inflammation in chronically inflamed cysts
Refer for colonoscopy, ophthalmology (CHRPE), and genetics evaluation when Gardner syndrome is suspected
Patients with multiple, painful, or rapidly growing lipomas or with strong family history warrant evaluation for syndromes (familial multiple lipomatosis, Madelung disease, Dercum disease)
Complications
Lipoma: rare misdiagnosis of liposarcoma; nerve compression; cosmetic concerns
Epidermoid cyst: recurrence after incomplete removal, infection/abscess, scarring
Rare malignant transformation of long-standing epidermoid cyst (SCC, BCC) — biopsy any rapidly growing, ulcerated, or unusually firm cyst
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