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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Question 1DermatologyMedium
A 52-year-old woman has a 1.5-cm firm, round nodule just behind her right ear that has slowly enlarged over 3 years. There is a tiny dark pore at its center, and when she squeezes it, a foul-smelling, cheesy white material occasionally comes out. The nodule is not red, warm, or tender. She asks to have it removed because it rubs against her eyeglass frame. Which of the following is the most appropriate management?
AShave removal of the cyst flush with the skin surface
BElliptical excision of the cyst and overlying skin
CIntralesional triamcinolone injection into the cyst
DCryotherapy of the cyst with liquid nitrogen spray
EIncision and drainage with expression of contents
Reveal answer & full explanation
Correct answer: B — Elliptical excision of the cyst and overlying skin
AShave removal of the cyst flush with the skin surface
BElliptical excision of the cyst and overlying skin✓
CIntralesional triamcinolone injection into the cyst
DCryotherapy of the cyst with liquid nitrogen spray
EIncision and drainage with expression of contents
Why Elliptical excision of the cyst and overlying skin is correct
A firm nodule with a central pore (punctum) that extrudes cheesy keratin is an epidermoid (epidermal inclusion) cyst. It is a sac lined by stratified squamous epithelium, usually arising from the follicular infundibulum, and the lining keeps making keratin.
This cyst is not inflamed: it is not red, warm, or tender. A non-inflamed cyst that bothers the patient is removed electively.
The lining produces the contents, so the cyst is cured only when the whole sac comes out. An ellipse of skin that includes the punctum is excised and the sac is dissected out intact, which makes recurrence uncommon.
The best time to operate is while the cyst is not inflamed, because the wall is distinct and peels away cleanly. After an inflammatory flare the wall becomes friable and scarred into the surrounding tissue.
Why the others are wrong
Incision and drainage with expression of contents — This empties the keratin but leaves the epithelial lining behind, so the cyst refills and recurs. I&D is a temporary measure for an inflamed, fluctuant cyst; this one is not red, warm, or tender, so there is no abscess to drain, and the goal is definitive removal. It is also not the minimal-excision technique, which works only because the entire sac is pulled out through the small incision (the trap is treating every cyst as something to drain).
Shave removal of the cyst flush with the skin surface — A flush shave takes off only the part above the skin surface. The sac sits in the dermis below the plane of the shave, so the retained wall regrows the cyst. Shave removal suits raised, superficial lesions such as seborrheic keratoses and skin tags, not a dermal cyst (the trap is assuming any removal of the bump will cure it).
Cryotherapy of the cyst with liquid nitrogen spray — Liquid nitrogen destroys superficial epidermal lesions such as actinic keratoses and warts. It does not reliably reach or destroy a sac lying in the dermis, so the lining survives and the cyst recurs, and the patient may be left with blistering and hypopigmentation (the trap is treating a dermal cyst like a surface growth).
Intralesional triamcinolone injection into the cyst — intralesional steroid can settle a red, swollen cyst, which makes it tempting, but it only reduces inflammation and leaves the keratin-producing lining in place. This cyst is not inflamed and she wants it removed, so injection neither cures nor removes it and can leave dermal atrophy or hypopigmentation (the trap is treating a cyst like an inflamed acne nodule).
Additional high-yield points
A minimal-incision technique (punch or small linear incision, expression of the contents, then extraction of the entire sac) is an acceptable alternative to elliptical excision if the whole wall is delivered.
Oral antibiotics have no role in an uncomplicated epidermoid cyst. The foul odor reflects the trapped keratin and lipid-rich debris; in a cyst that is not red, warm, or tender, it does not mean the cyst is infected, and antibiotics cannot remove the epithelial lining.
When an epidermoid cyst ruptures, the 'inflamed cyst' is usually a foreign-body inflammatory reaction to spilled keratin rather than a true infection, so antibiotics are not routinely needed.
'Sebaceous cyst' is a misnomer for an epidermoid cyst: the lining is epidermal and the contents are keratin, not sebum. A true sebaceous-duct cyst (steatocystoma) is a different lesion.
Many epidermoid cysts, especially at unusual sites or at a young age, together with osteomas and colonic polyps, suggest Gardner syndrome (a variant of familial adenomatous polyposis).
Malignant change in an epidermoid cyst is rare. If a cyst grows fast, ulcerates, or keeps recurring, send the excised specimen for histology.
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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
Multiple, prepubertal, or unusual-site cysts ± osteomas → Gardner syndrome; rapid growth or ulceration → histology
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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