Dermatology · Benign Skin Lesions
The facts most likely to be tested
An epidermal inclusion cyst is a benign, firm, mobile, subcutaneous nodule that originates from the infundibulum of the hair follicle.
The classic physical exam finding is a central punctum representing the keratin-filled pore that communicates with the surface.
The cyst contains a cheesy, foul-smelling keratinous debris that is often expressed if the lesion is ruptured.
Asymptomatic cysts require no treatment and are managed with observation unless they become inflamed or cosmetically bothersome.
Inflamed or infected cysts should be treated with intralesional triamcinolone or incision and drainage rather than immediate excision.
Complete surgical excision is the definitive treatment to prevent recurrence, but it must be delayed until any active inflammation has resolved.
Multiple epidermal inclusion cysts in a young patient should raise suspicion for Gardner syndrome, a variant of familial adenomatous polyposis.
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A 28-year-old male presents to the clinic for a persistent bump on his upper back. Physical examination reveals a 1.5 cm, firm, mobile, non-tender subcutaneous nodule with a visible central punctum. The patient reports that the lesion occasionally expresses a cheesy, malodorous material when squeezed. There are no signs of overlying erythema, warmth, or fluctuance.
What is the most appropriate management for this patient?
Observation
The patient presents with a classic asymptomatic epidermal inclusion cyst; because there is no evidence of infection or inflammation, no active intervention is required.
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Etiology / Epidemiology
Common benign lesion arising from trauma or hair follicle obstruction; most frequent in young to middle-aged adults.
Clinical Manifestations
Firm, mobile, subcutaneous nodule with a central punctum; expresses cheesy, foul-smelling keratin debris.
Diagnosis
Primarily clinical diagnosis; excision biopsy is the gold standard if malignancy is suspected.
Treatment
Observation for asymptomatic lesions; surgical excision (including the cyst wall) for symptomatic or cosmetic concerns.
Prognosis
Generally benign; rupture leads to intense inflammation mimicking an abscess.
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Epidemiology & Etiology
These cysts are the most common cutaneous cysts, often occurring on the face, neck, and trunk. They arise from the implantation of epidermal elements into the dermis or obstruction of the pilosebaceous unit. Gardner syndrome should be considered if multiple cysts appear in a young patient.
Pertinent Anatomy
The cyst is lined with stratified squamous epithelium containing a granular layer. It is located within the dermis or subcutaneous tissue, distinct from the epidermis itself.
Pathophysiology
The cyst wall produces keratin, which accumulates within the lumen over time. This creates a firm, round, slow-growing mass. If the wall is breached, the keratinous contents act as a foreign body, triggering a sterile inflammatory response.
Clinical Manifestations
Patients present with a slow-growing, painless nodule that may be tethered to the skin surface. The presence of a central punctum is the pathognomonic feature. Rapid expansion, erythema, and warmth suggest secondary infection or rupture, which may require incision and drainage.
Diagnosis
Diagnosis is typically made via physical exam. If the lesion is atypical, rapidly growing, or fixed to deep structures, excisional biopsy is the gold standard to rule out malignancy. Imaging is rarely required unless the lesion is deep or suspected to be a lipoma.
Treatment
Asymptomatic cysts require no intervention. Complete surgical excision is the definitive treatment; the entire cyst wall must be removed to prevent recurrence. Do not perform simple incision and drainage for non-inflamed cysts, as the remaining wall will lead to high recurrence rates.
Prognosis
Prognosis is excellent with complete removal. Recurrence is the most common complication if the wall is incompletely excised. Malignant transformation into squamous cell carcinoma is rare but possible in long-standing, neglected lesions.
Differential Diagnosis
Lipoma: soft, doughy, lacks a central punctum
Dermoid cyst: typically congenital, midline location
Pilar cyst: lacks a punctum, common on the scalp
Abscess: acute onset, fluctuant, signs of systemic infection
Steatocystoma: multiple small cysts containing sebum