Visual Appearance of Sebaceous Cysts in Children
Sebaceous cysts (more accurately termed epidermoid cysts) in children present as mobile, flesh-colored or slightly yellowish nodules with a characteristic central punctum (small opening), containing thick white-yellow cheesy keratinous material. 1, 2
Key Visual Features
Primary Characteristics
- Appearance: Smooth, round or oval, flesh-colored to slightly yellow nodules that are mobile under the skin 1
- Central punctum: A small, dark, pore-like opening in the center of the cyst is the pathognomonic feature that distinguishes epidermoid cysts from other masses 1, 3
- Size: Typically range from a few millimeters to several centimeters, though giant variants (>5 cm) can occur 4, 5
- Consistency: Firm, mobile, and non-tender unless inflamed 1, 2
Common Locations in Children
- Scalp (most common hairy area) 4, 6
- Face and neck 5, 6
- Trunk and back 4, 3
- Scrotum (less common but documented) 7, 6
Ultrasound Appearance (When Imaging Performed)
- Oval-shaped hypoechoic lesions in 96.6% of cases 3
- "Pseudotestis" pattern: Homogeneous appearance seen in approximately 50% of cases 3
- Visible skin pore (punctum) can be identified with high-frequency probes (18-20 MHz) 3
Critical Distinctions from Other Pediatric Lesions
When Inflamed or Ruptured
- Becomes painful, red, and swollen, mimicking an abscess but with a pre-existing longstanding nodule history 1, 2
- Contains thick white-yellow keratinous debris mixed with pus rather than pure purulent material 1
- Inflammation results from cyst wall rupture and extrusion of contents into dermis, not true bacterial infection 1, 2
Differential Diagnosis Pitfalls
Mastocytomas can mimic cysts in infants but have distinct features: they present at birth or within the first week, demonstrate positive Darier's sign (wheal formation after rubbing), and can rapidly progress to bullae formation within 24 hours 8. Sebaceous cysts lack these characteristics and do not exhibit Darier's sign 8.
Dermoid cysts are congenital and contain more complex structures (hair, teeth, cartilage) visible on ultrasound as hyperechoic components with acoustic shadowing, whereas epidermoid cysts show simpler homogeneous contents 1, 2.
Red Flags Requiring Biopsy in Children
- Rapid growth or ulceration 1
- Indurated, irregular borders or fixation to underlying structures 1
- Loss of normal tissue architecture or focal hair loss 1
- Chronic lesion unresponsive to standard therapy 1
- Marked asymmetry 1
Management Pearls
Avoid misdiagnosing inflamed epidermoid cysts as simple abscesses, which leads to inappropriate antibiotic-only treatment without addressing the cyst wall, resulting in inevitable recurrence 1. Effective treatment requires incision, thorough evacuation of contents, and probing the cavity to break up loculations 2. Systemic antibiotics are rarely necessary unless extensive surrounding cellulitis or systemic manifestations are present 2.