Epidermoid cyst - Hair and Scalp
Several etiologic factors have been implicated in the formation of epidermoid cysts, including traumatic or iatrogenic implantation of epidermal elements, sequestration of epidermal rests, occlusion of the eccrine duct or pilosebaceous unit, and human papillomavirus (HPV) infection. Epidermoid cysts are a feature of several hereditary syndromes, such as Gardner syndrome, pachyonychia congenita, and the basal cell nevus syndrome.
Epidermoid cysts are benign and usually asymptomatic, but they may be painful if ruptured or infected. Rarely, malignancies such as basal cell carcinoma, squamous cell carcinoma, and mycosis fungoides have developed within these cysts.
Pediatric Patient Considerations:
It is rare to see an epidermoid cyst in a pre-pubertal patient; in such cases, other diagnoses should be carefully considered.
L72.0 – Epidermal cyst
419893006 – Epidermoid cyst
Differential Diagnosis & Pitfalls
- Pilar cyst (trichilemmal cyst) – most commonly located on the scalp; usually has a more firm consistency on palpation
- Eruptive vellus hair cyst
- Calcinosis cutis
- Rheumatoid nodule
- Dermoid cyst
- Branchial cleft cyst or thyroglossal duct cyst
- Cutaneous metastatic malignancy
- Mixed tumor
- Proliferating trichilemmal cyst
Epidermoid cysts are rare before puberty, and alternative diagnoses should be strongly considered in infancy and childhood.
Cyst rupture with associated inflammation is often misdiagnosed as an "infection" of the cyst. Cultures are usually negative, and treatment with antibiotics is not required.
Superficial lymph nodes are palpated within the subcutaneous fat and are found within the course of lymphatics.
- Lipomas are soft, mobile subcutaneous nodules with normal overlying epidermis.
- Pilar cysts (trichilemmal cysts) may be clinically indistinguishable from epidermoid cysts but are more common in childhood and are typically found on the scalp.
- Pilomatricoma usually presents as a solitary skin-colored to faint blue nodule, frequently found on the head or upper trunk in children. Firmness is a reflection of calcification within this benign tumor.
- Steatocystomas occur as asymptomatic single or multiple cysts on the chest, axillae, and/or groin that may drain an oily substance if punctured. Multiple steatocystomas are seen in some patients with pachyonychia congenita.
- Dermoid cysts result from anomalies in embryonic closure zones. Surgical removal or biopsy of a cyst over the midline should not be attempted without proper imaging to rule out intraspinal or intracranial connection.
- Thyroglossal duct cysts present as midline cystic nodules on the neck in children.
- Branchial cleft cysts present in the second or third decade as a nodule in the preauricular area, mandibular region, or along the anterior border of the sternocleidomastoid muscle.
- Bronchogenic cysts are most frequently found in the suprasternal notch, and they represent sequestered respiratory epithelium during embryological development.