Pilar cyst (syn. trichilemmal cyst)

A pilar cyst is a common benign cyst usually found on the scalp. It contains keratin and its breakdown products, and is lined by walls resembling the external root sheath of hair.

This chapter is set out as follows:

• A family history may be present because the condition can have an autosomal dominant pattern of inheritance

• Mainly arise in middle-aged patients
• Woman are affected more than men
• Lesions tend to be asymptomatic although they can be painful if they rupture, or less commonly become infected

Distribution

• Over 90% arise on the scalp
• Approximately one-third of lesions are solitary and two-thirds are multiple

Morphology

• A smooth, mobile, firm, round nodule
• No punctum (unlike an epidermoid cyst)

• Make sure that the history fits with the clinical diagnosis - although the diagnosis is usually straightforward, beware of the possibility of dermoid cysts, which present from birth to early childhood and are found over fusion lines. Dermoid cysts on the face and scalp can have deep connections to the meninges and radiography is required where such a diagnosis is suspected

• Provide a patient information leaflet

• Surgical treatment of pilar cysts
  
  • Problematic cysts can be excised
  • Incomplete excision of the cyst, including the sac can lead to recurrence