Overview

A pilar cyst, also known as a trichilemmal cyst, is a benign, slow-growing lump that typically forms from a hair follicle. These cysts are most commonly found on the scalp but can also appear on other hair-bearing areas of the body, such as the neck or back. Pilar cysts are filled with keratin, a protein found in skin and hair, and are usually smooth, firm, and mobile beneath the skin. They are non-cancerous and generally harmless, although they may cause cosmetic concerns or discomfort, especially if they grow large or become infected. Pilar cysts are more prevalent in adults, with a higher occurrence in women, often with a familial predisposition.

Causes

The exact cause of pilar cysts is not always clear, but several factors contribute to their formation:

• Hair follicle obstruction: Pilar cysts develop when the outer root sheath of the hair follicle becomes blocked, causing keratin to accumulate and form a cystic structure.
• Genetic predisposition: These cysts often run in families, suggesting an inherited component, especially in individuals who develop multiple cysts.
• Trauma or irritation: Minor injury or repeated friction in areas with dense hair growth can trigger the development of cysts.
• Age factor: Pilar cysts are more commonly diagnosed in middle-aged adults, and their prevalence increases with age.
• Unknown triggers: In some cases, cysts develop spontaneously without any identifiable cause or contributing factors.

Symptoms

Pilar cysts usually present with distinct characteristics that make them easily recognizable. Typical symptoms include:

• Round, smooth lump: A dome-shaped bump under the skin, most commonly on the scalp.
• Firm and mobile: The cyst feels firm but moves slightly when pressed, as it is not attached to deeper tissues.
• Painless: Most pilar cysts are painless unless they become infected or irritated.
• Slow growth: The cyst typically enlarges gradually over time without causing significant discomfort.
• Multiple cysts: Some individuals, especially with a family history, may develop multiple pilar cysts.
• Signs of infection: If a cyst becomes infected, it may become red, swollen, tender, and may drain foul-smelling pus.

Diagnosis

The diagnosis of a pilar cyst is usually clinical, based on the characteristic appearance and location of the lump. Diagnostic steps include:

• Physical examination: A healthcare provider will inspect and palpate the cyst, assessing its size, mobility, and tenderness.
• Medical history: Information on family history, history of similar lumps, recent trauma, and progression of the cyst is considered.
• Differential diagnosis: Other conditions such as epidermoid cysts, sebaceous cysts, or lipomas may be considered and ruled out based on features.
• Ultrasound: Occasionally, ultrasound imaging may be used to distinguish pilar cysts from other types of soft tissue masses.
• Biopsy: In rare cases, especially when the cyst appears atypical or suspicious, a biopsy may be done to confirm the diagnosis and rule out malignancy.

Treatment

Treatment for pilar cysts depends on the size of the cyst, presence of symptoms, and patient preferences. Options include:

• No treatment: As pilar cysts are benign, asymptomatic cases may not require treatment and can be monitored over time.
• Surgical excision: The most definitive treatment is surgical removal, especially for large, painful, or cosmetically concerning cysts. Excision is typically performed under local anesthesia in a simple outpatient procedure.
• Infection management: If the cyst becomes infected, oral antibiotics may be prescribed. Surgical removal is often delayed until after the infection resolves.
• Incision and drainage: If an infected cyst develops into an abscess, incision and drainage may be necessary, but this is not a curative treatment and cysts often recur without full excision.
• Aftercare: Post-surgical care includes keeping the area clean, following wound care instructions, and monitoring for signs of infection or recurrence.

Prognosis

The prognosis for pilar cysts is excellent. They are non-cancerous and do not pose any serious health risks. Surgical removal offers a permanent solution with a low risk of recurrence when the cyst and its wall are completely excised. Individuals who choose to leave the cyst untreated can continue regular monitoring, especially if the cyst remains small and painless.

In cases where multiple cysts occur due to genetic factors, new cysts may develop over time. However, these too can be removed safely if necessary. With proper treatment and care, individuals with pilar cysts can expect full recovery and minimal complications.