Pilar Trichilemmal Cyst: Symptoms, Types, Causes and Treatment

Pilar trichilemmal cysts, often simply called “pilar cysts,” are a fascinating and sometimes misunderstood skin condition. Most commonly found on the scalp, especially in older women, these cysts can range from harmless bumps to rare, aggressive tumors. Understanding their symptoms, types, causes, and treatment options is vital for patients, caregivers, and clinicians alike. This article synthesizes current scientific research to provide a comprehensive, accessible guide.

Symptoms of Pilar Trichilemmal Cyst

Pilar trichilemmal cysts often present subtly, and many people may not realize they have one until it grows larger or causes discomfort. Being able to identify the key symptoms is the first step toward timely diagnosis and treatment.

Symptom	Description	Common Location	Source(s)
Lump	Firm, smooth, mobile nodule	Scalp	2 3 5
Ulceration	Open sore or breakdown	Scalp	3 8
Enlargement	Gradual increase in size	Scalp	5 8
Pain	Usually painless, but can hurt	Scalp	3 5

Table 1: Key Symptoms

Understanding the Clinical Presentation

Pilar trichilemmal cysts typically appear as round, firm, and well-circumscribed lumps beneath the skin. They are most often found on the scalp, especially in women, and may be present for many years before being noticed 2 5. These cysts tend to be painless; however, if they become inflamed, infected, or ulcerated, discomfort can occur 3 5.

Changes and Complications

• Ulceration and Infection: In rare cases, cysts can break down or become infected, leading to ulceration or the development of open sores that may ooze or bleed 3 8.
• Rapid Enlargement: While pilar cysts typically grow slowly, some may enlarge rapidly, signaling possible transformation into a proliferating or malignant form 5 8.

When to Seek Medical Attention

• Sudden growth
• Change in appearance
• Painful or ulcerated lesions
• Signs of infection (redness, warmth, pus)

Early evaluation by a healthcare provider is essential for unusual or changing cysts.

Types of Pilar Trichilemmal Cyst

Not all pilar cysts are created equal. They can range from benign and harmless to aggressive and even malignant. Understanding the different types is crucial for patients and clinicians to guide management.

Type	Features	Risk Level	Source(s)
Simple Pilar	Benign, slow-growing nodule	Low	2 6
Proliferating	Larger, may recur, locally invasive	Moderate	1 3 5
Malignant	Ulcerated, invasive, metastatic	High	1 7 8 9

Table 2: Types of Pilar Trichilemmal Cyst

Simple Pilar (Trichilemmal) Cyst

These are the most common form, typically presenting as smooth, mobile nodules on the scalp. They are benign and rarely cause problems beyond cosmetic concerns 2 6.

Proliferating Pilar Cyst

A subset of pilar cysts can develop into what’s known as proliferating trichilemmal cysts (PTCs). These lesions are larger, may recur after excision, and can sometimes invade surrounding tissue. The proliferating type is more likely to be mistaken for other tumors, including squamous cell carcinoma 1 3 5. They are histologically characterized by increased epithelial proliferation and abundant keratinization.

Malignant Proliferating Pilar Tumor

Malignant transformation is rare but serious. Malignant proliferating trichilemmal tumors (MPTT) can be locally aggressive, recur frequently, and in some cases metastasize to distant organs 1 7 8 9. These tumors often present as ulcerated, rapidly growing masses and require prompt, aggressive treatment.

Key Differences

• Histopathology: Simple cysts are well-circumscribed with typical keratinization; proliferating and malignant forms show cellular atypia, increased mitotic activity, and poorly defined borders 1 2 3.
• Clinical Course: Benign cysts rarely recur after removal, while proliferating and malignant forms have higher recurrence and complication rates 3 7 9.

Causes of Pilar Trichilemmal Cyst

What leads to the formation of these cysts? Pilar trichilemmal cysts have both genetic and environmental contributors, with recent research illuminating some of the underlying mechanisms.

Cause	Description	Inheritance Pattern	Source(s)
Genetic	Mutations (e.g., PLCD1 gene)	Autosomal dominant	4 6
Trauma	Injury or inflammation to scalp	Not inherited	5
Hair Follicle	Originates from outer root sheath	Not inherited	2 4 6

Table 3: Causes of Pilar Trichilemmal Cyst

Genetic Factors

Pilar cysts often run in families. Multiple cysts are commonly inherited in an autosomal dominant pattern, meaning only one mutated gene copy is necessary for the trait to be expressed 4 6. Recent studies have implicated variants in the PLCD1 gene as a potential driver in familial cases 6. The cysts originate from the outer root sheath of the hair follicle, which further supports a genetic predisposition 2 4 6.

Role of Trauma and Inflammation

In addition to genetic causes, trauma or inflammation to the scalp can trigger the development of pilar cysts. These factors may initiate abnormal proliferation of the outer root sheath, leading to cyst formation or transformation to more aggressive forms 5.

Hair Follicle Origin

All pilar cysts derive from the outer root sheath of the deeper parts of hair follicles, highlighting their close relationship to normal skin structures 2 4 6. This explains their predilection for the scalp, where hair follicles are most numerous.

Environmental and Other Factors

• Age and Gender: Most common in older adults, particularly women 2 5.
• Unknown Mechanisms: While much progress has been made, the exact pathway leading from gene mutation or trauma to cyst formation remains incompletely understood 4 6.

Treatment of Pilar Trichilemmal Cyst

The management of pilar trichilemmal cysts depends on their type and clinical behavior. While most benign cysts can be easily treated, proliferating or malignant forms require a more nuanced approach.

Treatment	Approach/Description	Indication	Source(s)
Surgical Excision	Complete removal of cyst	Benign/Proliferating	3 5 7
Mohs Surgery	Precise excision with margin assessment	Malignant	7
Photodynamic Therapy	ALA-PDT after excision	Malignant	9
Surveillance	Monitoring for recurrence	All types	3 7 9

Table 4: Treatment Strategies

Surgical Excision

For most benign and proliferating pilar cysts, complete surgical removal is curative. The cyst and its capsule should be excised entirely to prevent recurrence 3 5. For larger lesions or recurrent cases, reconstructive techniques such as skin grafting may be required 3.

Mohs Micrographic Surgery

In cases of malignant transformation, Mohs micrographic surgery offers the advantage of removing cancerous tissue while sparing healthy surrounding skin. This approach is especially valuable for tumors on the scalp, where tissue preservation is crucial 7.

Photodynamic Therapy (PDT)

A newer, adjunctive therapy for malignant cases involves the use of 5-aminolevulinic acid-mediated photodynamic therapy (ALA-PDT) following surgical excision. This can help reduce the risk of recurrence, especially in elderly or high-risk patients 9.

Surveillance and Follow-up

Given the recurrence risk—especially for proliferating and malignant cysts—regular follow-up is essential. Clinical and, when necessary, imaging surveillance help detect early recurrence or metastasis 3 7 9.

Multidisciplinary Approach

Optimal management often requires collaboration between dermatologists, surgeons, and pathologists to ensure accurate diagnosis, complete removal, and appropriate follow-up 3 8.

Special Considerations

• Differential Diagnosis: Pilar cysts may be confused with other tumors, such as squamous cell carcinoma, making accurate histopathology crucial 5 8.
• Social and Practical Barriers: Patients with limited access to care, as illustrated in some reports, may experience severe complications due to delayed treatment 8.

Conclusion

Pilar trichilemmal cysts are an intriguing and complex dermatological condition, spanning the spectrum from benign scalp lumps to rare, aggressive malignancies. Understanding their symptoms, types, causes, and treatments is key for effective management.

Key Takeaways:

• Pilar cysts most commonly appear as painless, firm lumps on the scalp, especially in older women 2 5.
• Types range from benign simple cysts to proliferating and rare malignant forms, with increasing risk and complexity 1 3 7.
• Genetics (notably PLCD1 mutations) and trauma are leading causes, with an autosomal dominant inheritance pattern seen in many families 4 6.
• Treatment is guided by type: simple excision for benign cysts, Mohs surgery and adjunct therapies for malignant forms, and vigilant follow-up for all 3 7 9.
• Accurate diagnosis and multidisciplinary care are essential, especially for atypical or aggressive lesions 3 8.

By staying informed and seeking timely medical care, patients and providers can ensure the best possible outcomes for this often-overlooked condition.