What is the likely diagnosis for a recurrent cyst in the subtemporal scalp that has been excised twice?

Recurrent Subtemporal Scalp Cyst: Most Likely Diagnosis

The most likely diagnosis for a twice-recurrent subtemporal scalp cyst is an epidermoid cyst, with incomplete excision being the primary cause of recurrence.

Primary Differential Diagnosis

The recurrent nature after two excisions strongly suggests incomplete removal of the cyst wall, which is the most common cause of recurrence in benign scalp cysts. The key differentials to consider include:

Most Common: Epidermoid Cyst

• Epidermoid cysts are the most frequent benign cutaneous lesions of the scalp 1
• Recurrence occurs specifically when the cyst wall is not completely excised 1
• Present as firm, mobile nodules often with a central punctum
• Surgical excision with complete cyst wall removal is definitive treatment 1

Alternative Diagnoses to Exclude

Trichilemmal (Pilar) Cyst:

• Second most common scalp cyst
• Can recur if incompletely excised 2
• May undergo malignant transformation to proliferating trichilemmal cyst (PTC) with high recurrence rates and local invasion 3
• Requires complete excisional biopsy and histopathological confirmation 3

Cylindroma:

• Rare benign adnexal tumor
• Known for recurrence after incomplete excision 4, 5
• Critical consideration: Can undergo malignant transformation, especially after multiple recurrences 5
• Presents as multi-nodular masses on scalp

Clinical Approach Algorithm

Immediate Management Steps:

1. Search for local causes of recurrence 6:

   • Retained foreign material from previous surgeries
   • Incomplete cyst wall removal
   • Pilonidal cyst characteristics
   • Hidradenitis suppurativa features

2. Culture if signs of infection present 6:

   • Drain and culture early if abscess formation
   • Consider 5-10 day antibiotic course based on culture results

3. Complete surgical excision with histopathological analysis:

   • Ensure complete cyst wall removal to prevent further recurrence 1
   • Send specimen for definitive pathological diagnosis
   • Rule out malignant transformation, particularly if cylindroma or PTC 5, 3

Critical Pitfalls to Avoid:

⚠️ Incomplete excision is the primary cause of recurrence - ensure the entire cyst capsule/wall is removed en bloc 1

⚠️ Do not assume benignity after multiple recurrences - proliferating trichilemmal cysts and cylindromas can undergo malignant transformation, especially after repeated incomplete excisions 5, 3

⚠️ Histopathological confirmation is mandatory - clinical diagnosis alone is insufficient for recurrent lesions 3

Definitive Recommendation

For this twice-recurrent subtemporal cyst, perform complete surgical excision with meticulous removal of the entire cyst wall and mandatory histopathological examination. The pathology will differentiate between epidermoid cyst (most likely), trichilemmal cyst, cylindroma, or rare entities like schwannoma or neurofibroma. If malignant transformation is identified on histology, wider excision margins and advanced reconstructive techniques may be necessary 5, 3.