What is a pilomatricoma?

Pilomatricoma: A Benign Skin Tumor with Distinctive Features

Pilomatricoma is a benign skin tumor arising from the hair follicle matrix cells that is common in children and young adults, especially in the head and neck region, but is frequently misdiagnosed.1

Definition and Characteristics

• Pilomatricoma (also known as pilomatrixoma or calcifying epithelioma of Malherbe) is a benign cutaneous adnexal neoplasm with differentiation towards the hair matrix, inner sheath of hair follicle, and hair cortex 1, 2
• It presents as a slowly enlarging, irregularly contoured mass that is fixed to the skin but slides freely over underlying tissues, often with a discoloration varying from red to purple-bluish 1
• These tumors have a stony-hard consistency due to calcification within the tumor 3
• Pilomatricomas are characterized histologically by basophilic cells and shadow cells (cells with nuclear disappearance) 2

Epidemiology and Location

• Most commonly affects children and young adults 1
• Predominantly found in the head and neck region (54.5% of cases in one series) 3
• Can occur in unusual locations including the limbs, laterovertebral region, and even subungual areas 3, 4
• May present as multiple tumors in some cases 3

Clinical Significance in Cancer Predisposition Syndromes

• Pilomatricomas have been identified as a clinical feature in certain cancer predisposition syndromes, particularly Constitutional Mismatch Repair Deficiency (CMMRD) 5
• In CMMRD patients, pilomatricomas are considered a potential marker for the syndrome, with multiple pilomatricomas scoring 2 points and a single pilomatricoma scoring 1 point in the C4CMMRD scoring system 5
• There is an increased recognition of the risk of malignant transformation of benign skin neoplasms including pilomatricoma in CMMRD patients 5
• Annual skin examinations are recommended for CMMRD patients starting at diagnosis, with early referral to a dermatologist in case of any concern 5

Variants and Complications

• Proliferating pilomatricoma is a rare variant that can rapidly increase in size and may be misidentified as a malignant tumor 2
• Ossifying pilomatricoma is a distinct variant characterized by florid osseous metaplasia within the tumor 6
• Malignant degeneration (pilomatrix carcinoma or trichomatrical carcinoma) is very rare but has significant aggressive potential 4
• Spontaneous regression has never been observed 1

Diagnosis

• Clinical diagnosis can be challenging, and pilomatricomas are frequently misdiagnosed 1, 4
• Diagnostic tools include:
  • Ultrasound examination
  • MRI scan
  • Fine-needle aspiration cytology (though this can lead to misdiagnosis as malignant tumors) 1, 2
• Definitive diagnosis requires histopathological examination of the excised specimen 2, 4

Management

• Surgical excision with clear margins is the treatment of choice 1
• Complete removal is necessary to prevent recurrence 1
• In patients with cancer predisposition syndromes like CMMRD, early removal of pilomatricomas is recommended to prevent potential malignant transformation 5

Prognosis

• Excellent prognosis following complete surgical excision 4
• Recurrence may occur due to incomplete resection 1
• Long-term follow-up is recommended, especially in patients with multiple lesions or those with cancer predisposition syndromes 5