P3D264: Rapidly Progressive Pilomatricoma: A Concerning Presentation of a Benign Tumor

Introduction: Pilomatricomas, also known as pilomatrixoma or calcifying epithelioma of Malherbe, are common benign skin neoplasms arising from hair follicles. These lesions typically present as small, painless, firm, subcutaneous nodules and predominantly affect females. They appear flesh-colored but can have an overlying red-blue discoloration. Lesions tend to be solitary, slow growing, and localized to the head and neck or upper extremities. We present a case of a pediatric patient with a rapidly progressive scalp tumor and concerning imaging, ultimately diagnosed as a pilomatricoma.

Case Description: Our patient is a previously healthy 5-year-old female who presented to the outpatient pediatrics clinic for evaluation of a progressively enlarging scalp mass over the past month. The patient denied inciting trauma to the area, had no drainage or bleeding, and had not reported any overlying warmth to the area. The lesion had never been painful. The patient had otherwise been in her usual state of good health without other concerns. Evaluation for the same complaint one month prior, when they first noticed the lesion, found a 10mm diameter cystic structure at the left hairline, thought to be a dermoid cyst. On our exam, there was a 2x3 cm soft, erythematous, non-tender, mobile subcutaneous mass along the left frontal scalp. She was referred to pediatric surgery for evaluation for resection of a presumed epidermoid cyst. At her surgical consultation four weeks later, the lesion was larger, now measuring 3x3 cm, with increased superficial vascularity and erythema. Head CT was obtained to evaluate for a potential vascular anomaly, followed by ultrasound, which showed a highly vascularized soft tissue mass most concerning for a sarcomatous soft tissue mass. Given these concerns, prompt surgical resection was completed. Pathologic diagnosis revealed a well-circumscribed dermal tumor of basaloid cells and shadow cells consistent with a pilomatricoma. Our patient tolerated complete resection without complications. There has been no recurrence to date.

Discussion: Although pilomatricoma is the second most common skin tumor in childhood, the variation in the clinical presentation of these lesions leads to frequent pre-operative diagnostic uncertainty. Imaging can serve as a diagnostic aid, though this case required surgical pathology for diagnosis due to concerning characteristics such as rapid growth and a high vascular soft mass on imaging.

Conclusion: Our case highlights the importance of recognizing clinical features that should hasten the evaluation of soft tissue masses and the inclusion of pilomatricomas on the differential for soft tissue masses.