Giant pilomatrixoma in a 12 year-old child

Pilomatrixoma, also known as Malherbe’s calcifying epithelioma, was first described in 1880 by Malherbe and Chenantais [3]. Diagnosing pilomatrixoma can be challenging due to its varied presentation. Histologically, pilomatrixomas presents as a well demarcated tumour, islands of basaloid cells with abrupt keratinization, shadow cells and basophilic cells with normal mitotic activity [4]. While it is predominantly seen in children and young adults, cases have also been reported in adults. Most cases present in the head and neck region, however, around 20% is reported on the trunk [5]. Studies have reported an average size of 1.2 cm [6]. Tumours exceeding four centimetres in size with rapid progression are classified as giant pilomatrixomas [7]. Giant pilomatrixomas can have ulceration, making it clinically difficult to extinguish from squamous cell carcinoma.  Pilomatrixomas often present as asymptomatic nodular lesions. The overlying skin is typically normal but may occasionally exhibit a bluish or reddish discoloration [1]. In this case, the patient had a light nodular element, the skin stretched out, causing part of the lesion to flatten and take on an angular, tent-like shape.

Differential diagnoses include dermoid cysts, neurofibromas, haematoma, basal cell epithelioma, and epidermoid cysts, among others. A rare malignant variant, pilomatrix carcinoma, has also been described. Pilomatrix carcinoma was first reported in 1980, and to date, only 125 cases have been documented in the literature [8,9].  A review on pilomatrix carcinoma from 2017 presented three cases of pilomatrixoma carcinoma in previous scar from benign pilomatrixomas. The majority of reported cases of malignant transformation have been observed in adults, particularly in the 40 to 50 year age range. However, rare cases have also been described in children.

In cases of multiple pilomatrixomas, further evaluation for syndromic associations is warranted, as this condition has been linked to Gardner syndrome and Turner syndrome, as well as others [10].  Additionally, pilomatrixomas have a higher prevalence among patients with myotonic dystrophy, a disorder associated with an increased risk of certain malignancies. There is no well-defined standard treatment protocol for pilomatrixoma; however, complete surgical excision is recommended to ensure total removal of the lesion and to prevent recurrence.

In conclusion, pilomatrixomas are rare and mostly benign tumour, albeit diagnosis is essential in order to exclude malignancy.