This research was supported by a grant from the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number: HI18C0364010018).
Pilomatrixoma is a benign tumor that originates from the hair follicle matrix. It usually presents as a hard, slow growing, solitary mass that can be easily misdiagnosed as other skin masses. The aim of this study was to clinically analyze a case series of pilomatrixoma in pediatric patients from Korea.
A total of 165 pediatric patients from 2011 to 2018 with a histological diagnosis of pilomatrixoma were included. A retrospective review was performed using the electronic medical records, including patient demographics, number and location of the mass, clinical and imaging presentation, and postoperative outcomes.
There were 61 male and 104 female patients with 152 solitary and 13 multiple pilomatrixomas. Among solitary pilomatrixomas, the lesion commonly occurred in the head and neck (84.2%), followed by upper limbs (11.2%), lower limbs (3.3%), and trunk (1.3%). The pilomatrixoma lesion presented as the following types based on our clinical classification: mass (56.02%), pigmentation (25.31%), mixed (12.65%), ulceration (4.82%), and keloid-like (1.2%). Ultrasonography showed a high positive predictive value (95.56%). There were no specific complications observed except for two cases of recurrence.
Pilomatrixoma has various clinical feature presentations and commonly occurs in the head and neck. Ultrasonography is a helpful diagnostic tool. Surgical removal of the lesion is the main treatment method with a low recurrence rate.
Pilomatrixoma, also known as pilomatricoma or calcifying epithelioma of Malherbe, was first described by Malherbe and Chenantais in 1880 [
Previous studies revealed pilomatrixoma presentation in young patients aged less than 20 years with a female predominance. The head, neck, and extremities are the main regions in which the tumor occurred. Pilomatrixoma typically presents as a solitary lesion, although some patients still present multiple lesions [
Clinically, pilomatrixoma commonly presents as a hard, freely mobile, and slow-growing mass. Patients are usually asymptomatic, but in some cases, patients complain of pain or discharge from the lesions [
All pediatric patients from 2011 to 2018 who were surgically treated for mainly subcutaneous mass at the department of plastic and reconstructive surgery were evaluated. We reviewed the electronic medical records of the patients, including their clinical and pathological results. A total of 165 pediatric patients with a histological diagnosis of pilomatrixoma were identified for this retrospective analysis. For this study, ethical approval was obtained from the Institutional Review Board of Seoul National University Hospital (IRB No. 1902-102-1011). The clinical data included the patients’ sex, age at operation, location of the mass, solitary or multiple lesions. The presentations were classified accordingly into five different types based on clinical characterization. Imaging results were reviewed to analyze the characteristics of pilomatrixoma and determine the diagnostic accuracy. Investigation of postoperative outcomes included complications or recurrence.
Among the 165 patients, 61 (36.97%) were male and 104 (63.03%) were female; there was an observed female predominance with a male-to-female ratio of 1:1.70. A total of 152 patients (92.12%) had a solitary pilomatrixoma (SP) wherein 53 were males and 99 were females. The remaining 13 patients (7.88%) had multiple pilomatrixomas (MPs) wherein eight were males and five were females (
In SP, the most commonly affected region was the head and neck (n=128), followed by upper limbs (n=17), lower limbs (n=5), and back (n=2) (
Among the 152 lesions in SP and 27 lesions in MP, medical documentations were obtained preoperatively in 166 lesions. These photos were evaluated by three plastic surgeons (JLH, HY, and BJK) based on the characteristic appearance of the pilomatrixoma. These lesions were classified into five clinical types, which included the mass, pigmentation, mixed type, ulceration, and keloid-like types. The mass type was the predominant presentation in 93 lesions characterized as a skin protrusion. Additionally, among the mass type lesions, two lesions showed a conspicuous “tent sign” with multiple facets and angles (
Preoperative diagnostic imaging was performed to identify pilomatrixoma. The imaging modalities included ultrasonography (US), computed tomography (CT), or magnetic resonance imaging (MRI). There were 90 patients who underwent US with a positive predictive value of 95.56% (86/90). According to the US images, the mean size of pilomatrixomas was 9.47±11.51 mm. Additionally, one patient underwent CT at a local hospital before visiting our institution and the result stated that the lesion was a pilomatrixoma. Furthermore, two patients underwent MRI in order to rule out vascular lesions in one case, and to confirm the anatomy of the facial nerve, to avoid neural injury as it was located close the lesion in the other case.
Surgical removal was performed in all patients under general anesthesia. Preoperative laboratory examinations, including blood tests, urine examination, chest radiography, and electrocardiogram, were performed in order to assess the general indications for anesthesia. There were no postoperative complications such as infection, hematoma, or wound dehiscence. The average follow-up period was 6.12±10.24 months. Two patients (1.2%) had recurrent pilomatrixoma that was located in the eyelid and preauricular area, with an average of 15.5 months recurrence time postoperatively. There were no cases of malignant transformation or metastatic malignant pilomatrixoma.
Pilomatrixoma, arising from the hair follicle matrix, is generally a benign tumor occurring in the deep dermis or subcutaneous layer. It usually presents as a solitary lesion, although it presents as multiple lesions in approximately 2% to 9% of cases [
Epidemiologically, pilomatrixoma can occur at any age. Previous studies showed that there are two age peaks in which pilomatrixoma occurs intensively: first peak is in young patients aged between 0 and 20 years, whereas the second is in older patients aged between 40 and 60 years [
Based on previous retrospective studies, both SP and MP presentation had a female predominance [
Moreover, the clinical manifestations of pilomatrixomas are diverse. Generally, pilomatrixoma is a hard, freely mobile, slow-growing mass covered by skin. Patients are asymptomatic, although in some cases pilomatrixoma may present with symptoms, such as pain, pruritus or discharge in lesions [
In order to improve the diagnostic rate of pilomatrixoma, preoperative imaging including US, CT, or MRI is recommended. Compared with CT and MRI, US is considered a non-anesthetic, noninvasive, low-priced, quick, and acceptable approach for children with high accuracy of more than 80% [
Complete surgical resection is the treatment of choice for pilomatrixomas. The tumor occurs predominantly in the head and neck region; thus, indirect incisions are often used for cosmetic reasons. Take, for example, a hairline incision adapted to approach the mass in the forehead or the temple for cosmesis. These surgical procedures should be carefully approached to avoid injury to the facial nerve or sensory nerve branches of the face. After tumor removal in the giant pilomatrixoma, the defective skin should be reconstructed with a flap [
Although recurrent pilomatrixoma is rare, approximately 2% of cases still recur [
Malignant transformation of the pilomatrixoma is very rare. Previous case reports and case series indicated that malignant transformation occurred only in adult patients [
In conclusion, pilomatrixoma commonly presents as a solitary mass lesion on the face. Although the clinical appearances of pilomatrixoma vary, making misdiagnosis common, the established clinical classifications of pilomatrixoma presentations may help in the identification when compared with other skin tumors. US is also a helpful imaging tool for the diagnosis of pilomatrixoma. Complete surgical excision is the treatment of choice with a low recurrence rate.
No potential conflict of interest relevant to this article was reported.
The study was approved by the Institutional Review Board of Seoul National University Hospital (IRB No. 1902-102-1011) and performed in accordance with the principles of the Declaration of Helsinki. Written informed consents were obtained.
The patients provided written informed consent for the publication and the use of their images.
Patient’s age at operation.
Affected regions in solitary pilomatrixoma. (A) Distribution of pilomatrixoma on the whole body. (B) Distribution of pilomatrixoma on the head.
Locations of multiple pilomatrixoma.
Clinical documentation of the different types of pilomatrixoma. (A) Mass type. (B) Typical mass type with the “tent sign.” (C) Pigmentation type with clearly demarcated vessels. (D) Pigmentation type with melanin-like pigmentation. (E) Mixed type. (F) Ulceration type. (G) Keloid-like type.
The ultrasound image shows a well-defined heterogeneous hyperechoic nodule with low echoic rim and internal calcifications in the subcutaneous layer of the right calf. Note the increased echogenicity in the surrounding subcutaneous fat layer and conspicuous acoustic shadowing.
Demographics of patients and clinical classifications of pilomatrixoma
Variable | No. (%) |
---|---|
Multiplicity (patients) | |
Solitary pilomatrixoma (n = 152, M/F) | 53/99 |
Multiple pilomatrixoma (n = 13, M/F) | 8/5 |
Clinical type (lesions) | |
Mass | 93 (56.02) |
Pigmentation | 42 (25.31) |
Mixed | 21 (12.65) |
Ulceration | 8 (4.82) |
Keloid-like | 2 (1.21) |
M, male; F, female.