Age / Sex : 8 / M

Chief complaint: A palpable mass in right upper arm for 12 months

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : Byeong Seong Kang, Department of Radiology, University of Ulsan College of Medicine, Ulsan University Hospital, Ulsan, Korea

Discussion

Answer: Pilomatricoma

Findings:

1) Plain radiograph

- Sharply demarcated subcutaneous mass with multiple calcifications

2) MRI

- Axial T2-WI: heterogeneous hypointensity with inner high signals

- Axial T1-WI: isointense relative to skeletal muscle

- Axial and coronal fat-suppressed contrast-enhanced T1-WI: intense and heterogeneous enhancement

Differential Diagnosis: Pilomatricoma / Dermoid cyst / Hemangioma

Diagnosis: Pilomatricoma

Discussion:

Pilomatricoma, also known as pilomatrixoma, is a benign skin tumor arising from the cortex of a hair follicle. The lesion is generally a well-demarcated, hard, mobile superficial nodule that grows slowly. It is usually encountered in patients younger than 20 years. Although all hair follicle–bearing skin surfaces can be involved, pilomatricoma most frequently occurs in the head and neck region, where the lesion is usually solitary.

Plain radiography demonstrated that pilomatricoma appeared as a solitary, sharply demarcated subcutaneous tumor with extensive sand-like or dense focal calcification. On CT, pilomatricoma has been described as well-defined subcutaneous masses with varying amounts of calcification and variable enhancement. On MRI, most of the pilomatricomas have been described as showing a homogeneous intermediate signal intensity on T1-weighted images, heterogeneous intermediate signal intensity on T2-weighted and fat-suppressed T2-weighted images, and ring-like and reticular enhancement on contrast-enhanced T1-weighted images.

References:

1. Bulman JC, Ulualp SO, Rajaram V, Koral K. Pilomatricoma of childhood: a common pathologic diagnosis yet a rare radiologic one. AJR Am J Roentgenol. 2016;206:182-8.


2. Yi KM, Chen K, Wang L, Deng XJ, Zeng Y, Wang Y. Pilomatricoma (calcifying epithelioma): MDCT and MR imaging findings in 31 patients with radiological-pathological correlation. Eur J Radiol. 2018;106:92-9.


3. Kato H, Kanematsu M, Watanabe H, Nagano A, Shu E, Seishima M, Miyazaki T. MR imaging findings of pilomatricomas: a radiological-pathological correlation. Acta Radiol. 2016;57:726-32.