Age / Sex : 10 / M

Age / Sex :  10/M
Chief complaint :

A 10-year-old boy presented with a palpable mass in the anterior aspect of the right proximal upper arm, which had been noticed 1 year previously.

pilomatricoma

Discussion

Findings:

1) Ultrasonography demonstrates a well-defined subcutaneous mass with an echogenic center and a thin hypoechoic rim. There is posterior acoustic shadowing from the echogenic

center indicating the presence of tiny calcifications.

2) Axial T1-weighted spin-echo MR image demonstrates a well-defined subcutaneous mass in the anterior aspect of the right proximal upper arm, adjacent to the cephalic vein. The mass is isointense as compared with the muscle.

3) Corresponding axial T2-weighted fast spin-echo MR image shows a homogenous low signal intensity mass without any surrounding edema.

4) Gadolinium-enhanced axial T1-weighted spin-echo MR image obtained with fat saturation shows the homogenous enhancement of the mass without a central necrotic portion.

5) Photomicrograph shows centrally located shadow cells (arrow) and peripheral basaloid cells (open arrow). Small calcific deposits are present (not shown here). (Hematoxylineosin stain; original magnification ×100).

Diagnosis: pilomatricoma

Differential Diagnosis:

 The differential diagnosis of pilomatricomas includes epidermoid or dermoid cysts, and hemangioma.

With the aid of ultrasonography, pilomatricoma can be distinguished from epidermoid and dermoid cysts by the presence of calcification and peripheral Doppler flow. Epidermoid cysts appear as hypoechoic masses with inner anechoic foci rather than echogenic foci and do not show Doppler flow.

Superficial nodules containing calcification should be included in the differential diagnosis of pilomatricoma. Hemangioma has a lobulated contour and a soft consistency. Their associated areas of calcification (phleboliths) are round, and low-frequency Doppler flows are evident within anechoic vascular channels.

Discussion:

1) Pilomatricoma, which is also called calcifying epitheliomas of Malherbe,

- is an uncommon benign skin neoplasm that is derived from the hair matrix .

- more common in children and young adults, and most cases of this disorder (approximately 60%) occur in the first two decades of life.

- Approximately half of all pilomatricomas occur in the head and neck, while other sites of predilection are the upper extremity, trunk and lower extremity, in order of decreasing frequency.

2) Clinical manifestation

- usually manifests as a solitary, slow growing, firm dermal nodule, which is often accompanied by inflammation or discoloration of the overlying skin.

- In most cases, the diameter of the tumor ranges from 0.5 to 3 cm, but a case of giant pilomatricoma with a maximum diameter as large as 18 cm has been reported.

- Most occurrences are solitary lesions, but multiple tumors occur in 2-3.5% of cases.

- The latter have been associated with Gardner’s syndrome, myotonic muscular dystrophy, sarcoidosis, and skull dysostosis.

3) Histopathology

- a deep, subcutaneous tumor occurring between the dermis and hypodermis, and is separated from the epidermis by a connective tissue capsule.

- Epithelial islands are embedded in a cellular stroma.

- These epithelial cell islands are arranged in a circular configuration, with nucleated basophilic cells being found on the periphery and enucleated shadow or ghost cells in the center.

- Calcification and bone metaplasia are observed in 69-85% and 15 % of cases, respectively.

4) Imaging findings :

A) Ultrasonography :

- a well-defined subcutaneous mass with an echogenic center and a thin hypoechoic rim.

- There was posterior acoustic shadowing from the echogenic center, indicating the presence of tiny calcifications.

- The echogenic center corresponds to the central islands of epithelial cells and the hypoechoic rim corresponds to the connective tissue capsule.

B) CT :

- a well-defined subcutaneous masses adherent to the skin with various amounts of calcification.

C) MR :

- De Beuckeleer et al. reported two cases of pilomatricoma in the forearm forearm

that were of homogenous intermediate signal intensity on the SE T1-weighted images and predominantly low-to-intermediate signal intensity on the T2-weighted images.

- Hoffmann et al. described the MRI findings in a case of pilomatricoma in the neck of a child. The T2-weighted images showed bands of hyperintense signal radiating away from a low signal intensity center towards the periphery. The authors suggested that the hyperintense bands

noted on the T2-weighted images might correspond to the basaloid bands present on the histologic specimens.

- On the other hand, Masih et al. put forward another possible explanation for this observation, suggesting that the high signal intensity reticulations might represent edematous stroma surrounding basaloid cells.

References:

1. Lee GK, Suh KJ. A Case of Pilomatricoma in the Upper Arm: Sonographic and MR Imaging Findings. J Korean Radiol Soc. 2005;52:427-430

2. Hwang JY, Lee SW, Lee SM. The common ultrasonographic features of pilomatricoma.

J Ultrasound Med. 2005;24:1397-402.