LAUSR

Pilomatricomas are relatively rare tumors, with an estimated incidence of 1.04% of all benign skin tumors [1]. This likely plays a role in their frequent confusion with other benign and malignant tumors [2]. The most common locations are the head and neck and upper extremity, respectively [3]. They typically present as a superficial, hard, slow-growing masses [3]. The majority occur within the first two decades of life [4]. They may be covered by blue, red, or normal skin, and in rare cases can ulcerate [4]. These lesions can occasionally be painful secondary to mass effect [3], although pain is not a defining presenting symptom. Accurate diagnosis of pilomatricomas prior to surgical excision or biopsy occurs in less than 50% of cases based on published case series [3]. Several authors have estimated that physicians outside of the field of dermatology arrive at the correct diagnosis only 3% of the time [3]. The differential diagnosis includes epidermoid cyst, hemangioma, squamous cell carcinoma, dermatofibrosarcoma, and soft tissue sarcoma. Pilomatricomas have previously described imaging findings that aid in accurate diagnosis. A key radiographic feature of pilomatricomas across all imaging modalities is their confinement to the skin and superficial soft tissue and lack of involvement of the deeper layers [5]. Plain radiographs may show a calcified mass with regular contours [6]. Calcifications have been reported as either having an homogenous sand-like appearance or large dense foci of calcification [6]. Ultrasonography has been recommended by some to be the preferred initial imaging test [5]. It shows a hypoechoic rim and extensive acoustic shadowing owing to the calcification of the tumor [5] (Fig. 1a). The presence of vascularity on color ultrasound has also been reported by several authors; however this feature is less ubiquitous and therefore of less diagnostic value [5]. The utility of Doppler evaluation is further undercut as many lesions are extensively calcified and not amenable to such evaluation [5]. Magnetic resonance imaging (MRI) can also be requested during the diagnostic evaluation. Its characteristics include an intermediate and homogeneous signal on T1-weighted imaging, and a contrast-enhancing hyperintense rim on T2-weighted imaging [4, 7]. Furthermore, on T2 fatsuppressed contrast-enhanced images, high signal bands can be seen radiating from the low signal center to the periphery [7] (Fig. 1b, c, d). The case presentation can be found at https://doi.org/10.1007/s00256017-2766-7