Ultrasound and Magnetic Resonance Imaging Features of Calcifying Aponeurotic Fibromas

Objectives: To report characteristic imaging findings of calcifying aponeurotic fibromas (CAFs) on ultrasound (US) and magnetic resonance imaging (MRI).

Methods: Eight patients with CAF based on our institutional pathology database from 2000 to 2019 were consecutively included. Images were assessed as follows: with plain radiographs for the presence of soft tissue calcifications; with US for the presence of microlithiasis (a nonshadowing hyperechoic focus <3 mm) and discrete calcifications, size, location, margin, echogenicity, and relationship with surrounding structures; and with MRI for the presence of MRI microlithiasis (scattered tiny signal-void dots), margin, signal intensity, contrast enhancement pattern, and relationship with surrounding structures.

Results: Calcifying aponeurotic fibromas occurred most commonly in the foot (n = 5), followed by the hand, ankle, and knee, respectively. Half of the lesions (n = 4) showed intralesional calcifications on plain radiographs. On US, all lesions showed microlithiasis. They involved the subcutaneous (n = 5), perifascial (n = 2), and intermuscular (n = 1) layers. Margins were circumscribed (n = 3) or irregular (n = 5), whereas the echogenicity of the underlying tumor matrix was hyperechoic (n = 4), isoechoic (n = 2), or hypoechoic (n = 2). All lesions were abutting (n = 7) or encasing (n = 1) an adjacent tendon. On MRI, all CAFs showed tiny signal-void dots and irregular margins. Signal intensity was mostly hyperintense (n = 5) on T2-weighted images and all hypointense on T1-weighted images. Three lesions showed heterogeneous contrast enhancement, and 3 showed uneven marginal enhancement.

Conclusions: A CAF should be considered a differential diagnosis if a soft tissue mass abutting or encasing the tendon or fascia shows US or MRI microlithiasis.