Infantile myofibromatosis: review of imaging findings and emphasis on correlation between MRI and histopathological findings

Background: Infantile myofibromatosis (IM) is the most common fibrous tumor of infancy. MRI is considered the gold standard in IM evaluation. Very little has been published about IM with histopathology correlation in the pediatric age. Purpose: Describe imaging findings in IM and correlate MRI findings with histopathology. Material and methods: Imaging findings of 17 patients with IM were retrospectively analyzed including CT, US and MRI. Signal characteristics on T1-, T2-weighted and STIR imaging, extent of T2-hyperintensity, degree & pattern of enhancement, diffusion restriction, location & margins, & involvement of adjacent structures were tabulated. Histopathology findings included cellularity, collagenization, myxoid changes, atypia, mitosis & microscopic invasion. Established grading scores were utilized. Results: Relative to normal skeletal muscle, on T1-weighted imaging, 9 lesions had similar signal while the remaining had a mixture of iso & hypo intensity; whereas on T2-weighted and STIR imaging, all 12 lesions demonstrated a mixture of iso, hypo & hyperintensity. T2-hyperintensity was grade 2 in one, grade 3 in 8 & grade 4 in 3 lesions. Intensity of enhancement was grade 2 in one, grade 3 in 8 & grade 4 in 3 lesions. Enhancement was predominantly peripheral in all 12 lesions. Extent of T2-hyperintensity & degree of enhancement corresponded to variable grades on histopathology. CT and US showed nonspecific findings. Conclusion: On MRI, IM has a mixture of signal intensity with predominant hyperintense signal on T2W images. However various signal & enhancement features correlated poorly with specific histopathologic grades.