The imaging appearance of crayons

A crayon fragment was determined to be the source of a foreign body inflammatory process in the masticator space of a 15-month-old boy. The appearance of the crayon on CT and MR imaging was unexpected, leading to a further analysis of the imaging features of crayons. To investigate and characterize the imaging appearance of crayons at CT and MRI. The authors obtained CT and MR images of 22 crayons from three manufacturers and three non-pigmented crayons cast by the authors. CT attenuation of the crayons and diameter of the MRI susceptibility signal dropout were plotted versus brand and color. All crayons demonstrated a longitudinal central hypo-attenuating tract. Crayon attenuation varied by brand and color. All of the crayons demonstrated a signal void on T1 and T2 imaging and signal dropout on susceptibility-weighted imaging, the diameter of which varied by brand and color. Understanding the imaging appearance of crayons could help in the correct identification of a crayon as a foreign body on imaging studies, even when it is located in unusual places.