An 18 month old male presents with fever and green discharge from the right external auditory canal. A temporal bone CT demonstrated an 8mm cylinderical structure 3cm in length isointense to muscle with linear central hypoattenuation. An MRI demonstrated a cylindrical signal void on all sequences performed; including T1, T2, and FLAIR sequences; within the masticator space corresponding to the foreign body on CT, although the dimensions appeared slightly larger. There was considerable surrounding edema with findings consistent with osteomyelitis of the mandible with right mastoid and middle ear effusions. In the operating room a small opening on the buccal mucosa was identified and a 3 cm green crayon fragment was removed. Upon further questioning the mother reports the child running with a green crayon, and tripping approximately 3 weeks prior to presentation. The child was treated with IV antibiotics following foreign body removal and is recovering well. Given the common understanding of a crayon as a solid stick of parafin wax, the imaging appearance as a foreign body on CT and MRI was unexpected. On CT the overall density was isointense to soft tissues and demonstrated a central linear area of hypoattenuation. The central hypoattenuation corresponds to a central air channel in some crayons by the method of manufacture. On MRI the low signal with apparent blooming is related to the pigments. In modern crayons these pigments are transition metal compounds. Iron oxide complexes are the most important and are responsible for the yellow, orange, red, brown, and black color families and their various permutations and mixtures. Other transition metal compounds such as titanium dioxide for white, and copper for blue are also used. Pigments make up to 10% of a crayon. In our case of a green crayon, the iron oxide particles responsible for the yellow portion of the green would explain the abscence of signal on routine MRI sequences with apparent blooming. Understanding the appearance of crayons can help positively identify them as foreign bodies, and may help identify small retained fragments. Read More

Meeting name: IPR 2016 Conjoint Meeting & Exhibition , 2016

Authors: Mcallister Aaron, Lall Neil

Keywords: foreign body, Crayon, MRI, CT, masticator space