Abstract
Malformations involving the brainstem are very rare and present with a varied spectrum of clinical symptoms due to multiple cranial nerve palsies and pyramidal tract involvement. Of these, pontine tegmental cap dysplasia is a very unusual malformation, characterized by ventral pons hypoplasia and an ectopic dorsal band of tissue, projecting into the fourth ventricle, from dorsal pontine tegmentum. A 4-year-old male child, presenting with left facial nerve palsy, revealed hypoplastic ventral pons and an ectopic structure on magnetic resonance imaging (MRI). The ectopic structure was isointense to pons, arose from the left side of dorsal pontine tegmentum, at pontomedullary junction and protruded into the fourth ventricle, impinging upon the left seventh and eighth cranial nerves. Diffusion tensor imaging (DTI) depicted abnormal white matter tracts in ectopic tissue with absent transverse pontine fibres and abnormal middle and superior cerebellar peduncles. The typical MRI appearance, coupled with DTI, helped us reach an accurate diagnosis of pontine tegmental cap dysplasia, in a setting of neurological dysfunction.