CT and MR Studies of Giant Dermoid Cyst Associated to Fat Dissemination at the Cortical and Cisternal Cerebral Spaces

This study focuses on CT and MR studies of adult patient with giant lesion of the posterior cranial fossa associated with micro- and macroaccumulations with density and signal like “fat” at the level of the cortical and cisternal cerebral spaces. This condition is compatible with previous asymptomatic ruptured dermoid cyst. Histological findings confirm the hypothesis formulated using the imaging. We also integrate elements of differential diagnosis by another giant lesion of the posterior cranial fossa. 1. Introduction Dermoid cyst is a congenital dysembryogenic lesion representing only 1% of intracranial lesions. The posterior cranial fossa is one of the possible development sites, and cystic growth is stimulated by many factors like sebum secretions and/or scaling of internal cystic wall. Symptoms are related to dislocation and compression of brain parenchyma. The progressive lesion growth favours the rupture followed to cystic material dissemination in the cortical and cisternal brain spaces. In ruptured cyst the chemical meningitis can be subsequent. We present a case report of giant dermoid cyst on the posterior cranial fossa associated to micro- and macroaccumulation (also termed fatty droplets) widespread in the cortical and cisternal cerebral spaces. Elements of differential diagnosis from other giant lesion interesting the posterior cranial fossa have been integrated into the discussion. 2. Case Report A 56-years-old woman was admitted at our neuroscience department complaining a recent slight diplopia and persistent headache which had arisen about five-six months before, initially NSAID responsive, that was progressively increasingly. A first medical examination showed peripheral right facial nerve and right abducent nerve paralysis. At the examination, vital signs and blood parameters were normal. No other neurological signs were detected. A CT brain scan was performed with reconstruction in 2D MPR and VR that showed a presence of a giant expansive lesion on the right side of posterior cranial fossa (Figure 1(a)). Figure 1: HRCT in axial plane showed heterogeneous hypodense lesion extending to middle and posterior fossa ((a) and (b)), and multiple bilateral hypodense collected disseminated along cerebral cisternal and cortical spaces ((c) and (d)). The lesion developed from the posterior cranial fossa toward foramen magnum (Figure 1(b)) till middle fossa, causing a compression of right temporal lobe, that was displaced upwards and laterally, and a more serious compression of brainstem that was displaced on the left side. A cerebellar vermis