Atypical epidermoid cyst of the fourth ventricle with minimal diffusion-restriction.

Background: Epidermoid cysts are benign, slow growing extra-axial lesions most commonly found in the cerebellopontine angle that have a characteristic imaging pattern of restricted diffusion on diffusion-weighted imaging (DWI).

Methods: A 10-year-old male with a history of asthma and diabetes was found to have a lesion within the fourth ventricle on a magnetic resonance imaging (MRI) brain study. MRI showed a well-circumscribed vermian lesion without contrast enhancement or restricted diffusion with mild hydrocephalus. He was referred to the neurosurgical service once he acutely developed symptoms of dizziness. He underwent a gross-total resection of the lesion on which histopathology confirmed an epidermoid cyst.

Results: Here, we report a case of an atypical epidermoid cysts found in the midline of the fourth ventricle without restricted diffusion on MRI.

Conclusion: Avid restricted-diffusion on DWI is usually pathognomonic for an epidermoid cyst when evaluating an extra-axial lesion, yet we report the second case in the literature of an epidermoid cyst without this classical imaging characteristic.