A T1-hypointense intracranial dermoid cyst

Computed tomography and magnetic resonance illustrating the main imaging features of the dermoid cyst. Microscopy photographs of the lesion. (A) Soft tissue window computed tomography demonstrating the presence of a posterior fossa cystic lesion, mostly hypodense (≃10 Hounsfield Units) (block arrow), with a few slightly denser elements in the left region (≃29 Hounsfield Units) (dotted arrow); (B) Bone window computed tomography demonstrating the presence of a sinus tract, representing a clue to the presence of a possible inclusion cyst; (C and D) Large area of reduced water diffusion, demonstrated by hyperintensity in diffusion-weighted imaging and hypointensity in apparent diffusion coefficient map; (E) Axial T2-weighted image, demonstrating a predominantly T2-hyperintense posterior fossa lesion (block arrow), with a small and irregular superior-posterior T2-isointense region (dotted arrow); (F) Sagittal T1-weighted image, demonstrating a predominantly T1-hypointense posterior fossa lesion (block arrow) with a few superior isointense elements (dotted arrows); (G) Sagittal T1-weighted image, demonstrating the presence of a few linear hyperintense components after gadolinium administration; (H and I) Histology images demonstrating a cystic lesion delineated by a keratinizing squamous epithelium (block arrow) with granular layer (thin arrow), sebaceous glands (dotted arrows) and wet keratin (double arrow), making the diagnosis of dermoid cyst