Huge destructive mass arising from the clivus and extending posteriorly into the prepontine cistern indenting the brainstem and cerebellum. On midline sagittal plane the tumour shows the thumb sign, then the mass extends to the foramen magnum and spinal canal and parapharyngeal space. The pituitary gland and sella are elevated with the mass separate from it. The C1 vertebral body is involved. Supratentorial hydrocephalus is noted.