In addition to increased head circumference (necessitating a cesarian birth) what would be evident to cursory palpation of the skull?
The fontanelles are markedly widened.
What are the two mechanisms of head size enlargement in this case?
The mass itself, and obstructive hydrocephalus by the mass at the level of the aqueduct.
What density tissue makes up this mass?
There are three main components: 1) soft tissue, generally somewhat hyperdense, 2) fluid attenuating cyst regions and 3) calcific areas.
What accounts for the hyperdense material in the occipital horns?
This represents blood layering in dependently in the ventricles.
What are some of the differential you should entertain in this case?
The differential for a very large heterogeneous, partially hyperdense mass in a child includes: supratentorial PNET, atypical rhabdoid / teratoid tumour (ATRT), immature teratoma and in older age children, ependymoma and choroid plexus carcinoma.
CT without contrast demonstrates a very large hyperdense mass in the supratentorial compartment which has markedly heterogeneous density with components of fat, fluid and soft-tissue attenuation. Hyperdense material layers dependently in the occipital horns consistent with blood.
Marked supratentorial obstructive hydrocephalus with transependymal CSF permeation.