Skull Base

Question 1

What is a chordoma?

Answer 1

Neoplasm arising from the remnants of the notochord which presents as a destructive midline mass.
Most common locations: sacrum (50%), clivus (35%), vertebral bodies (most commonly C2).
Typically it is T2 bright and has a predilection for the spheno-occipital synchondrosis.
Main differential is chondrosarcoma.

Question 2

Chondrosarcoma features.

Answer 2

1. Almost always just lateral to the midline

2. T2 bright but will have classic “arcs and rings” matrix on CT

Question 3

What skull changes do you see in Paget’s?

Answer 3

1. Osteolysis circumscripta - large areas of osteolysis in the frontal and occipital bones in lytic phase
2. “Cotton wool” appearance in mixed phase
3. Thickened and expanded in sclerotic phase.

Question 4

Skull base lesion differential.

Answer 4

1. Chordoma
2. Chondrosarcoma
3. Metastasis
4. Myeloma
5. Fibrous dysplasia
6. Paget’s disease