This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: ENT
Mastoid infection which erodes through the outer cortex of bone results in - 
Select and explain. 
A. Sub-periosteal abscess, B. Epidural abscess, C. Perichondritis, D. Lateral sinus thrombosis
A: Sub-periosteal abscess
Answer: A: Sub-periosteal abscess 
Explanation: None