This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Childhood Tumors, Subject name: Pediatrics
Retinoblastoma spreads to CNS through: 
Select and explain. 
A. Direct, B. Lymphatic, C. Arterial, D. Vitreous
A: Direct
Answer: A: Direct 
Explanation: a. Direct(Ref: Nelson's 20/e p 2476-2478, Ghai 8/e 614-615)Spread of Retinoblastoma:By direct extension to choroid; Along the optic nerve beyond lamina cribrosa to the CNS, orBy hematogenous or lymphatic spread to distant sites, including bones, bone marrow, and lungs.