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: Surgery
A 49 year old man suffering from carcinoma of prostate was x -rayed. He showed areas of sclerosis and collapse of T 10 and T11 veebrae in x-ray. The spread of this cancer to the above veebrae was through - 
Select and explain. 
A. Sacral canal, B. Lymphatic vessels, C. Internal veebral plexus of veins, D. Superior rectal vein
C: Internal veebral plexus of veins
Answer: C: Internal veebral plexus of veins 
Explanation: Ans is 'c' i.e. Internal veebral plexus of veins Prostatic cancer spreads to the bones through blood vessels; first into Batson's periprostatic venous plexus * and then into the internal veebral plexus of veins. This metastatis is possible because of valveless communication* between the periprostatic and veebral plexus of veins.