Which type of haemorrhoids is treated by the injection of sclerosing agent?

Injection sclerotherapy is the treatment of choice of internal hemorrhoids. It helps in reducing the size of the hemorrhoids and stop it from bleeding. A solution containing either quinine and urea or phenol is used as the sclerosing agent. Hemorrhoids are swollen veins around the anus and in the rectum that may protrude from the anus. Patients presents with itching, burning, pain, swelling, irritation and bleeding per rectum. Bleeding is bright red in colour and is associated with bowel movements. Ref:Bailey and Love's Sho Practise of Surgery, 24th Edition, Page 1255.