Which of the following is a type of benign tumor comprised of blood vessels?

The correct answer is a hemangioma, which is a type of benign tumor that consists of a mass of blood vessels. These tumors can occur in various parts of the body and are usually not harmful. Hemangiomas are often referred to as vascular tumors and are characterized by their rich vascularity, which is the result of an abnormal collection of blood vessels. They can range in size and are commonly diagnosed in infants, often resolving on their own without treatment.

In contrast, angiosarcoma is a malignant tumor that also arises from blood vessels but is cancerous and aggressive, making it distinctly different from benign hemangiomas. Cystic lesions are fluid-filled sacs that can be located in various tissues and aren't tumors made up of blood vessels; their composition is primarily fluid rather than vascular. Adenomas are benign tumors that arise from glandular tissue, which typically does not contain the vascular structure characteristic of hemangiomas. Each of these alternative options represents a different pathology, underscoring the unique classification that hemangiomas hold as benign vascular tumors.