Cavernous hemangioma

A cavernous hemangioma is a benign tumor made up of malformed blood vessels. Because of these structures, blood will leak from the vessels into surrounding tissue. They're usually congenital but, unlike other forms of hemangioma, they don't get smaller over time. Their cause is poorly understood, but it's believed they have a genetic component. It's also theorized they can be caused by radiation therapy. If they grow close to the surface, they can be disfiguring. They can grow anywhere in the body that has blood vessels, but are most common in the brain, liver, and eyes.
They can usually be diagnosed with an MRI alone as they have a distinctive shape. A biopsy is usually not necessary. However, the condition is often mistaken for other types of arteriovenous malformations.
In most cases, the condition merely has to be monitored and the patient has no symptoms. However, when the condition appears in the brain, it can cause bleeding and seizures. In such cases, neurosurgery is recommended.
Cavernous hemangioma at Wikipedia