THURSDAY, Feb. 3 (HealthDay News) -- A rare form of stroke that involves veins instead of arteries occurs more often than thought, according to a new American Heart Association/American Stroke Association scientific statement.

This type of stroke -- cerebral venous thrombosis (CVT) -- is caused by a clot in the dural venous sinuses, which are veins that drain blood from the brain toward the heart. It is most common in women who are pregnant or taking oral contraceptives, and in people age 45 and younger.

The incidence of CVT among pregnant women and those who have recently given birth ranges from one in 2,500 to one in 10,000. The risk is greatest during the third trimester of pregnancy and in the first four weeks after giving birth. Up to 73 percent of CVT cases occur immediately after childbirth.

But women who've suffered CVT have a low risk of complications during future pregnancies, according to the scientific statement.

Patients with suspected CVT should have blood tests to determine if they have an inherited or acquired factor in the blood that increases the risk of blood clots (prothrombotic factor).

In addition, patients should be screened for conditions that increase the risk of CVT, such as the use of oral contraceptives, inflammatory disease and infection.

"The most common symptoms of patients with CVT include headaches that progress in severity over days or weeks, and seizures. Some patients may develop a focal neurological deficit (weakness affecting the extremities, double vision, etc.)," Dr. Gustavo Saposnik, chair of the statement writing group and an assistant professor of medicine at Saint Michael's Hospital, University of Toronto, said in an American Heart Association news release.

Diagnosis of CVT can be challenging. For example, 30 percent to 40 percent of patients with CVT may develop an intracranial hemorrhage (bleeding within the skull).

"It's important to distinguish a hemorrhage caused by a ruptured brain artery from those associated with CVT. The mechanisms -- and treatment -- of the bleeding are quite different," Saposnik said.

The statement outlined the approach doctors should take to diagnose and manage CVT:

• Clinical suspicion of CVT.
• MRI, or alternative imaging technique at hospitals/medical centers with fewer resources.
• Confirm CVT.
• Begin anticoagulation therapy (IV Heparin).
• Continue anticoagulation therapy, lasting three to 12 months to a lifetime.

Other options may be considered in patients who continue to experience neurological deterioration despite medical treatment. These options include surgery to temporarily remove a section of skull to relieve pressure on the brain (hemicraniectomy), or minimally invasive surgery to remove clots in the affected veins (endovascular treatment).

The scientific statement, published in the Feb. 3 issue of Stroke, is endorsed by a number of organizations, including the American Academy of Neurology and the American Academy of Neurological Surgeons.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about stroke.