The clot is in the transverse sinus, a large vein that goes around the inner wall of the skull at the back of the head. Her clot is on the right side; there is a similar sinus on the left.
The condition can cause permanent brain damage, coma or death if not detected and treated in time. In Clinton’s case, however, it appears to have caused few if any symptoms and to be responding to treatment with blood-thinning drugs.
“In all other aspects of her recovery, the secretary is making excellent progress and we are confident she will make a full recovery,” her physicians, Lisa Bardack of the Mount Kisco Medical Group and Gigi El-Bayoumi of George Washington University, said in the statement. “She is in good spirits, engaging with her doctors, her family, and her staff.”
Almost three weeks ago, Clinton, who is 65, reportedly became severely dehydrated with an intestinal infection. She fainted, fell and hit her head, suffering a concussion. Whether those events are related to the blood clot is unknown, with experts offering divergent opinions.
Cerebral venous thrombosis — the general term for Clinton’s condition — is rare. It occurs in about four out of every million adults per year. It is somewhat more common in children. Head trauma, pregnancy, cancer, brain infection, autoimmune diseases and inborn clotting abnormalities are all predisposing factors. Some experts believe severe dehydration may be as well.
In 30 to 40 percent of cases, however, no cause is found.
Clinton has had at least one previous blood clot, in her right leg in 1998. She was treated with blood-thinning drugs for several months. In her memoir she attributed the clot to “my nonstop flying around the country.” Airplane flights lasting longer than six hours appear to be a slight risk factor for developing leg clots, known as deep venous thromboses (DVTs).
Head trauma can cause blood in a venous sinus to clot, but it almost always has to be severe enough to cause a skull fracture, said Aaron S. Dumont, director of cerebrovascular surgery at Thomas Jefferson University in Philadelphia.
“It’s probably a coincidence,” he said of Clinton’s fainting spell and the clot. He noted, however, that her history of a blood clot in the leg may indicate a predisposition to clotting.
But Gregory Piazza, a cardiologist and vascular medicine specialist at Brigham and Women’s Hospital in Boston, said he thinks a fall serious enough to cause a concussion could have caused the clot. It is also possible that a clot could have caused the fall. “Either could be a possibility in this case,” he said.