* No stroke or neurological damage detected, doctors say
* Clinton can leave hospital when blood thinner dosage set
* No long-term ill effects from clot anticipated
* Secretary of state suffered concussion in mid-December
By Arshad Mohammed and Jilian Mincer
WASHINGTON/NEW YORK, Dec 31 (Reuters) - U.S. Secretary of State Hillary Clinton suffered a blood clot in a vein between her brain and skull behind her right ear but is expected to make a full recovery, her doctors said on Monday in a statement released by the State Department.
Clinton did not suffer a stroke or neurological damage as a result of the clot, the doctors said, adding that "she is in good spirits, engaging with her doctors, her family and her staff."
The U.S. secretary of state, who has not been seen in public since Dec. 7, was revealed on Sunday evening to be in a New York hospital under treatment for a blood clot that stemmed from a concussion she suffered in mid-December.
The concussion was itself the result of an earlier illness, described by the State Department as a stomach virus she had picked up during a trip to Europe that led to dehydration and a fainting spell after she returned to the United States.
"In the course of a routine follow-up MRI on Sunday, the scan revealed that a right transverse sinus venous thrombosis had formed. This is a clot in the vein that is situated in the space between the brain and the skull behind the right ear," Clinton's doctors, Drs. Lisa Bardack and Gigi El-Bayoumi said in the statement released by the State Department.
"To help dissolve this clot, her medical team began treating the Secretary with blood thinners. She will be released once the medication dose has been established," the doctors said. "In all other aspects of her recovery, the Secretary is making excellent progress and we are confident she will make a full recovery."
MAY RAISE QUESTIONS ABOUT ANY WHITE HOUSE RUN
Clinton's illness may raise questions about her fitness to be president should she make a new run for the White House in 2016. Barack Obama defeated her in the 2008 Democratic primary and then, upon his election as president, took the unusual step of tapping her for the most important post in his Cabinet.
Clinton earlier this month played down the notion that she would run again for the White House in 2016, telling a TV interviewer: "I've said I really don't believe that that's something I will do again. I am so grateful I had the experience of doing it before."
The former first lady turned U.S. senator from New York turned diplomat has played down talk of possibly making another White House run. She is expected to step down when her replacement as secretary of state, Senator John Kerry, is confirmed by the Senate.
Clinton has kept up a punishing schedule as the top U.S. diplomat, flying more than 950,000 miles to visit 112 countries and spending more than a quarter of her tenure - 401 days - on the road, according to the State Department.
Her health setbacks have forced her to cancel an overseas trip and postpone testimony to Congress regarding a report on the deadly attack on the U.S. diplomatic post in Benghazi, Libya. Her two deputies testified instead.
Clinton has said she intends to appear before Congress to discuss the attack - in which four Americans, including the U.S. ambassador to Libya, died - but it is unclear when she will be back at work.
The doctors gave no estimate of when she may go home from the hospital.
On Sunday, a State Department spokesman said Clinton was "being treated with anti-coagulants and is at New York-Presbyterian Hospital so that they can monitor the medication over the next 48 hours."
'PIPES' DRAIN BLOOD FROM THE BRAIN
Clinton's condition is unusual, but by no means unheard-of.
"This condition is not very common, but it certainly happens," said Dr. Raj Narayan, chair of neurosurgery at North Shore University Hospital and Long Island Jewish Medical Center in New York. It probably happens more often than we realize, he said, because it must be diagnosed with an MRI, as Clinton's was.
Narayan, who is not treating Clinton, said it likely was caused by her dehydration and the concussion that occurred from her fall. Head trauma can cause blood clots, Narayan said, because the injury triggers the production of thromboplastin, a blood protein that causes the blood to clot.
The severity depends in part on how someone is built, he said.
People normally have two of the veins where Clinton suffered the clot. Some people, however, have only one, while others have two but one is much larger than the other. The prognosis is typically better if you have two normal veins because the blood could flow through the other vein if one is blocked.
"Think of it as two pipes draining all of the blood out of the brain," Narayan said. "If one is blocked and the other is open, there is no problem. But if both pipes are blocked, you are in trouble."
Dr. Geoffrey Manley, chief of neurosurgery at San Francisco General Hospital and professor of neurosurgery at the University of California San Francisco (UCSF), said the condition can be fatal if not treated but that most patients recover well.
"Left untreated, these things could be fatal. But typically, injuries to the transverse sinus, if treated appropriately, patients typically do very well," Manley said.
Manley, who is also not involved in Clinton's treatment, said it was quite possible she would be out of the hospital in a week or less and the condition was not likely to have long-term effects or to be the harbinger of more clots over time.
"One doesn't necessarily dictate another one," he said.
"This is ultimately not going to cause any long-term brain problems for her, and I think that it's a message to the public that when you fall and hit your head, you need to be evaluated by somebody that takes care of brain-injured patients," he added.