Thai king to have lumbar puncture operation - official

File photo of Thailand's King Bhumibol Adulyadej on a wheelchair as he looks at a Red Bull Formula One car (not in picture) at Siriraj Hospital December 17, 2010.

BANGKOK (Reuters) - Thailand's King Bhumibol Adulyadej, 83, who has been in hospital since September 2009, is to be operated on to remove cerebrospinal fluid, the Royal Household said in a rare statement on his health on Monday.

The lumbar puncture procedure, also known as a spinal tap, would be done on the night of May 2, the statement said.

The king has made the occasional public appearance since being hospitalised and the most recent footage has appeared to show him in better health.

He is revered by most Thais and his health is sensitive because of concerns his succession may be complicated at a time of continuing political tension.

The government is expected to dissolve parliament in coming days and call an early election. Anti-government protests in the first half of last year were put down by the military at the cost of 91 lives.

Public discussion of the monarchy is limited by strict lese-majeste laws that carry a penalty of up to 15 years in jail.

The Royal Household reiterated in its statement that the king had recovered from a lung infection but continued to stay in hospital for physical rehabilitation and to ensure good nutrition.

It explained that the excess cerebrospinal fluid had caused unsteadiness when he walked, which it said was normal in elderly people.

"The medical team consulted with both foreign and local specialists and agreed to perform a spinal tap," it said, adding that the king was otherwise fine and eating normally.

(Reporting by Bangkok bureau)