Roald Dahl invented a valve that helped thousands of people suffering from a rare medical condition

He came up with the Wade-Dahl-Till valve after his baby son became ill

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His stories have been celebrated around the world - but did you know that Welsh author Roald Dahl once invented a piece of medical kit which is still used in hospitals today?

Fascinated and frustrated by the medical profession, Dahl devised a treatment for his sick son which would go on to help thousands of children.

The creation has come to light in a new book by Professor Tom Solomon – who looked after Dahl in later life.

Still known in the medical profession today as the Wade-Dahl-Till valve, it was used to relieve hydrocephalus, a condition that can leave patients with enormously swollen heads due to an accumulation of fluid in the skull.

Dahl began work on the valve after five-month-old son Theo developed the condition after being struck by a New York taxi in December 1960.

Until his invention Theo used a Holter Shunt to drain excess fluid from his head. But these could jam, causing pain and blindness and risking brain damage.

"It is a long fight and a hard one to keep a hydrocephalic child going," Dahl wrote in Ladies Home Journal.

Small slits in the valve blocked up with debris that had accumulated. This was common in patients like Theo, where trauma and bleeding contributed to the hydrocephalus.

The shunt "had a terribly demanding life of its own", Dahl's first wife Pat said.

"Three times daily, the little pump under the scalp had to be pressed twenty times to ensure it had not clogged, and the fluid was flowing."

Cardiff -born Dahl couldn't believe science "couldn't produce one little clog-proof tube."

An article on the creation – made with the help of neurosurgeon Kenneth Till and hydraulic engineer Stanley Wade – was published in The Lancet in March 1964.

Dahl told Prof Solomon: "Infants all over the world were being subjected to all these traumatic brain operations simply because surgeons had to accept what they were given.

"There had to be something we could do, some way of improving on this slit thing."

He learned everything he could about the condition and its treatment, which was costing Dahl $408 each day in the US – the equivalents of more than $3,000 today.

By January 1961 the fees were "running well over $10,000" with family and friends helping to ease the burden. Among them Cary Grant's wife who sent a cheque for $1,000.

Dahl wrote to his mother: "Do they have anything better in England, something less likely to block and clog?"

There was an alternative in England, called a Pudenz.

When the family returned to Great Missenden in May 1961 Theo had one fitted. But it failed.

Dahl turned this old friend Stanley Wade.

"Wade was invited to watch the operations so he could understand exactly what was needed," Prof Solomon said.

Dahl saw Wade almost daily for three years, liaising with Till, and also keeping in touch with Neurosurgeon Joseph Ransohoff in New York, as well as Kenneth Shulman, a new member of the American team.

Dahl told him: "We produced this splendid little valve. Most precise. It had to be non-return, open at a certain pressure, not clog up."

Dahl drew a sketch for him on the back of the day's Times.

"Of course it was Ken and Stanley who really did it all, not me," Dahl said.

"Till worked tremendously. I did not really do much. I was just the go-between, finding out what he wanted and letting Stanley know."

In fact Dahl was the driving force behind the venture.

Documents revealed he was intimately involved in the inventing.

"When a way of checking the pressures at which the valve would open were needed, the papers show he devised a series of water tanks to create pressure differentials, with the valve sitting in the middle," Prof Solomon said.

A sheet of Dahl's yellow legal paper displayed his calculations for the length and diameter of a stainless steel capillary tube to allow excess cerebrospinal fluid to flow.

Another shows Stanley Wade's prototype sketches of the valve.

When Dr Ransohoff became director of neurosurgery at the Children's Hospital of Philadelphia he confirmed the WDT valve would be "first choice in treatment of hydrocephalus."

The WDT valve was produced in its thousands through engineering firms with which Wade had connections.

Wade, Dahl and Till agreed early it was not to be sold for profit.

They established the Children's Research Fund at London's Hospital for Sick Children that would own the exclusive rights of manufacture.

Dahl wanted the valve to be available to children with hydrocephalus all over the world.

"The valve was taken up, and used in all sorts of places – India, Kenya and Tanganyika,’ Dahl told Prof Solomon.

"We charged more for the rich countries – America and England – so that it was cheaper for the poorer ones."

Prof Solomon added: "Curiously. with the WDT valve, when Dahl clearly had a major role in a new medical invention that was used on thousands of children around the world, he seemed to shy away from the limelight.

"Like a shy Mr Hoppy in Esio Trot, Dahl seemed reluctant to claim any credit for this marvellous medicine."

*Roald Dahl's Marvellous Medicine, by Tom Solomon, is published by Liverpool University Press and priced £10