MARATHON operations to separate conjoined twins are fraught with danger, as
the doctors who operated on Jodie and Mary in Manchester this week know only too
well. But it might be possible to make future operations safer by creating a
complex model of the patients鈥� internal organs and blood vessels. At least,
that鈥檚 the view of a surgeon whose team used such a technique to help them
separate conjoined twins in Brisbane last month.
The 7-month-old twins, Tay-Lah and Monique Armstrong, were joined upside
down, at the rear of their heads over a circumference of about 25 centimetres.
Monique鈥檚 cerebellum bulged into Tay-Lah鈥檚 skull. To help navigate the complex
anatomy, the surgeons studied models of the twins鈥� skulls and certain blood
vessels. A company in Brisbane called Anatomics created the models鈥攗sing a
type of 鈥渞apid prototyping鈥� called stereolithography
(New Scientist, 30 September, p 25).
Studying the models before the operation helped cut the twins鈥� time in
theatre to just 12 hours, says Scott Campbell, who led the team of surgeons at
the Royal Children鈥檚 Hospital in Brisbane. 鈥淭ay-Lah had medical problems that
meant there was no way she was going to survive a 24-hour operation,鈥� says
Campbell. 鈥淭he model was tremendous. I constantly referred to it throughout the
operation.鈥� As New Scientist went to press, the Armstrong twins were in
a stable condition.
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Although each twin had her own set of organs, the risk of one baby dying
during or after surgery was thought to be as high as 70 per cent. The twins鈥�
skulls were joined close to where a major blood vessel drains from the brain to
the jugular vein. If the surgeons had accidentally cut the vessels, and had to
clamp them, sudden changes in blood pressure could have triggered a
life-threatening stroke.
To create the models, two-dimensional images from CT scans of the twins鈥�
heads were loaded into a computer, and turned into a single 3D image with
Anatomics鈥� software. The computer then sent instructions to a laser, directing
it to harden a vat of light-sensitive liquid plastic, layer by layer, into an
exact semi-transparent replica of the vital tissues. The blood vessels were
highlighted in pink by running the laser over them for a second time to
鈥渙vercure鈥� the plastic.
Similar see-through models have been used to help reconstruct the faces of
gunshot victims and in other surgical procedures鈥攂ut this is the first
time a model has been used to help separate twins who are joined at the head.
The models are more useful in surgery than 3D computer images, claims Paul
D鈥橴rso, a neurosurgeon at Addenbrooke鈥檚 Hospital in Cambridge and managing
director of Anatomics. 鈥淵ou might think it鈥檚 just a stupid, plastic model, but
it鈥檚 very powerful. It鈥檚 truly 3D鈥攜ou can look at it from any perspective.
And it鈥檚 tactile, that鈥檚 a big difference for a surgeon,鈥� he says.