Exploding Bubbles Can Trim Enlarged Prostate

Richard A. Lovett
for National Geographic News
June 2, 2009
A new technique using tiny, exploding bubbles has allowed doctors to shrink enlarged prostates quickly and virtually painlessly in dogs, researchers announced recently.

The method, called histotripsy, uses focused pulses of high-energy ultrasound sent through the skin to create microscopic bubbles in the prostate, which in humans is a squishy, walnut-size gland located under the bladder and in front of the rectum.

Because dogs and humans have similar prostates, the procedure is also promising in men, experts say.

(Explore an interactive of the human body.)

These bubbles grow and collapse in a process called cavitation, which liquefies tissue.

By changing the aim of the ultrasound pulses, researchers can quickly turn unwanted tissue to mush, Roberts said. The excess material is then washed out of the body via urine.

"Historically, no one believed that cavitation could be controlled like this," lead study author William Roberts, a urologist at the University of Michigan, said in a statement.

Prostate Roto-Rooter

Though all of the prostate's functions are unknown, one of its main roles in humans is to push fluid into the urethra to accompany sperm during sexual climax, according to the National Institutes of Health.

The added fluid energizes sperm and makes the vaginal canal less acidic.

Prostate enlargement is a common problem, affecting a third of U.S. men in their 50s and half of those in their 70s and 80s, Roberts said.

If left unchecked, enlarged prostates can create medical problems by impeding the flow of urine. Eventually, surgery is needed to keep urine from being completely shut off.

The current "gold standard" treatment is a procedure called a trans-urethral resection of the prostate, in which an instrument with rotating blades is inserted through the penis. That instrument can be used to scrape away enough prostate tissue to allow urine to flow normally.

"It's like a mini Roto-Rooter device," said Peter Kaczkowski, a senior engineer at the University of Washington's Applied Physics Laboratory who was not part of Roberts's team.

But complications are common, ranging from bleeding to incontinence to lack of sexual function.

"It's also fairly painful and clearly unpleasant," Kaczkowski said.

What's more, the mortality rate can be as high as one percent—"exceedingly high, given that this is a benign condition," study author Roberts said.

Pressure Washing

The team discovered that not only could they sculpt well-defined holes into the dogs' prostates, but that the procedure caused the dogs no discomfort.

"Very surprisingly, there was only a very minimal amount of bleeding," said Roberts, who presented his research in May at the Acoustical Society of America meeting in Portland, Oregon.

"It looks very promising."

(Related: "Dogs Smell Cancer in Patients' Breath, Study Shows.")

University of Washington's Kaczkowski agreed.

"If this pans out, everybody will be treating [enlarged prostates] this way," he said.

Kaczkowski compares it to replacing the surgically invasive method with something more like pressure washing.

"A pressure washer is innately more benign than rotating blades," he said.

In the long run, the technique may also help men with prostate cancer. "There's a wide-open range of targets," Roberts said.

But first scientists have to make sure that the ultrasound pulses don't create byproducts that promote metastasis, or the spread of cancer cells throughout the body.

"We're studying this now," Roberts said.

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