ATLANTAThe CaverMap Surgical Aid to help surgeons protect the
cavernous nerves during nerve-sparing prostatectomy appears not to be
specific enough to be clinically useful at present, Patrick Walsh,
MD, said at the 95th Annual Meeting of the American Urological
CaverMap is an electronic device combining nerve stimulation and
tumescence monitoring. During surgery, the surgeon uses a probe tip
to stimulate areas suspected to contain the neurovascular nerve
bundle responsible for erectile function and then checks for
Dr. Walsh, director, James Buchanan Brady Urological Institute, Johns
Hopkins Hospital, and his colleagues reported that, prior to surgery,
CaverMap stimulation of the presumed neurovascular bundle tissue did
lead to tumescence in most patients, but control
stimulation of other areas also caused tumescence in about half of
Data on 50 Patients
Dr. Walsh presented data on 50 patients, all under age 60, who had
clinically localized prostate cancer and underwent nerve-sparing
Most patients (88%) had bilateral nerve-sparing prostatectomy. Five
experienced surgeons tested the device.
At the time of surgery, we used the CaverMap machine in regions
where we thought the neurovascular bundle was located, to look for a
response to stimulation. As a sort of negative control, we also
stimulated areas where we thought the bundle wasnt, to see
whether we could demonstrate that the bundle was not there, Dr.
Walsh told ONI in an interview.
At the end of the surgery, he said, the CaverMap device was used to
see whether the researchers could predict which patients would remain potent
The researchers found that before the prostate was removed,
stimulation to the area thought to contain the neurovascular bundle
produced a positive response 88% of the time. But stimulation to
areas thought not to contain the neurovascular bundle also produced
tumescence in 46% of cases.
The question was whether this machine would be successful in
the hands of less experienced surgeons, enabling them to preserve
sexual function better. The answer is that the first-generation
machine we tested will not accomplish this, Dr. Walsh said.
It is not reliable enough to let surgeons know whether to
preserve tissue or excise it.
Sensitive but Not Specific
The problem with the machine, Dr. Walsh said, is that it is very
sensitive but not very specific.
There are spontaneous changes in the diameter of the penis that
occur during surgery, probably because we are putting pressure on the
nerves or doing something else to them, Dr. Walsh commented,
and this instrument is not specific enough for surgeons to use
to detect the difference between these spontaneous changes and the
effects of an intact cavernous nerve.