Many patients with VHL now follow the advice of their experienced physicians and have regular examinations for early detection and treatment of newly developing or small known lesions. The main targets of these re-investigations are hemangioblastomas of the cerebellum or spine, tumors of the kidneys and pheochromocytomas, usually but not always in the adrenal glands. The techniques used are classical CT or MRI, and for both i.v. contrast (gadolinium) should be used.

In the Freiburg VHL clinic and at patient-provider conferences such as the one recently held in Burlington, Massachusetts, we are repeatedly confronted with situations like this: "I just had my check-up and was told that my kidney tumor increased in size by 25%! Since there is such dramatic growth, I was advised to undergo surgery."

Growth of 25% sounds terrible. Having money in the bank at 25% is extremely high interest. But for a kidney tumor of 2 cm. in diameter, 25% growth means a diameter of 2.5 cm., which is still not very much.

I always want to know the growth exactly. Not being a radiologist myself, I have had many discussions with our radiologists on this subject. There are two major aspects we recognized.

1. It is very important, and often not easy, to use exactly the same methodology for the test, including having exactly the same Computed Tomography (CT) slices for comparison. Patients have to stop breathing for every CT slice, but they do not stop breathing in exactly the same place each time. The air volume in the lungs is not always exactly the same, and the position of the kidney, which moves during breathing, is slightly different. Even if you use the same slice depth, you may be taking a very different picture of the tumor (see Figure 1). Consequently the tumor may appear larger or smaller, simply because of the position of the image.

2. Techniques are improving rapidly. Most medical centers now have CT scanners of the third or fourth generation. With each improvement in design, the resolution of the imaging has improved a great deal, and the pictures are clearer. We also have larger films showing larger images. If the scale changes, the larger picture may give the impression that the tumor is larger, when that is not the case. All CT images have a built-in absolute scale, to provide a ruler to measure the structures in the image, which must be referenced to calculate the relative size of the tumor in each picture.

The improved resolution of the images enables us also to see very small tumors which could not be seen on first or second generation scanners. When we see these smaller lesions, we must inform the patient. "You have not three but six tumors in your kidney." The patient thinks: "There is new growth, I have three new tumors." But the radiologist cannot definitely say that those tumors are new unless he used a similar machine and has ruled out the breathing effect.

Furthermore, the improved image quality also adds to the impression that known tumors may have grown, since they can now be seen to have sharper margins. Patients should be aware that imaging is not precise.

In Freiburg, we prefer to have imaging controls avoiding radiation. Kidney lesions are now followed with MRI imaging. Because of the breathing problem, we developed a special program. We regularly perform imaging while the patient holds a breath for 12 seconds, which is comfortable even for disabled patients. In one cycle half of the kidney is imaged with 8 slices of 8 mm. thickness without any interslice distance. Two of these sequences cover the whole kidney. To measure the craniocaudal extensions a third coronal sequence is performed routinely. By application of two even faster sequences it will hopefully be possible to avoid the administration of i.v. contrast medium.

Helical or spiral CT is a new development covering an entire volume during one breathhold cycle: for patients with electrical implants, such as pacemakers, and other situations not permitting the use of MRI, helical CT is an alternative. Contrast application is required, and a disadvantage, particularly where multiple follow-up screenings are required, is the use of radiation.

Of course, all lesions which VHL patients have done some growing, and some are still growing. But growth may be less than a first glance impression might tell us. Different decisions may have to be made for each affected organ whether surgery has to be recommended or can be postponed. I prefer to have very well informed patients. I feel it facilitates making decisions about what to do.

Figure 1. Illustrations A and B show the possible technical error in measurement of CT scans caused by breathing. If A were taken before B, the tumor would seem to have grown; if B were taken before A, it would seem to have shrunk.

A. A 3 centimeter tumor (approximately one inch in diameter), as it might be shown on a scan. If images were taken at positions 1 and 2, the tumor would measure 2 centimeters. Figure 1c shows the view of the face of the slice, as it would appear in the scan. Picture slicing an orange at position 1 as shown, then turn the orange up so that you are looking at the round cut face of the slice.

B. If images were taken at positions 1, 2, and 3 the tumor would measure 3 centimeters.

As published in the VHL Family Forum, 3:2, June 1995. For permission to reprint, please contact the VHL Family Alliance, editor@vhl.org. Further information is available from the VHL Family Alliance, info@vhl.org