Planning percutaneous nephrolithotomy using multidetector computed tomography urography, multiplanar reconstruction and three-dimensional reformatting

Authors


Sir,

We read this paper [1] with great interest and applaud the authors’ efforts to define the role of 3D-CT urographic (CTU) reconstruction in the preoperative planning of percutaneous nephrolithotomy (PCNL). However, there are some points of technique and conclusions in the paper that need clarification, especially if readers are considering 3D CTU for preoperative planning of PCNL.

CTU should be considered a technique under development [2]; there are still unanswered questions about the technical aspects, e.g., abdominal compression, patient hydration and the use of a diuretic for optimum data acquisition. The authors applied abdominal compression followed 10 min later by 40 mg frusemide and a non-contrast enhanced supine scan. After injecting contrast medium, another supine scan was acquired 7 min later, with a 1 min of ‘rocking’ to encourage mixing of contrast medium. Thus two scans are acquired after a prolonged period of compression.

In our experience, patients find abdominal compression of >10 min quite uncomfortable against the diuretic background provided by the contrast agent and frusemide. Indeed, the value of abdominal compression has been questioned. Recent studies showed that 250 mL of i.v. saline before scanning results in significantly better opacification than abdominal compression [3,4]. The role of a diuretic before scanning also remains unclear; one study showed that low dose frusemide (10 mg) was more effective than 250 mL saline for opacification and definition [5].

As a result of these studies and our findings, we have modified our technique [6] to 10 mg frusemide before a non-contrast-enhanced supine scan, immediately followed by injection with i.v. contrast medium and 100 mL saline infusion, with an 8-min post-contrast scan taken with the patients prone. We use abdominal compression before contrast scanning but limit it to ≤ 5 min. There is an even density of contrast medium when we turn the patient prone. The authors found an uneven density in four of 10 patients, whilst with our technique we have had no such problems with over 13 consecutive patients to date. We also recommend scanning with the patients prone; this ensures an even opacification of the collecting system [7] and is more valuable for planning percutaneous access as it replicates the patient position during surgery [8].

Much also needs to be defined about reconstruction methods and display. The authors used reconstructions formatted onto two-dimensional monochrome film, which rely on a box for orientation. This cannot provide the surgeon with an overall ‘feel’ for anatomical information. In particular, the radiologist must decide before surgery what particular aspect of 3D anatomy the urologist may want to see, when often the information demanded changes during the procedure. In our view, this technique is crude and undervalues the true ability of 3D CT; the latter is more vivid with colour 3D MPEG interactive movie loops that can be readily scrutinised on standard computers in the theatre by all operators. This, with the other technical refinements described above, is allowing ‘Stars Wars’-like 3D reconstructions to become reality [9].

Finally, the authors conclude that 3D CTU should become the standard imaging method for PCNL in selected patients. However, it remains to be objectively confirmed that the expense and irradiation of 3D CT actually makes a difference. The medical literature is replete with wide-eyed, over-enthusiastic endorsements of new technologies which later fail critical analysis. 3D CTU needs to prove itself by detailed analysis against the standard PCNL planning investigation of IVU. The authors failed to provide these vital data. Indeed, two of their seven patients who had 3D CTU before PCNL were not rendered completely stone-free. Complication rates are also not mentioned. Only by comparing 3D CTU with IVU in a randomized study, which incorporates comprehensively assessed outcome measures such as stone clearance, complications and operative times, can it be concluded whether 3D CT planning results in real patient benefits.

Ancillary