COMPUTED TOMOGRAPHY UROGRAPHY FOR DIAGNOSING BLADDER CANCER

Authors


Sir,

Although CT urography (CTU) might replace IVU and ultrasonography for evaluating the upper tract in patients with haematuria [1], its role in the lower tract and in particular for diagnosing bladder cancer should still be viewed as speculative. The recent paper by Turney et al.[2] illustrates the controversies well. Initially a sensitivity of 0.93 and specificity of 0.99 for the CTU diagnosis of bladder tumour is impressive, but these values are over-generous, the final conclusions questionable and the risk of radiation is, we feel, disingenuously under-played.

In that study [2], 200 consecutive patients with macroscopic haematuria attending a fast-track haematuria clinic had ‘same-day’ CTU and flexible cystoscopy. The bladder on CTU was graded for possible tumour on a three-point scale (1, normal; 2, equivocal; 3, tumour) and compared to flexible cystoscopy findings (1, normal; 2, abnormal requiring immediate biopsy or referral for rigid cystoscopy; 3, tumour) and the final histopathology report. However, the 39 cases (20%) graded as equivocal on CTU were excluded from the final analysis. Clinicians correctly treat equivocal results from screening tests as no different from abnormal results, requiring further investigation; radiologists do likewise. Indeed, previous studies on the value of IVU and ultrasonography in the urinary tract have used a strictly binary diagnostic approach, and not discarded equivocal results as inconvenient [3]. The STARD initiative aims to improve the quality of reporting of diagnostic test accuracy, emphasising the importance of how indeterminate results are reported and handled in the final calculations [4]. If, as they should be, the equivocal results in the study by Turney et al. are included, we obtain a sensitivity of 45/48 = 0.94 and a specificity of 115/152 = 0.76. This better represents the diagnostic ability of CTU for bladder tumour in this study. They are not good enough to abandon flexible cystoscopy. Presumably, the authors also feel this because they do not say that they have now stopped flexible cystoscopy for normal CTUs in their practice.

A further methodological flaw is the absence of direct per case radiation measurement. A value of 9.7 mSv is quoted (only in the discussion) as the dose of a two-series CTU. This is inaccurate, and refers to the dose of a one-series CTU [5]. All patients had two- or three-series CTU, and thus the radiation dose could be two to three times greater, or nearly 10 times the quoted dose of a standard IVU. This is in line with published work; Nawfel et al.[6], using a more restricted three-series CTU, reported a mean dose of 14.4 mSv. There is a 1 : 2000 risk of inducing a fatal cancer with each 10 mSv increment. Excess irradiation of the bladder should be of special concern, as it is estimated to be one of the commonest radiation-induced cancers in the UK, particularly in young males [7].

To summarise, the case for routine CTU for the diagnosis of bladder cancer is not compelling and no better than conventional methods. CTU should be restricted to evaluating upper tracts and kidneys in those with persistent or unexplained haematuria. Only in this group will the risk-benefit equation justify the use of CTU.