CORRESPONDENCE
Experiences of using a single post-contrast CT scan of the urinary tract after triphasic contrast injection 1
To the Editor: In my article entitled ‘Experiences of using a single post-contrast CT scan of the urinary tract after triphasic contrast injection’ that was published in the SAJR Vol. 15, No. 4 (December 2011), I emphasised that we had not gained experience in this technique with renal pathologies such as pyelonephritis and small renal tumours. At a CT congress in South Africa last year, an international speaker and expert in CT also raised his concern about missing small renal tumours when questioned about this technique. I have had further experience since, and would like to share the following 2 cases, suggesting that this technique will demonstrate these 2 pathologies adequately.
Case 1
A 70-year-old man was diagnosed with a small right renal mass, using the classic post-contrast scan technique (arterial, nephrographic and delay excretory series). I performed a 6-month follow-up using the single post-contrast scan after a triphasic contrast injection.
Fig. 1 (a - d) shows the lesion identified at original scan and provi-sionally diagnosed as an oncocytoma. Fig. 2 (a - b) shows the lesion (arrow) at 6-month follow-up, unchanged. The lesion was a subtle lesion, difficult to identify on both examinations, but it is my opinion that it is seen as easily using the single post-triphasic contrast injection technique (Fig. 2) as on the classical 3 post-contrast series technique (Fig. 1).
Case 2
A 76-year-old woman presented with symptoms of urinary tract pathology. Pyelonephritis was diagnosed after a CT scan using the single-series post-triphasic contrast injection technique. We include a 3-hour post-contrast study on our patients if we suspect pyelonephritis.
These two cases show that this modified post-contrast technique is sensitive to small focal lesions and diffuse lesions within the kidneys. I acknowledge that a few cases do not constitute definitive scientific evidence that subtle lesions will not be missed; however, these types of case add to the radiologist’s confidence in using this technique, bearing in mind that this technique replaces 3 post-contrast scans with a single scan and also effectively halves the overall radiation dose to the patient.
I thank my partners Dr Jaco Parsons for his
initial diagnosis of the small renal mass (Case 1) and Dr
Etienne Steenkamp for his case of pyelonephritis (Case 2).
1. Pretorius, P. Experiences of using a single post-contrast CT scan of the urinary tract after triphasic contrast injection. South African Journal of Radiography 2011;15(4):140-145.
S
Afr J Rad
2012;16(3):122-123. DOI:10.7196/SAJR.699
Fig. 1a. Pre contrast
Fig. 1b. Arterial phase.
Fig. 1c. Nephrographic phase.
Fig. 1d. Delay excretory phase.
Fig. 2a. Axial view after single post-triphasic contrast injection series.
Fig. 2b. Sagittal reconstruction.
Fig. 3a. Axial left
kidney.
Fig. 3b. Axial left kidney after 3-hour post-contrast delay.
Fig. 3. The left kidney shows an area of inhomogenous poor contrast enhancement antero-medially on the initial scan (black arrow in Fig. 3a) after the triphasic contrast injection. On the 3-hour delay post-contrast scan, there is retention of contrast in the tubules, causing streaky contrast staining in the area of inflammation, typical of pyelonephritis (black arrow in Fig. 3b).