The Urographic Signs of Acute on Chronic Obstruction of the Kidney pETER DAVIES and HAZEL PRICE
The Department o f Radiology, City Hospital, Nottingham
The signs of acute obstruction of the kidney and of chronic obstruction are well recognised and the combi- nation of these signs enables a group of patients with acute-on-chronic obstruction to be recognised. The signs of acute obstruction are entirely nephrographic. They are manifested by an increasingly dense nephrogram, which may become striated, followed by an anatomically normal pyelogram. The signs of chronic obstruction are both pyelographic and nephrographic. The pyelographic signs are a dilated pelvicalyceal system. The nephro- graphic signs are a normal or low density nephrogram. Crescents may appear; these are due to opacification of the distorted medulla which retains its ability to concentrate the urine. In acute-on-chronic obstruction the signs of both conditions are present. Thus there is an increasingly dense nephrogram with a negative pyelo- gram. Crescents may appear. There is a slow flow in the dilated pelvicalyceal system.
If patients with intermittent loin pain are examined by excretion urography during an attack of pain (acute urography) some will show a pelvi-ureteric junction obstruction or a primary pelvic hydro- nephrosis (Davies et aI., 1978). A dense nephrogram has been observed in some of these cases (Davies et al., 1978) with either normal or dilated minor
calyces. Fig. 1 shows the difference between dilated and normal minor calyces. The dense nephrogram is accompanied by increased pressure in the renal pelvis (Johnston, 1969; Bretland, 1972). The combi- nation of a dilated pelvicalyceal system (due to chronic obstruction) and a dense nephrogram (due to acute obstruction) may be termed acute-on-chronic
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(a) (b) Fig. 1 - (a) Five minute film. The right pelvicalyceal system is not dilated and the ureter is filled. The left pelvicaiyceal system shows minimal hydronephrosis and the pelvis is not shown. (b) There has been drainage from the right kidney and the Calyces retain their sharp cups. The left kidney shows the same amount of dilatation as before and there is now filling of the ureter. The delayed filling of the ureter and 'slow flow' is a characteristic of both acute and chronic obstruction•
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Fig. 2 - A negative pyelogram shows as round lucent areas within a dense nephrogram.
(a) (b) Fig. 3 - (a) Fifteen minute film. Shows a dense nephrogram with a negative pyelogram and a single ball in the lower calyx. (b) A film at 14 h shows a prirnaxy pelvic hydronephrosis.
U R O G R A P H I C S I G N S O F A C U T E ON C H R O N I C O B S T R U C T I O N OF THE K I D N E Y 207
Fig. 4 - (a) One minute f'flm. A dense nephrogram is shown on the left.
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Fig. 4 - (b) Fifteen minute film, The nephrogram is n o w denser with a negative pyelogram.
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Fig. 4 -- (c) There is a pr imary pelvic hydronephros is with the ureter seen below the pelvis. This pat ient has a s tone in the lower end o f the ureter.
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(a) (b)
Fig. 5 - (a) The nephrogram on the right is less dense than on the left. (b) Fifteen minute film. The nephrogram is denser than previously and involves aU the renal parenchyma. There is a negative pyelogram and a hall pyelogram.
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Fig. 5 - (c) A prone film shows several crescents at the edge o f the negative pyelogram.
obstruction of the kidney. There does not appear to be a description of the signs of this condition in the hterature nor is it recognised as an important part of the spectrum of appearances in obstruction of the hdney.
METHODS
Thirteen patients have been seen with this condi- tion in the past five years. Several were included in a study of patients with renal colic who had urography at the time of pain (acute urography). These 13 patients were not selected on the basis of clinical features but on the two radiological signs of a dilated pelvicalyceal system and an increasingly dense nephrogram. Other nephrographic and pyelographic features were recorded. The kidneys and negative PYelograms were measured along the long axis of the kidney and the negative pyelogram from the medial edge of the kidney to the outer lobulated border along a line at right angles to this. The rate of opacifi- cation of the pelvis and ureter was recorded in all Cases.
RESULTS
There were 13 patients, 10 of whom had pain at the time of the examination while three did not. Six patients had primary pelvic hydronephrosis four had stones and three patients had both primary pelvic hydronephrosis and ureteric stones. Six of the affected kidneys were on the right and seven on the left. Operative confirmation of the pdvi-ureteric junction obstruction was not obtained in the last three patients (one refused operation, one died and one was lost to foUow-up). However in films taken after the acute episode had resolved, the pelvi- ureteric junction obstruction was unequivocal. Three of the four patients with stone had recurrent calculi, one having renal tubular acidosis and one hyper- parathyroidism. The fourth patient had an atrophic hydronephrosis with no pelvi-ureteric junction obstruction (Fig. 2).
All patients had increasingly dense nephrograms, in nine the initial nephrograrn was less dense than in the contralateral normal kidney, in three the densities were equal and in only one case was the nephrogram
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Fig. 6 - (a) One minute film. The left nephrogram is o f normal density, on the right the nephrogram is faint and the kidney small.
more dense than on the normal side. In two cases no positive pyelogram was seen. One of these patients had had a pyeloplasty previously and the kidney became obstructed by clot following haemorrhage.
The negative pyelogram presented a lucent area within the dense nephrogram (Fig. 2) its outer border being lobulated and the inner coinciding with the medial border of the kidney. The size of kidneys and negative pyelograms is given in the table (Table 1). In 11 cases a ball pyelogram (Fig. 3) appeared within the negative pyelogram and in 10 cases this was followed by opacification of the pelvis and ureter (Fig. 4). In none of the six cases of primary pelvic hydronephrosis without stone was the ureter seen. In five cases the dense nephrogram was followed by the appearance of crescents (Fig. 6) often seen best on the prone fdm. In all these cases a ball pyelo- gram was seen at the same time. In all cases the
opacification of the pelvicalyceal system and ureter was much slower titan in normal kidneys.
DISCUSSION
The signs of acute obstruction have been well described by Bretland (1972) and the signs of hydr0. nephrosis reviewed by Davies et al. (1972). It should be noted that delayed opacification of the distal parts of the pelvicalyceal system and ureter (slow flow in the system) is a feature of both conditions and delayed films are necessary to show the point of obstruction. Fig. 1 shows a patient with a normal pelvicalyceal system on the right and perceptibl0 dilatation of the pelvicalyceal system on the left and slow flow of contrast medium through the
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Fig. 6 - (b) Fif teen minute film. A dense nephrogram is now seen on the right.
minimally hydronephrotic system. Davies e t al. (1978) showed that in patients with intermittent loin pare due to pelvi-ureteric junction obstruction, acute obstruction without dilatation of the minor calyces and acute-on-chronic obstruction with dilatation of the minor calyces could be shown by acute urography at the time of pain when urography in the interval between attacks was entirely normal. Thus, acute obstruction with a dense nephrogram in primary pelvic hydronephrosis can occur intermittently. In the present series three of the 13 patients had an increasingly dense nephrogram with no pain and we have seen patients with ureteric stone, undilated Pelvicalyceal systems, increasingly dense nephro. grams and no pain. We do not agree with Bretland (1972) that an increasingly dense nephrogram is always accompanied by pain.
The signs seen in these kidneys fall into two gt0ups:
1. Those of acute obstruction, that is, an in- creasingly dense nephrogram.
2. Those of chronic obstruction, that is, a negative
pyelogram (Fig. 2) within the dense nephro- gram.
It was on the presence of these two signs that the patients were selected but other signs of chronic obstruction or hydronephrosis were seen on the films. These were a ball pyelogram (Fig. 3) and crescents (Fig. 5) often seen best on a prone film.
Most of the affected kidneys were larger than the normal kidneys (Table 1) but one case of atrophic hydronephrosis with a stone in the ureter showing an increasingly dense nephrogram was seen (Fig. 6). This is important as it implies that hydronephrotic atrophy does not impair the ability of the kidney to show the changes of acute obstruction.
The acute-on-chronic obstruction of the kidney was due in six cases to primary pelvic hydronephrosis, in four to stone and in three both causes were present, one causing the dilatation and the other the acute obstruction. Since both acute and chronic obstruction can be present at the same time in a kidney due to a single cause or to two separate causes we consider that they are different conditions
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Fig. 6 - (c) An examination a month later shows a dilated right pelvicalyceal system. This is a case of atrophichydronephr0sls
Table 1 - Analysis of findings
Patient Age Sex Pain at time Operative Kidney size length (cm) Size of negative pyelogram number* of urography confirmation (cm)
Affected Normal Longitudinal Transverse side side
1 43 M 0 + 15 15 t0 5 2 26 F + + 14 13 10 3.5 3 31 F + + 17 13 12 5 4 80 F 0 0 15 14 10 5 5 59 M + + Horseshoe 13 7.5
kidney 6 16 M + + 17 14 13 6 7 27 F + + 15 13 10 3 8 30 F + 0 14 12 11 7 9 45 F + 0 9 14 8 4
10 48 F 0 + 17 14 11 6 11 36 M + 0 13 13 9.5 4 12 25 F + 0 13 13 10.5 4 13 76 F + 0 13 9 8 4
*Patients 1 - 6 had primary pelvic hydronephrosis; patients 7 - 1 0 had stone; patients 1 1 - 1 3 had both.
UROGRAPHIC SIGNS OF ACUTE ON CHRONIC OBSTRUCTION OF THE KIDNEY 213
~d not one condition at two stages in its evolution. ~a~ concept o f acute obstruction passing gradually into chronic obstruction and hydronephrosis (Berdon el d., 1970) is misleadingly simple. The progression of hydronephrotic atrophy may be due to recurrent acute attacks of obstruction. Three o f our patients did not have pain and so the progression may be pain- less. We think the recurrent high pressure o f acute obstruction may be an important factor in the g0nesis of hydronephrotic atrophy.
Acknowledgements- We are grateful to Mrs W. Georgiades aad Mrs E. Whitemore for typing the manuscript and to Mr 6. Gtlbert who prepared the prints.
REFERENCES
Berdon,W. E., Levitt, S. B., Baker, D, M., Becket, A. & Uson, A. C. (1970). Hydronephrosis in infants and children, value of high dose excretion urography in predicting renal salvageability. American Journal o f Roentgenology, 109,380-389.
Bretland, P. M. (1972). Acute Ureteric Obstruction. Butter- worth, London,
Davies, P., Roylance, J. & Gordon, I. R. S. (1972). Hydro- nephrosis. Clinical Radiology, 23, 312-320.
Davies, P., Woods, K. A., Evans, C. M., Gray, W. M. & Kulafilake, A. E. (1978). The value of provocative and acute urography in patients with intermittent loin pain. British Journal o f Urology, 50, 227-232.
Johnston, J. M. (1969). The pathogenesis of hydronephrosis in children. Brittsh Journal of Urology, 4 l, 724-734.
