JOURNAL OF PATHOLOGY, VOL.

163: 343-349 (1991)

CHRONIC PYELONEPHRITIS: THE SIGNIFICANCE OF RENAL RENIN AND THE VASCULAR CHANGES IN THE HUMAN KIDNEY SUAT CHENG PEH AND GEORGE B. M. LINDOP*

Department of Pathology, University of Malaya, Kuala Lumpur. Malaysia; *Department of Pathology, Western Infrmary. Glasgow, U.K . Received 28 June 1990 Accepted I4 November 1990

SUMMARY Hypertension complicates chronic pyelonephritis. Since arterial narrowing is common in the damaged kidney, activation of the renin-angiotensin system due to renal ischaemia has been suggested as a pathogenetic mechanism. We used an antiserum to human renin and an immunoperoxidase technique to study the anatomy of renin-containing cells (RCC) in 18 kidneys removed for pyeloneophritis. We independently assessed the degree of arterial narrowing and correlated these variables with the clinical findings. There was histological evidence of hyperplasia of RCC in 5 of the 6 hypertensive patients and in 7 of the 12 non-hypertensive cases. There was no difference in the apparent number or distribution of RCC between the hypertensive and the non-hypertensive cases. Also, the degree of arterial narrowing did not correlate with either the hyperplasia of RCC or the blood pressure of the patients. Our results d o not support the hypothesis that narrowing of the intrarenal arteries is important in the pathogenesis of hypertension in pyelonephritis. In our cases, the renal veins were more severely damaged than the arteries and their lumina were often obliterated by organized thrombus. We suggest that such widespread obliteration ofthe renal venous tree could impair blood flow and contribute to the tissue damage in the pyelonephritic kidney. KEY WORDS-Renin,

immunocytochemistry, pyelonephritis, hypertension.

INTRODUCTION

logical studies of the juxta glomerular apparatus (JGA) in human pyelonephritis t o s u p p o r t this

Pyelonephritis is inflammation of the kidney due to bacterial infection of the renal pelvis, the calyces, and the renal parenchyma. Even when unilateral, both acute and chronic pyelonephritis may be complicated by hypertension which is sometimes in the malignant phase.',* In chronic pyelonephritis, the arteries are often thick-walled and appear n a r r ~ w e d .Since ~ . ~ renal artery stenosis is one of the classical causes of hypertension, the raised blood pressure of chronic pyelonephritis has also been attributed to ischaemia of the renal cortex, a situation analogous to intrarenal renal artery stenosis.* Raised plasma renin levels have been reported in some cases,4but, surprisingly, there are few morphoAddressee for correspondence: G. B. M. Lindop, Department of Pathology, Western Infirmary, Glasgow, U.K.

0022-341 7/91/04034347 $05.00 0 1991 by John Wiley & Sons, Ltd.

suggestion. The JGA is difficult to study in pathological human kidneys; the conventional histological stains are capricious and, in any case, are not specific. We have used a highly specific human renin antiserum and an immunoperoxidase technique to study the distribution of renin-containing cells (RCC) in the human kidney affected by renal artery stenosis' and polyarteritis.6 These renovascular diseases produce characteristic abnormalities in the distribution of RCC within the renal We therefore decided to assess whether similar abnormalities in the anatomy of RCC might occur in chronic pyelonephritis; and, if so, whether the changes in the amount or distribution of RCC Correlated with the degree of arterial narrowing or with the blood pressures of the patients.

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S. C. PEH AND G. B. M. LINDOP

MATERIALS AND METHODS Pat ien ts

We reviewed sections from all nephrectomy specimens diagnosed as chronic pyelonephritis in the University Department of Pathology, Kuala Lumpur from 1982 to 1987. We selected for further study 18 cases with sufficient tissue to allow the diagnosis to be confirmed histologically. We reviewed the case records and abstracted the relevant clinical data, and obtained the descriptions of the gross pathology from the pathology reports. Tissue sections Serial 4 ,um sections were cut from the formalinfixed, paraffin-embedded blocks. They were stained with haematoxylin and eosin, elastic/MSB, elastic/ van Gieson, and alcian blue/PAS stains. Adjacent sections were used for immunocytochemistry. Immunocytochemistry We used a specific rabbit antiserum raised to human renin purified from cadaver kidneys.' This antiserum has staining specificity identical to a panel of monoclonal antibodies and another wellcharacterized renin antiserum.8 The sections were incubated with the antiserum (diluted to l/lOOO) for 14 h at 4°C. Antibody binding was demonstrated by a peroxidase-antiperoxidase (PAP) technique. The sections were then counterstained with the periodic acid/Schiff (PAS) stain. We included appropriate negative control sections as before.' Since the smaller renal veins consist of only an endothelial-lined channel, we demonstrated them by staining with the lectin Ulex europeus and an antilectin-peroxidase conjugate. Histological criteria Pyelonephritis-All cases showed inflammation of the renal parenchyma and the pelvi-calyceal system. Arterial narrowing-Significant arterial narrowing was usually due to intimal thickening. We regarded the outermost internal elastic lamina as the outer boundary of the intima and we assessed the degree of narrowing of the lumen visually on a qualitative scale of mild, moderate, and severe narrowing (grades 1,2 and 3). Where there was variation in the severity of the arterial narrowing, the

assessment was made on the most severely affected vessel. The changes in the interlobar, arcuate, and interlobular arteries were graded separately in ignorance of the clinical data or the number of RCC in the renal cortex, using the mean score of three separate assessments. We included arteries in the scarred areas as well as those in the renal cortex with preservation of the architecture, but we also made one assessment in which we excluded changes in those vessels which were in scarred areas with little residual renal parenchyma. RCC-Sections were screened for the presence of RCC, and, as b e f ~ r e , ~ . ~we . " used previously established histological criteria'' to assess hyperplasia of the RCC. RESULTS Patients The patients were 12 females and 6 males, and the ages ranged from 3 months to 75 years. Three were children, two of whom had a duplex system and the other had a non-functioning kidney. In the remaining 15 adult cases (aged 22-75 years), the aetiology of the pyelonephritis was due to urinary obstruction; 11 had renal stones, 2 had obstructing tumours, 1 a renal cell carcinoma, and 1 a transitional cell carcinoma of the ureter. The remaining two cases had hydronephrosis of uncertain aetiology. Five of the females and one male were hypertensive and all of them were receiving antihypertensive drug therapy. None of them had malignant phase hypertension and there was no evidence that the level of the blood pressure was affected by nephrectomy. Pathology Pyelonephritis-Eleven cases had the histolgical features of chronic pyelonephritis. The affected areas varied from thin wedge-shaped areas of fibrosis to large areas of scarring with complete loss of the renal parenchyma extending from the pelvis to the renal capsule. All cases had an inflammatory infiltrate which contained large numbers of lymphocytes with smaller numbers of plasma cells and macrophages. When the chronic inflammatory infiltrate was extensive, it often contained germinal centres. Some cases also showed superimposed acute pyelonephritis with abscesses in three cases. The other seven cases had the histological features of xanthogranulomatous pyelonephritis. They had sheets of foamy macrophages with giant cells

RENIN AND VASCULAR CHANGES IN PYELONEPHRITIS

345

Fig. 2-A proximal interlobular artery which is severely narrowed by arteriosclerosis. There is intimal thickening with reduplication of the internal elastic lamina, atrophy of the media, and mild periarterial fibrosis. Elastic/MSB

Fig. I-A dilated thin-walled interlobar artery (top right) with accompanying veins (bottom left) in looseconnective tissue. These normalveins haveapoorly formed wall andcontainnodiscernible smooth muscle. Elasticivan Gieson

admixed with chronic inflammatory cells among which plasma cells were prominent, often containing Russell bodies. Vascular abnormalities-Some areas had a histologically normal vascular tree (Fig. 1). In the scarred areas, the arteries were always tortuous and thick-walled. We distinguished the following abnormalities: (A) Arteriosclerosis The most prominent feature of arteriosclerosis was the reduplication of the internal elastic lamina (Fig. 2). This was associated with fibrosis of the intima and a variable amount of alcianophilic glycosaminoglycans.

(B) Intimal fibroplasia This lesion was thickening of the intima without reduplication of the internal elastic lamina. It varied from an irregularly arranged lining of loose myxoid connective tissue to more collagenized endarteritis; occasionally, the intima was thickened by a concentric layer of smooth muscle cells. Intimal fibroplasia was sometimes superimposed on a vessel already affected by arteriosclerosis, in which case it formed a

Fig. 3-An interlobar artery showing moderate arteriosclerosis with reduplication of the internal elastic lamina. In addition, there is superimposed severe intimal thickening due to accumulation of myxoid connective tissue. Elastic/MSB stain

clearly defined inner layer (Fig. 3). It was present mainly in interlobar and arcuate arteries; it affected only the most proximal portions of interlobular arteries.

( C )Arteritis This usually affected the outer layers of the vessel. It caused damage to the adventitia, often with destruction of the elastica externa and in the healing phase, fibrosis of the outer layers of the media (Fig. 4). Occasional cases also showed defects in the internal elastic lamina, but transmural arteritis was never identified.

(D) Arteriolosclerosis This lesion was never prominent; it affected arterioles and terminal interlobular arteries. The wall

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S . C . PEH AND G. B. M. LINDOP

Fig. &A proximal interlobular artery which shows moderate arteriosclerosis. The external elastic lamina has been destroyed, and in places, the external media has been replaced by fibrous tissue containing a few residual chronic inflammatory cells indicating healed inflammation. Elastic/MSB stain

of the vessel was thickened due to replacement of the media by homogeneous hyaline material best seen by its strong positivity with the PAS stain. Inflammation increases vascular permeability and gives rise to similar lesions; and, since arteriolosclerosis causes neither hypertension nor hyperplasia of RCC,it was not considered further.

(E) Lesions of the veins In unaffected kidney, the interlobular and arcuate veins were always identified accompanying the arteries. Only in some sections were the interlobar veins identified. In both the scarred and the inflamed areas, interlobular veins were never identified, presumably because they were obliterated. We could identify lesions only in the arcuate and interlobar veins. These veins were often thick-walled and appeared narrowed due to a combination of hypertrophy of smooth muscle (see below) and an increase in fibrous and elastic tissue in the wall (Figs 5 and 6). In many cases, there was obliteration of the lumen by loose fibrous tissue which had the appearance of organized thrombus (Fig. 6). While organized thrombus was commoner in the arcuate veins, the interlobar veins more often had thickening of their walls. In areas of severely damaged renal parenchyma the arteries were usually readily identified; by contrast, in sections cut in the appropriate plane, the accompanying veins were frequently obliterated. Renin immunostaining Immunoreactive renin was present in 17 of the 18 cases; in the case without RCC, the kidney was

Fig. 5-A tortuous arcuate artery which iscut in two sections; it is slightly narrowed by mild intimal thickening. The adjacent arcuate vein (V) is almost completely obliterated by organized thrombus leaving two slit-likelumina. Thereis also hyperplasia of smooth muscle (SM). Elastic/MSB stain

severely scarred with almost complete loss of renal parenchyma. In the other cases, RCC were mainly in normal or near normal renal cortex at the edges ofthe inflamed areas. RCC were rare in completely scarred renal cortex. They were less common in chronically inflamed areas and were never identified where there was severe acute or chronic inflammation. RCC were found in three situations: in the JGA of surviving glomeruli, in the intrarenal arteries up to the size of interlobular arteries, and, in two cases, within glomerular tufts. Most RCC were in the glomerular arterioles in JGA of normal glomeruli, but some were in JGA of glomeruli which were in various stages of obsolescence, and persisted even when the tuft was completely sclerosed. In two cases, RCC were present within glomular tufts. These glomeruli were small, cellular, and appeared hypoplastic. In the hypertensive case (a male of 22 years), glomeruli containing RCC formed a cluster in an area of damaged renal cortex (Fig. 7); in the normotensive case, a single RCC was present in only one obsolete glomerulus. Owing to the complete loss of architecture of the glomerular

RENIN AND VASCULAR CHANGES IN PYELONEPHRITIS

347

pattern of the results. There was no difference in the vascular changes or in the pattern of distribution of the RCC between the xanthogranulomatous and the other types of chronic pyelonephritis. DISCUSSION

Fig. &An arcuate vein (V) which has been obliterated by organized thrombus. It contains occasional small endotheliai-lined channels (arrows) and a sprinkling of lymphocytes and plasma cells. There is also hyperplasia of smooth muscle cells (SM) related to part of its wall. MSB stain

tuft, the nature of the cells which contained immunoreactive renin could not be determined. In areas of hyperplasia, RCC were larger and plumper. They also extended proximally along the afferent arteriole as far as the interlobular artery. We found no RCC in arteries larger than interlobular vessels. In these cases, as many as 20 RCC were present in the afferent and efferent arterioles of the JGA at the glomerular root where they often formed a ring around the vessel. There was histological evidence of hyperplasia of RCC in 5 of the 6 hypertensive patients and in 7 of the 12 non-hypertensive cases. The hypertensive and non-hypertensive cases could not be distinguished by the number or the distribution of the RCC. The correlations between the hyperplasia of RCC, degree of arterial narrowing, and the blood pressures are shown in Table I. The venous lesions could not be graded, but only two cases had no venous lesions. The separate assessment of the degree of arterial narrowing in which we excluded arteries in scars showing intimal fibroplasia which we judged could be due to involution did not affect the overall

Chronic pyelonephritis has been the source of considerable debate in the literature and there is no doubt that it has been considerably overdiagnosed in the past. This is because some of the histological changes are non-specific; in particular, it has probably been confused with renal scarring due to interstitial nephritis and ischaemia. The macroscopic examination of the kidney and histological evidence of inflammation of the pelvi-calyceal system are essential for the diagnosis.'* In our series, the diagnosis of chronic pyelonephritis was based on the macroscopic and microscopic appearance of the kidneys combined with the clinical findings and the appearance of the intravenous pyelograms. Vesicoureteric reflux is an important cause of renal damage, and it is possible that in some of our cases episodes of reflux nephropathy may have preceded the urinary tract obstruction. Our series re-emphasizes the importance of obstruction to the urinary tract as a predisposing factor for pyelonephritis. One-third of our cases were hypertensive; this is in agreement with other series of unilateral pyelonephritis.* The hypertensive cases were younger than the normotensive patients and their age range made essential hypertension unlikely, since only one case was over 50 years old. Three mechanisms have been suggested for hypertension in pyelonephritis: first, volume overload due to renal failure; second, loss of renal medullary hypotensive agents; and third, activation of the renin-angiotensin system. None of our patients was in renal failure, and our cases were unilateral and hence the medulla of the opposite kidney could presumably contribute the necessary antihypertensive factors. We cannot assess the role of the circulating renin-angiotensin system as plasma renin levels were not measured. However, others have found elevated plasma renin levels in unilateral pyelonephritis and have shown that the chance of the hypertension responding to nephrectomy is greater when the diseased kidney secretes excess renin.4 In chronic pyelonephritis, the arteries are often thickened and appear narrowed. In the wake of the discovery of Goldblatt hypertension, it is understandable that hypertension in chronic pyeloneph-

348

S. C . PEH AND G. B. M. LINDOP

Fig. 7-Four abnormal glomeruli; three (B,C,D) have RCC in the arteriole at the vascular pole and three (A,B,C) also have RCC in the glomerular tuft. They are partially sclerosed but appear small and hypoplastic. Renin PAP counterstained with PAS; interference contrast microscopy

between hyperplasia of RCC, degree of arterial narrowing

Table I-Correlations and blood pressure Grading of arterial narrowing

Arteries Interlobar

Arcuate

Interlobular

Normal

3,8*,10

&I0

Mild

9,14,15*, 16*,

8*1-)-

9,14,15*, 16*

4,7,11,12, 14,15*,17*, 18*

2*,4>6,2,

1,2*,5,6,L3

1,5,13,12*

3,8*,10,18*

9 16*

17*,18*

Moderate

1,2*,4,5,6, 7,11,12,u

~-

Severe Key:

*Hypertensive

(six

cases:

2,8,15,16,17.18);

t

~

11,12

RCC

(twelve

cases:

1,2,3,4,6,7,8,9,13,15,16,17).

ritis has been attributed to renal ischaemia caused by narrowing of the intrarenal arteries.’ Like o t h e r ~ we , ’ ~could not distinguish an ischaemic component in the histological appearances of the renal damage. We found that intimal fibroplasia was a common cause of narrowed interlobar and arcuate arteries. This lesion can be a manifestation of arterial involution due to the decreased flow which

occurs as a result of loss of renal parenchyma. Exclusion of arterial lesions in scarred areas presumed to be due to involution did not alter the pattern of the relationships between the arterial changes and the hyperplasia of RCC or blood pressure. Indeed, most of our hypertensive cases had mild arterial narrowing. The possibility of sampling error makes caution essential, but our results do not

RENIN A N D VASCULAR CHANGES IN PYELONEPHRITIS

support the contention that the hypertension of chronic pyelonephritis is renovascular in origin. We suggest that much of the arterial narrowing seen in the kidney damaged by pyelonephritis is the result, rather than the cause, of the renal damage. We used the histological appearance to assess the hyperplasia of RCC as b e f ~ r e . ~ . ~Hyperplasia ,'' of RCC was present in 5 of the 6 hypertensive cases, and also in 7 of the 12 kidneys from non-hypertensive patients. Hence even if hyperplasia of the RCC is implicated in the pathogenesis of hypertension in pyelonephritis, it has no value in histological diagnosis. We have shown that RCC are not present in areas with confluent inflammation, regardless of whether this is acute or chronic. Arteritis affecting all layers of the vessel is rare in pyel~nephritis.'~ However, in the inflamed areas damage to the adventitia ofthe renal arterial tree was common. Since the RCC in the normal human kidney are mainly in the outer aspects of the a r t e r i e ~ ,it' ~is possible that the RCC in the inflamed areas were destryed by inflammation. In two of our cases, RCC were present in sclerosed glomeruli. Occasional RCC can be found in the glomerular mesangium in the fetal kidney (unpublished observation) and in renal artery ~ t e n o s i sIn .~ experimental Addison's diseaseI5 and in pseudoBartter's syndrome due to diuretic or cathartic abuse,I6 mesangial cells can undergo metaplasia to renin-secreting myoepithelioid cells. In our two cases, the glomeruli were so sclerosed that we could not discern the lineage of the cells which contained the immunoreactive renin. We are currently assessing whether changes in the anatomy of RCC in abnormal human kidneys are disease-specific; for a review see ref. 14. Our series highlights the severe damage to the renal venous tree in pyelonephritis. This affected both the non-specific and the xanthogranulomatous cases. In severely damaged renal cortex, interlobular veins were uniformly obliterated and organized thrombus was found in arcuate and interlobar veins. Venous thrombosis and phlebitis have been reported in active xanthogranulomatous pyelonephritis;'7~'80neofthesestudiesalso foundevidence of venous lesions in the larger veins of 1 1 per cent of 'control' cases of chronic pyelonephritis. The higher incidence of venous lesions in our series is probably accounted for by our appreciation of damage to the

349

small interlobular veins. These resemble enlarged capillaries with only an endothelial lining and are often mistaken for lymphatics. In contrast to the attention given to the arteries, most standard accounts of chronic pyelonephritis omit any reference to the veins. We suggest that obliteration of the renal venous tree by the sequelae of inflammation could contribute to a rise in intrarenal pressure, diminish perfusion of affected areas of the kidney, and contribute to the tissue damage of chronic pyelonephritis.

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