Study of intrarenal vasculature in cases of primary and secondary hypertension (by metallic impregnation technique on whole kidney section)BV Mittal
Dept of Pathology, Seth GS Medical College, Parel, Bombay, Maharashtra.
Study of intrarenal vasculature was carried out by using the metallic impregnation technique on whole kidney sections in 31 [corrected] cases of (primary and secondary) hypertension and 10 normal controls. Distinct patterns of intrarenal vasculature were noted in controls and in cases of hypertension. Gradual tapering of vessels, absence of tortuosity and good peripheral vascularisation were noted in controls. Abrupt tapering, tortuosity of vessels and poor peripheral vascularisation were noted in hypertensive cases. In essential hypertension moderate to severe changes of dilatation of the segmental and/or arcuate arteries was noted. The degree of dilatation was related to the level of systolic BP rather than diastolic in cases of essential hypertension. Secondary hypertension even if severe, rarely showed significant dilatation lesions. Avascular zones and conglomeration of vessels at poles was seen only in cases of pyelonephritis. This helped in distinguishing these, from cases of glomerulonephritis.
Keywords: Adolescent, Adult, Aged, Aged, 80 and over, Case-Control Studies, Child, Diagnosis, Differential, Female, Histological Techniques, Human, Hypertension, classification,diagnosis,epidemiology,etiology,Kidney, blood supply,Kidney Diseases, complications,pathology,radiography,Male, Matched-Pair Analysis, Middle Age, Severity of Illness Index,
Hypertension, the disease affecting about half the population over sixty years of age, has an increased risk of serious complications. The diastolic hypertension is more serious. Arteriolar lesions are seen in various organs in cases of hypertension with a definite predilection for the kidney. Renal disease in turn can also cause hypertension. Attention has therefore been focussed on the renal vasculature in cases of essential hypertension.
Angiographic studies,,, dye injection followed by corrosion technique and microdissection has been used as investigative tools for studying the intra-renal vasculature. Micro-angiography permits stereoscopic examination of the vasculature. However, filling defects due to incomplete filling of the arterial tree cannot be ruled out. Similarly structures judged to be vessels could be artefacts resulting from the rupture of the vessels. In addition, positional relationship between the vessels and other tissues cannot be assessed. Microdissection technique gives a three-dimensional view but does not allow histological examination. Whole organ sections allow semiquantitative or quantitative studies in addition to histological studies. It was thought that the whole organ section, like the whole lung section might allow quick appraisal of the vasculature and may reveal patterns, which are helpful in the differential diagnosis of the cause of hypertension. Hence it was decided to give a trial to this method.
Thirty-one cases of hypertension and 10 age matched normal control cases were included in this study. Clinical details of age, sex, systolic and diastolic blood pressure, duration of hypertension were noted from the medical records. Those cases with diastolic BP more than 90mm of Hg were diagnosed as definite hypertensives and were classified as borderline, mild, moderate and severe hypertensives if their diastolic blood pressure values were between 90-95 mm Hg, between 96-100mm Hg, 105-115mm Hg and more than 115 mm of Hg respectively. One half of each kidney (right and left) obtained at autopsy, was used for the whole kidney sections. Routine sections for histologic study were taken from the other half of each kidney and stained with hematoxylin-eosin stain,
Whole kidney sections: One half of each kidney obtained at autopsy from cases of hypertension as well as control cases were fixed in 10% buffered formalin. Metallic 6 impregnation technique of Hasegawa and Ravens was followed with modifications to adapt it for the kidney tissue as follows: initial steps for clearing the excess of lipids in the brain tissue were omitted as the kidney tissue is not as rich in lipids as the former. Initially, in 13 cases, 200 micron sections were cut; however, these were found to be too thick for interpretation, hence 100 micron thick sections were preferred. Whole kidney sections thus obtained were mounted on glass slides 1 mm thick and 10 cm x 14 cm in size. Similar slides were used to cover the section with DPX mounting medium.
Whole kidney sections were examined under hand lens and stereo microscope. Attention was focussed on the changes in the hilar, segmental, arcuate and interlobtilar vessels and peripharal filling in the cortex.
The changes in the vessels were graded as i. normal [Figure - 1], ii. grade 1 - mild dilatation [Figure - 2] iii. grade 2 - moderate dilatation [Figure - 3] and iv. grade 3 severe dilatation [Figure - 3]. Normalcy was decided by comparing the sections with those obtained from normal controls. Tortuosity of the vessels was recognised by the multiple cross-sections of the vessel seen. Peripheral cortical vascularisation was looked for.
The demographic data of patients of hypertension is illustrated in [Table - 1].
Gross pathology: Kidneys were markedly reduced in size in pyelonephritis and end stage renal disease with an average weight of 35gm each. Renal contours were irregular with scars on the external surface. Renal size was not much reduced in cases of essential hypertension with an average weight of 100 gm for each kidney. The values for kidneys in cases of glomerulonephritis were in between these.
Whole kidney sections: Intrarenal vessels of normal calibre were seen in 6 of 10 normal control cases while mild dilatation of the segmental and/or arcuate vessels was noted in 4 cases. All these 4 cases were more than 40 years old. Gradual tapering of vessels towards the cortex and good cortical filling was noted in all the normal cases [Figure - 1].
There were 13 cases with severe, 9 with moderate and 8 with mild hypertension. In 1 case, the exact level of BP was not known but was labelled as a 'known hypertensive' and was being treated for the same.
Based on the clinicopathologic data these cases were also classified, as secondary or essential hypertension. There were 13 cases of secondary hypertension [chronic pyelonephritis (4), chronic glomerulonephritis (4), end stage renal disease (3) and polyarteritis nodosa (2)] and 18 cases of essential hypertension [Table - 2].
Findings in cases with secondary hypertension: Moderate hypertension was noted in 3 of the 4 cases of glomerulonephritis while one case had mild elevation of diastolic pressure. All 4 cases showed grade 1 (mild) dilatation of intra-renal vasculature with abrupt tapering of vessels and poor peripheral filling of the cortex [Figure - 4] No avascular zones were seen and kidney contour was smooth.
Irregular renal contour with thinning of the cortex was seen in 3 out of 4 cases of pyelonephritis. Avascular zone indicating a scar was seen in 1 case while 2 cases revealed localised crowding of blood vessels [Figure - 5]. Severe grade 3 dilatation of arcuate and segmental vessels, were seen in 1 case of diabetes with calculous pyelonephritis [Figure - 6]. Severe degree of hypertension was found in the 3 cases of end stage renal disease; 2 cases revealed grade 1 dilatation and the third case showed grade 2 dilatation.
Two cases of polyarteritis nodosa were included in the study. One had mild diastolic hypertension while the other showed severe hypertension. Both the cases revealed increase in the outer diameter of the proximal vessels proportional to the increase in blood pressure (grade 1 in the first case and grade 3 in the second case), but their lumina were compromised, by intimal thickening in both cases.
Findings in essential hypertension: Severe hypertension was noted in 7 cases and moderate and mild in 5 cases each. In one case the level of BP was not known. Dilatation of mainly the segmental vessels and/or arcuate vessels with tortuosity of blood vessels, abrupt tapering of the vessels and poor peripheral filling were 'the salient features seen in majority of the cases. Five of the 7 cases with severe hypertension and 2 of the 5 cases with moderate hypertension showed marked dilatation (grade 3) of the segmental and some arcuate vessels [Figure - 4]. These changes were also noted in 2 cases with mild hypertension. On the other hand, 2 cases of severe hypertension revealed only grade 1 dilatation changes in the intrarenal vasculature though marked tortuosity of vessels and poor peripheral filling were noted in both these cases.
Hypertension causes changes in the vascular tree in various organs, especially in the renal vasculature. To study these changes the procedure of whole kidney section followed by metallic impregnation of the vascular tree has been adopted with some modification of the method described by Hasegawa and Ravens  for the cerebral vascular pattern e.g. steps for clearing the lipid were omitted as renal tissue is not as rich in lipids as the brain. The section thickness had to be reduced to 100 micron instead of 200 micron advised for the brain section, as kidney tissue is more dense as compared to brain.
This study enabled the analysis of patterns of intrarenal vasculature in normal and cases of hypertension. Based on this, separation of hypertensive cases from normal was possible; similarly, primary hypertensives can be distinguished from secondary. Since the rest of the tissue was available for histopathological examination, a comparison could be drawn with histologic changes in the blood vessels.
Patterns of intrarenal vasculature noted by this technique of whole kidney sections and metallic impregnation were similar to those of Meaney et al  on angiography performed on normal and hypertensive patients. In the 12 normal control cases that they studied, a gradual and uniform tapering of the vessels was noted. The cortical arteries were well filled, uniformly distributed and extended almost to the periphery of the renal parenchyma. A similar picture of the normal renal arteriography was described by Foster et al and Abram. Of the 10 normal controls in our study, uniformly distributed normal sized intrarenal vessels extending to the periphery and undergoing gradual tapering were noted. In 4 cases, mild dilatation lesions in segmental vessels were noted. All these cases were more than 40 years old, so this could be an age related phenomenon. Similar changes were noted by Ljungquest and lagergren in aging human kidneys.
Dilatation of the segmental and/or arcuate vessels with tortuosity of the blood vessels, abrupt tapering and poor peripheral filling of the cortex was seen in essential hypertension. These findirivs tallied with the angiographic findings of Halpern . There was no direct correlation between the level of blood pressure and the degree of dilatation changes. Five cases of severe hypertension showed severe dilation changes (grade 3) in the vessels. However, similar changes were also seen in 2 cases each with moderate and mild hypertension [Figure:7]. Secondary hypertension, even of severe degree, rarely showed severe dilatation lesions in the proximal vessels, on the other hand, mild dilatation changes were seen in only 1 case of severe essential hypertension.
In cases of prelonephritis, histopathological changes were reflected in the whole kidney sections. The renal size was small, with irregular contour. The interlobular branching pattern was seen to be distrubed by areas of avascularity because of the scar tissue. The tortuous vessels could be traced to the cortex because of thinning of the cortex. No avascular zone was seen in cases of chronic glomerulonephritis. This was helpful in distinguishing these cases from pyelonephritis. In end stage renal disease too, inspite of severe hypertension 3 cases showed mild and moderate dilatation of vessels.
Renal vessels are involved in 80% cases of polyarteritis nodosa. Two types of lesions have been described; in one termed as classical, the lesions are seen confined to the proximal arteries which show irregularity, occlusion, or aneurysm formation and peripheral avascular zones corresponding to the occuluded vessel. In the other microscopic variety, the lesions are predominently seen in small muscular arteries resulting in glomerulopathy. In this type, peripheral vessels may be narrowed. Two cases of polyarteritis were studied by us one was the classical variety, while the second one of the microscopic variety. The former showed marked aneurysmal dilatation of the vascular tree involving the hilar, segmental and arcuate vessels while the latter showed mild dilatation.
In conclusion, it can be said that this technique of demonstration of intrarenal vascular pattern by metallic impregnation in whole kidney sections was useful and gave results comparable with angiographic studies. The pattern was quite distinct in essential hypertension and secondary hypertension. In view of the high cost and poor availability of x-ray plates, this method could substitute the postmortem angiographic studies for the study of intrarenal vasculature.
The author wishes to thank the Dean, Seth GS Medical College, Mumbai, for the permission to carry out this work and for the publication of the same.
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6][Table - 1], [Table - 2]