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Renal diseases are common in birds. Appropriate non-invasive diagnostic tools capable of detecting early stage renal diseases are lacking. To the author´s knowledge comparative studies of renal in vivo diagnostic using a statistically significant number of birds with histopathologically unaltered kidneys are not available. The aim of the present study was to compare haematological and biochemical values, radiographs, computed tomography images (CT) and endoscopic findings of 48 falcons from one breeder concerning the diagnosis of renal alterations.
A kidney biopsy was taken from all 48 falcons examined by endoscopy. The biopsy was investigated histopathologically. 35 out of 48 falcons (72.9%) did not demonstrate histopathological alterations (Group A), whereas the remaining 13 falcons (27.1%) had histopathological alterations of the renal tissue (Group B). In the birds of Group B, iron storage disease in the renal tubules was most frequently observed (n = 7, 14.6 % of all birds examined, i.e. 46.7% of all renal alterations), followed by renal amyloidosis (n = 5, 10.4 % of all birds examined, i.e. 33.3 % of all renal alterations). Slight renal atherosclerosis, slight multifocal membranous glomerulonephritis and extreme focal chronic-active heterophilic nephritis followed with one occurrence each.
Haematological and biochemical parameters (albumin, anorganic phosphate, calcium, total protein, uric acid, BUN, potassium) were not suitable to distinguish between falcons with or without histopathological renal alterations.
During radiographic and computed tomography analyses reference values as 80%-percentiles were established for the kidney size and bone structures as basis for kidney ratios. The radiographic reference value for the kidney-size to sternum ratio was 0.477 to 0.595. The kidney-size to sternum ratio developed from the computed tomography scans demonstrated a statistically significant difference between Group A and B. The kidney-size to sternum ratio also proved to be suitable to distinguish statistically significant between falcons with iron storage disease and healthy birds. The computed tomography reference value for the kidney-size to sternum ratio for the right kidney showed to be 0.514 to 0.597, for the left kidney 0.522 to 0.596 and for the average size kidney 0.519 to 0.596.
Using computed tomography the density of the kidney was measured in the native scan, as well as 50 seconds and again five minutes after contrast media was injected. Density was measured in four specific areas within the cranial kidney division (density 1-4) and once within the caudal kidney division (density 5). Furthermore the density of the cranial kidney division was measured by circumscribing the area manually (density 100). The reference values (80%-percentiles) for the density of the kidney (density 100) were 52.22 to 67.91 HU (native scan), 208.25 to 300.09 HU (50 seconds after contrast media), 155.74 to 249.49 HU (5 minutes after contrast media) in the left cranial kidney division. Values for the right cranial kidney division were 53.15 to 67.47 HU (native scan), 212.13 to 308.81 HU (50 seconds after contrast media) and 159.21 to 252.39 HU (5 minutes after contrast media). The contrast media used was a nonionic iodine-based contrast media (Ultravist 300®) at a dose of 3ml/kg body weight. The four densities of the cranial kidney division (density 1-4) did not show significant differences between the right and left kidney. Statistically significant differences were observed between left and right kidney with density 100 and with density 5 in the caudal kidney division 50 seconds after applying contrast media. In addition to the measurements of the density of the kidneys both the concentration and elimination of the contrast media was additionally measured (concentration I: 50 sec contrast media / native scan; concentration II: 5 min contrast media / native scan; elimination: 5 min contrast media / 50 sec contrast media). Between Group A and B there were statistically significant differences in concentration II in the middle of the cranial kidney division (density 2 left kidney and density 3 right kidney). The other parameters examined did not demonstrate any significant differences between the two groups. A direct comparison of the renal pathologies found, revealed significant differences in the densities between the birds with iron storage disease and healthy birds and between the birds with renal amyloidosis and the healthy ones. The birds with iron storage demonstrated significant differences to Group A 5 minutes after contrast media was applyied. In the birds with iron storage disease, a prolonged elimination of the contrast material was noted in addition to a tendency to higher kidney densities. On the other hand, the birds with renal amyloidosis showed significant differences to Group A in the native scan with a tendency to lower kidney density.
For the first time, reference values for the kidney density of falcons were established using computed tomography which seem to be useful as a diagnostic tool. Further studies on falcons with renal diseases are necessary to verify the use of the reference value as a diagnostic tool.
The endoscopic examination revealed kidney alterations in all birds examined with renal amyloidosis, atherosclerosis and nephritis. Four out of seven birds examined with iron storage disease also demonstrated endoscopic alterations of the kidneys (swelling and/or yellow-whitish deposits). Statistically significant differences of kidney swelling between Group A and B were noted. The endoscopic examination of swollen kidneys seems to be of immense importance.
The present study clearly demonstrated so far that the endoscopic examination in combination with biopsy of the kidney and its histological examination is the best method to detect renal alterations in the life bird. Reference values were established for both the kidney density and the kidney-size to sternum ratio and form the basis for further computed tomographic based studies of falcons.