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Renal biopsy is often invaluable for the diagnosis of glomerular disease. Needle biopsy samples of the renal tissue are usually divided up into separate samples for light microscopy, immunofluorescence, and electron microscopy, preferably under a dissecting microscope.1 This is a relatively easy task if a sufficient amount of the sample is obtained. However, if biopsy samples are small or turn out to be composed mostly of medulla, priority is usually given to light microscopy. In such circumstances, one may have to use a part of the sample that does not definitely contain glomeruli. Although one may be lucky enough to find a glomerulus, there are many features that can simulate glomeruli under the dissecting microscope. Unfortunately, there are no instructive publications dealing with the macroscopic features of true or false glomeruli under the dissecting microscope. Here, I will describe the dissecting photomicrographic features of an example of false glomeruli.
Only one sample, about 10 mm in length, was obtained at biopsy. The specimen appeared to contain an inadequate number of glomeruli, so that I selected a focus at the thin edge of the sample with several round translucent spots as a sample for immunofluorescence (fig 1). Stepped sections of the snap frozen tissue were stained with haematoxylin and eosin, but no glomeruli were found. Instead, close aggregates of tubules with a roughly rounded contour were observed. The interstitium showed features of the medulla.
Glomeruli that form small red capillary conglomerates under the dissecting microscope are easily visible, but not all glomeruli within the sample show this feature. Sometimes, most of the glomeruli are anaemic looking. If glomeruli are partially cut, they may be easy to identify because they sometimes protrude above the cut surface. Anaemic glomeruli totally within the sample can sometimes be seen as a relatively well circumscribed and globular translucent area in the sample. Their globular nature can be identified by adjusting the screw of the microscope.1 A round flat translucent area situated at the thin edge of the sample can be most problematic. Close aggregates of tubules with a roughly rounded contour may, as illustrated in our case, produce a focus simulating glomeruli. The most reliable feature for differentiation should be whether the tissue surrounding the focus is cortex or medulla, which should be discernible from its paler colour, more monotonous texture, and parallel structures.1