**Core Concept**
Membrane-bound structures in the kidney, particularly the glomerular basement membrane, can be visualized and analyzed using electron microscopy. This technique is crucial for diagnosing various glomerular diseases that affect the filtration barrier.

**Why the Correct Answer is Right**
Electron microscopy is particularly useful in identifying and characterizing the changes in the glomerular basement membrane, which are essential for diagnosing conditions such as membranous nephropathy and membranoproliferative glomerulonephritis. The technique allows for the visualization of the lamina densa and lamina rara interna, which are critical for assessing the integrity of the glomerular filtration barrier.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not specified, so we will proceed with the assumption that it is incorrect. Electron microscopy may not be as useful in diagnosing acute tubular necrosis, which is typically diagnosed through light microscopy and clinical correlation.

**Option B:** This option is not specified, so we will proceed with the assumption that it is incorrect. Electron microscopy may not be as useful in diagnosing acute interstitial nephritis, which is typically diagnosed through light microscopy and immunofluorescence.

**Option C:** This option is not specified, so we will proceed with the assumption that it is incorrect. Electron microscopy may not be as useful in diagnosing polycystic kidney disease, which is typically diagnosed through ultrasound and clinical correlation.

**Clinical Pearl / High-Yield Fact**
Electron microscopy is a valuable tool in the diagnosis of glomerular diseases, particularly those affecting the glomerular basement membrane. A high index of suspicion and a thorough understanding of the disease's pathophysiology are essential for selecting the correct patient for electron microscopy.

**Correct Answer:** C. Fibrillary glomerulonephritis.