Organized deposits in the kidney and look-alikes.

Organized or structured deposits are encountered during electron microscopic examination of kidney tissue in a wide variety of primary renal and multisystemic disorders. They are most commonly seen in the renal glomerulus, though extraglomerular sites are occasionally involved. In some cases, organized deposits herald the presence of a specific disease process. Included in this category are organized substances containing immunoglobulin molecules or parts thereof as well as non-immunoglobulin-containing materials that accumulate in several rare heritable disorders. A second broad category of structured deposits includes substances that accumulate in response to nonspecific tissue injuries. In many instances, such "look-alikes" can be difficult to distinguish from disease-specific structured deposits. Ultrastructural pathology is central to the detection and characterization of organized deposits in the kidney and is the primary focus of this paper. Correlative light microscopic studies are often useful, however, and will be described as well.