Kidney Diseases: Diagnostic Terms and Features

The genetic, environmental, chemical and biological factors are known to influence the bio-physiology and microanatomy of kidneys. A possible clinical diagnosis of kidney diseases or renal disorders could be achieved through ultrasonography, biochemical investigations of blood and urine analysis. The pathological diagnosis of non-neoplastic and neoplastic kidney diseases needs light microscopy (LM), immunofluorescence microscopy (IFM) and electron microscopy (EM) study of the kidney biopsy. Narrowing down at the appropriate and accurate diagnosis of a kidney disease needs expertise in the evaluation of LM, IFM and EM features. The light microcopy has its limitations in the exploration of microanatomy of renal lesions due to its low resolution power. The initial task in the pathological diagnosis of a kidney disease is to decide the renal compartments associated with the primary lesion or initial site of injury. The glomeruli, tubules, interstitium, extraglomerular vessels or podocytes may be affected primarily in various combinations in various renal diseases. The history of hypertension or diabetes in addition to chronic inflammatory disease like rheumatoid arthritis, osteomyelitis, tonsillitis and tuberculosis has its own implications in renal disorders. In some kidney diseases multiple components may be affected simultaneously by the pathogenic process. The glomeruli and blood vessels are found affected in certain forms of vasculitis. Immunological findings are mandatory to achieve an accurate diagnosis of vasculitis associated kidney diseases. Tubules and interstitium are found affected in tubulointerstitial nephritis. The role of EM and ultrastructural morphometry is implicit in achieving a diagnosis of thin basement membrane disease (TBMD), Alport's syndrome (hereditary nephropathy), minimal change disease (MCD), amyloidosis and evaluation of podocyte injury. The thickness and texture of glomerular basement membrane (GBM), reorganization of foot processes of podocytes and podocyte injury are directly associated with the biophysiology of proteinuria (excretion of protein in urine) and hematuria in some kidney diseases. The histopathologic lesions in the affected kidneys could only be explained with a thorough knowledge of universally accepted appropriate terms which could be understood by a clinician. The term focal is used when <50% of glomeruli are involved and the term diffuse refers to the involvement of 50% or more glomeruli. The term segmental is used when a part of a glomerular tuft is affected and the term global is used when entire glomerular tuft is affected. The term mesangial hypercellularity means >4 nuclei in the matrix of a peripheral mesangial segment. The term sclerosis refers to increased collagenous extracellular matrix causing mesangial expansion, obliterating capillary lumen or forming contact to Bowman's capsule. Some of the important diagnostic features of kidney biopsy evaluation have been cited below in a tabulated form: (For a full view of the Table - Just click on the image below)

The neoplastic kidney disease are renal cell carcinoma, juxta glomerular cell tumor, renal adenoma, oncocytoma and metastatic tumors which need immunohistochemical (IHC) and EM study for an accurate diagnosis.