Non-neoplastic Renal Pathology for Surgical Pathologists

Renal pathology, exclusive of neoplastic lesions, is usually segregated from the overall sign out list for surgical pathologists. In the United States and Europe, as well as in many other places in the world, renal biopsies are typically read by pathologists with special training and interest in nephropathology. In many practices, all renal biopsies are sent to outside institutions to be processed and read. In other practices, some or most of the pathology dealing with transplanted kidneys is handled locally by nonrenal pathologists. Regardless of the practice they are in, non-nephropathologists deal with a number of situations where detailed knowledge about renal pathology becomes important. Non-nephropathologists sign out nephrectomies performed for cystic renal diseases, obstructive renal disorders, and benign and malignant renal masses; evaluate non-involved portions of kidneys that are surgically resected due to neoplasms and other mass lesions; and in some practices are also involved in the reading of frozen sections of donor kidneys and in the interpretation of transplant renal biopsies. The present issue addresses subjects of interest for those non-nephropathologists who may find challenges in the interpretation of these specimens in their practices. The articles in this issue aim at providing a clear, comprehensive, and yet concise view of each of the topics addressed. Some of the subjects deal with mass lesions that portray specific histopathologic findings that allow their accurate diagnosis. Occasionally, non-nephropathologists have relevant questions dealing with diagnosing tubular interstitial disorders, as there is overlap in their histological expressions, and this area of renal pathology has been covered in several of the contributions, each with a different perspective. I address how to look at cystic renal diseases in a logical fashion for proper classification of these disorders in one of my articles. The classification of cystic renal disorders has changed often, and it is now much more oriented toward clinical correlations and implications. My contribution also describes important pathogenetic issues and molecular/genetic considerations that have been elucidated in the recent past impacting greatly in the management of these patients and families. Dr. Truong provides an overview of obstructive nephropathy with diagnostic features to be looked for and emphasizes those diagnostic entities that may be found in these cases. Dr. Al-Delfi discusses xanthogranulomatous pyelonephritis, a unique form of tubular interstitial disease that may in some instances be clinically confused with a renal neoplasm. Xanthogranulomatous pyelonephritis has specific histological findings and important clinicopathologic correlations that are discussed in his presentation. He also discusses the important subject of non-neoplastic findings in nephrectomies performed for renal masses, highlighting the importance of careful evaluation of the nonneoplastic renal parenchyma in every one of these nephrectomies not to miss important medical renal diseases that may be present. Dr. Gu has selected 3 examples of tubular interstitial disorders where proper histological evaluation, sometimes requiring immunofluorescence and ultrastructural support, makes a definitive etiologic diagnosis in 2 of the cases that he presents. Dr. Turbat-Herrera discusses lesions that may be found in end-stage renal disease with emphasis on clinicopathologic correlations and importance of correct diagnosis of the various findings to guide patients’ management. Three articles of this issue address renal transplantation issues. Dr. Aufman recapitulates criteria to obtain the information that is required to be provided to clinicians resulting from the evaluation of transplant renal specimens and also addresses in a separate article important issues regarding humoral rejection, a subject of much interest at present. I summarize the information available regarding donor kidneys and how these must be evaluated with considerations regarding the reality that the donor pool has been expanded and donor kidneys that were previously rejected are now being considered for transplantation, creating for the pathologists new challenges associated with the evaluation of these specimens. Most of the subjects covered by the invited experts do not require special techniques such as immunofluorescence and electron microscopy, which are routinely used in the evaluation of medical renal biopsies. However, as the readers will see in a few instances, such techniques are needed to reach the level of diagnostic expectations in the current practice environment (see Dr. Gu’s article). We hope that the information provided, although not encyclopedic, is comprehensive enough to convey the important points to the readers and, most importantly, helpful to address diagnostic issues that come up frequently. References provided can be used to expand knowledge in the various areas covered in this issue, if such is desired.