Renal pathology has always been considered an “exotic” area of pathology. Perhaps more than one reason accounts for this perception. Limited exposure to renal pathology, reflecting the fact that kidney biopsies for medical renal diseases are not a common specimen and are mostly sent to specialized centers rather than being handled at local hospitals, is probably one of the most important reasons for this perception. The complexity of integrating different diagnostic modalities, including light microscopy, immunofluorescence, and electron microscopy, is perhaps another reason. Furthermore, proper renal biopsy interpretation usually requires significant clinical knowledge. The observation that very similar morphologic findings in renal biopsies may signify diseases of quite different nature and pathogenesis, impacting treatment and prognosis, is certainly somewhat unusual and daunting in diagnostic pathology.
Yet, knowledge in renal pathology is important in the daily practice. Correct handling of the renal biopsies to be sent for outside consultation, understanding the diagnostic and biologic significance of the renal biopsy reports, and effective communication with the referring nephrologists all depend on a significant understanding of various aspects of renal diseases from a morphologic perspective. Furthermore, the entire spectrum of renal medical diseases can be seen in the context of nephrectomy for neoplastic or nonneoplastic conditions. It is the responsibility of the general pathologist to make a correct diagnosis in the uninvolved renal parenchyma of these nephrectomy specimens.
Recent years have witnessed significant developments in the pathology of renal medical diseases. New disease entities have been recognized, diagnostic criteria have been revised and updated, and classic disease paradigms have changed. Furthermore, probably in no other field of pathology would the recent understanding of molecular mechanisms of disease have more potential impact on the classification, diagnosis, and treatment of these kidney diseases. We have not quite yet seen the full ramifications of the “revolution” that is about to take place in the treatment of medical renal diseases resulting from our enhanced understanding of molecular pathogenesis of these disorders.
This special section on renal pathology was developed in response to these considerations. The subjects were chosen to cover areas that have changed substantially during the last 5 years and to address subjects of interest to the general pathologist.
Patrick Walker, MD, provides a detailed account of what the proper examination of renal tissue obtained by various means for the evaluation of medical renal diseases entails. He discusses the basic requirements for a successful renal biopsy. There is no doubt that it is necessary to take into account a number of important factors so that the renal biopsy can provide the material that is required to establish a definitive diagnosis. He reviews the value of each of the ancillary diagnostic techniques used in the evaluation of renal biopsies. He also discusses historic aspects associated with the renal biopsy as a procedure to obtain tissue for diagnosis, current practices pertaining to the medical utilization of this procedure, and how the donor and allograft biopsies should be handled. He expands on practical aspects pertaining to the essential elements of the renal biopsy reports. This is a comprehensive article that should be of great value for the general pathologist who must handle but not necessarily “sign out” the renal biopsies.
Luan Truong, MD, and colleagues took on the challenge of addressing renal lesions associated with renal neoplasms, a subject of much interest to the general pathologist who signs out nephrectomy specimens and must look at the uninvolved renal parenchyma. There are alterations of clinical significance in the uninvolved renal parenchyma that can be missed if not carefully evaluated. Because the nephrectomy itself diminishes the overall number of nephrons available, the parenchyma that remains in the opposite kidney, if it is involved by a disease process, compromises remaining renal function. The nephrectomy specimen serves the purpose of being the diagnostic specimen for whatever is the underlying medical disease involving the kidney. This article carefully dissects the challenges that may be encountered when handling these specimens and how to adequately examine the specimens to document the presence of an underlying nephropathy.
Laura Barisoni, MD, and associates discuss the latest findings and diagnostic criteria in podocytopathies. Basic science has clearly advanced this field, and pathologists are taking advantage of this new information by applying it to diagnostic settings. These authors summarize available information and highlight the state of the art regarding this most interesting subject. This article links the morphologic classification of podocytopathies with molecular events that have been elucidated, proposing a classification of these diseases that is amenable to being used for the design of new therapies.
David Thomas, MD, summarizes the current view on focal segmental glomerulosclerosis, the most common cause of nephrotic syndrome, and provides a succinct historic account on the classification of this lesion. The recent Columbia classification of focal segmental sclerosis is described in detail and supplemented with clinical correlations. The strength and the limitation of this classification are discussed with practical diagnostic caveats.
Mark Haas, MD, PhD, was given the task of addressing the diagnosis of glomerular basement membrane disorders, a subject that has been completely revolutionized by information that has been obtained from basic research and applied to diagnostic pathology. Dr Haas summarizes in a succinct yet clear and complete manner the current diagnostic approach to this group of diseases.
Surya Seshan, MD, and J. Charles Jennette, MD, cover another very important subject; that is, renal pathology in systemic lupus erythematosus. Recently, a new classification of lupus nephritis has been approved by the Renal Pathology Society and the International Society of Nephrology based on clinical and pathologic information that has become available during the last 3 decades. They discuss the new classification in light of the older classifications and provide very useful points regarding the diagnosis of lupus nephritis. The considerations covered in this article are very important, not only to pathologists but also to clinicians.
Guillermo Herrera, MD, addresses in a practical fashion the diagnosis of some of the renal disorders associated with underlying plasma cell dyscrasias, emphasizing how research has improved our ability to better understand and diagnose these diseases. In some instances, the diagnosis of some of these conditions requires careful evaluation of the data emanating from all 3 diagnostic techniques used in the daily practice of renal pathology: immunofluorescence, light microscopy, and electron microscopy. This article clearly shows how these techniques work in concert in the diagnosis and characterization of these sometimes diagnostically challenging conditions.
Tibor Nadasdy, MD, and Lois Arend, MD, PhD, discuss a very important and timely subject; that is, renal lesions associated with new therapies. There is a plethora of new therapies with many new drugs entering the therapeutic arena, some with unclear side effects; their renal toxicity may result in a variety of alterations affecting all renal compartments. Because many of these drugs are cleared by the kidney, alterations in the renal parenchyma can be seen. There are also hypersensitivity reactions to these drugs that can become manifest in the renal parenchyma. This article summarizes the information available at the present time. Since one of the most effective ways to address these renal complications is to discontinue the therapy, linking the renal changes to a specific drug is essential, and it is the responsibility of those who examine renal specimens to do so.
This special section on renal pathology represents a compilation of routine but important issues in renal pathology and recent developments in this area. The editors have enjoyed preparing this special section and hope that it is useful to the readers of the Archives of Pathology & Laboratory Medicine. Hopefully, the “exotic” perception and mystery that surround the handling and interpretation of renal biopsies for medical renal diseases have been somewhat mitigated, and readers can start looking at this subject with more transparency and an increased depth of understanding.
The authors have no relevant financial interest in the products or companies described in this article.
Reprints: Luan Truong, MD, Department of Pathology, The Methodist Hospital and Research Institute, 6565 Fannin St, M227 (Main Bldg), Houston, TX 77030 (email@example.com)