Renal Papillary Rarefaction: An Artifact Mimicking Papillary Necrosis.

In histopathology, the presence of a tissue change that does not represent the tissue's normal appearance can often lead to an incorrect diagnosis and interpretation. These changes are collectively known as "artifacts" resulting from postmortem autolysis, improper fixation, problems with tissue handling or slide preparation procedures. Most tissue artifacts are obvious, yet some artifacts may be subtle, occur in relatively well-fixed tissue, and demand careful observation to avoid confusion with real biological lesions. The kidney often contains artifacts that may be observed throughout all regions of the renal parenchyma. Cortical tubule artifacts present the greatest challenge when discerning an artifact versus an induced lesion following exposure to a xenobiotic. However, confounding artifacts observed at the tip of the renal papilla may also be problematic for the pathologist. An uncommon artifact involving tinctorial alteration and rarefaction affecting the papillary tip of the rat kidney is described here and differentiated from treatment induced lesions of renal papillary necrosis.

Uterine Paramesonephric Cysts in Sprague-Dawley Rats from National Toxicology Program Studies.

Congenital uterine wall cysts arising from paramesonephric (Müllerian) and mesonephric (Wolffian) ducts are typically incidental findings in most species. We used immunohistochemistry to characterize and determine the origin of uterine cysts in Sprague-Dawley (SD) rats from multigeneration studies conducted by the National Toxicology Program. Subserosal uterine cysts were observed in 20 of the 2,400 SD rats evaluated in five studies, and 10 cysts were characterized for this study. Single cysts were unilocular, fluid-filled, and occurred throughout the uterus. Microscopically, all cysts had a well-developed smooth muscle wall, lined by flattened to cuboidal, sometimes ciliated, epithelium that stained intensely positive for cytokeratin 18 and paired box protein 8 (PAX8). Most cyst epithelia displayed weak to moderate positivity for progesterone receptor (PR) and/or estrogen receptor α (ER-α), as well as were negative for GATA binding protein 3 (GATA3). Cyst lumens contained basophilic flocculent material. The cysts appeared to be developmental anomalies arising from paramesonephric tissue based on positive PAX8 and ER-α and/or PR staining. Additionally, 70% of the cysts lacked GATA3 expression. Taken together, the subserosal uterine cysts observed in adult rats in these studies most likely arose from the paramesonephric duct.

A brief review of kidney development, maturation, developmental abnormalities, and drug toxicity: juvenile animal relevancy.

Nonclinical juvenile animal tests perform a valuable role in determining adverse drug effects during periods of organogenesis and/or functional maturation. Developmental anatomic and functional maturation time points are important to consider between juveniles and adults when regarding different organ toxicities in response to drug administration. The kidney is an example of a major organ that has differences in these time points in comparing juveniles to adults and in contrasting humans to laboratory animal species. Toxicologic pathologists, involved in juvenile studies, need to be aware of these time points which are age-related exposure periods of sensitivity to drug toxicity. Age-related developmental anatomic and functional maturation are factors which can affect the way that a drug is absorbed, distributed, metabolized, and excreted (ADME). Changes to any component of ADME may alter drug toxicity resulting in kidney abnormalities, nephrotoxicity, or maturational disorders. Juvenile animal kidneys may either be less resistant or more resistant to known adult nephrotoxic drug effects. Furthermore, drug toxicity observed in juvenile animal kidneys may not always correspond to similar toxicities in humans. Juvenile animal nonclinical toxicology studies targeting the kidneys have to be carefully planned to attain the maximum knowledge from each study.

A Survey of Mesenchyme-related Tumors of the Rat Kidney in the National Toxicology Program Archives, with Particular Reference to Renal Mesenchymal Tumor.

In order to harmonize diagnostic terminology, confirm diagnostic criteria, and describe aspects of tumor biology characteristic of different tumor types, a total of 165 cases of mesenchyme-related tumors and nephroblastomas of the rat kidney were reexamined from the National Toxicology Program (NTP) Archives. This survey demonstrated that renal mesenchymal tumor (RMT) was the most common spontaneous nonepithelial tumor in the rat kidney, also occurring more frequently in the NTP studies than nephroblastoma. Renal sarcoma was a distinct but very rare tumor entity, representing a malignant, monomorphous population of densely crowded, fibroblast-like cells, in which, unlike RMT, preexisting tubules did not persist. Nephroblastoma was characterized by early death of affected animals, suggesting an embryonal origin for this tumor type. Male and female rats were equally disposed to developing RMT, but most of the cases of nephroblastoma occurred in female rats and liposarcoma occurred mostly in male rats. This survey confirmed discrete histopathological and biological differences between the mesenchyme-related renal tumor types and between RMT and nephroblastoma. Statistical analysis also demonstrated a lack of any relationship of these renal tumor types to test article administration in the NTP data bank.

Spontaneous Age-related Lesions of the Kidney Fornices in Sprague-Dawley Rats.

The upper portion of the rat kidney pelvis has specialized anatomic structures referred to as fornices. Fornices have a role in urine concentration. Spontaneous lesions including mineralization, epithelial hyperplasia, and inflammatory cell infiltration may occur in the area of the fornices. However, little information regarding specific historical control data or the spontaneous development of these findings in male and female fornices is known. Understanding spontaneous age-related lesions in the area of the fornices versus other portions of the kidney pelvis may be relevant in the identification of test article-induced changes. A retrospective study was conducted of male and female Sprague-Dawley rat kidney fornices over several time points to determine the incidence and severity of mineralization, epithelial hyperplasia, and inflammatory cell infiltration. Based on this investigation, these lesions appeared to increase over time and, in general, occurred earlier and with a greater incidence in females. Regarding those chemicals that may result in lesions of the kidney pelvis, it may be important for pathologists to separately diagnose lesions of the fornices from other portions of the kidney pelvis to help differentiate between any spontaneous age-related and induced changes.

Regulatory Forum Opinion Piece*: Dispelling Confusing Pathology Terminology: Recognition and Interpretation of Selected Rodent Renal Tubule Lesions.

Renal tubule lesions often prove troublesome for toxicologic pathologists because of the diverse nature and interrelated cell types within the kidney and the presence of spontaneous lesions with overlapping morphologies similar to those induced by renal toxicants. Although there are a number of guidance documents available citing straightforward diagnostic criteria of tubule lesions for the pathologist to refer to, most are presented without further advice on the when to or to the why and the why not of diagnosing one lesion over another. Documents presenting diagnostic perspectives and recommendations derived from an author's experience are limited since guidance documents are generally based on descriptive observations. In this Regulatory Forum opinion piece, the authors attempt to dispel confusing renal tubule lesion terminology in laboratory animal species by suggesting histological advice on the recognition and interpretation of these complex entities.

Spontaneous incidence of oncocytic proliferative lesions in control rat kidney.

The spontaneous incidence of foci of oncocytic proliferation (oncocytic hyperplasia and oncocytoma) was assessed in a histopathological reevaluation of the kidneys of 2,391 male and female Fischer 344 (F344) groups of control rats from long-term carcinogenicity studies (involving 24 chemicals) that had been conducted by the National Toxicology Program. The overall incidence of oncocytic proliferation was 0.3%, with a male preponderance over females at 0.5% (6/1,236) versus 0.09% (1/1,155), respectively. In males, there appeared to be an association of oncocytic proliferation with advanced spontaneous chronic progressive nephropathy. Oncocytoma or oncocytic hyperplasia appear to be rare lesions in F344 rats, and observations from these carcinogenicity studies suggest that they are slow growing and tend to occur late in a rodent's life span.

Association of advanced chronic progressive nephropathy (CPN) with renal tubule tumors and precursor hyperplasia in control F344 rats from two-year carcinogenicity studies.

From the archives of the National Toxicology Program, National Institutes of Health, kidney sections from twenty-four carcinogenicity studies (representing twenty-three chemicals) in male and female F344 rats were histopathologically re-evaluated to grade the severity of chronic progressive nephropathy (CPN) on an expanded scale of 0-8, and to record the presence of renal tubule tumors (RTT) and their precursor, atypical tubule hyperplasia (ATH). The data were statistically analyzed using SAS software for logistic regression analysis. This histopathological survey of 2,436 F344 rats showed clear evidence of a qualitative and statistically significant association between advanced stages of CPN severity and the development of low-grade RTT and ATH. Advanced CPN severity therefore represents a risk factor for the development of RTT and appears to be an underlying basis for spontaneous occurrence of RTT in the F344 rat. The difference in incidence and severity of CPN between the sexes also explains the 9:1 male-to-female sex difference in the spontaneous occurrence of ATH and RTT observed here. The regulatory significance of this finding is that chemicals exacerbating CPN as their only renal effect are likely to show a numerical increase in RTT with dose, which does not represent a direct tumorigenic effect of the chemical.

Proliferative and nonproliferative lesions of the rat and mouse urinary system.

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the urinary tract of rats and mice. The standardized nomenclature of urinary tract lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for urinary tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Spontaneous renal tumors suspected of being familial in sprague-dawley rats.

Spontaneous renal tubule tumors (RTTs), with a distinctive morphological phenotype, were present in three Sprague-Dawley rats, 1 male and 2 females, out a total of 120 animals of each sex from untreated and placebo control groups in a 2-year carcinogenicity study. One female had one carcinoma, adenoma and hyperplasia, and the other female had five adenomas and many hyperplastic lesions; the male case had one carcinoma. From these cases, a biological continuum of hyperplasia, adenoma and carcinoma could be recognized. The tumors were present in the renal cortex and appeared as solid lobulated growths with occasional central necrosis. The lobules were divided by a small amount of fibrovascular tissue. Occasionally the larger tumors contained a cystic area. Tumor cells appeared distinctive and exhibited variable amounts of eosinophilic/amphophilic and vacuolated cytoplasm. Nuclei were round to oval with a prominent nucleolus. Mitotic figures were uncommon, and no distant metastasis was noted. The tumors were seen as multiple and bilateral lesions in two animals and had no apparent relationship to chronic progressive nephropathy (CPN). Foci of tubule hyperplasia were also noted to contain the same type of cellular morphology. The morphological and biological features of these 3 cases resembled the amphophilic-vacuolar (AV) variant of RTT that has been posited to be of familial origin. This is a report of spontaneous familial renal tumors in Sprague-Dawley rats from Japan.

Spontaneous occurrence of a distinctive renal tubule tumor phenotype in rat carcinogenicity studies conducted by the national toxicology program.

The Toxicology Data Management System (TDMS) of the National Toxicology Program, National Institutes of Environmental Health Sciences, National Institutes of Health, was surveyed for occurrence and distribution of a distinctive renal tubule tumor type in rats. The hallmark features of this tumor included eosinophilic/amphophilic staining, large finely granular cells, and numerous vacuoles and/or minilumens. It is referred to here as the amphophilic-vacuolar (AV) variant of renal tubule tumor. Of 154 studies in which renal tubule tumors had been recorded in the standard single sections of kidney in the TDMS, there were collectively 1012 rats with renal adenomas, carcinomas, or adenocarcinomas, and of these, 100 displayed the distinctive AV morphology, representing 74 studies involving mostly the F344 rat, but also the Sprague-Dawley and Wistar strains. The AV tumors (mainly adenomas but also some carcinomas) occurred usually as solitary lesions in the affected animals. However, they were multiple and bilateral in a few cases. They were equally distributed between the sexes, did not metastasize (at least to the lung), and were not associated with chronic progressive nephropathy. The distribution of this renal tumor type was random across studies and dose groups, underscoring the likelihood that it was of spontaneous origin and not chemically induced. Accordingly, it is suggested that this distinctive renal tumor phenotype be recorded as a separate category from conventional RTT when assessing the carcinogenic potential of a test compound.

Toxicology and pathology considerations for the design of juvenile animal studies.

Although exposure to drugs or toxicants can affect children and adults very differently, many compounds lack specific safety information for children. Studies in juvenile animals can help researchers assess pediatric patients' potential response to certain chemicals. Juvenile studies are highly sensitive to animal age, sex and species and must be planned with care to prevent misinterpretation of experimental data. The author reviews considerations for the design of these studies, focusing on toxicological and pathological aspects.

Re-evaluation of the kidney tumors and renal histopathology occurring in a 2-year rat carcinogenicity bioassay of quercetin.

Renal histopathology in the most recent 2-year carcinogenicity bioassay of quercetin, in Fischer 344 rats, was re-evaluated in an attempt to determine a mode of action underlying a small increase in renal tubule tumors reported in the males (). The re-evaluation confirmed the reported increase in renal tumors in mid- and high-dose males, including a single carcinoma in a high-dose male, as well as an exacerbation of spontaneous, chronic progressive nephropathy (CPN) in male rats only. The re-evaluation also showed that there were no cellular alterations in the kidney indicative of chemical toxicity at 6 months, 15 months, or 2 years. The evidence linked the occurrence of the predominant basophilic adenomas and foci of atypical tubule hyperplasia (ATH) with the exacerbation of CPN to advanced grades of severity, supporting a mode of action involving quercetin interaction with CPN. This mode of action represents a secondary mechanism for renal tumor development, with no relevance for extrapolation to humans. In addition, the single carcinoma present in the high-dose males, along with 4 other lesions ranging from ATH to adenoma in male and female groups, were considered to have a unique phenotype associated previously with neoplasms of spontaneous and familial origin.

Histological investigation of diagnostically challenging tubule profiles in advanced chronic progressive nephropathy (CPN) in the fischer 344 RaT.

Recently, guidelines were suggested for discriminating proliferative-appearing tubule profiles encountered in advanced spontaneous chronic progressive nephropathy (CPN) of rats, from hyperplastic precursors of renal tubule tumors (Hard and Seely, 2005). These recommendations were based on histological evaluation of a large number of cases of severe to end-stage CPN in male F344 rats from 8 separate 2-year carcinogenicity studies held in the Archives of the National Toxicology Program, NIEHS. This work has now been extended to characterize the various lesions further, mainly by serial sectioning to track their origin and fate within the adjacent renal tissue, but also by applying special staining procedures such as immunohistochemical assessment of proliferative activity, as well as fluorescence microscopy, to seek further differences from atypical tubule hyperplasia. The results obtained from these additional investigations support the contention that certain tubule profiles with a misleading proliferative appearance, sometimes found in advanced CPN, should be distinguished from preneoplastic tubule foci, and regarded as components of the nephropathy process.

Recommendations for the interpretation of renal tubule proliferative lesions occurring in rat kidneys with advanced chronic progressive nephropathy (CPN).

There is little guidance in the literature on the spectrum of proliferative tubule lesions in the kidneys of aging rats affected with spontaneously occurring, chronic progressive nephropathy (CPN), or their interpretation. Through accessing 2-year carcinogenicity studies in male F344 rats held in the Archives of the National Toxicology Program, NIEHS, a large number of cases of advanced CPN have been surveyed histopathologically for proliferative tubule lesions, and an attempt made to provide guidelines for discrimination of lesions common to the CPN process, from those representing precursors of neoplasia. Several proliferative lesions were identified as common in advanced CPN with no apparent evidence supporting a role in renal tubule carcinogenesis. It is recommended that these lesions be viewed generically as CPN tubule profiles, and not recorded separately from the diagnosis of CPN. Criteria were developed to distinguish these CPN-associated lesions from atypical tubule hyperplasia, a precursor of adenoma, both of which were also represented in this survey of advanced CPN.