Nephronophthisis: a pathological and genetic perspective.

Nephronophthisis (NPHP) is an autosomal recessive cystic kidney disease and is one of the most frequent genetic causes for kidney failure (KF) in children and adolescents. Over 20 genes cause NPHP and over 90 genes contribute to renal ciliopathies often involving multiple organs. About 15-20% of NPHP patients have additional extrarenal symptoms affecting other organs than the kidneys. The involvement of additional organ systems in syndromic forms of NPHP is explained by shared expression of most NPHP gene products in centrosomes and primary cilia, a sensory organelle present in most mammalian cells. This finding resulted in the classification of NPHP as a ciliopathy. If extrarenal symptoms are present in addition to NPHP, these disorders are defined as NPHP-related ciliopathies (NPHP-RC) and can involve the retina (e.g., with Senior-Løken syndrome), CNS (central nervous system) (e.g., with Joubert syndrome), liver (e.g., Boichis and Arima syndromes), or bone (e.g., Mainzer-Saldino and Sensenbrenner syndromes). This review focuses on the pathological findings and the recent genetic advances in NPHP and NPHP-RC. Different mechanisms and signaling pathways are involved in NPHP ranging from planar cell polarity, sonic hedgehog signaling (Shh), DNA damage response pathway, Hippo, mTOR, and cAMP signaling. A number of therapeutic interventions appear to be promising, ranging from vasopressin receptor 2 antagonists such as tolvaptan, cyclin-dependent kinase inhibitors such as roscovitine, Hh agonists such as purmorphamine, and mTOR inhibitors such as rapamycin.

Urologic Diseases Germane to the Medical Renal Biopsy: Review of a Large Diagnostic Experience in the Context of the Renal Architecture and Its Environs.

The kidney is one of the most complicated organs in development and is susceptible to more types of diseases than other organs. The disease spectrum includes developmental and cystic diseases, involvement by systemic diseases, iatrogenic complications, ascending infections and urinary tract obstruction, and neoplastic diseases. The diagnosis of kidney disease is unique involving 2 subspecialties, urologic pathology and renal pathology. Both renal and urologic pathologists employ the renal biopsy as a diagnostic modality. However, urologic pathologists commonly have a generous specimen in the form of a nephrectomy or partial nephrectomy while a renal pathologist requires ancillary modalities of immunofluorescence and electron microscopy. The 2 subspecialties differ in the disease spectrum they diagnose. This separation is not absolute as diseases of one subspecialty not infrequently appear in the diagnostic materials of the other. The presence of medical renal diseases in a nephrectomy specimen is well described and recommendations for reporting these findings have been formalized. However, urologic diseases appearing in a medical renal biopsy have received less attention. This review attempts to fill that gap by first reviewing the perirenal anatomy to illustrate why inadvertent biopsy of adjacent organs occurs and determine its incidence in renal biopsies followed by a discussion of gross anatomic features relevant to the microscopic domain of the medical renal biopsy. Unsuspected neoplasms and renal cysts and cystic kidney diseases will then be discussed as they create a diagnostic challenge for the renal pathologist who often has limited training and experience in these diseases.

Fluorescence in situ hybridization for the diagnosis of NPHP1 deletion-related nephronophthisis on renal biopsy.

Nephronophthisis is an autosomal recessive tubulointerstitial nephropathy that is a leading genetic etiology of end-stage renal disease in children and young adults. Approximately 60% of patients with a known genetic etiology of nephronophthisis are due to homozygous deletion of the NPHP1 gene. We identified a total of 45 renal biopsies from young patients with chronic kidney disease of undetermined etiology and analyzed them for the possibility of nephronophthisis due to NPHP1 deletion using interphase fluorescence in situ hybridization and/or polymerase chain reaction. Homozygous NPHP1 deletion was identified in 9 patients (20%). In cases with adequate tissue, both assays were performed and showed 100% agreement. Blinded histopathologic analysis was then performed and identified 6 lesions that were significantly more common in biopsies from patients with NPHP1 deletion-proven nephronophthisis than chronic kidney injury of other known etiologies. Many of the classically described nephronophthisis biopsy lesions such as tubular basement membrane duplication, presence of cysts, and mononuclear interstitial inflammation were not significantly associated with this disease when compared with biopsies from patients with chronic kidney injury due to other etiologies. There were, however, morphologic lesions that were strongly associated with NPHP1 deletion including tubular abnormalities such as diverticulum, florets, and macula densa-like change as well as interstitial Tamm-Horsfall aggregates, periglomerular fibrosis, and the absence of arteriosclerosis. Awareness of the histopathologic pattern of injury in nephronophthisis combined with testing for NPHP1 deletion enables renal pathologists to provide a definitive pathologic and genetic diagnosis in a subset of patients with this disease.

Challenges in Pathologic Staging of Renal Cell Carcinoma: A Study of Interobserver Variability Among Urologic Pathologists.

Staging criteria for renal cell carcinoma differ from many other cancers, in that renal tumors are often spherical with subtle, finger-like extensions into veins, renal sinus, or perinephric tissue. We sought to study interobserver agreement in pathologic stage categories for challenging cases. An online survey was circulated to urologic pathologists interested in kidney tumors, yielding 89% response (31/35). Most questions included 1 to 4 images, focusing on: vascular and renal sinus invasion (n=24), perinephric invasion (n=9), and gross pathology/specimen handling (n=17). Responses were collapsed for analysis into positive and negative/equivocal for upstaging. Consensus was regarded as an agreement of 67% (2/3) of participants, which was reached in 20/33 (61%) evaluable scenarios regarding renal sinus, perinephric, or vein invasion, of which 13/33 (39%) had ≥80% consensus. Lack of agreement was especially encountered regarding small tumor protrusions into a possible vascular lumen, close to the tumor leading edge. For gross photographs, most were interpreted as suspicious but requiring histologic confirmation. Most participants (61%) rarely used special stains to evaluate vascular invasion, usually endothelial markers (81%). Most agreed that a spherical mass bulging well beyond the kidney parenchyma into the renal sinus (71%) or perinephric fat (90%) did not necessarily indicate invasion. Interobserver agreement in pathologic staging of renal cancer is relatively good among urologic pathologists interested in kidney tumors, even when selecting cases that test the earliest and borderline thresholds for extrarenal extension. Disagreements remain, however, particularly for tumors with small, finger-like protrusions, closely juxtaposed to the main mass.

An integrated pathology and ultrasonography-based simulation for training in performing kidney biopsy
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BACKGROUND: Medical practice trends and limitations in trainees' duty hours have diminished the interest and exposure of nephrology fellows to percutaneous kidney biopsy (PKB). We hypothesized that an integrated nephrology-pathology-led simulation may be an effective educational tool. MATERIALS AND METHODS: A 4-hour PKB simulation workshop (KBSW), led by two ultrasonography (US)-trained nephrologists and two nephropathologists, consisted of 6 stations: 1) diagnostic kidney US with live patients, 2) kidney pathology with plasticine models of embedded torso cross-sections, 3) US-based PKB with mannequin (Blue Phantom™), 4) kidney pathology with dissected cadavers, 5) US-based PKB in lightly-embalmed cadavers, and 6) tissue retrieval adequacy examination by microscope. A 10-question survey assessing knowledge acquisition and procedural confidence gain was administered pre- and post-KBSW. RESULTS: 21 participants attended the KBSW and completed the surveys. The overall percentage of correct answers to knowledge questions increased from 55 to 83% (p = 0.016). The number of "extremely confident" answers increased from 0 - 5% to 19 - 28% in all 4 questions (p = 0.02 - 0.04), and the number of "not at all confident" answers significantly decreased from 14 - 62% to 0 - 5% in 3 out of 4 questions (p = 0.0001 - 0.03). Impact of the imparted training on subsequent practice pattern was not assessed. CONCLUSION: A novel KBSW is an effective educational tool to acquire proficiency in PKB performance and could help regain interest among trainees in performing PKBs.
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Tuberous sclerosis complex: Hamartin and tuberin expression in renal cysts and its discordant expression in renal neoplasms.

Tuberous sclerosis complex (TSC) results from mutation of TSC1 or TSC2 that encode for hamartin and tuberin. It affects the kidneys often in advance of extra-renal stigmata. We studied 14 TSC cases, and 4 possible TSC cases with multiple angiomyolipomas (AMLs) for hamartin and tuberin protein expression to determine if the staining profile could predict mutation status or likelihood of TSC with renal-limited disease. The 18 cases included 15 nephrectomies and 1 section of 6 TSC-associated renal cell carcinomas (RCC). Controls included the non-neoplastic kidney in 5 tumor nephrectomies, 4 sporadic cases of AML and 6 clear cell RCCs. In the 14 TSC cases, 9 had AMLs, 9 had RCCs, 5 had polycystic kidney disease and 8 had eosinophilic cysts (EC) lined by large eosinophilic cells. The controls and study cases showed luminal staining of proximal tubules (PT) and peripheral membrane staining in distal tubules/collecting ducts for hamartin and cytoplasmic staining for tuberin. Eosinophilic cysts had a luminal PT-like stain with hamartin and a cytoplasmic reaction for tuberin. Hamartin stained myoid cells in all AMLs. Tuberin was negative in all but 1AML, an epithelioid AML. All but 1 RCC were positive for tuberin; 13 RCCs (7 TSC/6 non-TSC) were negative for hamartin and 4 showed a weak reaction. We conclude that the ECs of TSC are proximal tubule-derived. The hamartin and tuberin staining profiles of AMLs and most RCCs are reciprocal precluding prediction of the mutation in TSC, and fail to predict if a patient with multifocal AML has TSC.

Lack of electron microscopy hinders correct renal biopsy diagnosis: A study from India.

Electron microscopy (EM) is performed routinely on all native kidney biopsies in the western world. However, in India, it is not regularly performed due to non-availability and financial constraints. The aim of this prospective study was to evaluate the usefulness of routinely performing EM on native kidney biopsies. In order to eliminate selection bias, all consecutive native kidney biopsies were included in this study, provided they had adequate tissue for light, immunofluorescence (IF), and EM. The biopsies were reported on the basis of light and IF microscopy. EM was performed on each case by another pathologist who also independently reviewed the light microscopic slides and IF images. The findings were then reviewed to assess how the ultrastructural features contributed to the primary diagnosis and assigned to one of the following categories: 1. Crucial for diagnosis, 2. Important contribution, or 3. Not required. Of the 115 cases evaluated, EM was crucial in 12% of the cases. In 20% of the cases, it provided important confirmatory information and in the remaining 68% cases, EM was not considered required. This study supports the use of EM as a routine diagnostic tool in the evaluation of native kidney biopsies. There is an urgent need for availability and accessibility of EM in our country.

Eosinophilic, Solid, and Cystic Renal Cell Carcinoma: Clinicopathologic Study of 16 Unique, Sporadic Neoplasms Occurring in Women.

A unique renal neoplasm characterized by eosinophilic cytoplasm and solid and cystic growth was recently reported in patients with tuberous sclerosis complex (TSC). We searched multiple institutional archives and consult files in an attempt to identify a sporadic counterpart. We identified 16 morphologically identical cases, all in women, without clinical features of TSC. The median age was 57 years (range, 31 to 75 y). Macroscopically, tumors were tan and had a solid and macrocystic (12) or only solid appearance (4). Average tumor size was 50 mm (median, 38.5 mm; range, 15 to 135 mm). Microscopically, the tumors showed solid areas admixed with variably sized macrocysts and microcysts that were lined by cells with a pronounced hobnail arrangement. The cells had voluminous eosinophilic cytoplasm with prominent granular cytoplasmic stippling and round to oval nuclei with prominent nucleoli. Scattered histiocytes and lymphocytes were invariably present. Thirteen of 16 patients were stage pT1; 2 were pT2, and 1 was pT3a. The cells demonstrated a distinct immunoprofile: nuclear PAX8 expression, predominant CK20-positive/CK7-negative phenotype, patchy AMACR staining, but no CD117 reactivity. Thirteen of 14 patients with follow-up were alive and without disease progression after 2 to 138 months (mean: 53 mo; median: 37.5 mo); 1 patient died of other causes. Although similar to a subset of renal cell carcinomas (RCCs) seen in TSC, we propose that sporadic "eosinophilic, solid, and cystic RCC," which occurs predominantly in female individuals and is characterized by distinct morphologic features, predominant CK20-positive/CK7-negative immunophenotype, and indolent behavior, represents a novel subtype of RCC.

Membranous-like glomerulopathy with masked IgG kappa deposits.

The diagnostic classification of glomerulonephritis is determined by the interplay of changes seen using light, immunofluorescence, and electron microscopy of the renal biopsy. Routine direct immunofluorescence on fresh tissue is currently considered the gold standard for the detection and characterization of immune deposits. We recently found a peculiar form of glomerular immune complex deposition in which masked deposits required an antigen-retrieval step to be visualized. Over a 2-year period, 14 cases were characterized by numerous, large subepithelial deposits visualized by electron microscopy and C3-predominant staining by routine immunofluorescence on fresh tissue with weak to negative immunoglobulin staining. Repeat immunofluorescence after digestion of the formalin-fixed paraffin-embedded tissue with pronase elicited strong IgG-κ staining restricted within the deposits. The patients were often young with a mean age of 26 years and commonly had clinical evidence of vague autoimmune phenomenon. The clinicopathologic findings in this unusual form of glomerulopathy do not fit neatly into any currently existing diagnostic category. We have termed this unique form of glomerulopathy membranous-like glomerulopathy with masked IgG-κ deposits.

Handling and staging of renal cell carcinoma: the International Society of Urological Pathology Consensus (ISUP) conference recommendations.

The International Society of Urologic Pathology 2012 Consensus Conference on renal cancer, through working group 3, focused on the issues of staging and specimen handling of renal tumors. The conference was preceded by an online survey of the International Society of Urologic Pathology members, and the results of this were used to inform the focus of conference discussion. On formal voting a ≥65% majority was considered a consensus agreement. For specimen handling it was agreed that with radical nephrectomy specimens the initial cut should be made along the long axis and that both radical and partial nephrectomy specimens should be inked. It was recommended that sampling of renal tumors should follow a general guideline of sampling 1 block/cm with a minimum of 3 blocks (subject to modification as needed in individual cases). When measuring a renal tumor, the length of a renal vein/caval thrombus should not be part of the measurement of the main tumor mass. In cases with multiple tumors, sampling should include at a minimum the 5 largest tumors. There was a consensus that perinephric fat invasion should be determined by examining multiple perpendicular sections of the tumor/perinephric fat interface and by sampling areas suspicious for invasion. Perinephric fat invasion was defined as either the tumor touching the fat or extending as irregular tongues into the perinephric tissue, with or without desmoplasia. It was agreed upon that renal sinus invasion is present when the tumor is in direct contact with the sinus fat or the loose connective tissue of the sinus, clearly beyond the renal parenchyma, or if there is involvement of any endothelium-lined spaces within the renal sinus, regardless of the size. When invasion of the renal sinus is uncertain, it was recommended that at least 3 blocks of the tumor-renal sinus interface should be submitted. If invasion is grossly evident, or obviously not present (small peripheral tumor), it was agreed that only 1 block was needed to confirm the gross impression. Other recommendations were that the renal vein margin be considered positive only when there is adherent tumor visible microscopically at the actual margin. When a specimen is submitted separately as "caval thrombus," the recommended sampling strategy is to take 2 or more sections to look for the adherent caval wall tissue. It was also recommended that uninvolved renal parenchyma be sampled by including normal parenchyma with tumor and normal parenchyma distant from the tumor. There was consensus that radical nephrectomy specimens should be examined for the purpose of identifying lymph nodes by dissection/palpation of the fat in the hilar area only; however, it was acknowledged that lymph nodes are found in <10% of radical nephrectomy specimens.

Retrograde venous invasion in renal cell carcinoma: a complication of sinus vein and main renal vein invasion.

Renal cell carcinoma, especially clear cell, gains access to the venous system as the initial route of extrarenal spread. Intravenous growth can involve extrarenal veins or renal veins in other portions of the kidney, referred to herein as retrograde venous invasion. This study investigates the incidence and defines the pathological features of retrograde venous invasion. Retrograde venous invasion is defined as rounded nodules of tumor separated from the primary tumor and in a location that conforms to the venous outflow. Nine cases of retrograde venous invasion were identified in a series of 115 renal cell carcinomas (8%). Two blocks from each case were stained with elastic van Gieson, Masson trichrome, CD31 and desmin to evaluate intravenous involvement. All cases were staged using the 2010 TNM staging schema. The tumors ranged in size from 4.2 to 17 cm. All cases showed sinus vein and main renal vein invasion (pT3a); three cases involved the vena cava (pT3b). Direct continuity between the primary tumor and tumor in the main renal vein was grossly evident in every case. Involved sinus veins could be followed retrograde to the cortex between renal pyramids with tumor nodules arrayed along the pyramid-cortex interface. Histologically, the involved parenchymal veins lacked a smooth muscle media and elastica. CD31 demonstrated an endothelial cell lining around many nodules. As intravenous nodules enlarged endothelium was lost, extra-venous invasion occurred and nodules coalesced and merged with the primary tumor. In conclusion, retrograde venous invasion occurred only with main renal vein involvement. Gross evaluation allowed detection in every case. Histological confirmation of intravenous nature is challenging due to the absence of smooth muscle in parenchymal veins. As retrograde growth becomes extensive nodules coalesce and merge with the primary tumor and may be included in measurement of primary tumor size if this process is unrecognized.

The non-neoplastic kidney in tumor nephrectomy specimens: what can it show and what is important?

Surgical nephrectomy is a procedure that has been performed for nearly 100 years. In the presence of a normal contralateral kidney, such as in a renal transplant donor or child with Wilms tumor, it is a benign procedure without deleterious consequences on the remaining kidney. However, many adults and some children postnephrectomy will develop chronic kidney disease. The non-neoplastic kidney in tumor resections may harbor a large number of developmental and acquired diseases predictive of this outcome or that convey other medically significant information. Examination of the non-neoplastic kidney is a fertile opportunity to identify these unsuspected conditions that may ultimately dictate the subsequent clinical course and influence the medical care provided. This review discusses the consequences of unilateral and partial nephrectomy, and illustrates many conditions that may be encountered in the non-neoplastic cortex with a discussion of their clinical implications.

The classification of renal cystic diseases and other congenital malformations of the kidney and urinary tract.

CONTEXT: Renal cystic diseases and congenital abnormalities of the kidney and urinary tract comprise a heterogeneous group of lesions whose pathogenesis has eluded physicians for centuries. Recent advances in molecular and genetic understanding of these diseases may provide the solution to this riddle. OBJECTIVE: The formulation of an effective classification system for these disorders has been elusive but is needed to introduce order while providing a conceptual framework for diagnosis. DATA SOURCES: This review discusses the evolution, beginning in the 19th century, of postulates regarding the pathogenesis of cystic and developmental renal diseases. Selected classification systems proffered during this period are discussed in pursuit of an ideal classification schema that would account for morphologic features and their clinical importance, with logical links to pathogenesis and treatment. Although this remains an elusive target, its general outline is becoming clearer. A classification approach favored by the author is presented, which incorporates many of the strengths contained in several previous classifications. CONCLUSIONS: Genetic-and molecular-based postulates regarding the pathogenesis of the renal cystic and developmental diseases have implicated mutated master genes and the modification of genes that are crucial in renal development and genes that are central to the sensory effects of the renal tubular primary cilium on cell physiology. These scientific advances provide pathogenetic links between morphologically and genetically distinct entities and certain cystic and neoplastic entities, associations that seemed implausible not long ago. These advances may eventually provide the basis for future classification systems while suggesting targets for therapeutic approaches in the prevention and treatment of these diseases.

Renal cystic diseases and renal neoplasms: a mini-review.

The past two decades have witnessed recognition of several new types of renal cell carcinoma, each with distinct cytogenetic abnormalities. Included are several genetic and acquired cystic kidney diseases associated with development of renal cell carcinoma, the topic of this review. The risk in patients with autosomal dominant polycystic kidney disease is not accurately known but may be slightly increased. The risk for patients with von Hippel-Lindau disease is substantial, and death from renal cancer is common. For patients with tuberous sclerosis complex, the challenge is recognition of the occasional malignancy arising in a field of many benign tumors. Patients with end-stage kidney disease and acquired cystic kidney disease may develop a variety of renal cell carcinoma types. Progress in understanding the molecular basis of renal cyst formation and neoplastic disease has fostered development of targeted therapies that now hold promise for a group of neoplasms whose cure was traditionally dependent on surgical approaches.

Lymphatic differentiation in renal angiomyolipomas.

Renal angiomyolipomas are mesenchymal neoplasms with varying proportions of smooth muscle, adipose tissue, and abnormal blood vessels. Although the presence of lymphangiomatous-like foci is frequently noted in large series of angiomyolipoma, lymphatic differentiation has not been previously studied. Twelve angiomyolipomas from 10 patients were identified. All tumors expressed a melanocytic marker, HMB-45 or Melan-A. Twenty-eight paraffin blocks (1-4 per tumor) were stained for lymphatic endothelial cell markers, podoplanin, and D2-40, and the presence and distribution of lymphatic differentiation were recorded. The angiomyolipomas ranged from typical triphasic tumors to leiomyoma-like and lipoma-like tumors. All 12 tumors showed positive staining with podoplanin, and all 6 tumors stained for D2-40 were also positive, indicative of lymphatic differentiation. Lymphatic differentiation was variably observed throughout the tumors. It was most prevalent in myoid areas of the triphasic angiomyolipomas and in the leiomyoma-like variant, but infrequent and widely scattered within the adipose regions of triphasic angiomyolipoma and in the lipoma-like variant. The lymphatics were usually small, often irregularly shaped, and isolated vessels in fat, whereas in myoid regions lymphatics were clustered and in some areas formed a sinusoidal or labyrinth-like pattern. Lymphatics were commonly adjacent to abnormal arteries. However, unlike the lymphatics in the normal renal cortex, a consistent adventitial association was not observed and the clustering around arteries is regarded as reflecting the myoid regions that typically exist in these areas. In conclusion, lymphatic differentiation is common in angiomyolipomas, preferentially located in myoid regions. These data expand the mesenchymal pluripotential profile of renal angiomyolipomas.

Interphase cytogenetic analysis with centromeric probes for chromosomes 1, 2, 6, 10, and 17 in 11 tumors from a patient with bilateral renal oncocytosis.

Renal oncocytosis is characterized by the presence of multiple tumors with oncocytic features, often associated with small clusters of tubule-like structures with oncocytic change. The morphologic features of the oncocytic nodules encompass a spectrum of appearances, with patterns typical of renal oncocytoma or classic chromophobe renal cell carcinoma, as well as 'hybrid' tumors with features resembling both oncocytoma and chromophobe renal cell carcinoma. We utilized interphase cytogenetic methods to study 11 tumors from the kidneys of a 45-year-old woman. The tumors included morphologically classical oncocytomas and 'hybrid' tumors with features reminiscent of chromophobe carcinoma. The kidneys also showed foci of oncocytic change in renal tubules. Fluorescence in situ hybridization was performed with centromeric probes for chromosomes 1, 2, 6, 10, and 17 in each of the 11 tumors to determine whether or not there were losses of the chromosomes that are most frequently lost in chromophobe renal cell carcinomas. Neoplastic nuclei from each tumor were evaluated for the number of hybridization signals and scored according to the percentage of nuclei with one, two, and three or more signals. The normal renal parenchyma surrounding the tumors was used as control tissue. All 11 tumors from this patient with renal oncocytosis showed no loss of any of the chromosomes 1, 2, 6, 10, or 17, a pattern identical to that found in normal control tissues. These observations weigh against the concept that hybrid tumors of oncocytosis are closely related to chromophobe renal cell carcinoma.

Xp11 translocation renal cell carcinoma in adults: expanded clinical, pathologic, and genetic spectrum.

The recently recognized Xp11 translocation renal cell carcinomas (RCCs), all of which bear gene fusions involving the TFE3 transcription factor gene, comprise at least one-third of pediatric RCC. Only rare adult cases have been reported, without detailed pathologic analysis. We identified and analyzed 28 Xp11 translocation RCC in patients over the age of 20 years. All cases were confirmed by TFE3 immunohistochemistry, a sensitive and specific marker of neoplasms with TFE3 gene fusions, which can be applied to archival material. Three cases were also confirmed genetically. Patients ranged from ages 22 to 78 years, with a strong female predominance (F:M=22:6). These cancers tended to present at advanced stage; 14 of 28 presented at stage 4, whereas lymph nodes were involved by metastatic carcinoma in 11 of 13 cases in which they were resected. Previously not described and distinctive clinical presentations included dense tumor calcifications such that the tumor mimicked renal lithiasis, and obstruction of the renal pelvis promoting extensive obscuring xanthogranulomatous pyelonephritis. Previously unreported morphologic variants included tumor giant cells, fascicles of spindle cells, and a biphasic appearance that simulated the RCC characterized by a t(6;11)(p21;q12) chromosome translocation. One case harbored a novel variant translocation, t(X;3)(p11;q23). Five of 6 patients with 1 or more years of follow-up developed hematogenous metastases, with 2 dying within 1 year of diagnosis. Xp11 translocation RCC can occur in adults, and may be aggressive cancers that require morphologic distinction from clear cell and papillary RCC. Although they may be uncommon on a percentage basis, given the vast predominance of RCC in adults compared with children, adult Xp11 translocation RCC may well outnumber their pediatric counterparts.

Dense deposit disease is not a membranoproliferative glomerulonephritis.

Dense deposit disease (first reported in 1962) was classified as subtype II of membranoproliferative glomerulonephritis in the early 1970s. Over the last 30 years, marked differences in etiology and pathogenesis between type I membranoproliferative glomerulonephritis and dense deposit disease have become apparent. The sporadic observation that dense deposit disease can be seen with markedly different light microscopy appearances prompted this study. The goal was to examine a large number of renal biopsies from around the world to characterize the histopathologic features of dense deposit disease. Eighty-one cases of dense deposit disease were received from centers across North America, Europe and Japan. Biopsy reports, light microscopy materials and electron photomicrographs were reviewed and histopathologic features scored. Sixty-nine cases were acceptable for review. Five patterns were seen: (1) membranoproliferative n=17; (2) mesangial proliferative n=30; (3) crescentic n=12; (4) acute proliferative and exudative n=8 and (5) unclassified n=2. The age range was 3-67 years, with 74% in the range of 3-20 years; 15% 21-30 years and 11% over 30 years. Males accounted for 54% and females 46%. All patients with either crescentic dense deposit disease or acute proliferative dense deposit disease were between the ages of 3 and 18 years. The essential diagnostic feature of dense deposit disease is not the membranoproliferative pattern but the presence of electron dense transformation of the glomerular basement membranes. Based upon this study and the extensive data developed over the past 30 years, dense deposit disease is clinically distinct from membranoproliferative glomerulonephritis and is morphologically heterogeneous with only a minority of cases having a membranoproliferative pattern. Therefore, dense deposit disease should no longer be regarded as a subtype of membranoproliferative glomerulonephritis.

Renal veins and venous extension in clear cell renal cell carcinoma.

The 2002 TNM formulation defines a pT3b tumor as one that 'extends into the renal vein or its segmental (muscle containing) branches.' This definition elicits uncertainty when veins with little muscle are involved or the relationship to the main renal vein is unknown. The diameter and medial thickness of 10 normal renal venous systems were studied and compared to sinus veins involved in 54 pT3b clear cell renal cell carcinomas (CC). All tumors were grossly examined and sampled for histology by the author. An immunoperoxidase cocktail containing CD 31 and actin, Masson trichrome and elastic stains were employed to aid identification of intravenous tumor. The venous dissections showed variable numbers of primary and secondary divisions with substantial overlap in diameter and medial thickness. The medial thickness decreased with each proximal division and ranged from being nonexistent to being thick. Study of the 54 pT3b CC revealed that the initial phase of extrarenal extension involved large caliber veins draining the primary tumor. With extensive venous involvement, tumor invaded through the vein wall into sinus fat or demonstrated retrograde venous extension into adjacent cortex. Correlation between gross and histology revealed that most nodules of tumor within the sinus fat contained evidence of pre-existing veins. The following observations were made: (1) the diameter of a sinus vein or the quantity of muscle is a poor indicator of vein segment or relationship to the main renal vein; therefore, the wording used to define pT3b should be clarified; (2) extrarenal spread in CC begins with intravenous extension whereas sinus fat invasion is usually secondary; (3) retrograde venous extension occurs in cases with massive renal vein involvement; and (4) nodules within the sinus fat usually represent venous involvement.

Pathologic characteristics of exophytic renal masses.

OBJECTIVE: Pathologic grade is an important prognostic factor for renal-cell carcinoma (RCC). The objective of this study was to determine if there is any association of radiologic characteristics with pathologic grade and type of small renal tumors. PATIENTS AND METHODS: We retrospectively reviewed the records of 500 patients who underwent extirpative renal surgery. Fifty-one patients met the inclusion criteria of solitary RCC <6 cm and adequate radiologic imaging available for review. The axial images with the largest area of tumor growing into the kidney were evaluated by a single radiologist to determine the percent of tumor that was exophytic. RESULTS: Nine patients had tumors that were >67% exophytic, and 42 patients had tumors <67% exophytic. There is a statistically significant difference in the mean Fuhrman grade for these 2 groups (1.78 v 2.25, P < 0.01). The distribution of histologic subtype was as follows: 34 patients with clear cell, 15 with papillary, and one each with chromophobe and unclassified tumors. Papillary RCC comprised 78% (7 of 9) of tumors that were >67% exophytic and 15% (3 of 20) that were <33% exophytic. The relative risk of a >67% exophytic tumor being papillary v nonpapillary is 4.1. CONCLUSIONS: Exophytic renal tumors are more likely to be of lower pathologic grade and of the papillary RCC subtype when compared with endophytic renal tumors. A larger prospective study is required to confirm these findings and determine the implications. This information may be useful when small tumors are being considered for watchful waiting or ablative therapies.