Atypical nephrogenic metaplasia of the urinary tract: a precursor lesion?

Diagnostic Approach to and Differential Diagnosis of Clear Cell and Glandular Lesions of the Lower Urinary Tract

CONTEXT.—

A variety of glandular and clear cell lesions may be seen in the urinary bladder and/or urethra, ranging from benign to malignant primary and secondary tumors. Lesions with no malignant potential include reactive processes, such as nephrogenic metaplasia, and may show similar morphologic features as an infiltrative neoplasm, particularly in small biopsies. Similarly, ectopic tissues of Müllerian origin may be seen in the lower urinary tract, and their distinction from a true glandular neoplasm is essential to avoid overtreatment. A wide variety of primary and secondary malignant tumors exist with varying degrees of glandular and clear cell features. Therefore, surgical pathologists must be aware of the full scope of possible lesions to avoid misdiagnosis.

OBJECTIVE.—

To provide a practical framework for approaching the diagnosis of clear cell and glandular lesions of the urinary bladder/urethra and prostate, highlighting the strengths and limitations of various diagnostic features and ancillary tests.

DATA SOURCES.—

A review of the current literature was performed to obtain data regarding up-to-date diagnostic features and ancillary studies.

CONCLUSIONS.—

In summary, distinct morphologic and immunohistochemical features and clinical and radiologic correlation are essential to establish an accurate diagnosis when such cases with glandular and clear features are encountered in the lower urinary tract.

Common and uncommon features of nephrogenic adenoma revisited

Nephrogenic adenoma is a common diagnosis in urological pathology that may be challenging for general pathologists. Due to its polymorphic appearance under the microscope, some cases can be misdiagnosed as malignancy and then unnecessarily overtreated. Aside from the typical tubules, cysts and papillae, nephrogenic adenoma may display a broad spectrum of histologic appearances and locations, some of them atypical or unexpected. These unusual and concerning features will have special consideration in this description. The goal of the review is to increase awareness of general pathologists of the varied histology of nephrogenic adenoma.

Updates in Benign Lesions of the Genitourinary Tract

The genitourinary tract is a common site for new cancer diagnosis, particularly for men. Therefore, cancer-containing specimens are very common in surgical pathology practice. However, many benign neoplasms and nonneoplastic, reactive, and inflammatory processes in the genitourinary tract may mimic or cause differential diagnostic challenges with malignancies. Emerging clinicopathologic, immunohistochemical, and molecular characteristics have shed light on the pathogenesis and differential diagnosis of these lesions. This review addresses differential diagnostic challenges related to benign genitourinary tract lesions in the kidney, urinary bladder, prostate, and testis, with emphasis on recent advances in knowledge and areas most common in diagnostic practice.

Nephrogenic Adenoma of the Urinary Bladder: A Review of the Literature

Background. Nephrogenic adenoma of the urinary bladder (NAUB) is a rare lesion associated with nonspecific symptoms and could inadvertently be misdiagnosed. Aim. To review the literature. Methods. Various internet search engines were used. Results. NAUB is a benign tubular and papillary lesion of the bladder, is more common in men and adults, and has been associated with chronic inflammation/irritation, previous bladder surgery, diverticula, renal transplantation, and intravesical BCG; recurrences and malignant transformations have been reported. Differential diagnoses include clear cell adenocarcinoma, endocervicosis, papillary urothelial carcinoma, prostatic adenocarcinoma of bladder, and nested variant of urothelial carcinoma; most NAUBs have both surface papillary and submucosal tubular components; both the papillae and tubules tend to be lined by a single layer of mitotically inactive bland cells which have pale to clear cytoplasm. Diagnosis may be established by using immunohistochemistry (positive staining with racemase; PAX2; keratins stain positive with fibromyxoid variant), electron microscopy, DNA analysis, and cytological studies. Treatment. Endoscopic resection is the treatment but recurrences including sporadic malignant transformation have been reported. Conclusions. There is no consensus on best treatment. A multicentre study is required to identify the treatment that would reduce the recurrence rate, taking into consideration that intravesical BCG is associated with NAUB.

Nephrogenic adenoma of the urinary tract: clinical, histological, and immunohistochemical characteristics

Nephrogenic adenoma is a benign condition of the urinary tract resulting from the displacement and seeding of renal tubular cells from the renal pelvis to the urethra. A retrospective series of 134 cases collected from four hospitals in three different countries was analyzed in this study. Recorded clinical data included age and sex, topography, urological antecedents, coexistent lesions, and follow-up. Cytonuclear and architectural features were reviewed, and PAX-8, p63, PSMA, S100A1, CEA, EMA, CD117, cannabinoid receptor CB1, AMACR, E-cadherin, and CD10 antibodies were included in an immunohistochemical panel. Males predominated (105 M/29 F) with an average age of 66 years (range, 14-96). Urothelial carcinoma was the most frequent clinical antecedent (43.2 %) and also the most common coexisting lesion (14 %). Tubular architecture was the most frequent pattern detected (40 %) although most cases showed a mixed pattern (45.5 %). Deep infiltrative growth into the muscularis propria occurred in two cases. EMA and PAX-8 were expressed in 100 % of nephrogenic adenomas, while E-cadherin reactivity was observed in 66.6 % of cases, cannabinoid receptor CB1 in 25 %, CD10 in 13.6 %, CD117 in 4.1 %, and AMACR in 2.7 %. For the rest of the antigens, no reactivity was found. The average time lapse between the pathological antecedent and the discovery of a nephrogenic adenoma was 32 months. We conclude that nephrogenic adenoma displays a broad spectrum of histological features that may mimic malignancy. In our experience, CB1 immunostaining adds a further argument in favor of a renal origin of this lesion. The combination of PAX-8+, p63-, and EMA + distinguishes nephrogenic adenoma from urothelial and prostate carcinoma, its most frequent malignant look-alikes.

Flat pattern of nephrogenic adenoma: previously unrecognized pattern unveiled using PAX2 and PAX8 immunohistochemistry

Nephrogenic adenoma is a benign lesion of the urinary tract, particularly the urinary bladder. It is a gross and microscopic mimicker of urothelial neoplasm or metastatic carcinoma. Several histological patterns (tubular, tubulocystic, polypoid, papillary, fibromyxoid) have been recognized, but a flat pattern has not been described. Histologically, nephrogenic adenoma consists of tubules, cysts or papillae lined by flat to polygonal cells with frequent hobnail appearance. The stroma is often edematous or has a granulation tissue-like appearance with acute or chronic inflammation. By immunohistochemistry, nephrogenic adenomas are positive for renal epithelial markers CK7, CD10 and alpha-methylacyl-coenzyme A racemase, and negative for bladder urothelium or prostate markers. Recent studies have shown that nephrogenic adenomas are positive for PAX2 and PAX8. We encountered an interesting case of tubular nephrogenic adenoma with adjacent areas suspicious of flat urothelial atypia. Immunohistochemistry for PAX2 and PAX8 were positive in these areas, unveiling a flat pattern of nephrogenic adenoma. This case prompted us to study 15 cases of nephrogenic adenoma to determine additional instances of flat pattern and to assess the value of PAX2 and PAX8 immunoreactivity to diagnose nephrogenic adenoma. PAX2 and PAX8 immunostaining was positive in 14/15 and 15/15 cases, respectively. The flat pattern was present at least focally adjacent to tubular, polypoid and papillary areas, in 8/15 cases of nephrogenic adenoma. In conclusion, the flat pattern is a common finding in nephrogenic adenomas, but easily under recognized by morphologic examination and may be confused with flat urothelial lesions with atypia. Immunostains for PAX2 and PAX8 are useful in the detection of nephrogenic adenomas and particularly unveil those nephrogenic adenomas with flat pattern.

The progression of nephrogenic metaplasia of the urinary bladder to clear cell adenocarcinoma: a case report

Nephrogenic metaplasia (or nephrogenic adenoma) and clear cell adenocarcinoma of the bladder are uncommon lesions that cause diagnostic dilemmas for pathologists due to their similar morphologic features. Nephrogenic metaplasia describes a lesion in the lower urinary tract that is composed of small tubules resembling renal medullary tubules. It has been suggested that nephrogenic metaplasia may progress to clear cell adenocarcinoma but this possibility is not widely accepted. We present a case of clear cell adenocarcinoma of the bladder arising from nephrogenic metaplasia and discuss the evidence behind the association of these two distinct rare lesions.

The spectrum of morphology in non-neoplastic prostate including cancer mimics

The spectrum of morphology in non-neoplastic prostate includes lesions of prostatic epithelial origin, the most common being atrophy, including partial atrophy, adenosis (atypical adenomatous hyperplasia), basal cell hyperplasia and crowded benign glands, as well as those of non-prostatic origin, such as seminal vesicle epithelium. These lesions often mimic lower-grade prostatic adenocarcinoma whereas others, such as granulomatous prostatitis, for example, are in the differential diagnosis of adenocarcinoma, Gleason grades 4 or 5. Diagnostic awareness of the salient histomorphological and relevant immunohistochemical features of these prostatic pseudoneoplasms is critical to avoid rendering false positive diagnoses of malignancy.

Recurrent nephrogenic adenoma in bladder diverticulum: Case report and literature review

Nephrogenic adenoma is an uncommon benign lesion of the urinary tract induced by chronic irritation of the vesical mucosa, due to infection, trauma, surgery, calculi, foreign bodies and chemical agents. A 68-year-old male was admitted to our linic for a periodical cystoscopic evaluation as part of a follow-up initiated due to a past transitional cell carcinoma. The scheduled cystoscopy revealed, within a bladder diverticulum, an unexpected and completely asymptomatic nephrogenic adenoma that we removed by transurethral resection. We followed up the patient at 24 months, then later we made the diagnosis of nephrogenic adenoma. During this time, the patient experienced three relapses within the same diverticulum, always involving a nephrogenic adenoma we persistently treated by transurethral resections. As the nephrogenic adenoma is considered a benign lesion without any direct evidence of a possible evolution to an overt cancer, we successful attempted a half-yearly cystoscopic follow-up to control the growth of a highly recurrent benign entity, interposing between controls a periodical imaging. This paper represents the second report of a nephrogenic adenoma within a bladder diverticulum, but the first case of a nephrogenic adenoma highly recurrent within the same diverticulum and managed conservatively by regular transurethral resection scheduled over the time.

Nephrogenic Adenoma of the Urinary Tract

Nephrogenic adenoma (NA) is an uncommon and intriguing lesion in the urinary tract. The pathogenesis of NA is not entirely clear. NA was considered to be a metaplastic process of the urothelium in response to chronic irritation of the urinary tract. However, recent evidence has shown that NA is not a metaplastic lesion but rather a proliferation of exfoliated and implanted renal epithelial cells in the urinary tract. Histologically, NAs exhibit, singly or in combination, tubules, small papillae, and microcystic structures lined by cells with little cytological atypia and focal hobnail changes. Solid formations and compressed spindled cells within a fibromyxoid background are rarely observed. Differential diagnosis includes, but is not limited to, malignant neoplasms occurring at the same sites, in particular urothelial carcinoma with deceptively bland morphology (with small tubules, microcystic and nested variants), prostatic adenocarcinoma, and clear cell adenocarcinoma. Immunohistochemical studies with antibodies targeting members of the paired box gene family (PAX2 and/or PAX8) in NAs may be helpful in the differential diagnosis of urothelial lesions and prostatic adenocarcinoma. NAs are most likely to be confused with clear cell adenocarcinoma, especially in small biopsy specimens. This is confounded by both lesions being frequently positive for PAX2, PAX8, and CK7 and not infrequently positive for p504S (α-methylacyl-CoA-racemase, AMACR) by immunohistochemistry. Recognition of its characteristic morphological patterns and awareness of its unusual architectural and cytological features are important in making the diagnosis of NA and distinguishing this lesion from its mimickers.

Hepatocyte nuclear factor-1β expression in clear cell adenocarcinomas of the bladder and urethra: diagnostic utility and implications for histogenesis

The histogenesis of clear cell adenocarcinoma of the bladder/urethra is uncertain. Hepatocyte nuclear factor-1β is a homeodomain protein that has been reported to be frequently overexpressed in ovarian clear cell adenocarcinoma in comparison with rare or no expression in other types of epithelial ovarian tumors. We assessed the expression of hepatocyte nuclear factor-1β in a series of 18 clear cell adenocarcinomas of the bladder and urethra and compared it with that of invasive high-grade transitional/urothelial carcinoma (n = 35); adenocarcinomas of the bladder, urethra, and paraurethral glands (n = 21); as well as nephrogenic adenomas of the bladder (n = 8). Staining intensity and extent were evaluated using a 4-tiered grading system (0-3). A case was considered positive for hepatocyte nuclear factor-1β if 10% or more of tumor cells showed at least weak nuclear staining or if any moderate or strong nuclear staining was observed. All 18 clear cell adenocarcinomas exhibited nuclear staining in at least 50% of tumor cells (16 strong, 1 moderate, and 1 weak with focal strong nuclear staining) in comparison with positive nuclear staining (moderate) in 1 of 21 bladder adenocarcinoma, 1 of 35 invasive high-grade transitional/urothelial carcinoma (weak to moderate staining), and 2 of 8 nephrogenic adenomas (1 weak and 1 moderate to strong staining). We concluded that hepatocyte nuclear factor-1β is a useful marker in differentiating clear cell adenocarcinomas of the bladder/urethra from invasive high-grade transitional/urothelial carcinoma and other types of bladder adenocarcinomas and to a lesser extent from nephrogenic adenomas. Hepatocyte nuclear factor-1β is of no diagnostic utility in discriminating primary bladder/urethral clear cell adenocarcinomas from metastatic clear cell adenocarcinomas of the female genital tract to the bladder/urethra. From a histogenesis standpoint, although the expression of hepatocyte nuclear factor-1β in both gynecologic and urologic tract clear cell adenocarcinomas may point to a Müllerian derivation/differentiation, this immunohistochemical evidence is insufficient to completely exclude an urothelial association.

Clear cell adenocarcinoma of the bladder and urethra: cases diffusely mimicking nephrogenic adenoma

Although clear cell adenocarcinoma have been described focally mimicking nephrogenic adenoma, we have identified a subset of clear cell adenocarcinoma that diffusely resembles nephrogenic adenoma (nephrogenic adenoma-like clear cell adenocarcinoma). Twelve classic clear cell adenocarcinomas of the bladder and urethra and 7 nephrogenic adenoma-like clear cell adenocarcinomas were compared to 10 nephrogenic adenomas. Classic clear cell adenocarcinomas and nephrogenic adenoma-like clear cell adenocarcinomas comprised 4 men and 15 women. The following features were seen in classic clear cell adenocarcinomas: nephrogenic adenoma-like clear cell adenocarcinomas: predominantly solid pattern (7/12:0/7), marked nuclear pleomorphism (7/12:1/7), prominent nucleoli (5/12:1/7), clear cytoplasm in 50% or greater of tumor (7/12:0/7), and necrosis (8/12:3/7), although the necrosis in nephrogenic adenoma-like clear cell adenocarcinomas was often focal and intraluminal. Both patterns of clear cell adenocarcinomas showed prominent hobnail features, although more pronounced in nephrogenic adenoma-like clear cell adenocarcinomas. Muscularis propria invasion was seen in 5 of 9 classic clear cell adenocarcinomas and 6 of 6 nephrogenic adenoma-like clear cell adenocarcinomas, where evaluable. Classic clear cell adenocarcinoma was associated with urothelial carcinoma (n = 2) and endometriosis (n = 1). The Ki-67 rate in clear cell adenocarcinomas ranged from 10% to 80% compared with 0% to 5% in nephrogenic adenoma. The following antibodies were not helpful in distinguishing nephrogenic adenoma-like clear cell adenocarcinoma from nephrogenic adenoma: CD10, estrogen receptor, p63, high-molecular-weight cytokeratin, and alpha-methylacyl coenzyme-A racemase. PAX2 expression was more frequent in nephrogenic adenoma (89%) compared to both patterns of clear cell adenocarcinoma (29%-32%). The key features discriminating between nephrogenic adenoma-like clear cell adenocarcinoma and nephrogenic adenoma include occasional clear cells, more prominent pleomorphism especially hyperchromatic enlarged nuclei, and extensive muscular invasion. Presence of mitoses and a high rate of Ki-67 expression in lesions resembling nephrogenic adenoma require clinical correlation, close follow-up, and repeat biopsy with more extensive sampling.

Tumor-like lesions of the urinary bladder

Tumor-like lesions of the urinary bladder are reviewed emphasizing those that are most diagnostically challenging for the pathologist and may result in serious errors in patient care if misinterpreted. The first category considered, pseudocarcinomatous proliferations, represents an area of bladder pathology only recently appreciated as being particularly treacherous because of the extent to which irregular islands of benign epithelial cells may seemingly penetrate the lamina propria and cause confusion with carcinoma. Somewhat orderly proliferations of this type have been known for years, von Brunn's nests, and are rarely a challenge for the experienced, but proliferations of an irregular nature such as may be seen most often as a result of prior radiation therapy, but sometimes due to chemotherapy or even ischemia, represent a challenging interpretation. The clinical history may be very important in arriving at the correct diagnosis as is the appreciation that the morphology, although architecturally problematic, is different from that of any of the familiar patterns of invasive carcinoma. Florid epithelial proliferations in fibroepithelial polyps are also briefly noted. Within the category of glandular proliferations, emphasis is placed on the wide spectrum of morphology of nephrogenic adenoma including its pseudoinfiltrative pattern and occasional propensity for tiny tubules to be misconstrued as signet-ring cells. The spectrum of müllerian glandular lesions including the relatively recently described mucinous variant, endocervicosis, is reviewed. The reactive papillary proliferation, papillary-polypoid cystitis, is then discussed. This entity has long been known but has recently been re-emphasized. Other non-neoplastic papillary lesions include florid papillary forms of nephrogenic adenoma. The past 25 years has seen a great expansion of knowledge concerning non-neoplastic spindle cell proliferations, including those related to a prior procedure, the postoperative spindle cell nodule and those without such a history, variously designated inflammatory pseudotumor, pseudosarcomatous myofibroblastic proliferation, or even other terms. The morphologic spectrum is explored and it is recommended that the two categories be retained.

Benign Diseases of the Bladder

Benign diseases of the bladder often present diagnostic challenges to practicing pathologists due to their diverse nature and ability to mimic a variety of epithelial or mesenchymal neoplasms. Categories of benign bladder disease include infectious cystitis, noninfectious cystitis, reactive proliferative processes, and benign processes that secondarily involve the bladder. An understanding of the key clinical and morphologic features of these lesions and the useful ancillary techniques specific for these entities is critical to the correct diagnosis of these lesions. This article reviews the key features of these benign bladder diseases and highlights methods to distinguish these lesions from other benign and malignant processes involving the bladder.

Urothelial Carcinoma and its Variants

Bladder cancer is the ninth most common cancer worldwide, and the most common malignancy affecting the urinary tract, with approximately 330,000 new cases and more than 130,000 deaths per year. Bladder cancer is primarily attributable to smoking, which accounts for 65% of male and 30% of female cases in some developed countries. Other major risk factors include analgesic abuse, some types of chemotherapy, occupational exposure to chemicals, and in Egypt and some Asian regions, endemic infection with Schistosoma haematobium. Approximately 90% of bladder tumors are classified as urothelial carcinoma (UC), also referred to as transitional cell carcinoma (TCC), and are believed to originate from transformation of the normal urothelium. UCs often exhibit elements of squamous or glandular differentiation. The spectrum of microscopic forms of urothelial carcinoma has been expanded recently to include several histologic variants, the recognition of which is important to avoid diagnostic misinterpretation, to predict outcome, and to guide the selection of the most appropriate therapeutic approach. This article reviews characteristic pathologic features and key clinical aspects of UC and its most common variants.

Divergent differentiation in urothelial carcinoma and other bladder cancer subtypes with selected mimics

Conventional urothelial carcinoma accounts for most carcinomas of the urinary tract lining. However, neoplastic urothelium has the capacity to demonstrate enormous plasticity. A variety of unusual architectural patterns of urothelial carcinoma, such as the nested, microcystic and inverted variants, can be mistaken for reactive processes or benign tumours. Others such as the micropapillary, plasmacytoid and discohesive variants, can mimic metastatic tumour from other sites. The micropapillary variant in particular is more aggressive. In addition, urothelial carcinoma has a propensity to demonstrate divergent differentiation with glandular, squamous, small cell neuroendocrine, lymphoepithelioma-like, sarcomatoid or other elements. Pure squamous carcinoma or adenocarcinoma (the latter in particular) can be difficult to distinguish from contiguous or metastatic spread. Some variants have prognostic and potential therapeutic implications. Molecular genetic evidence has emerged recently supporting a close relationship between urothelial carcinoma and various divergent elements. Sarcomatoid carcinoma and its differential diagnosis with other spindle cell lesions of urinary tract will be covered in a separate review.

Clear cell adenocarcinoma of urinary bladder and urethra: another urinary tract lesion immunoreactive for P504S

CONTEXT

Clear cell carcinoma of the urinary bladder/ urethra is a rare tumor histologically resembling the neoplasms in the female genital tract. Adequate characterization of this tumor has been hampered by its rarity. alpha-Methylacyl-CoA racemase (AMACR)/P504S has been reported to be positive in prostatic adenocarcinoma, papillary renal cell carcinoma, and gastrointestinal neoplasmas; however, it has never been studied in clear cell carcinoma of the lower urinary tract.

OBJECTIVE

To investigate the immunohistochemical staining profile in 4 primary clear cell carcinomas of the urinary tract, including P504S, which has not been previously evaluated in these tumors.

DESIGN

Four cases of clear cell adenocarcinoma were retrieved from our archives: 2 cases from the urinary bladder (one each from a man and a woman) and 2 cases from the urethra (both from women, 1 in a diverticulum). Immunohistochemistry performed on the cases were P504S, K903, cytokeratin (CK) 7, CK20, CA 125, and p63.

RESULTS

We found that clear cell carcinomas had a distinct immunoreactive profile: strongly positive for P504S, K903, and CK7, and negative for p63. Two cases were also positive for CA 125 and CK20.

CONCLUSION

The immunohistochemical profile of clear cell carcinomas shares some similarity to conventional urothelial carcinoma; however, it deviates from those tumors in being positive for P504S and negative for p63. This staining profile may suggest a nonurothelial origin for these tumors, may serve as a useful tool in the differential diagnosis of this tumor, and may reflect its etiology. Because similar expression of P504S is also seen in nephrogenic adenomas, this marker should not be used to differentiate nephrogenic adenomas from clear cell adenocarcinomas.

Expression of PAX8 in nephrogenic adenoma and clear cell adenocarcinoma of the lower urinary tract: evidence of related histogenesis?

Recent evidence has showed that nephrogenic adenoma is a true "nephrogenic" lesion derived from the proliferation of exfoliated and implanted renal tubular cells in the urinary tract, a process that closely resembles the formation of endometriosis. This new concept has led to the identification of renal transcription factor PAX2 as a diagnostic marker for nephrogenic adenoma. PAX8 is another transcription factor structurally and functionally related to PAX2. Both are cell lineage restricted transcription factors expressed in normal and neoplastic tissues of related origin, including renal tubular cells in both fetal and adult kidneys. In this study, we investigated the expression of PAX8 in nephrogenic adenoma and its mimics. We report here that PAX8 was detected in all nephrogenic adenomas (N=35) and clear cell adenocarcinoma of the lower urinary tract (N=7), but not in prostate adenocarcinoma (N=100), adenocarcinoma (N=9), squamous cell carcinoma (N=5), or urothelial carcinoma (N=48) of the urinary bladder and its variants. PAX8 was neither detected in normal urothelium of the urinary bladder nor in prostate glands and stroma. PAX2 was also detected in 2 of the 7 clear cell adenocarcinomas of the lower urinary tract. We suggest that PAX8 is an additional marker for identifying nephrogenic adenoma. Expression of PAX8 or PAX2 in both nephrogenic adenoma and clear cell adenocarcinoma of the lower urinary tract may indicate a possible related tissue origin for these 2 lesions; both may be derived from proliferating renal tubular cells in the urinary tract. In addition, detection of PAX8 or PAX2 in clear cell adenocarcinoma of the lower urinary tract is helpful in differentiating it from urothelial carcinoma and its variants and adenocarcinomas of the urinary bladder or of the prostate.

Recurrent nephrogenic adenoma in a 10-year-old boy with prune belly syndrome : a case presentation

Nephrogenic adenoma is a rare benign lesion of the urinary tract that is associated with a history of irritation or injury of the urothelium. Predisposing factors include infection, calculi, surgery, trauma, and renal transplantation. Nephrogenic adenoma commonly presents with lower urinary tract symptoms or hematuria. We present the case of recurrent nephrogenic adenoma in a 10-year-old boy with a history of prune belly syndrome and discuss management of this disease in the pediatric population. To our knowledge this represents the first reported case of recurrent nephrogenic adenoma associated with prune belly syndrome.

Nephrogenic adenoma: an update on an innocuous but troublesome entity

Nephrogenic adenoma (NA) is a rare benign lesion of the urothelial tract that is typically preceded by some form of genitourinary insult. The pathogenesis of NA is not entirely clear. Although generally presumed to be a metaplastic process of the urothelium, recent evidence suggests that NA may in fact be derived from detached renal tubular cells implanting along the urothelial tract in previously injured areas, at least in cases associated with a kidney transplant. On light microscopy, NA shows a variety of patterns, including tubulocystic, papillary, and much less frequently solid, that often coexist. Recognition of its characteristic patterns, and awareness of its unusual architectural and cytologic features, is key to making the diagnosis of NA and distinguishing this lesion from malignant neoplasms occurring at the same sites, in particular, clear cell carcinoma, nested or microcystic variants of urothelial carcinoma and prostatic adenocarcinoma. Although straightforward in most cases, the correct diagnosis may be difficult to make on limited tissue samples. A number of immunohistochemical markers have been studied in an attempt to characterize NA; however, to date there is no specific immunohistochemical profile to distinguish this lesion from its malignant mimickers, although PAX2, a new marker, may prove to be helpful in this regard. Clinicopathologic correlation with careful attention to morphology remains the pillar in establishing the correct diagnosis.

PAX2: a reliable marker for nephrogenic adenoma

Nephrogenic adenoma is a rare lesion of the urinary tract. The diagnosis usually is straightforward when characteristic microscopic and clinical findings are present, and the entity is familiar. However, misdiagnosis, in particular of adenocarcinoma of the prostate gland, may occur. Immunohistochemical stains often are needed to make such a distinction, but currently available markers offered only partial help. It recently was demonstrated that nephrogenic adenoma in renal transplant patients originated from the renal tubular epithelium. This newly proved, but long sought information may be helpful in the differential diagnosis of nephrogenic adenoma. In this study, we investigated the expression of a renal transcription factor, PAX2, in 39 nonrenal transplant-related nephrogenic adenomas, 100 adenocarcinomas of the prostate gland, and 47 urothelial carcinomas of the urinary tract. A strong and distinct nuclear staining of PAX2 was found in all 39 cases of nephrogenic adenoma (100%), but not in normal prostate tissue, normal urothelium, adenocarcinomas of the prostate gland, and invasive urothelial carcinomas. Focal CD10 was detected in six of 13 nephrogenic adenomas in the superficial papillary component and in normal prostate epithelium, normal urothelium, lymphocytes, adenocarcinoma of the prostate gland, and urothelial carcinoma. There was no uroplakins detected in nephrogenic adenoma. Therefore, these findings are suggesting that nephrogenic adenoma in nonrenal transplant patients may also arise from the renal epithelium, as did the comparable lesions after transplantation. PAX2 is a specific and sensitive immunohistochemical marker in identification and differential diagnosis of nephrogenic adenoma.

Molecular evidence for progression of nephrogenic metaplasia of the urinary bladder to clear cell adenocarcinoma

Nephrogenic metaplasia or nephrogenic adenoma of the urinary tract may present a diagnostic challenge in surgical pathology practice. Previous case reports suggest the possibility of nephrogenic metaplasia progressing to clear cell adenocarcinoma, but a malignant potential of nephrogenic metaplasia is generally not acknowledged. A case of a 70-year-old female patient with multiple recurrences of nephrogenic metaplasia of the urinary bladder and subsequent development of clear cell adenocarcinoma is described. Immunohistochemical studies help to differentiate the 2 entities. Results of molecular studies, particularly comparative genomic hybridization analysis, suggest clonal evolution of nephrogenic metaplasia to clear cell adenocarcinoma in this case.

Nephrogenic Adenoma of the Urinary Bladder

INTRODUCTION

The nephrogenic adenoma (NA) is a benign metaplastic lesion of the urothelium and is attributed to chronic irritation of the mucosa, by injury, infection, stone disease or intravesical instrumentations. We present our experience on this morbid entity, its clinical appearance in the urinary bladder, its frequency and relapses. Furthermore we reviewed the related recent literature and focused on its potential to neoplastic degeneration and the value of the new diagnostic modalities.

PATIENTS AND METHODS

Four patients with NA of the urinary bladder are presented. The papilloid or polypoid formations observed by the cystoscopy were identified after the TUR, as NA of the urinary bladder. Their mean follow-up was 3.5 years.

RESULTS

Remission of the symptoms was observed after TUR in all patients. Three out of four patients presented 1-7 relapses, while in one case, after seven NA relapses, a urothelial carcinoma of the bladder was diagnosed.

CONCLUSIONS

Unlike histological features, the clinical - endoscopic characteristics of NA are non-specific. Even if it is not definitely considered like a premalignant condition, NA has to be followed up frequently and long lasting, because of its high recurrence rate. The combination of Cytology, Flow cytometry, DNA image analysis and Fluorescence in situ hybridization of bladder washings or voided urine, are of high value in monitoring NA of the urothelium.

Nephrogenic adenoma of the urinary bladder

INTRODUCTION

The nephrogenic adenoma (NA) is a benign metaplastic lesion of the urothelium and is attributed to chronic irritation of the mucosa, by injury, infection, stone disease or intravesical instrumentations. We present our experience on this morbid entity, its clinical appearance in the urinary bladder, its frequency and relapses. Furthermore we reviewed the related recent literature and focused on its potential to neoplastic degeneration and the value of the new diagnostic modalities.

PATIENTS AND METHODS

Four patients with NA of the urinary bladder are presented. The papilloid or polypoid formations observed by the cystoscopy were identified after the TUR, as NA of the urinary bladder. Their mean follow-up was 3.5 years.

RESULTS

Remission of the symptoms was observed after TUR in all patients. Three out of four patients presented 1-7 relapses, while in one case, after seven NA relapses, a urothelial carcinoma of the bladder was diagnosed.

CONCLUSIONS

Unlike histological features, the clinical--endoscopic characteristics of NA are non-specific. Even if it is not definitely considered like a premalignant condition, NA has to be followed up frequently and long lasting, because of its high recurrence rate. The combination of Cytology, Flow cytometry, DNA image analysis and Fluorescence in situ hybridisation of bladder washings or voided urine, are of high value in monitoring NA of the urothelium.

Expression of alpha-methylacyl-coenzyme A racemase in nephrogenic adenoma

Nephrogenic adenoma is a benign lesion composed of small glandular structures that develops along the urothelium with uncertain pathogenesis. Some investigators believe that nephrogenic adenoma develops by a metaplastic process in response to injury to the urothelium, while others believe that it arises from detached renal tubules. Nephrogenic adenoma may be present in the prostatic urethra and morphologically mimic prostatic adenocarcinoma. Alpha-methylacyl-coenzyme A racemase (AMACR), a recently identified prostate cancer marker, is typically negative in normal urothelium and prostatic glands, and positive in distal convoluted renal tubules in addition to prostatic adenocarcinomas. Therefore, evaluation of AMACR expression in nephrogenic adenoma will have significance in the pathologic diagnosis and in understanding pathogenesis of this lesion. We studied 38 nephrogenic adenomas by clinical, histologic, and immunohistochemical analyses for AMACR (P504S) and high molecular weight cytokeratin (34betaE12). Twenty-two of 38 nephrogenic adenomas (58%) demonstrated strong cytoplasmic positivity for AMACR, ranging from patchy, focal to diffuse staining. In addition, 16 of 26 (62%) nephrogenic adenomas were negative for 34betaE12. To our knowledge, this is one of the first report of a completely benign lesion, which can be found in the prostate, showing strong AMACR immunoreactivity. Our findings suggest using caution when interpreting positive AMACR immunostaining in prostatic specimens. These findings could be explained by possible renal tubular origin or renal differentiation, at least in a subset, of nephrogenic adenomas.

Expression of α-Methylacyl-CoA Racemase (P504S) in Nephrogenic Adenoma: A Significant Immunohistochemical Pitfall Compounding the Differential Diagnosis With Prostatic Adenocarcinoma

Alpha-Methylacyl-CoA racemase (AMACR, P504S) has recently been shown to be a useful marker for the diagnosis of prostatic adenocarcinoma and a potential aid in its distinction from its many mimics, one of which is the benign lesion, nephrogenic adenoma (NA). The goal of this study was to assess the expression of AMACR in NA by immunohistochemistry, as well as other potentially useful markers, high-molecular-weight cytokeratin clone 34betaE12, p63, and prostate-specific antigen (PSA). AMACR was expressed in 4/4 NAs involving the prostatic urethra and underlying stroma, and in 3/16 NAs involving the bladder. The prostatic cases showed circumferential granular cytoplasmic AMACR expression of at least moderate intensity, in >75% of tubules in 3 cases and in <10% of tubules in the remaining case. The AMACR-positive cases in the bladder typically showed focal weak noncircumferential staining of the tubules and stronger staining of the cells lining the papillae. 34betaE12 staining was observed in 1/4 prostatic NAs and 4/16 bladder NAs, typically in a cytoplasmic pattern in a minority of cells. p63 and PSA were negative in all cases. Our data indicate that NA of the prostatic urethra commonly expresses AMACR and lacks basal cell-specific markers, making it not only a potential morphologic mimic of prostatic adenocarcinoma but also a significant immunohistochemical mimic as well. Awareness of NA as a significant pitfall in the diagnosis of prostatic adenocarcinoma and careful examination of hematoxylin and eosin-stained sections remains the key to the correct diagnosis, which can be supported by a negative PSA stain.

Lésions bénignes diverses de la vessie et de la voie excréto urinaire

Miscellaneous benign lesions of the bladder are composed of morphologic aspects of the urothelial mucosa. They are epithelial lesions (von Brunn nests, glandularis cystitis, nephrogenic adenoma, polypoid cystitis and epidermoid metaplasia), myofibroblastic proliferations and heterotopias (endometriosis, endocervicosis, endosalpingiosis and ectopic prostatic tissue). Etiology, morphologic aspects and differential diagnosis are discussed.

Microcystic transitional cell carcinoma: a report of 2 cases arising in the renal pelvis

Microcystic transitional cell carcinoma is a rare variant of urothelial carcinoma; to date, it has been described only in the urinary bladder. We report 2 cases of microcystic transitional cell carcinoma arising in the renal pelvis. The first case occurred in a 73-year-old man with a history of superficially invasive transitional cell carcinoma who presented with macroscopic hematuria and anemia. The second case occurred in a 62-year-old woman who had no relevant medical history and presented with hematuria. Computed tomographic scan revealed a tumor of the renal pelvis. In both cases, microscopic examination showed invasive transitional cell carcinoma with prominent cystic features. The cysts were irregular in size and were deeply infiltrative. The cysts were lined by single or multiple layers of cuboidal or flattened cells with minimal cytological atypia. The first patient died of his disease 18 months after presentation. The second patient remained well at her 6-month follow-up examination. Microcystic transitional cell carcinoma is an unusual, deceptively bland variant of urothelial carcinoma, which can mimic benign lesions.

Clear cell carcinoma of the urinary bladder: a report and comparison of four tumors of mullerian origin and nine of probable urothelial origin with discussion of histogenesis and diagnostic problems

Carcinomas of the bladder that resemble clear cell carcinoma of mullerian type are rare. Whether such neoplasms 1) arise from mullerian elements in the bladder and are histogenetically identical to the female genital tract cancer, 2) are a peculiar variant of vesical adenocarcinoma of nonmullerian derivation, or 3) represent a peculiar morphologic expression of transitional cell (urothelial) carcinoma with gland differentiation is often uncertain. We reviewed the clinical, conventional pathologic, and immunohistochemical features of 13 neoplasms with exclusive, or predominant, morphologic features of clear cell carcinoma. The 11 female and two male patients were 22-83 (mean 57) years of age. The clinical and gross features had no unique aspects. On microscopic examination the most common pattern, present in all cases, was tubulocystic, with a papillary pattern, present in six tumors and a predominant solid growth in one. Cells with abundant clear cytoplasm were conspicuous in nine tumors and hobnail cells were seen in eight. Four tumors showed focally recognizable patterns of transitional cell (urothelial) carcinoma in the available material. In five other tumors pseudostratified epithelium reminiscent of transitional epithelium was present focally. Endometriosis was present in two cases. In two other cases benign cysts focally lined by ciliated epithelium and surrounded by elastosis were interpreted as most likely mullerian. Immunohistochemistry was performed in 10 cases. All tumors stained for CA 125 (usually strong, ranging from focal to diffuse) and nine tumors stained for CK7 (usually strong and diffuse). CK20 was focally and weakly positive in four tumors and extensively positive in another. The same immunohistochemical panel was performed on 10 typical transitional cell carcinomas, 4 transitional cell carcinomas with gland differentiation, not otherwise specified, and 5 pure adenocarcinomas of the bladder (one of urachal origin). Minimal CA 125 positivity was seen in two transitional cell carcinomas. CA 125 staining was seen in the areas of gland differentiation in three of four transitional cell carcinomas and three of five pure adenocarcinomas but was focal in most cases. All transitional cell carcinomas and transitional cell carcinomas with gland differentiation showed extensive CK7 positivity. In contrast, only one of four positive pure adenocarcinomas showed >5% CK7-positive cells. Although all groups showed CK20 positivity, the percentage of CK20 positive cells was higher in pure adenocarcinomas. Prostate specific antigen was negative in all tumors. The cytokeratin immunoprofile of clear cell carcinomas of the bladder is closer to transitional cell carcinomas and transitional cell carcinomas with gland differentiation than pure adenocarcinomas arguing against an unusual form of adenocarcinoma. Our finding of CA 125 expression in bladder tumors of apparent urothelial origin contrasts with some studies that have regarded CA 125 expression as evidence for a mullerian origin. The frequency of gland differentiation in transitional cell carcinomas and the rarity of vesical endometriosis could be taken to suggest that these tumors are mostly of urothelial derivation, but the strong female preponderance in our series argues for a mullerian origin in at least some cases, and this is almost certain in the four cases with benign mullerian components. In the absence of endometriosis or conventional foci of transitional cell carcinoma, it may be impossible to determine whether a tumor with the morphology of clear cell carcinoma is of mullerian or transitional (urothelial) cell lineage, and at this time immunochemistry does not solve this problem.

Nephrogenic adenoma of the prostatic urethra: a mimicker of prostate adenocarcinoma

Nephrogenic adenoma, thought to be a benign metaplastic response of the urothelium to injury, can rarely affect the prostatic urethra. Extension of small tubules of nephrogenic adenoma into the underlying prostatic fibromuscular stroma can lead to the misdiagnosis of prostatic adenocarcinoma in transurethral resection specimens and prostate biopsies. We reviewed 26 cases of nephrogenic adenoma involving the prostatic urethra, seen at The Johns Hopkins Hospital from 1990 to 1998, to evaluate the histologic features, which may better define this lesion. Immunohistochemical results were evaluated for cases where the lesion was present on deeper sections. Histologic patterns included the following: tubules in 96% (25 of 26), structures resembling vessels in 73% (19 of 26), cords and individual cells in 46% (12 of 26), papillary configurations in 19% (5 of 26), and signet ring cell-like tubules in 12% (3 of 26). Other features of nephrogenic adenoma, such as thyroidization, were identified in 38% (10 of 26), and peritubular sheaths were seen in 65% (17 of 26) of cases. Nucleoli were prominent in 54% (14 of 26), and no case had mitoses. In the region of nephrogenic adenoma, urothelium was noted in 69% (18 of 26); in 61% (11 of 18) it showed cuboidal metaplasia and 28% (5 of 18) showed squamous metaplasia. Extension of nephrogenic adenoma into muscle was observed in 77% (20 of 26) of cases, 75% (15 of 20) of which had identifiable urothelium overlying the lesion. Blue-tinged mucinous secretions were observed in 32% (8 of 25) of cases. Inflammation was found in all but one case. Nephrogenic adenomas were diffusely positive for 34betaE12 in 11% (1 of 9) of cases, focally positive in 44% (4 of 9), and negative in 44% (4 of 9). In 100% (9 of 9), cytokeratin 7 stains were positive. Focal prostate specific antigen and PSAP positivity were seen in 36% (4 of 11) and 50% (5 of 10) of nephrogenic adenoma cases, respectively. In conclusion, nephrogenic adenoma of the prostatic urethra can mimic prostate cancer because of: 1) the presence of tubules, cords, and signet ring-like tubules; 2) prominent nucleoli; 3) muscle involvement; 4) blue-tinged mucinous secretions; 5) focal prostate specific antigen and PSAP positivity; and 6) negative staining in some cases for 34betaE12. Features useful in the diagnosis of nephrogenic adenoma include the following: 1) distinctive nephrogenic patterns, such as papillary and "vascular," 2) adjacent urothelium, 3) thyroidization, 4) peritubular sheaths, 5) associated inflammation, and 6) positivity for cytokeratin 7 and, in some cases, 34betaE12.