Introduction
The transformation of the lesion into a clear-cell adenocarcinoma may or may not happen, as there is no theory confirming the same. In this lesion, the lower urinary tract comprises small tubules resembling renal medullary tubules. This is speculation that it transforms into clear-cell adenocarcinoma. The incidence of nephrogenic metaplasia converting into adenocarcinoma is very rare. The upper urinary tract consists of kidneys and ureters, and the lower urinary tract consists of the bladder and the urethra. Histologically, it is tough to differentiate between nephrogenic metaplasia and clear-cell adenocarcinoma. Abnormal cells may occur in nephrogenic metaplasia cytologically. Nephrogenic metaplasia can be small and is frequently found alone or apart from other cells. Nephrogenic metaplasia has the distinct characteristic of being tiny and being differentiated from other cells.
What Is Nephrogenic Metaplasia?
Nephrogenic metaplasia can be stated as a lesion that may transform into clear-cell adenocarcinoma and is found in the lower urinary tract, consisting of small tubules resembling renal medullary tubules. It affects the urinary bladder, urethra, ureter, and renal pelvis in descending order. It is also converted into atypical nephrogenic metaplasia when it is left untreated. It is a rare, benign type of tumor. Davis first described nephrogenic adenoma/metaplasia. Friedman and Kuhlenbeck introduced the terminology of nephrogenic adenoma/metaplasia.
What Is Metaplasia?
Metaplasia is a reversible change of cells into a form that does not normally occur in the tissue in which it is found. It is generally triggered by stimuli from the environment and may act in correlation with the harmful effects of inflammation. Metaplasia is a benign condition; however, if left untreated, the cells that undergo metaplasia undergo dysplastic changes, eventually leading to cancer. Epithelial cells are affected by metaplasia.
What Are the Types of Metaplasia?
Intestinal and squamous metaplasia are the two types of metaplasia. Nephrogenic metaplasia looks like a subtype of squamous metaplasia.
What Are the Alternative Names for Nephrogenic Metaplasia?
The alternative names for nephrogenic metaplasia are nephrogenic adenoma, mesonephric adenoma/metaplasia, adenomatoid tumor, or adenomatoid metaplasia.
What Happens in Nephrogenic Metaplasia?
Nephrogenic metaplasia is marked by a circumscribed proliferation of tubules, cysts, and papillae lined or covered by cells with enlarged hyperchromatic nuclei and prominent nucleoli.
It is a metaplastic process of the urethra, ureters, and bladder. However, it is more commonly found in the urinary bladder, neck, and urethra. The tubules are circumscribed, surrounded by prominent basement membranes, and often contain eosinophilic or basophilic secretions.
What Does Nephrogenic Metaplasia Represent?
Most likely, it represents a host response to local traumatic irritation, such as a surgical or cystoscopic procedure, chronic infection, calculi, prolonged catheterization, intravesical therapy, or renal transplantation. In a few studies, it was indicated that nephrogenic metaplasia had the same alterations as urothelial cancer. Histologically, papillary or cryptic structures are seen, which consist of hollow tubules, the same as mesonephric tubules, where a bland cuboidal or hobnail’s single layer is seen and is surrounded by basophilic and eosinophilic secretions.
Who Is Affected by Nephrogenic Metaplasia?
Nephrogenic metaplasia affects the male population more than the female population, with a ratio of 2:1. An age range of 4 to 81 years is observed. It is more common in adults but affects ten percent of children. Patients with immunosuppression may be affected by it.
What Factors Lead To Nephrogenic Metaplasia?
Smoking, trauma, and viral infection are a few of the multiple causes which lead to nephrogenic metaplasia. Smoking should be strictly prohibited to avoid the probability of nephrogenic metaplasia. Immunosuppression or organ transplant may also give birth to the condition. Irritative bladder symptoms, urinary frequency, and urgency can also be symptoms of it.
What Are the Suggestive Symptoms of It?
Hematuria, dysuria, or urgency are some non-specific suggestive symptoms of nephrogenic metaplasia.
What Is the Differential Diagnosis of Nephrogenic Metaplasia?
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CCA (Clear Cell Adenocarcinoma): Clear cell adenoma usually occurs in women; it lacks the clinical characteristics of adenoma. Clear Cell Adenomas tend to be very large tumors; they exhibit mostly clear cells, and there is an additional high mitotic rate; also, necrosis can be seen in clear cell adenomas in CCA. Clear cell adenoma exhibits strong staining with the p63 stain.
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Endocervicosis can also be associated with a mucinous variant of nephrogenic adenoma.
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Papillary urothelial carcinoma is also another differential diagnosis.
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Prostatic adenocarcinoma of the urinary bladder.
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There is a resemblance in the nested variant of urothelial carcinoma of the bladder.
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Tse et al. experiment associated nephrogenic adenoma/metaplasia with urinary bladder carcinoma.
What Are the Treatment Options for Nephrogenic Metaplasia?
Surgical intervention with transurethral resection or electrocoagulation of the lesion and eliminating the root cause of irritation. The resection of the lesion is important, and as recurrence may occur, regular follow-up is necessary. Some patients were treated with sodium hyaluronate who could not undergo surgical intervention.
What Are the Various Examples of Nephrogenic Metaplasia?
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Hungerhuber et al. described a case of a male who was 25 years old, had experienced trauma in a car accident, and developed nephrogenic metaplasia after recovering from the trauma.
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Vemulakonda et al. stated a case of a 10-year-old who had recurrent events of nephrogenic metaplasia and had a history of prune belly syndrome.
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In patients with an Ibuprofen abuse history, nephrogenic metaplasia in the urinary bladder was quite evident.
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Chen and Cheng hypothesized nephrogenic adenoma is an uncommon benign metaplastic lesion in the urothelium.
Conclusion:
Nephrogenic metaplasia is a rare, benign urothelial tumor most frequently situated in the bladder. There is no evident study that links nephrogenic metaplasia to malignancy. Nephrogenic metaplasia having cytologic atypia (atypical nephrogenic metaplasia) is sometimes encountered, and its biological potential is uncertain. It sometimes displays substantial cytologic abnormalities without any apparent clinical significance. The presenting clinical signs are nonspecific and usually related to predisposing factors (infections, inflammation, bladder tumor). The nephrogenic metaplasia looks like carcinoma. It may get misdiagnosed or create confusion with malignancy. Only a histological examination can provide actual proof of the benign nature of this lesion. Endoscopic resection, therefore, has two objectives: diagnostic and therapeutic. Recurrences characterize the clinical course.
