Nephrogenic metaplasia

NEPHROGENIC METAPLASIA/ ADENOMA

• It is a reactive process which results in tubular and papillary growths from the reminiscent of immature urothelial or metanephric structures

• Though the term “adenoma” is used, it is not neoplastic lesion but is recognized as metaplasia

• Nephrogenic changes are almost always associated with conditions like chronic irritation of urothelium due to recurrent infections of bladder

• Also seen at sites of previous surgery or in diverticula

Clinical features

• Sex – Shows male predilection with male to female ratio of 2:1 to 3:1

• Age – Can occur at any age from 20 to 80 years but more common in 40 to 49 years

• Patient has history of urinary bladder infections, stones, radiation, instrumentation, intravesical instillation or trauma

• Can be seen in renal transplant patients with immunosuppression

• Patient presents with hematuria and irritating voiding

Morphology

Gross

• Cystoscopy – polypoid or fungating velvety to flat lesions which can be single or multiple

• Size – usually smaller than 1cm but can reach up to 7cms

Microscopy

• Histologically foci of nephrogenic metaplasia replaces the urothelium and involve the lamina propria

• Muscularis propria is spared

• Lesion is distinguished by the presence of single layer of cytologically bland cuboidal cells that line the stalks and tubules

• Lesion is composed of tubules lined by bland cuboidal to low columnar epithelium. Surrounding the tubules rim of hyalinized collagen may be seen

• Other histological patterns which can be seen are

  • Cysts lined by hobnail or flattened cells

  • Atrophic tubules with eosinophilic colloid like material

  • Small mucin containing tubules simulating signet ring cells

  • Papillary structures with or without fibrovascular cores

  • In post radiotherapy patients, fibromyxoid stroma with spindle cells and occasional cords or atrophic tubules are found in the lesion

  • Clear cell change and rare foci of solid pattern of cells may be present

• Stroma is usually edematous with inflammatory cells. Desmoplasia is absent.

• Nuclear anaplasia will be absent but degenerative atypia with enlarged nuclei and prominent nucleoli may be present

• Features which contradict the diagnosis of nephrogenic adenoma are – conspicuous solid growth patterns, prominent cytologic atypia, diffuse clear cell change and mitotic activity

Immunohistochemistry

• Positive for – CD 10, CK7, PAX 2, PAX 8, α- methyl acyl-coenzyme A racemase

• Weakly positive for PSA and prostate specific acid phosphatase

• Negative for – High molecular weight cytokeratin and P63

Differential diagnosis

• Capillary hemangioma but nephrogenic adenoma shows positive reactions for cytokeratins

• Adenocarcinoma of prostate, Mullerian clear cell adenocarcinomas, Clear cell adenocarcinoma of bladder, signet ring cell carcinoma, infiltrative mucinous carcinoma. All these tumors have nuclear atypia which is not present in nephrogenic adenoma

Prognosis and treatment –

• Transurethral resection with follow up is the treatment of choice

• Recurrence rate in these tumors is 0.5%  to 80%