CASE OF THE WEEK
2019-29 / SEPTEMBER 2
(CONTRIBUTOR: FRANCESCA KHANI)
A 4 year old boy presented with gross hematuria and a solitary bladder mass was identified on a renal/bladder ultrasound. Cystoscopic biopsy confirmed malignancy, and a partial cystectomy was performed. Representative H&E images and an immunostain for INI1 are shown. The tumor was also negative for pan-cytokeratin, EMA, S100, desmin, myogenin, myoD1, and CD34.
Quiz
1. What is the correct diagnosis?
a. Rhabdomyosarcoma
b. Proximal type epithelioid sarcoma
c. Neuroblastoma
d. Extrarenal malignant rhabdoid tumor
e. Wilms tumor
1. d
1. Extrarenal malignant rhabdoid tumor
Malignant rhabdoid tumors typically occur in the kidney of young children, however, extrarenal primary sites have been reported, including the bladder. (Rhabdoid tumors occurring in the central nervous system are termed atypical teratoid/rhabdoid tumors) Histologically, these tumors are characterized by sheets of large tumor cells with vesicular chromatin, prominent nucleoli, and eosinophilic cytoplasm with eosinophilic inclusions. Malignant rhabdoid tumors may have many different patterns, including epithelioid, sclerosing, lymphomatoid, and histiocytoid. Loss of INI1 is characteristic of this tumor. Clinically, they are highly aggressive tumors with poor prognosis.
In the pediatric population, the most common malignant neoplasm in the genitourinary tract is a rhabdomyosarcoma. As such, it should always be included in the differential diagnosis in this location and patient population. However, in contrast to the current case, rhabdomyosarcomas in the bladder are typically embryonal type with small, spindled cells, often in a myxoid stroma. They characteristically show expression of myogenin, myoD1, and desmin, and retention of INI1, none of which were seen in this case. Thus, the morphology and immunoprofile seen in the current case are incompatible with a rhabdoymyosarcoma. Proximal type epithelioid sarcomas may display similar morphology to malignant rhabdoid tumors and characteristically show INI1 loss, but they are almost always positive for pan-cytokeratin and EMA and more typically occur on the limbs of young to middle-aged adults. Wilms tumors occur in the kidney of very young children and do not show INI1 loss. Neuroblastomas also occur in very young children but more often occur in the adrenal gland and also do not show INI1 loss.
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Francesca Khani
Weill Cornell Medicine
Frk9007@med.cornell.edu
Bladder
Malignant rhabdoid tumor, pediatric, soft tissue, INI1 loss