Okay, let's tackle this question. The user is asking about the histological finding in a resected kidney that indicates bilateral Wilms' tumor. First, I need to recall what Wilms' tumor is. It's a type of kidney cancer that primarily affects children. The key here is the term "bilateral," meaning it affects both kidneys.

I remember that Wilms' tumor, also known as nephroblastoma, is characterized by a specific histological appearance. The classic triad of cells in the tumor includes blastemal, epithelial, and stromal elements. The blastemal cells are small, round, and blue with minimal cytoplasm, which is a hallmark. The epithelial cells form tubules and glands, and the stromal component can be myogenic or osseous. So the presence of these three cell types would be the key histological feature.

Now, looking at the options (even though they're not provided), the correct answer would mention the presence of blastemal, epithelial, and stromal elements. The other options would likely describe other types of renal tumors or conditions. For example, a renal cell carcinoma in adults has different histology, maybe clear cells. A sarcoma might not have the blastemal component. A benign tumor like an angiomyolipoma would have different cell types. Also, other pediatric tumors like clear cell sarcoma or rhabdoid tumors have distinct features.

The clinical pearl here is that Wilms' tumor is the most common primary malignant renal tumor in children, and the presence of blastemal cells is crucial for diagnosis. Bilateral cases are important because they might be associated with genetic syndromes like WAGR or Denys-Drash. So, the student should remember that the histological triad is essential for differentiating Wilms' from other tumors.

**Core Concept**
Wilms' tumor (nephroblastoma) is the most common primary malignant renal tumor in children. Its histological hallmark is the presence of **blastemal, epithelial, and stromal elements**, distinguishing it from other renal neoplasms. Bilateral tumors are seen in 5–10% of cases and often correlate with genetic syndromes like WAGR (Wilms, Aniridia, Genitourinary anomalies, Mental retardation).

**Why the Correct Answer is Right**
The correct histological finding is the presence of **blastemal cells** (small, round, blue cells), **epithelial tubules/glands**, and **stromal components** (e.g., cartilage, muscle). This triphasic pattern reflects the embryonal origin of Wilms' tumor, arising from metanephric blastema. Blastemal cells are pathognomonic, while epithelial and stromal differentiation confirms the diagnosis. Bilateral tumors often share identical histology, supporting a common clonal origin.

**Why Each Wrong Option is Incorrect**
**Option A:** Clear cell sarcoma lacks the triphasic pattern; it shows spindle cells and melanotic pigments.
**Option B:** Rhabdoid tumor exhibits large cells with eosinophilic cytoplasm and prominent nucleoli, absent in Wilms.
**Option C:** Renal cell carcinoma in adults lacks blastemal elements and has clear cells or papillary architecture.

✓ Correct Answer: B. Nephrogenic rests