**Core Concept**
The Flexner-Wintersteiner rosette is a characteristic histopathological feature associated with certain types of cancer. It is a specific arrangement of neoplastic cells that resemble a rosette, a flower-like structure. This rosette is formed by the polarization of cells around a central lumen, often indicating neural or neuroendocrine differentiation.

**Why the Correct Answer is Right**
In the context of retinoblastoma, the Flexner-Wintersteiner rosette is a classic histopathological finding. This rosette is composed of a central lumen surrounded by a ring of tumor cells, which are often arranged in a polarized manner. The presence of these rosettes is indicative of the neuroblastic differentiation of retinoblastoma cells. The cells forming the rosette are typically small, round, and have a high nuclear-to-cytoplasmic ratio, with hyperchromatic nuclei and a prominent nucleolus. The rosettes are thought to represent an attempt by the tumor cells to differentiate towards a neural lineage.

**Why Each Wrong Option is Incorrect**
**Option A:** Hepatoblastoma is a malignant tumor of the liver in children, but it is not typically associated with Flexner-Wintersteiner rosettes. Hepatoblastoma cells may exhibit glandular or embryonal differentiation, but this is not characterized by the formation of rosettes.
**Option B:** Nephroblastoma, also known as Wilms tumor, is a malignant tumor of the kidney in children. While nephroblastoma cells may exhibit embryonal differentiation, they do not typically form Flexner-Wintersteiner rosettes.
**Option C:** Neuroblastoma is a malignant tumor of the sympathetic nervous system, and it can exhibit a range of histopathological features, including rosettes. However, the rosettes seen in neuroblastoma are typically Homer Wright rosettes, not Flexner-Wintersteiner rosettes.

**Clinical Pearl / High-Yield Fact**
Retinoblastoma is a malignant tumor of the retina that typically affects young children. It can be associated with genetic mutations in the RB1 gene, which is a tumor suppressor gene. The presence of Flexner-Wintersteiner rosettes in a retinal tumor is a key diagnostic feature that can help differentiate retinoblastoma from other types of intraocular tumors.

**✓ Correct Answer: D. Retinoblastoma**