<s>[INST] context: Rosettes

Rosettes are pathological findings characterized by a halo or spoke wheel arrangement of cells surrounding a central core or hub.

Type of Rosette
1. Flexner - Wintersteiner Rosettes

A halo of cells surrounds a largely empty central hub but small cytoplasmic extension from cells project into the lumen.
It is characteristic of retinoblastoma.
May also be seen in → Medulloblastoma, Primitive neuroectodermal tumor, Pineoblastoma.

2. Homer Wright rosettes

A halo of cells surrounds a central hub that contains a meshwork of fibres (neutrophil rich centre).
Homer-Wright rosettes are characteristic of neuroblastomas and medulloblastomas.
May also be seen in → Primitive neuroectodermal tumors (PNET), Pineoblastomas, Retinoblastomas.

3. True ependymal Rosette

A halo of cells surrounds an empty lumen.
It is characteristic of ependymomas.

4. Perivascular pseudorosettes

A halo of cells surrounds a blood vessel.
The term pseudo is used because the central structure is not formed from the tumor itself, and represents a nonneoplastic element.
May be seen in
	Ependymonas
	Glioblastomas
	Medulloblastomas
	Retinoblastoma
	Primitive neuroectodermal tumors   
	Monimorphous pilimyxoid astrocytoma
	Central neurocytoma [/INST] question: Homer wright rossette are seen in-a)  Neuroblastomab)  Astrocytomac)  Meningiomad)  Pinealoma | options: A: ad B: c C: ac D: ab | answer: A </s>