Step I Rosette vs Pseudo-Rosette
Started by thinkenergy
That's a good question.
As far as I'm aware, a rosette is a term used to describe cells that circumferentially surround a lumen. Ependymoma is the classic example of that, where tumor cells surround what's considered to be an "embryologic ependymal canal," as I remember from Robbin's. However, FA says "pseudorosettes" for ependymoma, as well as for medulloblastoma. Pseudorosettes are essentially the same as rosettes, except there's a small, intervening quantity of tissue separating the tumor cells from the actual lumen. In the case of ependymomas, there's usually circumferential tumor cells on the outside, a thin layer of ependymal cellular processes circumferentially inside of that, and then a vessel (lumen) in the center; that in turn = perivascular pseudorosette.
The main difference between ependymoma and medulloblastoma is that the former, as FA says, has rod-shaped intracytoplasmic eosinophilic inclusions called blepharoplasts. Medulloblastoma is characteristically basophilic, with prominent nuclei with little cytoplasm.
Remember that medulloblastoma occurs in the midline @ the cerebellar vermis (I'm fairly sure I've encountered a practice question asking exactly where the tumor occurs).
Bottom line: rosettes are tumor cells surrounding a lumen. Pseudorosettes are the same except a tissue substance separates the tumor cells from the lumen.
As far as I'm aware, a rosette is a term used to describe cells that circumferentially surround a lumen. Ependymoma is the classic example of that, where tumor cells surround what's considered to be an "embryologic ependymal canal," as I remember from Robbin's. However, FA says "pseudorosettes" for ependymoma, as well as for medulloblastoma. Pseudorosettes are essentially the same as rosettes, except there's a small, intervening quantity of tissue separating the tumor cells from the actual lumen. In the case of ependymomas, there's usually circumferential tumor cells on the outside, a thin layer of ependymal cellular processes circumferentially inside of that, and then a vessel (lumen) in the center; that in turn = perivascular pseudorosette.
The main difference between ependymoma and medulloblastoma is that the former, as FA says, has rod-shaped intracytoplasmic eosinophilic inclusions called blepharoplasts. Medulloblastoma is characteristically basophilic, with prominent nuclei with little cytoplasm.
Remember that medulloblastoma occurs in the midline @ the cerebellar vermis (I'm fairly sure I've encountered a practice question asking exactly where the tumor occurs).
Bottom line: rosettes are tumor cells surrounding a lumen. Pseudorosettes are the same except a tissue substance separates the tumor cells from the lumen.
Just to elaborate:
A rosette is halo or "spoke-wheel" arrangement of cells around a central structure (which can be a lumen or cytoplasmic processes).
The "rosette" associated with medulloblastoma is actually a Homer-Wright Pseudorosette which is defined by the tumor cells being arranged concentrically around a central space filled with neuropil (as opposed to a lumen). This formation is also seen in neuroblastomas
The "rosette" also associated with ependymoma is the True Ependymal Rosette which is defined by the cells encircling a completely empty lumen (this is where you might see ependymal canals as the tumor is trying its best to make a ventricle).
The "rosette" of ependymoma is a Perivascular Pseudorosette which is defined by tumor cells lined up around vessels with an intervening zone of thin ependymal processes direct toward the wall of the vessel (spoke-wheel) and is "pseudo" since this the lumen or central structure was not created by the tumor but by lining up on a pre-existing structure.
For completeness, the "rosette" of retinoblastoma is the Flexner-Wintersteiner rosette which is defined by the a tumor cells surrounding a lumen with cell processes of encircling cells projecting into the lumen (no neuropil here).
Good summary. And I found the points in bold helpful.
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