Palisade (pathology)

In histopathology, a palisade is a single layer of relatively long cells, arranged loosely perpendicular to a surface and parallel to each other.

For example, regressive cell swelling may centripetally displace the cytoplasm as the nucleus is squeezed to the periphery, forming a secondary rosette.

Although the presence of primary rosettes may suggest a given diagnosis, usually this finding alone is not considered absolutely pathognomonic for one specific tumor type.

The cell populations exhibiting neuronal differentiation are believed to secrete surface glycoproteins and glycolipids which mediate cell-to-cell recognition and adhesion.

Frieda and Pollak conceptualize the architecture of ependymomas as a primitive neural tube turned inside out with the submesenchymal poles converging toward a central vessel, thus forming a pseudorosette rather than projecting centrifugally toward the pia.

[11][12][13] In 1897, Austrian ophthalmologist Hugo Wintersteiner confirmed Flexner's observations and noted that the cell clusters resembled rods and cones.

A perivascular pseudorosette consists of a spoke-wheel arrangement of cells with tapered cellular processes radiates around a wall of a centrally placed vessel.

The modifier “pseudo” differentiates this pattern from the Homer Wright and Flexner-Wintersteiner rosettes, perhaps because the central structure is not actually formed by the tumor itself, but instead represents a native, non-neoplastic element.

Unfortunately, perivascular pseudorosettes are also less specific in that they are also encountered in medulloblastomas, PNETs, central neurocytomas, and less often in glioblastomas, and a rare pediatric tumor, monomorphous pilomyxoid astrocytomas.

[2] The neuropathologic diagnosis of brain tumors entails the microscopic examination of conventional formalin-fixed paraffin-embedded tissue samples surgically removed from a radiographically defined lesion.

Although more advanced methods of tissue examination have been developed, such as histochemical and immunohistochemical profiling, genetic analysis, and electron microscopy, the microscopic review of H&E stained material remains a critical component of tumor diagnosis.

Some medulloblastomas may also display other forms of differentiation as demonstrated by the presence of the astrocytic marker glial fibrillary acidic protein.