Pseudopalisading

Pseudopalisading is a histopathological pattern in which tumor cells align in elongated, fence-like rows around a central area of necrosis, producing a palisade-like appearance. It is most classically described in high-grade gliomas, particularly glioblastoma multiforme (GBM), and is used as a diagnostic clue in neuropathology. The pattern can also be seen in other tumors with central necrosis, but GBM remains the archetype.

Morphology and mechanism: Perinecrotic tumor cells migrate away from a hypoxic, necrotic core, forming narrow bands of hypercellular tissue at the margin. The cells typically have elongated or pleomorphic nuclei and may display mitotic activity nearby; microvascular proliferation is often present at the tumor edge. The necrotic core is usually acellular and debris-filled, while the surrounding pseudopalisading cells create the characteristic fence-like arrangement.

Diagnostic significance: Pseudopalisading necrosis is a hallmark feature that supports the diagnosis of GBM when observed with other criteria such as microvascular proliferation and high mitotic activity. It is not completely specific to GBM and must be interpreted in the broader histopathological and molecular context, including IDH mutation status and other molecular markers that influence classification and prognosis.

Terminology: The term “pseudopalisading” distinguishes this pattern from true palisading seen in other tissues; the arrangement arises around necrosis rather than from preexisting organized architectural structure.