"Pseudopalisading" arrangement of malignant cells is characteristic of:
"The highest grade tumor of astrocytoma, known as glioblastoma, has a histologic appearance similar to anaplastic astrocytoma with the additional features of necrosis and vascular or endothelial cell proliferation and pseudo-palisading nuclei."

Glioblastoma is type of infiltrating astrocytoma (Classified as Grade 4).
Necrosis in glioblastoma often results in a SERPENTINE pattern in areas of hyper-cellularity.
Tumor cells collect along the edges of the necrotic regions, producing histologic pattern referred to as pseudopalisading pattern.

GLIOMAS
Gliomas are tumors of the brain parenchyma that histologically resemble different types of glial cells. The major types of tumor in this category are:
a. Astrocytomas
b. Oligodendrogliomas
c. Ependymomas.

ASTROCYTOMAS

Two major categories of astrocytoma, infiltrating and non-infiltrating types.
Infiltrating astrocytomas account for about 80% of adult primary brain tumors.
They are most frequent in the fourth through sixth decades.
They are usually found in the cerebral hemispheres.
The most common presenting signs and symptoms are seizures, headaches and focal neurologic deficits related to the anatomic site of involvement.
Infiltrating astrocytomas show a spectrum of histologic differentiation that correlates well with clinical course and outcome.

Based on the degree of differentiation, they are classified into four groups:

Pilocytic astrocytoma - Grade I - Most common
Astrocytoma - Grade 2
Anaplastic astrocytoma - Grade 3
Glioblastoma multiforme - Grade 4 - Least differentiated

PILOCYTIC ASTROCYTOMA

Pilocytic astrocytomas are relatively benign tumors, often cystic, that typically occur in children and young adults.
They are usually located in the cerebellum; also in the floor and walls of the third ventricle, the optic nerves, and occasionally the cerebral hemispheres.
A pilocytic astrocytoma is often cystic, with a mural nodule in the wall of the cyst; if solid, it is usually well circumscribed.
The tumor is composed of areas with bipolar cells with long, thin “'hairlike” processes that are GFAP positive: Rosenthal fibers, eosinophilic granular bodies, and microcysts are often present.
Necrosis and mitoses are absent.

OLIGODENDROGLIOMAS

These tumors constitute about 5% to 15% of gliomas and are most common in the fourth and fifth decades.
Patients may have had several years of neurologic complaints, often including seizures. The lesions are found mostly in the cerebral hemispheres, with a predilection for white matter.
Oligodendrogliomas are infiltrative tumors that form gelatinous, gray masses, and may show cysts, focal hemorrhage and calcification.
On microscopic examination, the tumor is composed of sheets of regular cells with spherical nuclei containing finely granular chromatin (similar to normal oligodendrocytes) surrounded by a clear halo of cytoplasm.
The tumor typically contains a delicate network of anastomosing capillaries. Calcification, present in as many as 90% of these tumors, ranges from microscopic foci to massive depositions.
With increasing cell density, nuclear anaplasia, increased mitotic activity and necrosis, the tumor becomes higher grade (anaplastic oligodendroglioma.)
Patients with oligodendrogliomas have a better prognosis than do patients with astrocytomas.
Current treatment with surgery, chemotherapy, and radiotherapy yields an average survival of 5 to 10 years.
Patients with anaplastic oligodendroglioma have a worse prognosis.

EPENDYMOMAS

Ependymomas most often arise next to the ependyma-lined ventricular system, including the central canal of the spinal cord.
In the first two decades of life, they typically occur near the fourth ventricle and constitute 5% to 10% of the primary brain tumors in this age group.
In adults, the spinal cord is their most common location; tumors in this site are particularly frequent in the setting of neurofibromatosis type 2.
Because ependymomas usually grow within the ventricles. CSF dissemination is a common occurrence.
In the fourth ventricle, ependymomas are typically solid or papillary masses extending from the floor of the ventricle.
These tumors are composed of cells with regular, round to oval nuclei with abundant granular chromatin.
Between the nuclei there is a variably dense fibrillary background.
Tumor cells may form round or elongated structures (rosettes, canals) that resemble the embryologic ependymal canal, with long, delicate processes extending into a lumen. More frequently present are perivascular pseudo-rosettes in which tumor cells are arranged around vessels with an intervening zone consisting of thin ependymal processes directed toward the wall of the vessel.
Anaplastic ependymomas show increased cell density, high mitotic rates, necrosis and less evident ependymal differentiation.
The clinical outcome for completely resected supratentorial and spinal ependymomas is better than for those in the posterior fossa.
Glioblastoma
Ependymoma
Oligodendroglioma
Medulloblastoma