We’ll start out our little series on brain tumors with astrocytomas, the most common type of brain tumor in adults (accounting for 80% of all primary brain tumors in adults). Backing up a moment to our little classification scheme, astrocytomas are within a larger category of brain tumors called gliomas, which arise from – you guessed it – glial cells. Astrocytomas, oligodendrogliomas and ependymomas all fall under this group.

Astrocytomas are divided into two groups: those that infiltrate (this is the group of astrocytomas people are usually referring to when they say “astrocytoma”), and those that do not (there is a special kind of astrocytoma called “pilocytic astrocytoma” that falls into this group). We’ll start with infiltrative astrocytomas in this post, and then move on to pilocytic astrocytomas in our next post.

Infiltrative astrocytomas are usually found in the cerebral hemispheres, and are most common in patients between 30 and 60. Patients most commonly present with seizures, headaches, and focal neurologic deficits (depending on where the tumor is).

Histologically, infiltrative astrocytomas have a spectrum of differentiation that is well-correlated to prognosis. Diffuse astrocytomas (also called grade II) have the best prognosis; anaplastic astrocytomas (grade III) do worse, and the worst of all is glioblastoma (grade IV). Grade I astrocytomas are actually pilocytic astrocytomas (which we’ll talk about in another post).

Diffuse astrocytomas are poorly-defined, gray tumors that range in size from a few centimeters to huge tumors that replace an entire hemisphere. An important thing to know about these tumors, especially if you are a surgeon, is that even if the tumor appears well-demarcated, it always infiltrates beyond the outer margins of the tumor. (Weird but true: you rarely hear “always” in pathology…what you hear is “almost always” or “usually” or “virtually always.” So when you hear “always,” take note!) Microscopically, diffuse astrocytomas are moderately cellular. The tumor cells resemble normal astrocytes, but with a varying degree of nuclear pleomorphism. The background is fibrillary due to all the astrocytic processes.

Anaplastic astrocytomas are similar to diffuse astrocytomas grossly, but microscopically, the tumor cells are more numerous and more pleomorphic. There are often mitoses, too. Sometimes the tumor cells have bright red cell bodies and lots of fat astrocytic processes; these are called “gemistocytic astrocytomas.”

Glioblastomas vary in appearance grossly (maybe that’s why they used to be called “glioblastoma multiforme”). Some areas of the tumor are firm, others are soft and necrotic, and still others are cystic and hemorrhagic. Glioblastoma looks similar to anaplastic astrocytoma, but in addition, it has necrosis and vascular proliferation. The necrosis looks kind of worm-like (“serpentine”), with areas of pseudopalisading (where the tumor cell nuclei line up in rows). Check out the photo above for a nice example of this. In addition, you might see some ball-like collections of vessels in glioblastoma; these are called glomeruloid bodies (because they look like glomeruli in the kidney).

The prognosis for astrocytoma is pretty different for the different types. Patients with well-differentiated, diffuse astrocytomas have a mean survival of over 5 years (in time, areas of higher histologic grade develop, and the patient’s clinical course takes a downward turn). Patients with glioblastoma have a much worse prognosis. Even with the best treatment around (which consists of surgery, radiation and chemotherapy), mean survival is only 15 months.