While nobody wants to get a brain tumor, if you had to pick one, meningioma would be a good choice. Weird to think of tumors in this way, but it does put things in perspective.

Meningioma is, as the name implies, a tumor that is usually found attached to the dura. It usually arises from the meningothelial cell of the arachnoid – which is why you usually find these along the exterior surface of the brain (although occasionally they show up in the ventricle lining – in which case, they arise from stromal arachnoid cells of the choroid plexus).

Anyway. They’re usually nicely-defined, encapsulated, rounded masses that are easily separable from the brain parenchyma. Which means that resection usually works well for these tumors. They tend to grow slowly, and they present either with vague symptoms, or with focal findings related to compression of the underlying brain. Some common places meningiomas show up are: the parasagittal aspect of the brain convexity; the lateral brain convexity; the sphenoid wing; the olfactory groove; the sella turcica; and the foramen magnum. One weird thing about meningiomas: they often express progesterone receptors! Weird. This means that during pregnancy, they may grow more rapidly.

Histologically, meningiomas may show different patterns. Often, the tumor cells sit in tight little whorled clusters, like the cells in the image here (this is called a “meningothelial” or “syncytial” growth pattern). Sometimes, though, the cells are elongated, with abundant collagen (“fibroblastic”); sometimes they show characteristics of both the syncytial and fibroblastic pattern (“transitional”);  sometimes they have lots of psammoma bodies (“psammomatous”). There’s also a secretory pattern (with little PAS-positive intracytoplasmic droplets) and a microcystic pattern (with a loose, spongy appearance). It’s only important to know about these patterns so you can make the diagnosis. The patient’s prognosis doesn’t differ depending on which pattern the tumor shows – all of these are considered benign, and have very little risk of recurrence after resection.

There are a few variants that don’t play nice. Atypical meningiomas grow more aggressively, and have a higher rate of recurrence. You can identify these histologically by their higher mitotic rate (four or more mitoses per 10 high power fields).  They might also have some other atypical features – increased cellularity, small cells with a high nuclear-to-cytoplasmic ratio, prominent nucleoli, a lack of a pattern, or necrosis.

Another one that’s not nice at all is anaplastic (or malignant) meningioma. This type of meningioma looks like a bad-ass sarcoma – but you can still see some evidence of meningiothelial origin . The mitotic rate is very high (over 20 mitoses per 10 high power fields). Papillary meningioma (with – surprise surprise – a papillary growth pattern) and rhabdoid meningioma (with sheets of pink cells) are also considered bad meningiomas, because they have an unusual tendency to recur.

In general, though, most meningiomas are solitary, slow-growing, benign tumors that are easily resected and don’t recur. Nice characteristics to have in a brain tumor.