#neoplasms

Pilocytic astrocytomas are the most common primary brain tumor in children. They are well-circumscribed and grow very slowly. They prefer the cerebellum and brainstem. Their most distinguishing feature are the Rosenthal fibers (pilocytic means fiber) and red inclusions. These can usually be treated with resection alone. Look how pretty it is:

Low grade gliomas are the majority of adult brain tumors. They are infiltrating and are WHO grade 2-4. Both diffuse astrocytomas and oligodendrogliomas are going to be basically in the middle of the brain. Oligodendrogliomas prefer white matter of the cerebral hemispheres and infiltrate to the cortex. Microcalcifications are common. Oligodendrogliomas have a "fried egg" and "chickenwire" appearance, but this is usually stated as uniform cells with clear cytoplasm and branching, delicate blood vessels on board exams.

Diffuse astrocytomas show irregular, angulated, and hyperchromatic nuclei, and have a tendency to recur, spread, and progress to higher stages.

Now to the malignant gliomas. Malignant astrocytomas are the most common primary brain tumor in adults. You'll see a hypercellular glioma with poorly differentiated astrocytes. It tends to recue, and shows significant nuclear atypia and miotic activity (it's dividing!!). These can develop from other types of astrocytomas or de novo. They usually progress to glioblastoma.

Glioblastomas are the most common and most malignant gliomas. They are poorly defined, infiltrating, and will distort the brain. Some people say they look like butterflies on MRI (I say these people are full of shit). You'll see serphintine or psuedopalisading necrosis and microvascular proliferation. The morphology of the cells is highly variable (from giant and bizarre to small and tightly packed). There is about a one year median survival from disgnosis.

Medulloblastomas

This is the most malignant brain tumor in children, and is only found in the cerebellum (by definition, obviously). All of them are WHO grade IV. The classic (aka the kind on board exams) is composed of sheets of densly packed cells with round to oval nuclei (or sometimes carrot-shaped lol), and little cytoplasm. They are poorly differentiated and primitive. In 40% of them, there are Homer-Wright (neuroblastic) rosettes (circled below).

Sometimes you see spinal drop metastasis of these, which means the tumor has spread to the spinal cord. This will show up as a "sugar coated" spinal cord on MRI. If the tumor compresses the 4th ventricle, you'll also see increased intracranial pressure.

Ependymomas

These are slow-growing tumors that originate from either the walls of the ventricles or the spinal canal. In kids, they're usually in the brain. In adults, they're usually in the spine. There are like nine subtypes, but the most common feature on histology is perivasuclar psuedorosettes. They have a poor prognosis.

Choroid Plexus Papillomas

These come from the cuboidal cells of the choroid plexus within the ventricles (the things that make CSF). 85% are in kids less than 5 years old, and most are found in the lateral ventricles. They look like cauliflower. Under the microscope, they show papillary structure with delicate fibrovascular cores, with a cuboidal lining. Complete resection is the main treatment.

Neuronal Tumors

We're only gonna talk about gangliocytomas, gangliogliomas, and dysembryoplastic neuroepithelial tumors, but there are other types. Gangliocytomas are the most common tumors associated with chronic temporal lobe epilepsy, but they are rare overall. They show prominent single nucleoli and cytoplasmic basophilic Nissl substance. They also may have pilocytic elements. They may progress to gangliogliomas.

Dysembryoplastic neuroepithelial tumors are low-grade tumors that are seen in kids. Usually they cause seizures. You'll see multinodular lesions in the cortices (usually temporal). Histology looks like prominent clusters of oligodendroglial-like cells, which seem to float in cystic spaces. Resection is the treatment, and usually stops the seizures.

Meningiomas

These are the most common benign tumors in adults, with resection being the primary treatment (unless they're radiation-induced, those fuckers are aggressive). These are attached to the dura mater and compress the brain without invading it. The meningothelial subtype is the only one you need to know the histology of. It has characteristic whorls (can be mineralized) called psammoma bodies. Grossly, they look like an egg yolk.

Primary CNS Lymphomas

PCNSL are usually diffuse large B-call lymphomas. Therefore, they express CD markers. Grossly, they are circumscribed and somewhat necrotic. On histology, they have lymphoid-appearing cells around blood vessels. They're honestly not that interesting in my opinion.

Craniopharyngiomas

These are benign and their origin has to do with some embryology I don't care to explain here. They have neuroendocrine effects, and can usually not be reached for resection, and are therefore considered a lifelong illness. They're usually cystic, solid, and calcified all at once (yum). They are separated into adamantinomatous (kids and adults) and papillary (only in adults). You'll see palisading epithelial cells and wet keratin.

CNS Metastasis

Most common tumor of the CNS, and can occur at any age. Lung cancer is the most common primary tumor. You're going to see edema, and usually they lodge at the gray-white junction. They will be well circumcised and will have histology consistent with the primary lesion.

Peripheral Tumors

We got Schwannomas, Neurofibromas, and Malignant peripheral nerve sheath tumors (MPNSTs). Schwannomas are painless and slow rowing, and just kinda look like a round knot on a nerve. Histologically, they are biphasic, with Antoni A (tight) and Antoni B (loose) areas. You'll also see nuclear palisading with Verocay bodies.

Neurofibromas are either solitary or plexiform. They will present with pain and loss of function. On histology, you'll see myxomatous matric and collagen fibrils leading to intense staining with reticulin.

MPNSTs are highly malignant and aggressive, and are difficult to diagnose. Grossly, you'll see necrosis. Histologically, you'll see hypercellularity, atypia, and pleomorphism.

Neurocutaneous Syndromes

You got neurofibromatosis 1 and 2, tuberous sclerosis, and Von Hippel Lindau disease. With NF1, you have a mutation on chromosome 17, which causes dark skin spots, cutaneous neurofibromas, Lisch nodules on the iris, optic gliomas, seizures, etc.

NF2 is from chromosome 22, and the patient will also sometimes have meningiomas and ependymomas. The biggest thing is bilateral vestibular schwannomas, causing hearing loss, vertigo, and facial weakness. Also common are juvenile cataracts.

Tuberous sclerosis is a disorder of cellular differentiation and proliferation. You'll see ash leaf spots, facial and fingernail angiofibromas, shagreen patches, heart tumors, renal tumor, retinal tumor, lung tumor, epilepsy, etc.

Von Hippel Lindau disease is caused by a deletion on chromosome 3. It is characterized by hemangioblastomas in the retina and CNS. You'll see symptoms from local mass effect and hemorrhage. Patient may also have renal cysts, pheochromocytomas, or pancreatic tumors.